U.S. patent application number 12/940809 was filed with the patent office on 2011-12-15 for audio and animation blending.
This patent application is currently assigned to Harmonix Music Systems, Inc.. Invention is credited to Isaac Adams, Matthew C. Boch, James Fleming, Marc A. Flury, Riseon Kim, Sachi Sato, Dean N. Tate.
Application Number | 20110306397 12/940809 |
Document ID | / |
Family ID | 43414228 |
Filed Date | 2011-12-15 |
United States Patent
Application |
20110306397 |
Kind Code |
A1 |
Fleming; James ; et
al. |
December 15, 2011 |
Audio and animation blending
Abstract
Presented herein are methods, apparatuses, programs, and systems
for providing a smooth animation transition in a game. An event
timeline is provided with event markers denoting points in time on
the event timeline. Each event marker is associated with an
animation segment from the number of animation segments. A first
marker on the event timeline is provided, which indicates a first
animation segment to be displayed on the display (at a point in
time with respect to event timeline). A second marker on the event
timeline is also provided, which indicates a second animation
segment to be displayed on the display (at a second point in time
with respect to event timeline). Then as the game progresses, and
the second point time on the timeline is approaching, a set of
animation segments that need to be blended together is determined,
to provide a smooth transition from the first animation segment to
the second animation segment. Once the set of animations have been
determined, a blend is performed among the set of animation
segments.
Inventors: |
Fleming; James; (Brighton,
MA) ; Flury; Marc A.; (Cambridge, MA) ; Tate;
Dean N.; (Cambridge, MA) ; Boch; Matthew C.;
(Somerville, MA) ; Adams; Isaac; (Revere, MA)
; Kim; Riseon; (Dorchester, MA) ; Sato; Sachi;
(Belmont, MA) |
Assignee: |
Harmonix Music Systems,
Inc.
Cambridge
MA
|
Family ID: |
43414228 |
Appl. No.: |
12/940809 |
Filed: |
November 5, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61354073 |
Jun 11, 2010 |
|
|
|
Current U.S.
Class: |
463/7 ; 463/31;
463/35 |
Current CPC
Class: |
A63F 2300/6081 20130101;
A63F 2300/6607 20130101; A63F 13/44 20140902; A63F 2300/61
20130101; A63F 2300/1093 20130101; A63F 2300/638 20130101; A63F
13/814 20140902; A63F 13/428 20140902; A63F 13/46 20140902; A63F
13/5372 20140902; G06F 3/017 20130101; A63F 2300/8047 20130101;
G06F 3/011 20130101; A63F 13/67 20140902; A63F 13/213 20140902;
A63F 13/54 20140902; A63F 2300/69 20130101 |
Class at
Publication: |
463/7 ; 463/35;
463/31 |
International
Class: |
A63F 9/24 20060101
A63F009/24; A63F 13/00 20060101 A63F013/00 |
Claims
1. A method, executed on a game platform, for providing a smooth
animation transition in a game comprising: (a) providing, during
play of the game, an event timeline comprising event markers
denoting points in time on the event timeline, each event marker
associated with an animation segment from a plurality of animation
segments; (b) providing a first marker on the event timeline
indicating a first animation segment to be displayed on the display
at a first time with respect to event timeline and a second marker
on the event timeline indicating a second animation segment to be
displayed on the display at a second time with respect to event
timeline; (c) determining, during play of the game, that the second
time is approaching; (d) determining a set of animation segments to
be blended together to provide a smooth transition from the first
animation segment to the second animation segment; and (e) blending
among the set of animation segments based on the determination made
in step (d).
2. The method of claim 1 wherein the set of animation segments to
be blended comprises the first animation segment and the second
animation segment and blending comprises blending at least some of
the first animation segment with at least some of the second
animation segment.
3. The method of claim 1 wherein the set of animation segments to
be blended comprises the first animation segment, a bridge
animation segment, and the second animation segment, and blending
comprises blending at least a some of the first animation segment
with at least some of the bridge animation segment and blending at
least some of the bridge animation segment with at least some of
the second animation segment.
4. The method of claim 1 further comprising: before the first time,
judging a first player's performance of the game; and at and after
the second time, judging a second player's performance of the
game.
5. The method of claim 1 wherein the second animation segment is
determined based on a difficulty of the game.
6. The method of claim 1 wherein determining the set of animation
segments to be blended comprises determining if there is a bridge
animation segment in a table, where the bridge animation segment is
looked up based on the first animation segment and the second
animation segment.
7. The method of claim 1 wherein the first marker and the second
marker are associated with the same animation.
8. A method, executed on a game platform, for providing smooth
audio transitions in a song comprising: (a) providing, during play
of a game, an event timeline comprising event markers denoting
points in time on the event timeline, the event timeline associated
with an audio track played during play of the game, the audio track
comprising a first audio segment and a second audio segment; (b)
providing a first marker on the event timeline indicating a first
time associated with the first audio segment and a second marker on
the event timeline indicating a second time with respect to the
event timeline associated with the second audio segment; (c)
determining, during play of the game, that the second time is
approaching; (d) determining a set of audio segments to be blended
to transition from the first audio segment to the second audio
segment; and (e) blending among the set of audio segments based on
the determination made in step (d).
9. The method of claim 8 wherein the set of audio segments to be
blended comprises the first audio segment and the second audio
segment.
10. The method of claim 9, wherein blending among the first audio
segment and the second audio segment comprises crossfading from at
least some of the first audio segment to at least some of the
second audio segment.
11. The method of claim 8 wherein the set of audio segments to be
blended comprises the first audio segment, a bridge audio segment,
and the second audio segment.
12. The method of claim 11, wherein blending among the first audio
segment, the bridge audio segment, and the second audio segment
comprises: crossfading from at least some of the first audio
segment to at least some of the bridge audio segment; and
crossfading from at least some of the bridge audio segment to at
least some of the second audio segment.
13. The method of claim 11, wherein blending among the first audio
segment, the bridge audio segment, and the second audio segment
comprises muting at least some of the first audio segment, playing
at least some of the bridge audio segment, and muting at least some
of the second audio segment.
14. The method of claim 13 wherein muting at least some of the
first audio segment, playing at least some of the bridge audio
segment, and muting at least some of the second audio segment
comprises muting the first audio segment for its final beat, muting
the second audio segment for its first two beats, and playing the
bridge audio segment for three beats during the muted last beat of
the first audio segment and muted first two beats of the muted
second audio segment.
15. The method of claim 9 wherein the first marker and the second
marker are associated with the same audio segment.
16. The method of claim 11 wherein the first marker and the second
marker are associated with the same audio segment.
17. The method of claim 11 wherein determining the set of audio
segments to be blended comprises determining if there is a bridge
audio segment in a table, where the bridge audio segment is looked
up based on the first audio segment and the second audio
segment.
18. A computer program product, tangibly embodied in a
non-transitory computer readable storage medium, for providing a
smooth animation transition in a game, the computer program product
including instructions being operable to cause a data processing
apparatus to: (a) provide, during play of the game, an event
timeline comprising event markers denoting points in time on the
event timeline, each event marker associated with an animation
segment from a plurality of animation segments; (b) provide a first
marker on the event timeline indicating a first animation segment
to be displayed on the display at a first time with respect to
event timeline and a second marker on the event timeline indicating
a second animation segment to be displayed on the display at a
second time with respect to event timeline; (c) determine, during
play of the game, that the second time is approaching; (d)
determine a set of animation segments to be blended together to
provide a smooth transition from the first animation segment to the
second animation segment; and (e) blend among the set of animation
segments based on the determination made in step (d).
19. A computer program product, tangibly embodied in a
non-transitory computer readable storage medium, for providing
smooth audio transitions in a song, the computer program product
including instructions being operable to cause a data processing
apparatus to: (a) provide, during play of a game, an event timeline
comprising event markers denoting points in time on the event
timeline, the event timeline associated with an audio track played
during play of the game, the audio track comprising a first audio
segment and a second audio segment; (b) provide a first marker on
the event timeline indicating a first time associated with the
first audio segment and a second marker on the event timeline
indicating a second time with respect to the event timeline
associated with the second audio segment; (c) determine, during
play of the game, that the second time is approaching; (d)
determine a set of audio segments to be blended to transition from
the first audio segment to the second audio segment; and (e) blend
among the set of audio segments based on the determination made in
step (d).
20. An apparatus for providing a smooth animation transition in a
game, the apparatus comprising: (a) means for providing, during
play of the game, an event timeline comprising event markers
denoting points in time on the event timeline, each event marker
associated with an animation segment from a plurality of animation
segments; (b) means for providing a first marker on the event
timeline indicating a first animation segment to be displayed on
the display at a first time with respect to event timeline and a
second marker on the event timeline indicating a second animation
segment to be displayed on the display at a second time with
respect to event timeline; (c) means for determining, during play
of the game, that the second time is approaching; (d) means for
determining a set of animation segments to be blended together to
provide a smooth transition from the first animation segment to the
second animation segment; and (e) means for blending among the set
of animation segments based on the determination made by element
(d).
21. An apparatus for providing smooth audio transitions in a song,
the apparatus comprising: (a) means for providing, during play of a
game, an event timeline comprising event markers denoting points in
time on the event timeline, the event timeline associated with an
audio track played during play of the game, the audio track
comprising a first audio segment and a second audio segment; (b)
means for providing a first marker on the event timeline indicating
a first time associated with the first audio segment and a second
marker on the event timeline indicating a second time with respect
to the event timeline associated with the second audio segment; (c)
means for determining, during play of the game, that the second
time is approaching; (d) means for determining a set of audio
segments to be blended to transition from the first audio segment
to the second audio segment; and (e) means for blending among the
set of audio segments based on the determination made by element
(d).
22. A system for providing a smooth animation transition in a game,
the system comprising: a display; and a game platform configured
to: (a) provide, during play of the game, an event timeline
comprising event markers denoting points in time on the event
timeline, each event marker associated with an animation segment
from a plurality of animation segments; (b) provide a first marker
on the event timeline indicating a first animation segment to be
displayed on the display at a first time with respect to event
timeline and a second marker on the event timeline indicating a
second animation segment to be displayed on the display at a second
time with respect to event timeline; (c) determine, during play of
the game, that the second time is approaching; (d) determine a set
of animation segments to be blended together to provide a smooth
transition from the first animation segment to the second animation
segment; and (e) blend, for display on the display, among the set
of animation segments based on the determination made in step
(d).
23. A system for providing smooth audio transitions in a song, the
system comprising: an audio output; and a game platform configured
to: (a) provide, during play of a game, an event timeline
comprising event markers denoting points in time on the event
timeline, the event timeline associated with an audio track played
during play of the game, the audio track comprising a first audio
segment and a second audio segment; (b) provide a first marker on
the event timeline indicating a first time associated with the
first audio segment and a second marker on the event timeline
indicating a second time with respect to the event timeline
associated with the second audio segment; (c) determine, during
play of the game, that the second time is approaching; (d)
determine a set of audio segments to be blended to transition from
the first audio segment to the second audio segment; and (e) blend,
for output through the audio output, among the set of audio
segments based on the determination made in step (d).
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims benefit of priority to Application
No. 61/354,073, filed Jun. 11, 2010 and entitled "Dance Game and
Tutorial" by Flury et al., the disclosure of which is incorporated
herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to gesture-based
video games and, more specifically, to dance video games based on
positional input from a user.
BACKGROUND
[0003] Although video games and video game consoles are prevalent
in many homes, game controllers, with their myriad of buttons and
joysticks, are still intimidating and confusing to people that do
not often play video games. For these people, using a game
controller to interact with the game is an obstacle to enjoying it.
Also, where the game is a dance game, often an additional
controller is required in the form of a dance mat or dance pad.
These dance mats have specific input sections (similar to buttons
on a traditional controller) that react to pressure from the user's
feet. But these mats take up a lot of space and are often single
use controllers--they are used just for dance games and must be
rolled up and stored when not in use.
[0004] To increase a user's feeling of immersion in the game, as
well as to overcome the cumbersome nature of game controllers or
dance mats for users not familiar with them, some game platforms
forego the use of traditional controllers and utilize cameras
instead. The cameras detect a user's physical movements, e.g., the
waving of his arm or leg, and then interpret those movements as
input to the video game. This allows the user to use a more
natural-feeling input mechanism he is already familiar with, namely
the movement of his body, and removes the barrier-to-entry caused
by the many-buttoned controller.
