THREE DIMENSIONAL ANIMATION SYSTEM AND METHOD
Background of the Invention
This invention relates generally to a system and method for animating a
computer image on a computer display and in particular to a system and method
for generating realistic three-dimensional animation of an object over a low
bandwidth communications network.
There are many different techniques for generating an animation of a
three dimensional object on a computer display. Originally, the animated
figures looked very much like stick figures or block figures since the animation
was not very good. In particular, the user would see a block representing the
arm move relative to a block representing the forearm. The problem was that
there was no skin covering the blocks so that the figure looked unrealistic and
not very life-like. More recently, the figures for animation have improved so
that a skin may cover the bones of the figure to provide a more realistic
animated figure.
Some techniques and systems, such as those used to generate three
dimensional animation for a movie, are very high-end and expensive. In
addition, these high-end three dimensional animations may be viewed by a
consumer on a movie screen, for example, but cannot be interacted with in any
way. In particular, the consumer may view the three dimensional animations
which tell a story such as in a movie but the consumer cannot interact with the
WO 00/77742 PCT/USOO/l 5817
-2- animations in any manner. These high-end animation systems are very useful
for a movie, but cannot be readily used by the general public due to the costs of
the system.
Other animation systems, such as dedicated game playing systems or
personal computers executing a software application, permit the user to interact
with the animations. These systems, however, require a large amount of
memory for storing the animation data and a fairly state-of-the-art processor or
graphics coprocessor in order to produce realistic three dimensional animation.
The problem with a dedicated game playing system is that it cannot be used for
other computing related tasks and therefore are relatively expensive due to the
limited functions that they perform. The problem with most personal computers
is that the personal computer is not optimized to produce the animations and
therefore usually requires an expensive graphics co-processor and a sound
board. In the above conventional animation systems, the user may interact with
the animation during the game play, but the entire game with the graphics and
animation are stored on a cartridge or on a hard disk or CD of the personal
computer.
Recently, a number of animation systems have been introduced which
harness the Internet or the World Wide Web (the Web) to communicate the
animation data to the user. In particular, the user may use a personal computer
which is executing a browser software application. The user may direct the
browser application to a particular uniform resource locator (URL) of a web site
-3- which then may download the animation data from the web site. The problem is
that the web site typically downloads the entire animation data so that the
amount of animation data downloaded is large. An example of this type of
animation system uses the virtual reality markup language (VRML) protocol.
For a user with a slow communications link, such as the Internet or the Web and
a modem, the large amount of animation data leads to a very slow download.
The slow downloading time in turn leads to the consumer waiting a long period
of time before viewing the animation. This long period of waiting before the
animation is not acceptable since people become bored during the waiting
period, cancel the animation and thus never see the animation displayed. It is
desirable, however, to provide a three dimensional animation system in which
the animation data which may be downloaded rapidly over a very slow
communications link and it is to this end that the present invention is directed.
Summary of the Invention
The invention provides a three dimensional animation system and
method in which the animation data may be downloaded over a relative slow
communications link, such as the Internet or Web and a modem, to a local
computer in a relatively short amount of time. The local computer may then
execute a downloaded software application to animate the object. The user of
the local computer may interact with the animated object (i.e., change its
behaviors or actions). In a preferred embodiment, the main portion of the
system may reside as a plurality of software applications on a web server and a
-4- client computer may access the web server to download the animations. To
accomplish the shorter download time, the system may generate an initial
animation download package containing the data about the actual object (e.g.,
the persistent data) and a few basic actions of the object (e.g., behavior data).
For example, each downloaded object may have an idle behavior associated with
it which is executed any time that the object is not executed another behavior.
Then, as additional actions or behaviors or sound tracks for the object are
required, the system may stream the behavior data down to the client computer
before the action is required so that the behaviors are asynchronously
downloaded (i.e., the behaviors for the three dimensional animated object do not
need to be downloaded at the same time as the three dimensional animated
object is downloaded). In this manner, the client computer may more quickly
begin the animation while other yet unneeded actions or behaviors are being
downloaded. For example, as the animated object moves through a landscape,
the object may cross a bounding box which causes an action that will be needed
shortly to be downloaded to the client computer so that the action is available
when needed. The one or more behavior or action files for a particular object
may contain information about the movements of the joints in the object which
correspond to a particular behavior and any other data necessary to execute the
behavior. For example, a head nod behavior may involve the movement of the
neck joint. As another example, a sound track for the object, such as saying
"Hello", may involve the movement of the various pieces of the lips and a sound
track synchronized to the movement of the lips.