[0005] One example of a camera-based controller is the EyeToy
camera developed by Logitech and used with the Sony PlayStation 2
game console. The EyeToy, and similar cameras, typically include a
camera and a microphone. The EyeToy sends a 640.times.480 pixel
video stream to the PlayStation, and the game executing on the
PlayStation parses the frames of the video, e.g., calculating
gradations of color between pixels in the frame, to determine what
in the camera's field-of-view is the user ("player") and what is
the background ("not player"). Then, differences in the stream over
time are used to determine and recognize the user's movements,
which in turn drive the user's interaction with the game
console.
[0006] Other cameras used by game platforms include the DreamEye
for the Sega Dreamcast, The PlayStation Eye (a successor to the
EyeToy) for Sony's PlayStation 3, and the Xbox Live Vision for
Microsoft's Xbox 360. These cameras all provide a typical
single-input camera that can stream video or take still
photographs, and some, such as the PlayStation Eye, additionally
provide a microphone for audio input.
[0007] Microsoft is currently developing a depth-aware camera
system in the form of Project Natal. A Natal system provides an RGB
camera, a depth sensor, a multi-array microphone, and software that
processes the inputs from the camera, depth sensor, and microphone.
Beneficially, the Natal software provides, based on the input, a
three-dimensional skeleton that roughly maps to the user's body.
Specifically, rather than just determining a difference between
"player" and "not player" like prior game cameras, Natal determines
what is the user's right hand, left hand, head, torso, right leg,
and left leg. This skeleton is preserved as a user moves his body
in the camera's field of view, allowing for the tracking of
specific limbs. This skeleton framework, however, is the extent of
what Natal provides. Namely, no user interface is provided by
Natal, and users must still use a game controller to interact with
a game or menu system.
[0008] Other systems, based on non-camera technologies, have also
been developed that attempt to track a user's movements. For
example, the Nintendo Wii provides players with an infrared
transmitter "Wii remote" that the user holds in his hand. The Wii
remote is used as pointing device and has a built-in accelerometer
to track changes in the Wii remote's position. The Wii remote is
often paired with a "nunchuk" (which also has an accelerometer)
that is held in the player's other hand, allowing the Wii to, in a
sense, track the movements--or at least changes in the
movements--of the user's hands. Another technology based on a
hand-held controller is sixense, which is demonstrated at
http://www.sixense.com
[0009] High-end motion capture ("mocap") systems have also been
used to track a user's movements. Typically mocap systems involve
the user wearing a body suit that has dozens of white spheres
located at relevant locations. The mocap cameras detect these
spheres and use them to infer positional information about the
user's body. Mocap systems, however, are expensive and not
practical for the average user.
SUMMARY OF THE INVENTION
[0010] The invention includes methods, systems, computer program
products and means for providing a dance video game that, by
utilizing a camera-based system, obviates the need for, or use of,
a typical game controller or dance mat for input. Though Natal is
used as an example herein, the invention is not limited to a Natal
implementation.
[0011] In one embodiment, there is a filter system for capturing
and scoring what a user is doing. The user's input is normalized to
a reference framework and compared against key frames of a target
performance, which has also been normalized to the reference
framework. The closer the user's input is to the correct move at
the correct time, the better the rating awarded to the user.
[0012] Advantageously, the game and its filters behave similarly
for a short person and a tall person relative to their own bodies.
In one embodiment of the invention, appendage and body position
determinations are made based on, and relative to, the skeleton of
the person interpreted by the system, not on an absolute coordinate
system within the camera's field of view. Other embodiments can
utilize an absolute coordinate system to infer information about
the user's body to create a skeleton for use with the
invention.
[0013] Typically, ranges are used to determine if a user has
successfully performed a move because motion-tracking input is
inherently noisy. Determining precisely where a user's appendages
are is difficult due to the natural movement of the user over time
and the lag between receiving camera input and processing it. This
is complicated when the user is trying to perform a particular
dance move at a particular time--he may start or end the move too
early or too late, or some appendages may be positionally
inaccurate, or a combination of these. Therefore, the filter system
allows for variation in both timing and position when scoring the
user.
[0014] The invention can also be used to teach a user how to dance.
In some implementations, there is a means for teaching a specific
move or series of moves to a user using audible cues and
repetition. To facilitate this functionality, an additional aspect
of the invention is an animation blending technique that uses
animation transitions from an idle state into a move, and from the
move into an idle state, along with the animation of the move in
the context of the entire dance, to allow the teaching avatar to
demonstrate and repeat a single move.
[0015] There are also scripted transitions, or "bridge animation
segments" that allow for seamless reuse of portions of a motion
capture performance, that, in the performance, are not actually
adjacent. Beneficially, these bridge animation segments can be used
in a variety of contexts. For example, a difficult dance routine
with many different moves can be simplified into a lower difficulty
routine by repeating a subset of the moves, which requires jumping
to non-adjacent animation segments. Also, the bridge animation
segments can be used in a practice mode to repeat moves until the
player has successfully performed them. And, bridge animation
segments can be used to extend the motion capture performance in a
multiplayer mode by looping a segment of the motion capture
performance.
[0016] The invention also provides seamless audio track transition
playback during multi-player modes. It is more fun for users to
trade off dancing during a song than it is for each user to play
all the way through while the other waits. But songs are often
written for a single play-through and do not facilitate smooth
"rewinding" from an audible standpoint. Specifically, the music at
time t.sub.1 (later in the song) does not usually lend itself to a
smooth transition to t.sub.0 (earlier in the song). The invention
solves this by providing segments of transition audio to use
between different parts of the song, selectively muting the
original audio and unmuting the appropriate transition segment when
a transition to a different part of the song is necessary. As with
bridge animations, these bridge audio segments can be used in a
variety of contexts. For example, the bridge audio segments can be
used in a practice mode to repeat sections of the song the player
is practicing until the player has successfully performed them.
And, bridge audio segments can be used to extend the song in a
multiplayer mode by looping a segment of the song audio.
[0017] In one embodiment, there is a method, executed on a game
platform, for scoring a player performance that includes one or
more poses in a dance-based video game based on input received via
a sensor. The method and the components it interacts with can also
be expressed as a system, in the form of a computer program
product, or as an apparatus with means for accomplishing the
interaction, where the structures correspond to a game platform and
a sensor (e.g., a camera) in communication with the game platform.
In cases where results are displayed, a display in communication
with the game platform may also be used. The method includes
receiving a performance 3D skeleton indicating a pose of the
player, then calculating a score by comparing a position, a timing,
or both, associated with one or more joints of the performance 3D
skeleton to a position, a timing, or both, associated with one or
more joints of a target pose; and then altering one or more
characteristics of the dance-based video game based on the
score.
[0018] In another embodiment, there is also a method, executed on a
game platform, for evaluating a player performance based on input
from a sensor. As described above, the method and the components it
interacts with can also be expressed as a system, in the form of a
computer program product, or as an apparatus with means for
accomplishing the interaction, where the structures correspond to a
game platform and a sensor (e.g., a camera) in communication with
the game platform. In cases where results are displayed, a display
in communication with the game platform may also be used. The
method includes receiving a performance 3D skeleton indicating a
portion of the player performance, providing a target 3D skeleton
indicating a portion of a target performance, defining a per joint
error function, calculating an error using the per joint error
function based on the performance 3D skeleton and the target 3D
skeleton, and producing, with the game platform, an audio or visual
indication of the error.
[0019] In one implementation, there is a method, executed on a game
platform, for scoring a player performance that includes one or
more poses in a dance-based video game based on input received via
a sensor. As described above, the method and the components it
interacts with can also be expressed as a system, in the form of a
computer program product, or as an apparatus with means for
accomplishing the interaction, where the structures correspond to a
game platform and a sensor (e.g., a camera) in communication with
the game platform. In cases where results are displayed, a display
in communication with the game platform may also be used. The
method includes providing a target 3D skeleton indicating a target
pose and receiving a number of 3D performance skeletons indicating
player poses. Then an overall score for a particular 3D performance
skeleton is generated by comparing a position associated with one
or more joints of the 3D performance skeleton to a corresponding
position associated with one or more joints of the target 3D
skeleton. Then the score generating step is repeated for each of
the of 3D performance skeletons that fall within a predetermined
temporal range. This generates a number of overall scores, and an
audio or visual indication of the accuracy of the performance, that
is based on one or more of the overall scores, is displayed on the
display.
[0020] In one embodiment, there is a method, executed on a game
platform, for scoring a player performance that includes one or
more poses in a dance-based video game based on input received via
a sensor. As described above, the method and the components it
interacts with can also be expressed as a system, in the form of a
computer program product, or as an apparatus with means for
accomplishing the interaction, where the structures correspond to a
game platform and a sensor (e.g., a camera) in communication with
the game platform. In cases where results are displayed, a display
in communication with the game platform may also be used. The
method begins by receiving a performance 3D skeleton indicating a
pose of the player. Then a score is calculated by comparing a
measurement of one or more reference points, e.g., joints, bones,
or derivations of either, of the performance 3D skeleton to a
measurement of one or more reference points, e.g., joints, bones,
or derivations of either, of a target pose. Some examples of
measurements are displacement, velocity, acceleration, but other
measurements would be understood by one of skill in the art. Then,
one or more characteristics of the dance-based video game are
altered based on the score.
[0021] Any of the above embodiments may enjoy one or more of the
following benefits. In some versions, the target pose, expressed as
a 3D skeleton, is generated based on motion capture data. This is
then provided during the game for weighting, comparison against the
player's performance, and/or scoring. And in some instances, the
target pose is selected based on its importance to the target
performance, e.g., a transitional movement is not important, but a
particular orientation of the player's body at a particular time is
for the movement to be recognized as a particular dance move.
[0022] Also, in some implementations, the position associated with
the one or more joints of the 3D skeleton and the position
associated with the one or more joints of the target pose are based
on a normalization of the spatial position of the one or more
joints of the 3D skeleton and the one or more joints of the target
pose, respectively. For example, normalizing the spatial position
of a joint can include computing a unit vector reflecting an offset
of the joint relative to an origin joint. It can further involve
defining a coordinate system originated at the origin joint; and
translating the unit vector into the coordinate system. Examples of
potential origin points are the left shoulder, the right shoulder,
the left hip, or the right hip.
[0023] Alternatively, normalizing the spatial position of a joint
could be based on computing a first vector reflecting the offset of
the joint relative to an origin joint, computing a second vector
reflecting the offset of an intermediate joint relative to the
origin joint, and then computing a third vector reflecting the
offset of the joint relative to the intermediate joint. Then the
first vector is divided by the sum of the magnitudes of the second
and third unit vectors.
[0024] In some implementations, a second target 3D skeleton is
provided indicating a second target pose and a second number or
group of 3D performance skeletons are received indicating player
poses. An overall score is generated for a second particular 3D
performance skeleton by comparing a position associated with one or
more joints of the second 3D performance skeleton to a
corresponding one or more joints of the second target 3D skeleton.
Then, the score generating step is repeated for each of the second
group of 3D performance skeletons that fall within a second
predetermined temporal range to generate a second number of overall
scores. Lastly, a second audio or visual indication--based on one
or more of the first and second plurality of overall scores--is
produced on the display. The overall score can be based on a
positional score and/or a timing-based score. Additionally or
alternatively, the overall score can be based on a displacement
score, a velocity score, or an acceleration score.
[0025] In some implementations, the target pose is associated with
a target performance timing, and a timing-based score varies
inversely as the difference between the target performance timing
and a timing of performance of the player pose. In some
implementations, the timing-based score is based on a first
constant if the difference is less than a first predetermined
threshold. In some, it varies inversely as the difference if the
difference is between the first predetermined threshold and a
second predetermined threshold. And in some implementation, the
score is a second constant if the difference is greater than the
second predetermined threshold. And in some implementations,
computing the timing-based score uses a combination of the
foregoing techniques.
[0026] In some embodiments, the positional score can include one or
more per-joint scores, where the contribution of each per-joint
score to the overall score is weighted. Additionally or
alternatively, the positional score can include one or more body
part scores, with each body part score having one or more per-joint
scores. And as above, the contribution of each body part score to
the overall score can be weighted.
[0027] In some versions, comparing the joints of the 3D performance
skeleton to the joints of the target 3D skeleton includes
calculating a Euclidean distance between the position associated
with the more joints of the 3D performance skeleton and the
corresponding position associated with the joints of the target 3D
skeleton to generate a per-joint score. And this per-joint score
can vary inversely as the Euclidean distance. In some embodiments,
for example, the per-joint score can be a first constant if the
Euclidean distance is less than a first predetermined threshold. In
some embodiments, it varies inversely as the Euclidean distance if
the Euclidean distance is between the first predetermined threshold
and a second predetermined threshold. And in some embodiments, it
is a second constant if the Euclidean distance is greater than the
second predetermined threshold. And in some implementations,
computing the per-joint score uses a combination of the foregoing
techniques.
[0028] Additionally or alternatively, calculating the Euclidean
distance can include weighting the contributions of the x, y, and z
axes to the Euclidean distance, with the orientations of the x, y,
and z axes are relative to each body zone. For example, the x, y,
and z axes of an arm body zone can originate at a shoulder
connected to the arm and are based on a first vector from the
shoulder to an opposite shoulder, a second vector in the direction
of gravity, and a third vector that is a cross product of the first
and second vectors. Alternatively, the x, y, and z axes of a leg
body zone can originate at a hip connected to the leg and are based
on a first vector from the hip to an opposite hip, a second vector
in the direction of gravity, and a third vector that is a cross
product of the first and second vectors. And, the orientations of
the x, y, and z axes can also be relative to the target 3D
skeleton. That is, the x, y, and z axes are rotated based on an
angle between a vector normal to a plane of the target 3D skeleton
and a vector normal to a view plane.
[0029] In some embodiments, the audio or visual indication
comprises a visual indication of a score for a body part, such as
flashing the body part green or red for success or poor performance
respectively. Or, the audio or visual indication comprises an
audible indication of the score for a body part, e.g., "nice arms!"
or "you need to move your feet more!" The audio or visual
indication can also include one more graphics, with the number of
graphics being based on the one or more overall scores. The audio
or visual indication can also be a simulated crowd, where one or
more characteristics of the simulated crowd varies based on the one
or more of the plurality of overall scores, e.g., the number of
people in the crowd can grow or shrink. The audio or visual
indication can also be a simulated environment, where one or more
characteristics of the simulated environment varies based on the
one or more of the plurality of overall scores, e.g., there can be
fireworks or flashing lights if the player is performing well and
destruction or dimming of the environment if the player is
performing poorly.
[0030] There is also a method of providing a smooth animation
transition in a game. As described above, the method and the
components it interacts with can also be expressed as a system, in
the form of a computer program product, or as an apparatus with
means for accomplishing the interaction, where the structures
correspond to a game platform and a display in communication with
the game platform. The method includes, during gameplay, providing
an event timeline with event markers denoting points in time on the
event timeline. Each event marker is associated with an animation
segment from the number of animation segments. The first marker on
the event timeline is provided, which indicates a first animation
segment to be displayed on the display (at a point in time with
respect to event timeline). A second marker on the event timeline
is also provided, which indicates a second animation segment to be
displayed on the display (at a second point in time with respect to
event timeline). Then as the game progresses, and the second point
time on the timeline is approaching, a set of animation segments
that need to be blended together is determined, to provide a smooth
transition from the first animation segment to the second animation
segment. Once the set of animations have been determined, a blend
is performed among the set of animation segments. For example, a
blend between the first animation segment and the second animation
segment may be all that is needed and portions of each are blended
together. More specifically, a number of beats at the end of the
first animation segment may be blended with a number of beats at
the beginning of the second animation. Alternatively, a smoother
result may be achieved using a bridge animation segment, where a
portion of the first animation segment is blended with the bridge
animation segment and then a portion of the bridge animation
segment is blended with the second animation segment. In some
versions, the existence of a bridge animation segment is determined
by the presence of a bridge animation segment or a reference to a
bridge animation segment listed in a lookup table, keyed off the
animations that are being blended from and to. If the entry in the
lookup table exists, the bridge animation segment is used. If not,
no bridge animation segment is used, and the first animation
segment is blended directly into the second animation segment.
[0031] These blending techniques are useful for multiplayer
gameplay as well, where a first player is scored before the blend
occurs and a second player is scored after the blend. Beneficially,
the second animation can be based on the difficulty of the game, so
if the first player is very good and is performing a complex move,
the transition to the second player's move, which is easier, will
not be jarring because of the transition. Or, where a series of
animations are recorded and then "cut up" and reused to form
progressively easier routines (with animation sequences from the
hardest difficulty being arranged for each difficulty level), the
transitions can be used to create a dance routine using
non-contiguous or looping animation sequences. The technique can
also be used to blend an animation with itself, that is, blend the
ending position of the dancer with the starting position of the
dancer. This can be used for repeated moves.
[0032] Another technique is to blend audio segments. In one
embodiment, there is a method, executed on a game platform, for
providing smooth audio transitions in a song. The method includes
providing, during play of a game, an event timeline with event
markers denoting points in time on the event timeline. The event
timeline is associated with an audio track played during play of
the game. The audio track has a first audio segment and a second
audio segment. Then, a first marker on the event timeline is
provided to indicate a first point in time (that is associated with
the first audio segment). Also, a second marker on the event
timeline is provided that indicates a second point in time with
respect to the event timeline (and is associated with the second
audio segment). During game play it is determined that the second
time is approaching and a set of audio segments to be blended is
determined that will ensure a smooth transition from the first
audio segment to the second audio segment. Then, based on the set
of audio segments that will be used for blending, a blend is
applied among the set of audio segments based on the prior
determination made. For example, the set of audio segments that are
used for the blend could be just the first audio segment and the
second audio segment, and the blend could be accomplished by
crossfading between the two. Or, a bridge audio segment may also be
necessary, and the blend can be applied to a portion of the first
audio segment and blended with a portion of the bridge audio
segment, and then a blend can be applied from a portion of the
bridge audio segment to a portion of the second animation. As
above, a blend can be a crossfade, but can also be an attenuation,
e.g., the first audio segment can be reduced in volume or silenced
completely (muted) while the bridge audio segment is played and
then the bridge audio segment can be reduced in volume or stopped
completely and the second audio would be played. For example, the
first audio segment can be muted for its final beat, the second
audio segment can be muted for its first two beats, and the bridge
audio segment is played in the three beat-long "hole", i.e., during
the muted last beat of the first audio segment and muted first two
beats of the muted second audio segment.
[0033] In some implementations, the first audio segment and the
second audio segment are the same audio segment, as would be the
case of a repeated section of audio. The bridge audio segment or a
reference to a bridge audio segment can also be stored in a lookup
table that is keyed based on the audio segment that is being
transitioned from and the audio segment that is being transitioned
to.
[0034] Other aspects and advantages of the present invention will
become apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating the
principles of the invention by way of example only.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The foregoing and other objects, features, and advantages of
the present invention, as well as the invention itself, will be
more fully understood from the following description of various
embodiments, when read together with the accompanying drawings, in
which:
[0036] FIG. 1A depicts a game platform with a Project Natal camera
system;
[0037] FIG. 1B depicts an example of a skeleton provided by Project
Natal;
[0038] FIG. 1C depicts an example of a skeleton that includes
vectors used in determining normalized joint position;
[0039] FIG. 2A shows a series of movements spread over four beats
that begin a representative dance move;
[0040] FIG. 2B shows a representative window to determine a user's
timing error in performing a move;
[0041] FIG. 3A shows a distance calculation between the target
performance skeleton (shown in outline) and the user's input (shown
solid);
[0042] FIG. 3B shows a window of acceptable error for position when
performing a move;
[0043] FIG. 4 depicts how a mocap for a dance routine may be
refactored to create a dance routine of an easier difficulty;
[0044] FIG. 5 depicts one embodiment of an authoring system for the
dance game.
DETAILED DESCRIPTION
[0045] One embodiment of the present invention is based on the
Project Natal framework developed by Microsoft Corporation of
Redmond, Wash. As indicated in FIG. 1A, the Project Natal system
includes an RGB camera 105, a depth sensor 110, a multi-array
microphone 115, and a processor (not shown). The RGB camera 105
delivers a three-color (Red, Green, Blue) video stream to the game
console, enabling facial recognition and full-body tracking. The
depth sensor 110 is an infrared projector combined with a
monochrome CMOS sensor. This allows a game console 120 utilizing
Natal to recognize objects in the camera's field of view in three
dimensions instead of forcing the game console to parse a
two-dimensional video-stream. The multi-array microphone 115 parses
voices and sound input, while simultaneously extracting and
nullifying ambient noise. Project Natal also features a processor
with proprietary software that coordinates the inputs of the Natal
system and provides a three-dimensional, skeleton-based system to
game developers. Developers can use this system to utilize
three-dimensional position information of the joints in the user's
body to interact with the game platform.
[0046] Although Project Natal provides a framework for determining
positional information of a user's body, it does not provide a
means for grading a dance performance or teaching a user to dance.
While in some embodiments, a camera-based system is used to
determine positional information about the user's body in three
dimensions to produce a skeleton model, in other embodiments,
transducers attached to the user's body are used to detect the
positions of the user's limbs and produce a skeleton model. Other
embodiments use infrared pointing devices or other motion tracking
peripherals. All that is required is a system than can parse
movement in two dimensions to produce a skeleton model; adding
dimension information from a third dimension, typically depth,
simply makes the invention easier to implement due to the
additional information provided to the system. In embodiments where
the system is already provided a skeleton, such as Natal, relative
body scale mapping is easier to accomplish.
[0047] Also shown in FIG. 1A is an exemplary game platform 120. The
game platform typically includes a Central Processing Unit (CPU)
125, a graphics processor 130, storage component 135 such as a hard
drive, Read Only Memory (ROM) 140, Random Access Memory (RAM) 145,
all in signal communication via a bus 150. The bus 150 also
connects to an input for the Project Natal System. In some
embodiments, the Natal system connects to the game platform 120,
e.g., an Xbox 360, via a Universal Serial Bus (USB) connection.
[0048] As used herein, the terms "joint", "bone", and "skeleton"
are intended to have the meaning one of skill in the art of motion
capture and animation would ascribe to them. For example, a
skeleton can comprise bones, but the number of bones and their
positions are a function of the motion capture equipment and the
animation rig and do not necessarily correlate to the number and
positions of bones in a human skeleton. Similarly, a joint can be
at the distal endpoint of a single bone (e.g., a fingertip or the
head), and need not be at a point where two bones come together. An
example of the Natal skeleton is shown in FIG. 1B. The skeleton
provided by the Natal system provides a framework for the dance
game, and allows for tracking of not only limbs generally, but
specific joints as well. For example, the wrist joint 160 on the
right arm is treated separately from the right elbow 165, which is
treated differently than the right shoulder 170. Additional
portions of the body are also recognized, such as the pelvis,
middle of the torso, the head, the neck, and the knees and
feet.
[0049] One of the benefits provided by the skeleton-based system is
that the skeletal model can be used to calculate scale vectors
based on two or more joints. This provides a spatially relative
system, i.e., what is the positional distance from body part X to
body part Y compared to the positional distance from body part X to
body part Z, instead of an absolute coordinate system.
[0050] A "filter" as used herein, is in effect a test, e.g., is the
user's right hand in a particular position at time t.sub.n?
Although typically a producing a Boolean outcome, e.g., if the
condition is true, the filter is satisfied and registers a success,
and if not, then the filter is not satisfied. Filters may also
output a contiguous score indicating the degree to which the
condition is being satisfied spatially or temporally.
Advantageously, multiple filters can be checked simultaneously,
e.g., is the user's right hand in position x and is his left foot
in position y? These filters can then be combined to determine if a
user has successfully completed a pose. But pose-matching, in and
of itself, is not a complete solution to scoring a sequence of
dance moves.
Creating a Target Representation
[0051] The process of one implementation begins by using motion
capture technology (known in the art as "mocap") to create a
three-dimensional model of a target performance of a dance or part
of a dance. Motion capture is a recording of human actor which can
be used by a computer to reproduce the actor's performance. When
the mocap session is recorded, sensors at various points on the
actor's body provide the recording computer with information such
as joint and limb position data over time. In the case of a dance
game, the mocap is typically a recording of a dancer performing a
particular dance move, or series of movements that makes up a dance
move, and in one implementation, the mocap is a recording of an
entire dance routine for a song. The mocap performance becomes a
representation of the dance in a form usable by the game system
(i.e., a "target performance"). Beneficially, the positional
information received during mocap is similar to the positional
information received by a camera-based game system when a user is
playing a game. This similarity can be exploited to grade a user on
how well he is dancing at a particular time by comparing a user's
performance (the input performance) to a keyframe of the target
performance. Also beneficially, the mocap data can be used to drive
on-screen animations of avatars, thus demonstrating to the user the
exact movements he must perform to maximize his score.