WO 00/77742 PCT/USOO/l 5817
-5-
In accordance with the invention, the total size of each behavior
downloaded to the client computer is also relatively small in size so that the
download time of the behavior, over a relatively slow communications link, is
not too slow. To reduce the size of each behavior, the initial object downloaded
to the client computer may include an object tree containing data about each
portion of the object. For example, a person would include a leg object. Then,
each piece of skin on the object (e.g., each polygon) may include a contribution
chart which lists each joint in the object, such as the knee or ankle, and the
contributions that the movement of each joint makes to movement of the
particular polygon. For example, a polygon near the knee joint would probably
be mostly influenced by knee movement while a polygon midway between the
knee and ankle would be influenced by the movement of both the ankle and the
knee. Thus, when a behavior commands the knee of the object to move, the
client computer may easily determine the movement for each particular polygon
based on the model of the object and the movement of the joints. Thus, for any
downloaded behavior, only the movements of the joints in the object need to be
specified in the downloaded behavior file since the movement of each piece of
skin on the model may be determined by the model based on the movement of
the joints. Thus, if the model has twelve joints and 6000 polygons, the
downloaded behavior file may contain data about the movement of the twelve
joints whereas the behavior may cause the 6000 polygons on the model to move.
In accordance with the invention, the system also permits a downloaded
behavior to be streamed to the player application residing on the user's
-6- computer. In particular, the behavior may start playing on the player application
before the entire behavior is downloaded. For example, if a behavior is five
minutes long, the user of the player application is not likely to wait 5 minutes
for the behavior to be downloaded. Therefore, in accordance with the invention
the system downloads a predetermined amount of the behavior(e.g., a two
second portion of the behavior data) at a time so that the behavior may start
executing the first predetermined portion of the behavior data while the second
and subsequent portions of the behavior data are downloaded. Thus, a long
behavior being downloaded to the player application does not prevent the
animated character's behavior from being started.
The system may also permit the user to interact with the animated
objects in various different ways using actions and scripts which include one or
more actions or behaviors. For each interaction with the object, there may be an
action or behavior associated with that interaction. For example, when the user
clicks on an animated door being displayed to the user, a behavior to open the
door and show the door slowly opening with a creaking soundtrack may be
downloaded to the client computer and executed. On the client computer, the
user may see the door slowly open and hear the door creak as it opens. As
another example, when the user drags a cursor over an object, such as a gray
knife, a behavior to turn the knife red will be downloaded and executed so that
the knife turns red when the user places the cursor over it. When the user moves
the cursor off of the knife, the knife returns to its idle behavior which is having a
gray color.
To shade the animated object using a lighting model, the invention may
use a spherical environmental map. In particular, the pixels resulting from a
particular lighting condition is determined for a half-sphere and then the
corresponding lighting for an object is determined based on the pixels in the
half-sphere. The lighting model for the half-sphere may be downloaded to the
client computer so that, for each pixel of the object, the client computer may
look up the corresponding point on the half- sphere and apply the pixel value on
that portion of the half-sphere to the object. Thus, in accordance with the
invention, the system does not attempt to calculate, in real-time, the lighting for
an object. The system may also provide a character cache in the client computer
that permits the character data to be stored in the client computer so that it does
not need to be constantly refreshed. In contrast, in a conventional Web based 3-
D system, such as VRML, the character may be stored in the cache of the
browser application which is periodically flushed.
Thus, in accordance with the invention, a system for animating a
character on a computer is provided, comprising a first computer and a second
computer connected to the first computer. The first computer may store one or
more pieces of data associated with a particular animated character. The pieces
of data may include a persistent data file containing one or more of a geometric
model of the animated character, a texture associated with the animated
character and a sound associated with the animated character. The pieces of data
may further comprise one or more behavior files wherein each behavior file
contains data about a particular behavior of the animated character and each
-8- behavior specifies the movement of the model. The second computer may
initially download the persistent data file from the first computer in order to
begin the animation of the animated character on the second computer and then
asynchronously download a behavior file from the first computer just prior to
the execution of the behavior of the animated character by the second computer.