[0052] At least one notable problem arises though that prevents a
direct comparison between the user's performance and the target
performance: because the user and the mocap actor could have
different heights and appendage lengths, or have different body
types, a direct comparison of positional information of the input
performance and the target performance could result in the user
scoring poorly, even if he is performing the moves correctly. For
example, the actor in the target performance could have an arm
fully extended which, based on the dimensions of the actor's body,
positions the actor's wrist two and a half feet in front of his
shoulder. The user's input, also reflecting a fully extended arm,
could have the (shorter-in-stature) user's wrist positioned two
feet in front of his shoulder. In a purely comparative system, the
user has not satisfied a test of "is the user's wrist in the same
position as the wrist of target performance actor?" because the
user's wrist, even though his arm is fully extended, is still a
half foot closer to the reference point, i.e., the shoulder.
Therefore, it is advantageous to express both the target
performance and the user's performance in the same frame of
reference.
Normalizing the Input Performance and Target Performance
[0053] To create a consistent frame of reference, the mocap data,
which is expressed in its own representation (in some
implementations even its own skeleton), and the user's input are
both normalized, creating a normalized target performance and a
normalized input performance. In one implementation, normalization
of each joint is achieved by deriving unit vectors reflecting
offsets of one specific joint relative to another specific
joint.
[0054] In one embodiment, there are four different
player-normalized coordinate systems: left arm, right arm, left
leg, and right leg. The left arm coordinate system's origin is at
the left shoulder, the up vector is away from gravity (in Natal
systems, based on Natal's accelerometer). The right vector is from
the left shoulder to the right shoulder, the forward vector is the
cross product of the up vector and the right vector. The right arm
coordinate system is just the mirror of this. The left leg
coordinate system's origin is the left hip, the up vector is
gravity, the right vector is from the left hip to the right hip,
and the forward vector is the cross product of the up vector and
the right vector. The right leg coordinate system is the mirror of
this.
[0055] As an example, referring to FIG. 1C, the normalized position
of joints on the left arm can be determined as follows. The left
shoulder joint 175 is treated as the origin of the vector 185 from
the shoulder to the elbow 180 and that vector 185 is transformed
from the skeleton's coordinate system into the left arm coordinate
system. The vector is then normalized by dividing it by its
magnitude. The resulting vector is a "normalized elbow position." A
similar process is applied to the input skeleton to determine a
normalized elbow position for the user. This method can be used for
other joints as well, e.g., the wrist position can be normalized by
determining the vector 190 from the elbow 180 to the wrist 182,
transforming that vector from the skeleton's coordinate system into
the left arm coordinate system, and dividing it by the magnitude of
that vector 190. A knee's position can be normalized based on the
vector 195 between the hip and the knee, transformed from the
skeleton's coordinate system into the appropriate-side leg
coordinate system, and divided by the magnitude of that vector. An
ankle's position can be determined based on the vector from the
knee to the ankle, and so forth. Other joints such as hips are
usable as well: foot raises are determined as a "squish" from foot
to waist where the foot's position is drawn in towards the waist.
In one embodiment, the normalized joint positions in the entire
skeleton are computed, using the joint more proximal to the body
core as the reference joint. In other embodiments, only a subset of
the joints that have a correspondence in both skeletons are
normalized, and normalization occurs on a limb-by-limb basis. In
either embodiment, the normalization of the target performance can
be carried out in advance of gameplay, or can be carried out during
gameplay.
[0056] There are several options for normalizing joints that are
not directly connected to an origin joint. Continuing the previous
example with the shoulder 175 being the origin joint, the wrist's
position could be normalized by determining the vector 197 from the
shoulder 175 to the wrist joint 182, transforming the vector 197
from the skeleton's coordinate system into the left arm coordinate
system, and dividing the resulting vector by the sum of the
magnitude of the vector 185 from the shoulder to the elbow and the
magnitude of the vector 190 from the elbow to the wrist.
Alternatively, the vector 197 from the shoulder to the wrist could
be determined, transformed, and divided by the magnitude of that
vector 197. For legs, an ankle position could be based on foot
position, transformed from the skeleton's coordinate system into
the appropriate-side leg coordinate system, and divided by the sum
of the magnitudes of the vector from the hip to the knee and from
the knee to the ankle
[0057] Typically, normalizing the target performance and the input
performance yields positional information analogous to both, e.g.,
both have elbow position representations, both have wrist position
representations, etc. Where data is not available in the mocap data
or the user input for a particular joint though, in some
embodiments, the game interpolates between two joints to create a
"pseudo-joint" that maps to a joint in the other skeleton. For
example, if the mocap skeleton has a left hip joint and a right hip
joint, but a user skeleton only has a mid-pelvis joint, a
mid-pelvis pseudo-joint can be synthesized for the mocap skeleton
at the midpoint of the two hip joints, and used in further
normalization and scoring. Alternatively, pseudo-joints could be
interpolated from both data sets/skeletons to map to a third
idealized skeleton. Additionally, where the input camera system is
a Project Natal system, adjustments are typically made to conform
the mocap skeleton to the Natal skeleton, or vice versa, e.g.,
dropping the hips, adjusting the shoulder height, and others. In
some embodiments, the game creates a "pseudo-joint" even when data
is available in both the mocap data and the user input, in order to
provide a reference point or measurement that is more stable than a
joint in the existing skeleton.
Comparing the Input Performance to the Target Performance
[0058] In one embodiment of the invention, every "frame" of the
input performance is compared with the corresponding frame of the
target performance to produce a score for that frame. This
strategy, however, does not allow the game to account for
inaccuracies in the user's timing, such as dancing a move with
perfect position but slightly late or early. In another embodiment,
the invention addresses this issue by scoring each frame of the
input performance against the corresponding frame of the target
performance and a range of adjacent frames. The scoring process
incorporates positional and temporal score using a technique
described below. For a given target frame, a score is determined by
finding the maximum score of all input frames scored against that
target frame.
[0059] This approach, however, can be prohibitively expensive
computation-wise on some game consoles. To alleviate this, in some
embodiments, only a fraction of the input frames are compared with
target frames (e.g., half of the input frames). The specific frames
in the input performance that are chosen for comparison can be
regularly spaced, or the frames can be chosen randomly with a
probability matching that fraction.
[0060] This approach, however, does not capture the intent behind a
dance move where certain intermediate poses are more important and
the transition movements into or out of those poses are less
important. In a preferred embodiment, the input frames should be
compared to the target frames most important to the dance
itself.
[0061] In one embodiment, each frame of the target performance is
assigned a weight (e.g., in the range 0.0 to 1.0). As stated above,
each target frame receives a score based on the maximum score of
all input frames scored against that target frame. In this
embodiment, that score is multiplied by the weight to produce a
weighted score for each target frame. The score for a move is
determined by combining the weighted scores using a sum or
average.
[0062] In one embodiment, each frame of the target performance is
assigned a weight (e.g., in the range 0.0 to 1.0) that is computed
based on the target performance. The weight for a frame of the
target performance may be computed based on any number of
neighboring frames of the target performance. The computation
determines which target frames are the most important to the dance
by detecting inflections in direction of parts of the target
skeleton, or inflections in distance between parts of the target
skeleton.
[0063] For example, the initial weight for a frame may be 0.0. A
velocity vector can be computed for each joint in a target frame by
subtracting its position in the previous frame from its position in
the current frame. Whenever any joint's velocity experiences a
derivative of zero with respect to time, along the x, y, or z axis
in the camera-based coordinate system, or along the x, y, or z axis
in the skeleton-based coordinate system (see below for a technique
for computing a skeleton-based coordinate system), that frame's
weight is increased. For example, if the weight of the target frame
before considering the joint was w0, the new weight might be
(1+w0)/2, or it may be set to a predetermined "one joint
zero-derivative" value such as 0.5. If another joint's velocity
simultaneously experiences a derivative of zero, the frame's weight
is increased by substituting the previous weight into (1+w0)/2
again, or it may be set to a predetermined "two joint
zero-derivative" value such as 0.75. Likewise, additional joints
that experience simultaneous derivatives of zero make the current
frame have a higher weight using the formula or a lookup table that
references number of contributing joints to a weight value between
0.0 and 1.0.
[0064] Although derivatives of joint positions can be used to
determine the weight for a frame of the target performance, other
measurements can also contribute to the weight. For example,
distances between specific joints can be computed for each frame
and tracked across frames, and zero-derivative measurements can
contribute to the weight. For example, the distance between wrist
joints may be measured for each frame. Frames in which the distance
experiences a zero derivative would increase the frame's weight by
substituting its previous weight into (1+w0)/2 or looking up a
value from a table as above.
[0065] Other measurements can also contribute to the weight, such
as zero-derivative measurements of the overall bounding rectangle
of the skeleton along x, y, or z axes in a camera-centered
coordinate system or x, y, or z axes in a skeleton-based coordinate
system.
[0066] However the target weight is computed, the final weight
assigned to each target frame is used in the same way as described
previously.
[0067] In a preferred implementation, a subset of the frames of the
target performance are marked as keyframes, each keyframe
representing a specific frame in the target performance with which
the input performance should be compared. The target
performance--comprising an entire dance routine--is aligned with a
timeline, the performance being divided into moves, each move
having a start time and an end time relative to the beginning of
the dance, measured in units of measures/beats/ticks.
Alternatively, each move can have a start time and a duration.
[0068] All times and durations are typically measured in units of
measures, beats, and ticks, but alternatively can be measured in
units of seconds. Times are measured relative to the beginning of
the dance, but alternative reference points are possible, such as
the end of the dance, the start of the previous move, the end of
the previous move, or any other moment in time within the
timeline.
[0069] Each keyframe includes a time offset relative to the
beginning of the move. In addition to timing information, each
keyframe can include weighting information for x, y, and z axes
relative to the camera (explained below). Additionally or
alternatively, each keyframe can include weighting information for
x, y, and z axes relative to the entire skeleton in the target
performance, or weighting information for x, y, and z axes relative
to each "body zone" (limb-centered coordinate systems) in the
target performance (explained below). In one implementation,
relaxing the scoring is achieved by unevenly weighting the
contributions of the x, y, and z axes to the Euclidean distance
measurement above, where x, y, and z are taken to be in the left
arm coordinate systems, right arm coordinate system, left leg
coordinate system, or left leg coordinate system.
[0070] In addition to weighting information for the axes, the
keyframe also includes weights for different bone groups themselves
to emphasize performing a particular motion, e.g., moving the
user's arms during the "shopping cart," or deemphasizing other
motions one, e.g., ignoring or forgiving poor leg position during
"the shopping cart".
[0071] Keyframes are placed wherever necessary on the timeline to
capture the most important poses in the dance sequence. Often,
keyframes are placed at eighth-note boundaries, but they may be
spaced irregularly depending on the dance or move to be tested.
[0072] In a preferred embodiment, the target performance is
expressed as mocap data associated with a Milo file. The Milo file
contains a timeline and allows for events, tags, or labels to
trigger events in the game. Advantageously, the target performance
is aligned to the timeline. The Milo file is also typically
associated with a music track, which is also aligned to the
timeline. This allows the developer to assign events to certain
portions of the music track. The Milo file also has instructional
timelines for providing audio cues to the user (explained below).
Another benefit of using the Milo file is the ability to mark parts
of the timeline, and therefore parts of the target performance, as
keyframes. Keyframes are placed at specific measures or beats on
the timeline and represent times to test user input.
[0073] Comparing the input performance to the target performance
input at a particular keyframe may be accomplished in several ways.
In one embodiment, each keyframe has a time window associated with
it, beginning before the keyframe and extending beyond it. The time
window is typically symmetrical around the time of the keyframe,
but may be adjusted for a longer intro if a move is difficult to
get into or a longer outro if the move is harder to get out of. The
time window is typically of a fixed width in seconds.
Alternatively, the time window can be expressed as fixed width in a
variable unit of time such as beats, so that the window expands and
contracts as the dance tempo slows down or speeds up,
respectively.