Brief Description of the Drawings
Figure 1 is a block diagram illustrating the three dimensional animation
system in accordance with the invention;
Figure 2 is a flowchart illustrating a method for downloading three
dimensional character files in accordance with the invention;
Figure 3 is a diagram illustrating an example of an object hierarchy in
accordance with the invention;
Figures 4A and 4B are diagrams illustrating an example of a three
dimensional object in accordance with the invention;
Figure 5 is a diagram illustrating an articulation of a joint;
Figure 6 is a diagram illustrating a morphlink in accordance with the
invention;
Figure 7 is a diagram illustrating an example of the area of influence of a
joint in accordance with the invention;
Figures 8 A and 8B are diagrams illustrating an example of the bones
within a model in accordance with the invention;
-9-
Figures 9 and 10 are diagrams illustrating an example of a model with
the bones and polygons in accordance with the invention;
Figure 11 is a diagram illustrating an example of a rendered, unlighted
model in accordance with the invention;
Figure 12 is a diagram illustrating an example of a rendered, lighted
model in accordance with the invention;
Figure 13 is a diagram illustrating an example of an environmental map
lighting model in accordance with the invention;
Figure 14 is a diagram illustrating an example of the rendered model
shown in Figures 11 and 12;
Figures 15 and 16 are diagrams illustrating the bones in a leg model in
accordance with the invention;
Figure 17 is a diagram illustrating the leg of Figures 15 and 16 showing
the area of influence for each joint;
Figure 18 is a diagram illustrating an example of a behavior in
accordance with the invention;
Figures 19A, 19B and 19C are diagrams illustrating another example of
a behavior in accordance with the invention;
Figure 20 is a flowchart illustrating a method for streaming behaviors in
accordance with the invention;
Figure 21 is a diagram illustrating the details of the streaming behaviors
in accordance with the invention;
-10-
Figure 22 is a diagram illustrating more details of the streaming behavior
shown in Figure 21;
Figure 23 is a diagram illustrating a portion of a streamed behavior in
accordance with the invention; and
Figures 24 and 25 are flowcharts illustrating the operation of the player
in accordance with the invention.
Detailed Description of a Preferred Embodiment
The invention is particularly applicable to a Web-based three
dimensional animation system and method and it is in this context that the
invention will be described. It will be appreciated, however, that the system and
method in accordance with the invention has greater utility, such as to other
types of three dimensional animation systems including stand-alone computer
systems and the like.
Figure 1 is a block diagram illustrating a three dimensional animation
system 40 in accordance with the invention. The system 40 may include a
character creator 42, a server 44 and one or more client computers (CLIENT #1
- CLIENT #N) 46. In this example, the client computers may be connected to
the server by a communications network 48 that may include various
communication or computer networks such as the Internet, the World Wide Web
(the Web), a local area network, a wide area network or other similar
communications networks which connect computer systems together. The
creator 42 may be used to generate a three dimensional animated character as
WO 00/77742 PCT/USOO/l 5817
-11- described below. In a preferred embodiment, the creator 42 may be a software
application being executed by a computer system. The creator 42 may be stored
on the server 44 or may be executed by a separate computer system as shown in
Figure 1. The creator 42 may generate one or more web files, as described
below, which may be downloaded to the server 44 so that each client computer
may then download the web files from the server. Each client computer may
then interpret the downloaded web files and generate a three dimensional
animation based on the web files as described in more detail below. Now, each
portion of the system 40 will be described in more detail.
The creator 42 may accept various information from either user input or
other external files in order to generate a three dimensional realistic object or
character which may be animated using the system. For example, the creator
may receive three dimensional models 50 which may be, for example, wire
frame models of an object generated by a third party modeling system. The
generation of a three dimensional wire frame model from a three dimensional
object in well known and therefore will not be described here. The creator 42
may also receive texture map information 52 which may be used to place a
texture over the polygons painted onto the three dimensional object. The texture
may provide, for example, a realistic flesh color and texture for the skin of a
human character or a realistic set of teeth. The creator 42 may also receive a
sound file 54 so that a sound track may be incorporated into a behavior file in
accordance with the invention. The sound file may be generated by a third party
system which receives a sound and generates a digital representation of the
-12- sound which may be incorporated into a file. The creator may also receive a
behavior file 56. The behavior file may be combined with any sound file to
generate a behavior for a three dimensional animation in accordance with the
invention. The behavior file may be generated by the user using a separate
software module of the creator 42. The creator 42 may combine the three
dimensional model information, the texture information, the sound file and the
behavior file into one or more web files which are stored on the server.
In accordance with the invention, the creator 42 may generate more than
one file for each animated object. In particular, the creator may generate a file
containing persistent data 58 and then one or more files containing behavior data
60. The persistent data file may be initially downloaded to the client computer
to begin the animation of the object and may include one or more of the three
dimensional object (including joints and polygons), any textures, any
morphlinks as described below, and an idle behavior for the three dimensional
object. The idle behavior may be the action or movement of the animated
object when no other behavior is being executed. For example, the idle behavior
for an animated monster may be that the monster may breath which causes his
chest to expand and contract.
The persistent data file may also include the morphlink data associated
with each polygon in the model in accordance with the invention. The model
may include one or more joints connected together by one or more bones and a
skin of polygons which cover the bones and joints. For each polygon on the
WO 00/77742 PCT/USOO/l
-13- model, the morphlink data permits the client computer to easily determine the
movement of the polygons based on the movement of the joints of the object. In
a conventional animation system, the movement of each polygon must be
independently calculated which is very slow. When a model is generated, the
user of the creator defines the morphlinks so that the movement of a particular
polygon based on the movement of the joints is determined by the user. Thus,
the movement of each polygon relative to movement of the joints of the model
is defined in the persistent data. Therefore, when a behavior of the three
dimensional animation is executed, the behavior may contain only information
about the movement of each joint in the model and the client computer, based on
the morphlinks, may determine the movement of each polygon on the model.
Thus, the size of the behavior file downloaded to each client computer in
accordance with the invention is reduced which speeds up the download speed
of each behavior. In addition, the speed with which the three dimensional
animation may be animated is increased since the client computer does not need
to calculate the movement of each polygon on the three dimensional object or
character each time a behavior occurs. The persistent data file 58 may also be
compressed to further reduce the size of the persistent data. As an example, due
to the compression and the structure of the persistent storage file in accordance
with the invention, a persistent storage file may be approximately 10 - 200 Kb
depending on the complexity of the three dimensional animation whereas a
typical animation file may be approximately 1 Mb.
-14-
The one or more behavior files 60 may each contain a data structure
which contains data specifying the movement of each joint in the three
dimensional object or character during a behavior and any sound file which is
associated with the particular behavior. In accordance with the invention, each
different behavior of the three dimensional animation, such as smiling, talking
about a particular subject, sitting, etc., may be contained in a separate behavior
file. In accordance with the invention, each behavior file may be downloaded to
the client computer only when the behavior is required. For example, a behavior
to pick up an object from the ground for a game player may only be downloaded
when the game player nears an object which may be picked up. As another
example, a behavior to say "Good-bye" is only downloaded to the client
computer when the user clicks on a good-bye button on the user interface. Thus,
the system may download the behavior files asynchronously with the persistent
data file. Due to the morphlinks in the persistent data, the size of the behavior
files, as described above, is very small. It should be realized, however, that each
behavior file is associated only with a particular persistent data file (since the
structure of the behavior and the persistent storage are tied together) and
therefore a walking behavior for two separate models will be slightly different.
The behavior files may be generated by the creator 42 in response to user input.
The behavior files may be compressed in that the data for any joints which do
not move during a predetermined time during the behavior is not downloaded to
the client computer.
-15-
Once the behavior and persistent data files are generated, they may be
downloaded to the server 44 and stored in a character and behavior storage
device 62 which may be a persistent storage device such as a hard disk drive, a
tape drive or the like. The server 44 may also include a player store 64 which
contains a player web file. The player web file is the software application which
is first downloaded to the client computer so that the client computer may then
interprets the persistent data file as well as the behavior files. Thus, the server
44 may first download the player software application to the client computer (if
necessary) and then, based on user input into a Web user interface application
66, download the persistent data file so that the animation may begin. Then, as
behaviors of the three dimensional animation are needed by the client computer,
the server may download the appropriate behavior file to be executed by the
player on the client computer.
Each client computer 46 may include a CPU 68, a memory 70 containing
one or more software application to be executed by the CPU 68, a character
cache 74 which may reside on a persistent storage device of the client computer
and a display 76. The character cache 74 may store the persistent data 58 when
it is downloaded to the client computer the first time so that it may not be
necessary to downloaded the persistent data again when the particular client
computer again wants to view the same animation. Unlike conventional
animation systems in which the character data is stored in the cache of the
browser application so that the character data is periodically flushed, the system
has its own character cache.