[0074] FIG. 2A provides an illustrative example. FIG. 2A shows a
series of movements spread over four beats that begin a move called
"Push It." The first beat is a move marked "hands out", the second
is a move marked "hands in," the third is a "right hand up", and
the fourth is "left hand up" move. In FIG. 2A, three keyframe
windows are displayed, each centering on a beat: the first keyframe
200 is for the "Hands out" move at beat 1, the second keyframe 205
is for the "Hands in" move on beat 2, and the third 210 is for the
"Right hand up" move on beat 3. The user's input, sampled a certain
number of times per second, e.g., 30, is examined to determine if
it matches the target performance. For example, on beat 1 (and for
a period before and after beat 1 illustrated by the umbrella around
200) the user's input is sampled to determine if, in this case, the
user's hands are stretched out in front of him in a way that
matches the target input which is based on the mocap performance.
Then, on beat 2 (and before and after), the user's input is sampled
to determine if it matches the target performance where the user's
hands are pulled back in. The windows around each keyframe are to
allow for variation in time for the user to complete the move.
Variation is allowed for in both time and positional displacement
because rarely will the user have their limbs exactly in the
expected position at exactly the right time. Additionally, as
stated above, some leeway is provided because the camera is an
inherently noisy input.
Allowing for Variation in Time
[0075] Referring to FIG. 2B, if any of the user's inputs match the
target performance within a certain inner time window around the
keyframe, e.g., in the range to d.sub.-inner to d.sub.+inner, the
user is given full score for performing that portion of the move
that aligns with that keyframe (+/- to allow for the user to reach
the move early or late, and the allowances either before or after
are not necessarily symmetrical). This is accomplished by examining
each frame of input during the window and selecting the closest
match.
[0076] Between an inner time window and an outer time window, e.g.,
in the range d.sub.-outer to d.sub.-inner and the range
d.sub.+inner to d.sub.+outer, a score is still given for performing
the move, but the score for that performance is reduced as the
temporal "distance" outside the inner window increases. Outside the
outer windows, i.e., before d.sub.-outer and after d.sub.+outer,
respectively, no score (or a score of zero) is given for performing
the move because the user is just too early or too late. The fall
off function for the score during the periods of d.sub.-outer to
d.sub.-inner and d.sub.+inner to d.sub.+outer is typically a
variation of 1-x.sup.2. This yields a parabolic shape that starts
from 0 and builds to 1 between d.sub.-outer and d.sub.-inner, and
then falls from 1 to 0 between d.sub.+inner to d.sub.+outer. More
specifically, in one embodiment, the scoring curve is assembled
piecewise:
For frames before d.sub.-outer, y(x)=0. For frames between
d.sub.-outer and d.sub.-inner:
y ( x ) = 1 - ( x - x 0 + d - inner d - outer - d - inner ) 2 .
##EQU00001##
For frames between d.sub.-inner and d.sub.+inner (including
x.sub.0), y(x)=1. For frames between d.sub.+inner and
d.sub.+outer:
y ( x ) = 1 - ( x - x 0 - d + inner d + outer - d + inner ) 2
##EQU00002##
For frames after d.sub.+outer: y(x)=0.
[0077] But other variations are possible as well, e.g., a linear
function, a constant, a parabolic function, a square-root, 1/x,
1/(x.sup.n) (e.g., inverse square, inverse cube, etc.), polynomial,
exponential, logarithmic, hyperbolic, Gaussian, sine, cosine,
tangent, or any combination or piecewise combination thereof.
[0078] Beneficially, in some embodiments, as shown in FIG. 2A, the
windows for keyframes can overlap, e.g., keyframe 205 overlaps 200.
In these cases, an input frame in the overlapping area is scored
against both keyframes. The maximum score of all input frames that
are scored against a given keyframe is assigned as the score for
that keyframe. Any keyframe that the user can match, i.e., that his
input falls within an umbrella for, is considered an "active
keyframe" for that input frame.
Allowing for Variation in Position
[0079] As discussed above, the user's positional success is
determined based on comparing the normalized input performance to
the normalized target performance. When comparing the input
performance to a keyframe (again, preferably done for each sampling
of the input performance), the aggregate distance is taken between
the two to determine how close the normalized input performance is
to the normalized target performance of the keyframe. This can be
done for the whole skeleton of the target performance or can be
done on a limb by limb basis. Distances are calculated as the
Euclidean distance between the normalized input performance's joint
position in the input frame and the normalized target performance's
joint position in the keyframe.
[0080] FIG. 3A shows a distance determination between the target
performance skeleton (shown in outline) and the user's input (shown
solid). The distance between the user's elbow joint 300 and the
target performance skeleton's elbow 305 is determined, reflecting
the error the user is committing in terms of positioning his limb.
If a filter is just testing elbow position, the analysis stops with
comparing 300 and 305. If the filter also tests wrist position, the
distance is determined between the user's wrist position 310 and
the target performance skeleton's wrist position 315. As shown in
FIG. 3A, the user's elbow position is only slightly off the target
performance's elbow, whereas the user's wrist significantly out of
position. These differences are then used to determine how well the
user is satisfying the filter. Although arms are shown in FIG. 3A,
differences between the user's leg and the target performance's leg
are determined similarly.
[0081] For hips, hip velocity is a vector from the hip position in
the previous keyframe to the hip position in the current keyframe.
The vector is divided by the amount of time elapsed between the
keyframes. To normalize the hip velocity, the velocity vector is
then divided by the length of the spine. Then the resulting vector
is then used for Euclidean comparison similar to that described
with respect to arms and legs. Advantageously, dividing by the
length of the spine normalizes the velocity measurement to account
for the size of the user, e.g., a child needs to displace his hips
a smaller amount than a taller adult, in order to receive the same
score.
[0082] In some embodiments, the total skeleton score is an
aggregate (e.g., sum) of five different scores, i.e., left arm
score, right arm score, left leg score, right leg score, and hip
velocity score. These are each made up of score calculations
themselves for the individual joints and represent how well the
user performed the move for each "body zone". For example, the left
arm score is an aggregate of the wrist score and elbow score, and
the leg score is an aggregate of the knee score and ankle score.
Beneficially, displacement of the body, measured by hip velocity,
may also be incorporated into the score calculation. Also
beneficially, contributions to the aggregate skeleton score by the
aggregate body zone score may be weighted per keyframe to enhance
the contribution from zones that are more important to executing
the keyframe pose. For example, if the left arm is most important
to a particular pose, the weight of its contribution to the score
can be increased, or contributions of other body zones' scores can
be decreased, or some combination thereof. Beneficially,
contributions to aggregate body zone score by individual joint
score may be weighted per keyframe, to enhance contribution from
individual joint positions that are more important to executing the
keyframe pose. For example, the elbow is more important than the
wrist for the "Funky Chicken" pose, so the weight of the elbow
joint's score can be increased, or the weight of the wrist joint
score can be decreased, or some combination thereof. Typically
though, if a user's joint or body zone is in the correct position,
the user will be given full credit for the correct position and the
weight of that limb's contribution will not be decreased.
[0083] Referring now to FIG. 3B, like timing, there is a window of
acceptable error for position. The error for position is determined
based on the distance between the normalized input joint position
and the normalized target joint position. If the distance is below
a threshold (using the same convention as timing: d.sub.+inner),
e.g., 0.25 or less, the error is considered zero for that joint, so
input frame receives a 100% score. If the distance is greater than
the d.sub.+inner, the score will fall off quickly as the distance
increases to some outer boundary, d.sub.+outer. Between
d.sub.+inner and d.sub.+outer, the input frame still receives some
score, but the further the scored limb or joint is from the target
position, i.e., the closer it is to d.sub.+outer, the less score
the user receives. Once the joint's position is so far off position
that the distance falls outside d.sub.+outer, the user receives no
score (or zero score) for that frame. Unlike timing errors, which
may represent times before or after the keyframe and may therefore
be positive or negative, distances are always positive.
[0084] The score of an input from for a particular keyframe is
determined aggregating the positional score and the timing score.
In a preferred embodiment, the positional score for an input frame
compared against a particular keyframe is then multiplied by the
timing score for that input frame to produce an overall score for
the input frame for that keyframe. If the score for an particular
input frame is greater than the score of any other input frame for
a particular keyframe, i.e., that input frame is the "closest" to
the keyframe in terms of the combination of weighted timing and
position scores, that score is the assigned score for that keyframe
and is used to determine the player's overall score for the move.
When the user has satisfied a certain percentage of the filters for
the bar, e.g., 80%, the user is considered to have successfully
performed the entire move for that bar (because it is unlikely that
a user will satisfy 100% of the filters). In implementations with
graduated feedback (discussed below), completing 80% may be
"Perfect," 60% may be "Good," 40% may be "Fair," and 20% may be
"Poor."
Compensating for the Limits of the Camera and User
[0085] The present invention overcomes one limitation of the user's
ability to parse input presented on the display. Certain movements
of the on-screen dancer along the z axis (into and out of the
screen) are difficult for the user to parse precisely. For example,
when the avatar's arm is held out directly in front of its body,
and the wrist is then moved closer to or further from the avatar's
body along the z axis, the degree of that motion is hard to see
from the user's perspective. This is problematic for a dance game
because the game may require the user to replicate this movement,
and the user cannot easily judge the distance well enough to
execute the movement well.
[0086] In one implementation of the present invention, this is
overcome by unevenly weighting the contributions of the x, y, and z
axes to the Euclidean distance measurement above. This has the
effect of "flattening" the error space in a dimension if that
dimension is difficult to detect visually. This is typically
expressed as a front-to-back relaxing of the scoring along the z
axis, because movements in a camera-based system towards the camera
(forward) or away from the camera (back) are the ones being
compensated for. The relaxation of scoring along an axis is
automatically provided by the invention by reducing the
contribution along that axis by a coefficient in the Euclidean
distance calculation. The developer may also specify, for a given
keyframe, coefficients for one or more axis to reduce or enhance
the contribution of error along that axis to the final score.
[0087] The present invention also overcomes the limitation caused
by occlusion that is inherent to any camera-based input. When a
dance move requires one or more parts of the body to be moved
behind other parts of the body, the occlusion of the joints makes
it very difficult to determine their positions with accuracy. This
is problematic because joints can be occluded in normal dance
moves, such as when an arm goes behind the back, or when a move
requires the user to turn sideways to the camera.
[0088] The present invention additionally overcomes a limitation
with a user attempting to reproduce the target performance when the
mocap for the target performance was executed by a professional
dancer who is very flexible. This is problematic because a
professional dancer can place his body in positions that cannot be
achieved by a casual user, and therefore the user cannot score well
on the move. For example, a professional dancer can touch his
elbows together behind his back, but it would be unfair to penalize
a typical user for this lack of flexibility, so the scoring for
these moves can be relaxed.
[0089] In one implementation of the present invention, relaxing the
scoring is achieved by unevenly weighting the contributions of the
x, y, and z axes to the Euclidean distance measurement above, where
x, y, and z are taken to be in the mocap performer's frame of
reference. The frame of reference of the mocap skeleton is computed
per-frame as a rotation about the z axis of the camera's frame of
reference. The angle of rotation can be computed by finding the
plane created by the shoulders and the center of the pelvis,
finding the forward-facing normal, and rotating the frame of
reference through the angle from the view plane normal to the
forward-facing normal. Alternatively, the frame of reference of the
mocap skeleton can be computed by starting with the plane created
by both hips and the head.
[0090] In one implementation, relaxing the scoring is achieved by
unevenly weighting the contributions of the x, y, and z axes to the
Euclidean distance measurement above, where x, y, and z are taken
to be in the left arm coordinate systems, right arm coordinate
system, left leg coordinate system, or left leg coordinate
system.
[0091] One the frame of reference has been rotated, relaxing
scoring along an axis has the effect of "flattening" the error
space in a dimension. For example, if a move requires the elbows to
be pulled back very far, relaxing scoring along the z axis in the
frame of reference of the mocap performer will reduce the distance
the elbows need to be pulled back in order to achieve a good score.
The relaxation of scoring along an axis is specified with the
keyframe information as coefficients for the Euclidean distance
calculation.
[0092] Beneficially, the game developer can manually weight certain
moves to be more forgiving along any axis simply because a move is
hard to perform.
[0093] In some implementations, weighting is based on the
"confidence" that the camera system may provide for detecting a
joint's position. For example, in some versions of Project Natal,
the camera system provides "tracked" positional information in the
form of a position for a joint and a confidence level that the
position is correct. When the joint is off-screen, Natal also
provides an "inferred" position. When a joint's position is
inferred, e.g., when the joint is clipped or occluded, neighboring
joints can be examined to better assess where the inferred joint
is. For example, if an elbow is raised above the user's ear, there
are only a few possible locations of the user's wrist, e.g.,
straight up above the elbow, down near the user's chin, or
somewhere in between. In these scenarios, because the object of the
game is to be fun, the maximum positional window, e.g., 0 to
d.sub.+outer, is widened so that the filtering is looser to allow
for greater variation in positional differences. Additionally, the
inner window of "perfect" position, zero to d.sub.+inner, may also
be widened.