WO 00/77742 PCT/USOO/l 5817
-16-
The memory 70 may store a browser application 78 which permits the
client computer to interact with the server 44 by specifying a uniform resource
locator (URL) of the server in order to receive the web files stored on the server
using a hypertext transfer protocol (HTTP). The memory may also store the
player software application 64 to interpret the persistent data file and the
behavior files and generate the animated object, a character file 82 generated
from the persistent data file, a first behavior file 84 containing the idle behavior
and a second behavior file 86 that may contain a behavior that will be executed
soon. Thus, the character file and the current behavior files are both stored in
the memory 70 while being executed by the player. As new behaviors are
needed, those behaviors are downloaded to the client computer and one of the
old behaviors may be deleted to make room from the new behavior. The
number of behaviors stored in the client computer at any time depends on the
amount of memory space available for the animation system. The animation
generated by the player 64 based on the persistent data and the behavior files
may be displayed on the display 76. Now, a method for downloading three
dimensional character files in accordance with the invention will be described.
Figure 2 is a flowchart illustrating a method 100 for downloading three
dimensional character files to a particular client computer in accordance with the
invention. The downloading method permits the animation to begin rapidly
since the downloading time is reduced due to the asynchronous download of the
behavior files and the persistent data file. In step 102, the server may determine
WO 00/77742 PCT/USOO/l 5 17
-17- if the player application has previously been downloaded to the client computer
and may downloads the player software in step 104 if it has not already been
downloaded. Once the player is downloaded to the client computer, the server
may download the persistent data file (that may include the character file and an
idle behavior file) to the client computer in step 106. The client computer may
then create a character cache if one does not exist and store the character file and
the idle behavior file in the character cache. Next, the player application is
executed by the client computer and the player application may use the
persistent data to animate the character and execute the idle behavior in step
108. In accordance with the invention, all of the behaviors for an animated
object do not need to be initially downloaded so that the download time for the
persistent data is reduced and the animation may begin more quickly. Next, the
player application may determine if a new behavior for the animated object is
needed in step 110 and continue to execute the idle behavior in step 112 if no
new behavior is needed. If a new behavior is needed, then the server may
download the new behavior in step 114 in response to a request by the player
application. The player application may then determine if the new behavior has
finished downloading in step 116 and continue to execute the prior behavior
until the new behavior is downloaded. If the new behavior is downloaded, then
the player may execute the new behavior in step 118 and return to step 108. In
accordance with the invention, the behaviors are downloaded to the client
computer as they are needed so that the start time of the animation is reduced.
In addition, since the size of the behavior files is small due to the morphlinks,
-18- the total download time for any behavior file is also short. Now, an example of
the object hierarchy in the three dimensional animation system will be
described.
Figure 3 is a diagram illustrating an example of an object hierarchy 130
in accordance with the invention. As shown, the object hierarchy may include a
tree of objects organized underneath a root node 132. The objects used in the
three dimensional animation system may include a texture object 134, a sound
object 136, a geometry object 138 and a behavior object 140. Each of these
objects may then include sub-objects as shown for the geometry and behavior
objects. In particular, the geometry object 138 may include a polygon object
142 containing the polygons associated with a particular model, a morphlinks
object 144 containing the morphlinks associated with each polygon in the
model, a particle system object 146 for storing smaller objects such as rocket
ship exhaust and a camera object 148 for storing information about the camera
position and angle with respect to the model. The geometry may further include
additional information about the model as shown in Figure 4B.
The behavior object 140 may include a transform object 150 containing
movement information for the joints of an object to transform the object, a
texture track object 152 containing an animated texture of a model, a sound
object 154 containing a sound track associated with a behavior and a script
object 156 containing a sequence of behaviors combined together to form a new
behavior. For example, a script may be for interacting with the animated
-19- character and may include a behavior for each response that the character makes
to the user in response to user input. Each animated object may include one or
more of the above objects. Now, an example of the object for a particular
character/model will be described.