[0094] In some embodiments, the invention will suspend the game if
too much of the skeleton is occluded or off-screen for more than a
threshold amount of time, e.g., 10 second, or 6 beats, rather than
continuing to reward the user for incorrect positioning.
[0095] To assist the user in completing moves correctly, per-limb
feedback is given to the user when performing a move. In some
embodiments, if the user is not satisfying a filter for a limb, the
game renders a red outline around the on-screen dancer's
corresponding limb to demonstrate to the user where they need to
make an adjustment. In some embodiments, the per-limb feedback is
on the mirror-image limb from the limb that is not satisfying the
filter. For example, if the user is satisfying the filter for both
feet, the hips, and the left arm, but not satisfying the filter for
the right arm, the game renders a red outline around the on-screen
dancer's left arm. This indicates to the user that his right arm is
not correct, since the user is facing the on-screen dancer and
mimicking the on-screen dancer in mirror image.
[0096] Other per-limb feedback is also possible. In some
embodiments, an indicator such as a "phantom" limb is drawn in the
target location. Alternatively or additionally, an indicator is
anchored on the errant limb and its direction and length are based
on the direction and degree of error in the user's limb position.
For example, if the user's wrist is below the target location, the
game draws an arrow starting from where the user's wrist is located
in the input performance and ending where the on-screen dancer's
wrist is in the target performance. Alternatively, in embodiments
where a representation of what the user is doing is displayed
on-screen, the arrow is drawn starting from the user
representation's wrist. In some embodiments, the indicator persists
until the user satisfies the filters for the target performance's
arms. In some embodiments, the intensity, geometry, material, or
color characteristic of the indicator may be changed based on the
degree of error for that limb. For example, the color of the
indicator may become a more saturated red if the error for a limb
becomes greater. Other highlighting may also be used, as may verbal
cues such as "get your <limbs> movin`" where <limbs> is
any body zone that is not satisfying the filter.
[0097] In some embodiments, there is an additional indicator
showing how well the user is cumulatively satisfying all filters in
a move, such as a ring of concentric circles under the on-screen
dancer's feet. If the user has satisfied a certain percentage of
the filters, e.g., 20%, the inner ring of circles is illuminated.
When the user successfully performs the next threshold percentage
of filters, e.g., 40%, the next set of rings is illuminated. This
is repeated such that when the user has successfully performed the
entire move, the outermost set of rings is illuminated. A notable
side effect is that as the user is satisfying filters, the ring
grows under the on-screen dancer's feet. In some embodiments, the
success indicator moves with the on-screen dancer, e.g., is based
on the position of the mid-point of the pelvis of the skeleton of
the target performance, so that the user does not have to look at a
different part of the screen to determine how well he is
performing. While described in terms of discrete rings, the effect
can occur continuously. Also, other shapes or graphical effects may
be used, e.g., a meter indicating how many filters are satisfied,
and bigger and bigger explosions or fireworks may be displayed to
indicate the user satisfying more and more filters. Beneficially,
in some embodiments, a qualitative evaluation is also displayed,
e.g., good!, great!, or awesome!
[0098] Beneficially, the setting of the game may react to changes
in the user's performance. For example, as the user is satisfying
filters, a crowd of spectators may begin to circle or gather near
the on-screen dancer. Or the venue in which the on-screen dancer is
performing may become brighter, more colorful, or transform into a
more spectacular, stimulating, or elegant venue. Correspondingly,
if the user is performing poorly, on screen crowds may dissolve and
walk away or the venue may become darker, less colorful, or
transform into a less spectacular, stimulating, or elegant venue.
Changes in venue and setting can based on the consecutive number of
moves completed, e.g., after five successful moves the venue and
dancers on screen change to an "improved mode." After ten
successful moves the venue and dancers may change to a "more
improved mode" and so forth. Changes in venue and setting can also
be based on the overall score of the input performance, or on the
overall score of the input performance as compared to an average
performance.
Dance Training
[0099] In some implementations, there is a trainer mode to assist
the user in learning a dance. In trainer mode, a dance move is
demonstrated using the on-screen dancer and audible cues and no
score is kept. The user is then expected to mimic the on-screen
dancer's movements. If the user performs the move correctly, an
indicator indicates he has performed the move correctly, the next
move is demonstrated, and the user may continue practicing. If the
user does not perform the move correctly, the move is repeated and
the user must keep trying to perform the move before he is allowed
to continue.
[0100] When the user does not perform the movement correctly,
additional instruction is provided. In some embodiments, a verb
timeline, normal_instructions, runs simultaneously with the target
performance, and has multiple verb labels indicated on it. The verb
labels refer to pre-recorded audio samples that have both waveform
data and offsets. The offset indicates where the stress--or
important accent--is located in the waveform data. For example, if
the wave form data represents the spoken word "together," the
offset indicates the first "e" sound such that playback of
"together" begins before the point of the verb label on the
timeline and the playback of the "e" sound aligns with the point of
the verb label on the timeline. This allows the developer to
specify which point on the timeline a particular syllable of the
audible cue falls on. As the target performance is displayed, the
waveform data is played back according to the positions of the verb
labels and the offsets to provide instruction to the user that is
synchronized with the movement of the on-screen dancer.
[0101] In some embodiments, a second verb timeline,
slow_instructions, runs simultaneously with the target performance
and may have a different or more detailed set of verb labels
indicated on it. These verb labels also refer to pre-recorded audio
samples with waveform data and offsets, similar to those described
above. When the user cannot successfully perform a particular move
after a threshold number of attempts, the game slows down and the
slow_instructions timeline is used to provide additional, more
detailed instruction to the user. For example, on the
normal_instructions timeline, there may be a verb label that refers
to an audio cue of "step and clap." On the slow_instructions
timeline, this may be represented by three labels, "left foot out,"
"right foot together," and "clap." When the game is slowed down,
rather than referencing verb labels on the normal_instructions
timeline to trigger audio cues, the game references the verb labels
on slow_instructions timeline. Beneficially, when the game is
slowed down, there is enough time between body movements that the
additional instructions can be played. In some implementations, the
slowed down audible cues are stored in a different file or a
different audio track than the normal speed audible cues. When the
user has successfully reproduced the move, the game is sped back up
and the normal_instructions timeline is used, or alternatively, the
additional instructions are muted or not played.
Fitness Mode
[0102] In some embodiments, there is a calorie counter displayed on
the display during the dance game to encourage users to dance. As
the user dances, the calorie counter is incremented based on the
Metabolic Equivalent of Task ("MET", and generally equivalent to
one kcal/kg/hour) value of what the user is doing. As an example,
sitting on the couch has a MET value of 1. Dancing and most low
impact aerobics have a MET value of approximately 5. High impact
aerobics has a MET value of 7. To determine the MET for a frame of
input skeleton data, the joint velocities for all joints on the
user's input skeleton are summed. To determine a joint's velocity,
the joint's position (in three dimensional space) in the previous
frame is subtracted from its position in the current frame. This
yields a vector. The vector is divided by the elapsed time between
the previous frame and the current frame. The length of the
resulting vector is the velocity of that joint.
[0103] Once the sum is determined, it is exponentially smoothed to
reduce transient noise. The result is a mapped to a MET scale of 1
to 7 with, in some embodiments, a sum of 0 mapping to 1 and a sum
of 40 mapping to 7, with 1 representing no movement and 7 being a
large or vigorous movement. Beneficially, any sum less than five
can map to 1 to account for the noise inherent in the input. The
mapping can be linear, piecewise linear, or any interpolation
function. Using the MET value, and knowing the user's body weight
(which can be input via a menu, or can be inferred based on the
camera's input and a body/mass calculation), calories burned can be
estimated.
[0104] METs are converted to calories-consumed-per-second using the
equation of (METs*body weight in kilograms)/seconds in an
hour=calories/second. This value can then be displayed on the
screen, or summed over time to produce a value displayed on the
screen for total calories. The value for calories/second or total
calories can stored as a "high score" and, in some embodiments, can
be used to increase or decrease the tempo of a song or the
difficulty of a series of moves. Advantageously, this allows the
user to track total calories burned, average rate burned, and other
statistics over time.
Reusing Elements of a Mocap Performance
[0105] In some embodiments of the dance game, the most difficult or
complex target performance is recorded as one linear mocap session
and only parts of the recorded performance are used to simulate
easier versions of the performance. For example, in FIG. 4, the
most difficult or "expert" dance routine comprises a series of
movements following pattern of A, B, C, D, A, B, D, C. In some
embodiments, these moves are marked on the expert timeline using
"move labels," which each denote the name of a move animation and
where in the timeline the move animation begins. In other
embodiments, these moves are marked on a timeline that parallels
the expert timeline, called "anim_clip_annotations." Rather than
capture multiple target performances for each difficulty level,
e.g., a dance with the previous pattern for "expert," and
progressively simpler sequences for "hard," "medium," and "easy,"
the game can re-use the motion capture recorded for expert to
simulate a pattern for any of these difficulty levels by referring
to the move labels on the expert timeline. For example, given the
expert sequence above, the easy sequence might be A, B, A, A, A, B,
A, A. In other words, for the easy routine, a repetition of the A
move replaces both the C and D moves.
[0106] The easier routines can be created programmatically, e.g.,
the game determines how often to repeat a movement based on a
difficulty value for the move, favoring easier moves for easier
difficulty levels. The easier routines can also be authored by the
game developer by creating an "easy" timeline and referencing the
move labels on expert track. An example of this is the "easy" track
in FIG. 4, where the A sections reference the A move in the expert
track and the B sections reference the B move. C and D sections,
that involve a more complicated knee raise (C) and knee slap (D),
are omitted from "Easy" so the user only needs to repeat the "arms
out" move of A or "arms up" move of B.
[0107] Reusing moves allows space savings on the storage medium
(only one target performance needs to be stored) and it allows the
game developer to later change the performances of the other
difficulties after the game is released if it is later determined
that the performance for a difficulty setting is too hard or too
easy or is boring. Since the expert performance is linear, each A
section in expert will be slightly different because the mocap
actor likely did not have his limbs in the exact same position
every time. Examples of this are A' and B' where the skeletons are
similar to A and B respectively, but the arm positions are slightly
different. To make an easier difficulty target performance, the A
move that is repeated in the easier difficulties can be A or it can
be A', or some combination. In some embodiments, a move that is
repeated in an easier difficulty uses the most recent version of
that move in the timeline. In some embodiments, a move that is
repeated in an easier difficulty uses the earliest version of that
move that appeared in the routine. Beneficially, the animations
from the expert track can also be reused when creating the "easy"
performance.
[0108] A sequence of moves for an easier routine may correspond to
a sequence of moves in the original expert linear mocap such that a
specific pattern of moves is present in both (although they may not
correspond on the timeline). In this case, the sequence of moves
may be copied from the expert performance into the desired position
in the easier routine's timeline. But if a sequence of moves for an
easier routine does not correspond to a sequence of moves in the
original expert linear mocap, individual moves may be separately
copied from the expert performance into the desired position in the
easier routine's timeline. Beneficially, copying larger sequences
of moves from the linear mocap produces sequences with fewer
animation artifacts.
Animation Blending
[0109] When moves or sequences of moves are used in easier
difficulties, the moves can abut other moves that were not adjacent
in the linear mocap. The transitions in the move animations between
these moves can be jarring, since the skeleton in the last frame of
one move can be in a completely different pose than the first frame
of the next move, which would produce a sudden, nonlinear
animation. Animation blending can be used to transition smoothly
from the end of one move to the beginning of the next move in the
sequence, if the two moves were not adjacent in the linear mocap.
Using the example above of an expert performance following the
pattern of A, B, C, D, A, B, D, C, when creating the easier
difficulty performance, there may be a pattern of A, A that is not
part of the linear mocap. Animation blending is used to transition
from the end of the first A animation to the beginning of the same
A animation to produce an A, A pattern. In one embodiment, the last
beat of the move before an animation transition is blended with the
beat before the beginning of the next move. In the example of the
A, A pattern, the last beat of the A move is blended with the beat
before the A move for the duration of one beat. Then the animation
continues with the first beat of the second A move.