Figures 4A and 4B are diagrams illustrating an example of a character
object and a three dimensional object associated with that object in accordance
with the invention. Figure 4A is a diagram illustrating a geometry object 160
for a human character in which the object models the joints of the character. For
example, the object shown includes a head, a neck, two elbows, two wrists, hips,
two knees and two ankle joints. As described above, the movement of a
character is specified by the movement of the joints of the character which may
then be turned into movement of the polygons on the model based on the
morphlinks. A three dimensional object tree 162, as shown in Figure 4B, which
models this human character has a similar structure. In particular, the object tree
162 may include a WORLD node connected to a CAMERA node and a BODY
node. The BODY node may further include various objects modeling the
various joints in the body. As shown, the BODY node may include a HIP
JOINT node, a LFT KNEE object and a RT KNEE object connected to the HIP
JOINT node and a LFT ANKLE and RT ANKLE node connected to the
appropriate knee nodes. Each object in the object tree that is connected to an
object above it in the tree inherits the attributes of the object above it. For
example, any movement of the LFT KNEE object may cause the LFT ANKLE
object to inherit the same movement. This inheritance of the knee movement by
-20- the ankle provides a good model of the human body. Similarly, if the HIP
JOINT object moves, both of knee objects and both of the ankle objects inherit
the movement of the HIP JOINT object. Therefore, once the movement of the
HIP JOINT object is specified in a behavior, the movements of the knees and
ankles caused by the HIP JOINT movement do not need to be specified. Now,
the articulation of a joint in accordance with the invention will be described.
Figure 5 is a diagram illustrating an example of the articulation of joints
of a character. In particular, an arm 170 of a three dimensional character is
shown for illustration purposes. The arm may include a shoulder joint 172, an
elbow joint 174, a wrist joint 176, an upper arm 178, a lower arm 180 and a
hand 182. Similar to a human arm, each joint has six degrees of freedom since
each joint may move in a positive or negative X direction, a positive or negative
Y direction and/or in a positive or negative Z direction. For each predetermined
period of time referred to as a key period, each joint may move in each of the six
directions. The key period may preferably be 1/10th of a second and the player
may interpolate the movement of the joint in each direction in between the key
period to ensure that the motion of the joint is smooth. The key period may be
set by the user. As each joint moves, the part of the body near that joint may
also move. In a three dimensional animation character in accordance with the
invention, the synchronization of the movement of the body part and the
polygons which make up the "skin" of the body part with the joints of the
character are accomplished by the morphlinks in accordance with the invention
that will now be described in more detail.
-21-
Figure 6 is a diagram illustrating a morphlink in accordance with the
invention for the upper arm 178 shown in Figure 5. In this example, the
polygons covering the upper arm may be influenced by both the shoulder joint
172 and the elbow joint 174. For this example, the movement of a polygon 184
on the outside of the upper arm based on the movement of the shoulder joint and
the elbow joint will be described. If the movement of the polygon 184 is
influenced only by the shoulder joint's movement, the polygon 184 may move
to position x,. If the movement of the polygon 184 is influenced only by the
movement of the elbow joint, the polygon may move to position x2. To
realistically model the movement of the polygon, however, neither of the above
positions is accurate and would be perceived by the user viewing the animated
character as an aberration. Therefore, the polygon 184 should be influenced by
both the shoulder joint and the elbow joint so that the polygon 184 moves to
position x3 when the influence of both joints are used. In accordance with the
invention, the relationship of each polygon on the character to the joints in the
character may be stored in the morphlink data which is stored with the persistent
data file. The morphlink data permits a behavior file to only specify the
movement of the joints in the character (a small amount of data) and then the
player application on the client computer may determine the movement of each
polygon of the character based on the morphlink data. The actual influence
areas of each joint on particular polygons on the three dimensional object is
controlled by the user during the creation of the three dimensional character so
that once the character is created, each polygon on the character has a fixed
movement relationship with respect to the joints of the character. Now, an
example of the area of influence of a joint will be provided.
Figure 7 is a diagram illustrating an example of the area of influence of a
joint in accordance with the invention. In this example, a joint 190 may have an
inner area of influence 192 and an outer area of influence 194. A body part 196
surrounding the joint 190 is shown by the dotted lines. For polygons on the
body part within the inner area of influence 192, the joint 190 contributes 100%
of its movement to the movement of those polygons. In this example, the
movement of polygons A and B have 100% contribution from the joint 190 so
that, for example, if joint 190 moves 1" in the positive X direction, then
polygons A and B also move 1" in the positive X direction. Then, if another
joint moves 1" in the Y direction and also contributes 100% to the movement of
polygons A and B, polygons A and B also move 1" in the Y direction in
addition to the movement in the X direction. For polygons in the outer area of
influence 194, the amount of influence on the particular polygon decreases as
the polygon is located farther away from the joint. Thus, at the periphery
between the inner and outer areas of influence, the contribution is still 100%
while the contribution for a polygon at the outside edge of the outer area of
influence is 0%. Thus, for polygon C in this example, the joint contributes 50%
to the movement of polygon C so that if the joint moves 1" in the positive X
direction, polygon C moves 1/2" in the positive X direction. For polygons D
and E in this example, the joint 190 contributes 0% movement so that the
movement of the joint does not affect those polygons. Thus, for each polygon
-23- on a three dimensional animated character, the contributions for each joint in the
model is set by the user using the creator user interface and then stored in the
morphlinks by the system in accordance with the invention. Now, an example
of the process for creating a three dimensional animated character in accordance
with the invention using the creator will be described.
Figures 8 A and 8B are diagrams illustrating an example of the bones
within a model in accordance with the invention. The bones in the model are
generated using a user interface 200 in the creator application. The user
interface 200 may include an object window 202 which lists the objects, such as
the geometry and materials (textures) associated with the particular three
dimensional character being generated. The user interface 200 may also include
a geometry window 204 which lists all of the geometry associated with the
particular three dimensional character such as the neck, the left shoulder
(ShouldL), the left upper leg (UpLegL) and the like. To help the person creating
the character, the geometry is listed in object order so that the associations of
objects with other objects and the attributions of the characteristics (such as the
association of the upper left arm with the left shoulder) may be viewed by
glancing at the geometry window. The geometry window also permits the user
to make certain portions of the character invisible, if desired. The user interface
200 may also include a three dimensional character viewing window 206 which
shows the user the current view of the character. In this example, only one or
more bones of the character 208 and one or more joints 210 are shown by
clicking the appropriate locations in the geometry window. The bones and
-24- joints of the three dimensional model may be generated by the creator
application or by a well known third party piece of software. Once the bones of
the character have been laid out and set by the user, the user may place a "skin"
of polygons over the bones as will now be described with reference to Figure 9.
Figures 9 and 10 are diagrams illustrating an example of a model with
the bones and polygons in accordance with the invention and an example of a
character displayed with only the polygons, respectively. Once again, the user
may create the three dimensional animated character using the user interface 200
of the creator. In this figure, the user has selected to have the bones 208 and
joints 210 shown in window 206 with a polygon skin 212 placed over the bones
and joints. The polygon skin may be generated by the creator application or by
a third party piece of software. The polygon skin 212 forms the actual surface
seen by a person when viewing the three dimensional animated character and
any texture mapped onto these polygons. Figure 10 shows the character with
just the polygons 212 being displayed to the user in the user interface 200. The
character shown in Figure 10 accurately depicts what the three dimensional
animated character may look like with the exception of a texture being placed on
the polygons. A three dimensional animated character with a texture placed on
the polygons will now be described with reference to Figures 11 and 12.
Figure 11 is a diagram illustrating an example of a rendered, unlighted
character 220 in accordance with the invention within the viewing window 206
while Figure 12 is a diagram illustrating an example of a rendered, lighted
character 230 in accordance with the invention. As shown in Figure 11, the
three dimensional character has been covered with textured polygons so that, for
example, the character has long hair, eyebrows, a nose, a mouth with lips and
eyes. The textures may be generated by a third party piece of software and then
positioned onto the animated character by the user using the creator application.
The entire unlighted character 220 is shown in Figure 14.
In Figure 12, the same character has a chrome texture and has been
lighted with a particular lighting model. To texture the character with the
chrome surface, a material window 232 may be displayed which permits the
user to select a material/texture. In this example shown, the chrome material
was selected. The material window may include a palette 234 of materials
which may cover the polygons, such as a body material, a bottom teeth material,
a chrome material, a hair material and a top teeth material. The lighting may be
applied to the character by specifying a lighting model for the character. An
example of a lighting model will now be described with reference to Figure 13.
Figure 13 is a diagram illustrating an example of an environmental map
lighting model 240 in accordance with the invention which may be applied to a
three dimensional character such as the one shown in Figure 12. The
environmental map 240 is generated by having the selected lighting choice
illuminate a surface of a sphere. Thus, as shown in Figure 13, the particular
lighting model causes the sphere's surface to have a particular appearance made
up of individual pixels having different intensities. To transfer the lighting
model onto a three dimensional character, the appearance of the character at a
particular location is the same as the appearance of the sphere at the same
location. For example, the left side of the sphere has a bright spot 242 and the
character, shown in Figure 12, also has a bright spot 244 along the left side of
the character. Similarly, the sphere has a light shadow 246 near the top of the
sphere and the character 230 has a corresponding light shadow 248. Thus, in
accordance with the invention, the lighting model for the character is generated
by looking up the appearance of the lighting model on a particular location on a
sphere and then mapping the sphere's lighting at the particular location onto the
polygons of the animated character at the same particular location. In
accordance with the invention, it is not necessary to calculate the lighting for
each pixel of the character. In a typical three dimensional animation system, the
lighting model may be transferred onto the character by calculating the lighting
of each pixel on the character which is a slow process. Now, an example of a
morphlink associated with the leg of a character will be described.