[0110] In some cases, the animation blending technique described
above produces animations that are still jarring. This is often due
to the large differences between the pose at the end of one move
and the pose at the beginning of the next move, that can't be
overcome through simple blending. In these cases, the animation can
appear to jerk from one position to another during the transition,
or to move in a way that's physically impossible. In some
embodiments, additional mocap is recorded to produce bridge
animation segments. A bridge animation segment is designed to make
the transition between two other animations smooth. For example,
using the example above, if the end of the A move was a very
different pose than the beginning of the A move, a simple animation
blend might produce a poor result. An A, A bridge animation segment
would be recorded, wherein the actor would actually perform the
transition from the end of the A move to the beginning of the A
move. In one embodiment, the bridge animation segment is three
beats long. The next-to-last beat of the first A move is blended
with the first beat of the bridge animation segment in such a way
that contribution from the bridge animation segment is interpolated
linearly over the course of the beat from 0% to 100%. The second
beat of the bridge animation segment is played without blending,
then the first beat of the second A move is blended with the third
beat of the bridge animation segment in such a way that the
contribution from the bridge animation segment is interpolated
linearly over the course of the beat from 100% to 0%. The bridge
animation segment may be any number of beats long, for example two
beats, and the blending can also be done over the course of any
number of beats, for example two beats. The interpolation may be
done in a way that is not linear, such as parabolic,
inverse-squared, etc.
[0111] In some embodiments, a table is provided that is keyed by
the start and end move labels associated with two animations that
may abut. If a bridge animation segment is required to produce a
smooth transition between the associated animations, the table will
contain an entry indicating the bridge animation segment that
should be used. This table is consulted for all pairs of animations
that are displayed.
[0112] Beneficially, the move animations and the results of the
animation blending, e.g., from A to A, or from prior move to first
A or from second A to next move, can be used as the target
performance, and can therefore be scored similarly to the normal
gameplay performance. This provides a fluid game experience and
rewards users that accurately mimic the dancer on the screen.
[0113] In a training mode, it is often necessary to isolate and
repeat a move or series of moves, with a gap in between the
repetitions. For example, when demonstrating the A move, it is
useful for the game to count in the beat while the animation is in
an idling state, then execute the move animation, then return to an
idle animation. This can be accomplished in a way that is similar
to the bridge animation segments described for gameplay above. In
one embodiment, a three beat bridge animation segment of the
transition from an idle state to the first beat of a move is
recorded as mocap data. This is blended with the idle animation and
move animation as described above.
[0114] FIG. 5 shows one embodiment of an authoring system for the
dance game. In FIG. 5, the keyframes 500 are depicted with their
respective timing umbrellas. Each body zone being tested 505 is
shown as having a corresponding portion of the filter to be
satisfied (each square in the rectangle 510). The move is
completely satisfied when all body zone filters are satisfied
(although in some difficulty settings, only a percentage of the
body zone filters need to be satisfied). The labels 515a, 515b,
515c (Hip_Hop_Break.move, Arm_Twist_R.move, and Arm_Twist_L.move,
respectively) applied to each move are shown on the timeline 520.
As stated above, these labels can be reused to create easier dance
routines based on the mocap recording. The mocap skeleton 525 shows
the desired joint movements, and the input skeleton 530 shows what
the user is currently inputting. Look-ahead icons show the user
what move is coming next, e.g., Arm Twist, and the current move
icon 535 is displayed prominently. The dancer 540 on screen is a
representation of what the user is supposed to input and the
skeleton of the on-screen dancer 540 resembles that of the mocap
skeleton 525.
Determining an Active Player with Multiple Skeletons Available
[0115] When more than one player is within the field of view of the
camera, the system must determine which player is the active
player, and which player is the inactive player, for the purposes
of shell navigation and gameplay.
[0116] For this discussion of determining the active player, it is
useful to define two terms. A skeleton is considered "valid" if it
is not sitting and it is facing the camera. Also, "queuing a
skeleton for activation" means setting a timer to go off at
particular time, at which point the active skeleton is set to be
inactive and the queued skeleton is set to be active.
[0117] In some embodiments, queuing a skeleton for activation does
not set a timer if that skeleton is already queued for activation.
In some embodiments, queuing a skeleton for activation does not set
a timer if any skeleton is already queued for activation. In some
embodiments, the timer is always set for 1 second in the
future.
[0118] In some embodiments, determining the active player begins
when a frame of skeleton data is received by the system. In some
embodiments, a frame of skeleton data is received and processed
every thirtieth of a second. In each frame, there may be any number
of distinct skeletons in the skeleton data. At any time, one of the
skeletons in the skeleton data is considered active, and the rest,
if any, are considered inactive.
[0119] In some embodiments, if the active skeleton is
behind--further from the camera than--an inactive skeleton, or the
active skeleton is near the edge of the camera's view, then the
system can search for an inactive skeleton to activate. In some
embodiments, the active skeleton is considered near the edge of the
camera's view if its centerline is in the left or right fifth of
the camera's view. If there is an inactive skeleton nearer to the
center of the camera's view than the active skeleton, the inactive
skeleton can be queued for activation.
[0120] In some embodiments, if an inactive skeleton that is queued
for activation is not present in the current frame, or is not
valid, or is crossing its arms, or is behind the active skeleton,
the queued activation of that skeleton is cancelled. In some of
these embodiments, the queued activation of the inactive skeleton
is not cancelled if the active skeleton is near the edge of the
camera's view.
[0121] In some embodiments, if the active skeleton is not in the
frame, or if the active skeleton is invalid, but there is at least
one inactive skeleton, the system immediately activates one of the
inactive skeletons.
[0122] In some embodiments, if an inactive skeleton's hand is
raised and the active skeleton's hand is not raised, the inactive
skeleton is queued for activation or scoring for dancing.
Beneficially, this allows a user to express intent to control the
shell or have their performance be the one that is graded by
raising their hand.
Multi-Player Modes--Animation
[0123] A dance game can be more satisfying if it provides
multi-player competitive or cooperative game modes. One difficulty
that arises is that the original song and the choreography for the
song may not be balanced such that two players can have equal
opportunities to contribute to their competing or combined scores
(for competitive and cooperative modes, respectively). In addition,
the song may be too short to give either player sufficient
opportunity to perform for a satisfying duration.
[0124] In one embodiment, the invention addresses these
shortcomings by artificially extending the song and its
choreography by looping back to previous parts of the song to give
multiple players an opportunity to dance the same section.
Beneficially, this provides the same potential scoring for all
players in a multi-player mode. Although animation blending in this
context is primarily intended for looping back to previous parts of
a song, the mechanism applies equally well to any non-contiguous
jump between points in the song, or jumps between jumps points in
more than one song.
[0125] In one embodiment, a section that is to be repeated in
multi-player mode is indicated in a MIDI file, in a track called
multiplayer_markers, aligned with the audio timeline.
Alternatively, the markers can be located in the same MIDI track as
other MIDI data, or can be indicated across multiple MIDI files, in
respective tracks called multiplayer_markers, or can be located in
the same MIDI track as other MIDI data, spread across multiple MIDI
files. The section indicators are special multiplayer text events,
MP_START and MP_END. During gameplay, when the game time reaches
the time of the MP_END text event the first time, the game time
jumps to MP_START and the other player begins play. When the game
time approaches the time of MP_END the second time, it continues
without jumping.
[0126] In one embodiment, when the game jumps to a non-contiguous
point in the song, for example to the point designated by MP_END,
animation blending can be used, as described above for creating
easier difficulties, to make the transition less jarring. For
example, if it is determined that a single section should be
repeated, the animation of the last beat of the section can be
blended with the animation the beat before the beginning of the
first beat of the section. The animation blending can take place
over two beats, or it can extend over multiple beats. In all cases,
the animation for the end of the section is blended with the
animation before the beginning of the section such that the blend
begins with 100% contribution from the end of the section and ends
with 100% contribution from before the beginning of the section.
The interpolation can be linear, or can use any other interpolating
function such as polynomial.
[0127] As in animation blending for easier difficulties, the blend
from the end of a section to the beginning of the section can
produce an unrealistic movement. In this case, bridge animation
segments can be used, as discussed above regarding producing an
easy difficulty.
Multi-Player Modes--Audio
[0128] Extending a song by looping back to previous sections brings
with it some inherent difficulties in animation. The invention
addresses these difficulties using animation blending and bridge
animations. Non-contiguous jumps in the timeline of the song, or
jumps between songs, also cause difficulties with continuity of the
audio track. As with animation, the audio for the end of a section
does not always merge smoothly into the audio for a section that is
not adjacent in the song's timeline. Jarring discontinuities in the
audio track can interfere with the users' enjoyment of multi-player
modes. The invention provides seamless audio track transition
playback during multi-player modes to address this difficulty. For
example, if the audio follows the sequence of sections A, B, C, it
may be desirable in a multiplayer mode to loop from the end of the
B section back to the beginning of the B section. The invention
allows this extension to happen seamlessly.
[0129] In one embodiment, a section that is to be repeated in
multi-player mode is indicated in a MIDI file in a track called
multiplayer_markers, with MP_START and MP_END text events, as
described above. In the example above, an MP_START text event in
the MIDI file would be aligned with the beginning of the B section,
and an MP_END text event would be aligned with the end of the B
section, indicating that the entire B section is to be repeated in
multi-player mode. Alternatively, a section that is to be repeated
in multi-player mode can be indicated across multiple MIDI files,
in respective tracks called multiplayer_markers, or can be located
in the same MIDI track as other MIDI data, spread across multiple
MIDI file.
[0130] In one embodiment, when there will be a transition from one
part of the song to a non-adjacent part of the song, the audio
track for a period of time before the origin of the transition is
blended with the audio track for the same duration before the
target of the transition, or the audio track for a period of time
after the origin of the transition is blended with the audio track
for the same duration after the target of the transition, or some
combination. This is similar to how animations are blended when
producing an easy difficulty. For example, one beat worth of audio
before the MP_END event could be blended with one beat worth of
audio before the MP_START event, then one beat worth of audio after
the MP_END event could be blended with one beat worth of audio
after the MP_START event. The blending is done such that at the
beginning of the blend, the contribution from the audio before the
MP_END event is 100%, and at the end of the blend, the contribution
of the audio from after MP_START is 100%. This can be a linear
crossfade, or it can use any other interpolating function, such as
polynomial.
[0131] In some cases, as with animation blending, the result of
audio blending is still jarring. This is often due to the
discontinuity in the harmonic progression of the song when moving
to a different place in the music, or presence or absence of vocal
or instrument parts before or after the transition. In some
embodiments, as with bridge animation segments, additional audio is
recorded to produce waveform data for a bridge audio segment. The
bridge audio segment is designed to make the audio transition
between two non-adjacent parts of the song sound smooth. Using the
example above with sections A, B, and C, if the game will repeat
section B, a bridge audio segment can be provided that smoothly
transitions from the last part of section B into the first part of
section B.
[0132] In one embodiment, the waveform data for bridge audio
segments are included in one or more additional bridge audio tracks
in the multi-track audio data, and the bridge audio tracks are
muted unless non-sequential looping is taking place. However, each
bridge audio segment could be located in its own file referenced by
the game authoring, or all bridge audio segments could be located
in a single file, and the offset and duration of each segment of
bridge audio in the single file would be stored as unique text
events in the MIDI file.
[0133] In some embodiments, all bridge audio segments are of a
fixed duration in beats, with a fixed number of beats before the
transition. In these embodiments, the original song audio is played
until a fixed amount of time in beats before the end of the
transition. Then the original song audio track or tracks are muted,
and the bridge audio segment is played until the transition point.
Then the "current time" is moved to the target of the transition
and the remainder of the bridge audio segment is played. At this
point, the bridge audio track is muted and the original song audio
track or tracks are unmuted. For example, all bridge audio segments
might be three beats long, with one beat before the transition.
Using the example above with sections A, B, and C, if the game will
repeat section B, a 3-beat-long bridge audio segment from the end
of B to the beginning of B may be provided. One beat before end of
B, the original audio tracks are muted and the B-to-B bridge audio
segment is played. When the end of B is reached, the current time
is moved to the beginning of B, and the bridge audio segment
continues playing for two more beats. After two beats, the bridge
audio track is muted and the original tracks are unmuted.
Beneficially, aligning the audio and changing the current time in
this way allows for a single, consistent timeline for audio
playback, animation, and other aspects of gameplay. Alternatively,
the current time may be changed at the end of the bridge audio
segment's playback, and moved directly to two beats after the
beginning of B section. This example discusses bridge audio
segments that are all 3 beats long, which start playing one beat
before the transition, but other embodiments may have bridge audio
segments that are all longer or shorter, or that all begin earlier
or later with respect to the transition.
[0134] In some embodiments, the song audio and bridge audio
segments may be muted and unmuted, as described. Alternatively, the
song audio and bridge audio segments may be mixed, such as by
lowering the normal song audio volume to 10% and playing the bridge
audio segment at 90%. It is also possible to cross-fade the song
audio and bridge audio segments. For example, the last beat of the
B section would start with 100% of the song audio and end with 100%
of the bridge audio segment, then the bridge audio segment would
play at 100%, then the second beat of the B section would start
with 100% of the bridge audio segment and end with 100% of the
second beat of the song audio. The interpolation can be linear, but
it can also use any other interpolating function, such as
polynomial.
[0135] In some embodiments, as described above, the bridge audio
segments can be of a fixed duration in beats or seconds. In other
embodiments, each bridge audio segments can be of different
durations. Beneficially, the ability to specify bridge audio
segments of different durations makes it easier to provide a
musically seamless transition, using more time if necessary, to
achieve the proper harmonic and orchestration transitions, and less
if possible, so that the playback departs as little as possible
from the original music.
[0136] In one embodiment, all the waveform data for bridge audio
segments is located on a single bridge audio track, bridge_audio,
in the multi-track audio data file. The bridge audio waveform data
for a given transition is divided into the sub-segment before the
transition and the sub-segment after the transition. The
sub-segment before the transition is positioned in the bridge_audio
track so that it ends exactly at the transition point,
corresponding to the MP_END text event in the associated MIDI file.
The sub-segment after the transition is positioned in the
bridge_audio track such that it begins exactly at the target of the
transition, corresponding to the MP_START text event in the
associated MIDI file.
[0137] In some embodiments, where the bridge audio segments are of
a fixed duration, the beginning and end of the bridge audio
segments is implicit in the fixed duration and the fixed amount of
time before the transition, as described above.
[0138] In the preferred embodiment, the specification of the
beginning and end of bridge audio segments is provided in a MIDI
file, in the multiplayer_markers track, although the beginning and
end of the bridge audio segments could be in their own MIDI track,
or in their own MIDI file whose timeline is aligned with the audio
timeline. In the multiplayer_markers track, special multiplayer
text events, MP_BRIDGE_START and MP_BRIDGE_END, denote the
beginning and end of a bridge audio segment. As the game is played
in a multi-player mode, when an MP_BRIDGE_START text event is
encountered on the timeline of multiplayer_markers, the original
audio track or tracks are muted and the bridge_audio track is
unmuted. As described above, attenuation of the original track or
crossfading with the bridge audio track can be used instead of
muting and unmuting. Playback continues until the transition point
itself, which is indicated by the MP_END text event. At this point,
the "current time" is set to the target of the transition, marked
by the MP_START text event, and the bridge audio track continues.
When the MIDI MP_BRIDGE_END event is encountered, the original
audio track or tracks are unmuted, and the bridge audio track is
muted. Note that when the transition is backwards in time, the
MP_BRIDGE_END event occurs earlier on the timeline than the
MP_BRIDGE_START event, since the current time is modified between
them. Beneficially, dividing the bridge audio segments and
modifying the current time at the transition point as described
allows there to be a single concept of current time for the audio,
animation, and gameplay. In other embodiments, the current time is
modified only after the playback of the bridge audio segment is
complete, and at that point it is set to the location of MP_START
plus the length of the second sub-segment of the bridge audio
segment. As described above, a section that is to be repeated in
multi-player mode also can be indicated across multiple MIDI files,
in respective tracks called multiplayer_markers, or can be located
in the same MIDI track as other MIDI data, spread across multiple
MIDI file.
Additional Variations
[0139] The examples given herein of a user satisfying a filter by
completing a series of moves can be adapted to satisfy a "mirror
mode" as well, where the user provides input that mirrors the
target performance, e.g., providing input using a right hand when
the target performance uses a left hand, providing right leg input
when the target performance uses a left leg, and so forth.
[0140] Additionally, where a target performance skeleton is
provided, it can be generated beforehand, or can be generated
during execution of the game based on the motion capture data.
[0141] Any system that can detect movement can be used as long as
positions of the scored joints can be determined in either
two-dimensional space or three-dimensional space to create or
simulate a skeleton. For two-dimensional implementations, scoring
is typically adjusted to compare the projection of the target
performance and the projection of the input performance onto a
plane parallel to the screen. Although the system and technology
has been described in terms of a camera input system like Natal,
camera systems that utilizes sensors on the user's body, e.g.,
PLAYSTATION.RTM. Move, or systems that use sensors held in the
user's hand, e.g., the NINTENDO.RTM. Wii, may also be utilized. In
those implementations where only hand held sensors are utilized by
the user, testing for leg input is ignored or not performed.
[0142] Although the embodiments described herein use dancing as an
example, and the performance is typically accompanied by a song,
the performance can also be movements that occur on a timeline with
no musical accompaniment, e.g., a series of yoga poses, movements
in a martial arts kata, or the like.
[0143] In some implementations, the mocap data is mapped to a
skeleton similar to that used to reflect the user's input. Thus,
the mocap data is used to generate an ideal skeleton that
represents a performance of the dance routine in a format that is
directly comparable to the skeleton representing the user's input.
Then, during the game, as the user provides input, the user's
skeleton is compared to the ideal skeleton, in effect normalizing
the target input (the target performance) and actual inputs (the
user's performance) to the same frame of reference, i.e., both
performances are expressed in terms of the same skeleton-based
technology.
[0144] In some embodiments, rather than matching position
necessarily within a time window as described above, filter types
are predefined and used to test user input. For example, proximity
filters tests if a joint in a particular position, or close to a
particular other joint, e.g., "are the left wrist and right wrist
less than, greater than, or within a delta of a certain distance of
one another. Another filter is a displacement filter which tests if
a joint has moved a certain distance between times t.sub.0 and
t.sub.n. Another example is the angle filter, which tests if a
joint is at a particular angle from the origin. One or more of
these filters is then hand-inserted (or "authored") into the
timeline and bound to joints such that at a particular time, the
condition is tested, e.g., "has the RIGHT WRIST moved from x.sub.0
to x.sub.n since I began tracking it?" would be a displacement
filter. If the user's wrist had, the filter would be satisfied. Yet
another filter is an acceleration filter which tests if a joint or
bone has accelerated or decelerated between times t.sub.0 and
t.sub.n. An acceleration filter can also test whether the magnitude
of the acceleration matches a predetermined value.
[0145] In these embodiments, multiple filters can be overlaid on
the timeline, and tested, in effect, simultaneously. An overall
score for the frame is determined based on contributions from all
of the active filters during a given frame. The filters can output
a Boolean, and the score is computed from those. Or--in some
implementations--the outputs are continuous, and the aggregate
score is computed from those. Similar to the system described
above, contributions from each active filter can be weighted
differently in their contributions to the score. For Boolean
filters, successfully completing 3 out of 5 filters gives the user
a score of 0.6. In some implementations, each keyframe comparison
gives a percentage credit for the move as a whole being correct.
The user's score may be adjusted based on the aggregate score for a
keyframe. Or the aggregate score for a keyframe may be quantized
into groups, each group being compared to one or more thresholds,
each group associated with a score that is added to the user's
score. In any of these, if the user achieves a threshold score for
a move, where if the user meets or exceeds the threshold, e.g.,
80%, the user is considered to have successfully performed the
move.
[0146] In some embodiments, execution of game software limits the
game platform 120 to a particular purpose, e.g., playing the
particular game. In these scenarios, the game platform 120 combined
with the software, in effect, becomes a particular machine while
the software is executing. In some embodiments, though other tasks
may be performed while the software is running, execution of the
software still limits the game platform 120 and may negatively
impact performance of the other tasks. While the game software is
executing, the game platform directs output related to the
execution of the game software to a display, thereby controlling
the operation of the display. The game platform 120 also can
receive inputs provided by one or more users, perform operations
and calculations on those inputs, and direct the display to depict
a representation of the inputs received and other data such as
results from the operations and calculations, thereby transforming
the input received from the users into a visual representation of
the input and/or the visual representation of an effect caused by
the user.
[0147] The above-described techniques can be implemented in digital
electronic circuitry, or in computer hardware, firmware, software,
or in combinations of them. The implementation can be as a computer
program product, i.e., a computer program tangibly embodied in a
machine-readable storage device, for execution by, or to control
the operation of, data processing apparatus, e.g., a programmable
processor, a computer, a game console, or multiple computers or
game consoles. A computer program can be written in any form of
programming language, including compiled or interpreted languages,
and it can be deployed in any form, including as a stand-alone
program or as a module, component, subroutine, or other unit
suitable for use in a computing environment. A computer program can
be deployed to be executed on one computer or game console or on
multiple computers or game consoles at one site or distributed
across multiple sites and interconnected by a communication
network.
[0148] Method steps can be performed by one or more programmable
processors executing a computer or game program to perform
functions of the invention by operating on input data and
generating output. Method steps can also be performed by, and
apparatus can be implemented as, a game platform such as a
dedicated game console, e.g., PLAYSTATION.RTM. 2, PLAYSTATION.RTM.
3, or PSP.RTM. manufactured by Sony Corporation; NINTENDO WII.TM.,
NINTENDO DS.RTM., NINTENDO DSi.TM., or NINTENDO DS LITE.TM.
manufactured by Nintendo Corp.; or XBOX.RTM. or XBOX 360.RTM.
manufactured by Microsoft Corp. or special purpose logic circuitry,
e.g., an FPGA (field programmable gate array) or an ASIC
(application-specific integrated circuit) or other specialized
circuit. Modules can refer to portions of the computer or game
program and/or the processor/special circuitry that implements that
functionality.
[0149] Processors suitable for the execution of a computer program
include, by way of example, special purpose microprocessors, and
any one or more processors of any kind of digital computer or game
console. Generally, a processor receives instructions and data from
a read-only memory or a random access memory or both. The essential
elements of a computer or game console are a processor for
executing instructions and one or more memory devices for storing
instructions and data. Generally, a computer or game console also
includes, or be operatively coupled to receive data from or
transfer data to, or both, one or more mass storage devices for
storing data, e.g., magnetic, magneto-optical disks, or optical
disks. Data transmission and instructions can also occur over a
communications network. Information carriers suitable for embodying
computer program instructions and data include all forms of
non-volatile memory, including by way of example semiconductor
memory devices, e.g., EPROM, EEPROM, and flash memory devices;
magnetic disks, e.g., internal hard disks or removable disks;
magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor
and the memory can be supplemented by, or incorporated in special
purpose logic circuitry.
[0150] To provide for interaction with a user, the above described
techniques can be implemented on a computer or game console having
a display device, e.g., a CRT (cathode ray tube) or LCD (liquid
crystal display) monitor, a television, or an integrated display,
e.g., the display of a PSP.RTM., or Nintendo DS. The display can in
some instances also be an input device such as a touch screen.
Other typical inputs include a camera-based system as described
herein, simulated instruments, microphones, or game controllers.
Alternatively input can be provided by a keyboard and a pointing
device, e.g., a mouse or a trackball, by which the user can provide
input to the computer or game console. Other kinds of devices can
be used to provide for interaction with a user as well; for
example, feedback provided to the user can be any form of sensory
feedback, e.g., visual feedback, or auditory feedback; and input
from the user can be received in any form, including acoustic,
speech, or tactile input.
[0151] The above described techniques can be implemented in a
distributed computing system that includes a back-end component,
e.g., as a data server, and/or a middleware component, e.g., an
application server, and/or a front-end component, e.g., a client
computer or game console having a graphical user interface through
which a user can interact with an example implementation, or any
combination of such back-end, middleware, or front-end components.
The components of the system can be interconnected by any form or
medium of digital data communication, e.g., a communication
network. Examples of communication networks include a local area
network ("LAN") and a wide area network ("WAN"), e.g., the
Internet, and include both wired and wireless networks.
[0152] The computing/gaming system can include clients and servers
or hosts. A client and server (or host) are generally remote from
each other and typically interact through a communication network.
The relationship of client and server arises by virtue of computer
programs running on the respective computers and having a
client-server relationship to each other.
[0153] The invention has been described in terms of particular
embodiments. The alternatives described herein are examples for
illustration only and not to limit the alternatives in any way. The
steps of the invention can be performed in a different order and
still achieve desirable results.
* * * * *
References