Figures 15 and 16 are diagrams illustrating an example of the bones in a
leg and the morphlink associated with the leg in accordance with the invention.
In particular, Figure 16 shows the display window 206 of the creator with a
bottom half 250 of a character. In this example, a hip joint 252, a knee joint 254
and an ankle joint 256 are shown inside of the character. Each pixel of each
polygon forming the "skin" of the character may then have its motion
-27- determined by the creator of the character by setting the morphlinks that
associate a particular pixel's movement with the contributions from each joint in
the character.
Figure 16 illustrates the user interface 200 with the main window 202,
the geometry window 204 and the display window 206. When viewing the
morphlinks in the character, the user interface may also include a morphlink
window 258 which contains a list of each polygon in the character along with
the contributions of each joint's movement to the movement of that polygon. In
this example, the right leg has moved upwards and a polygon 260 has been
selected. The morphlink window 258 may then highlight the selected polygon
(Body_Geo Vert 188 in this example) along with the contribution from the knee
joint which is 77.62% in this example. Thus, if the knee moves 10" in the
positive X direction, the selected polygon moves 7.762" in the positive X
direction. As described above, each polygon may be influenced by one or more
joints and the contributions of each joint are added together to determine the
movement of that polygon. The morphlink permits a downloaded behavior files
to specify only the movement of each joint and then the player on the client
computer may determine the movement of each polygon based on the movement
of the joints and the morphlinks. Now, the areas of influence of a joint will be
described in more detail using the character shown in Figures 15 and 16.
Figure 17 is a diagram illustrating the character 250 of Figures 15 and 16
showing the area of influence for each joint. The areas of influence for each
WO 00/77742 PCT/USOO/l 5
-28- joint may include an inner region 270 and an outer region 272. During the
creation of a character, the user of the creator may adjust these inner and outer
regions which adjusts the influence of that joint. In this example, the areas of
influence for the hip joint 252, the knee joint 254 and the ankle joint 256 are
shown. The details about the areas of influence are described above and will not
be described here. Now, an example of a behavior will be described.
Figure 18 is a diagram illustrating an example of a behavior 280 in
accordance with the invention which may be downloaded to a client computer.
As shown, the structure of the behavior may follow the structure of the objects
within a character. In particular, the behavior may include a root node 282, a
dance hips node 284 specifying the movement of the hips of the character during
the dance behavior, a dance-rt. knee and dance-lft knee nodes 286, 288 which
specify the movement of the knees during the dance behavior, etc. Thus, the
objects in the behavior map to the objects in the character since the objects in
the behavior specify the movement of the objects in the character. In addition to
the movement, the behavior may also specify a sound track associated with the
behavior. For most behaviors which occur over time, the behavior may be
broken down into one or more key periods so that the movement of each object
during the behavior may change at each new key period and the system may
interpolate between the key periods. The behavior may also be compressed in
that, if an object, such as the head, is not moving or the object is not changing its
movement during the behavior, the object for the head may be left out of the
behavior file since the player will assume that any joint not in a behavior file
WO 00/77742 PCT/USOO/l
Attorney Docket No. P0644-995100 -29- will do the same time that it was doing before. To better understand the
behavior, an example of an object within the behavior will be described in more
detail.
For purposes of illustration, the dance-hips object 284 will be described
in more detail, although each object in the behavior may have a similar data
structure even if each object moves in a different manner. Thus, for each key
period (shown in Figure 18 as 0.1 second intervals), the object 284 may specify
the movement of the object in the three dimensions (X,Y,Z). As shown, the
movement in each dimension may change during each key period. Between the
key periods, the player may use interpolation to ensure a smooth movement.
Another example of a behavior will now be described.
Figures 19A, 19B and 19C are diagrams illustrating another example of
a behavior in accordance with the invention. In this example, the behavior is
having a character's mouth form the syllable "Ah" and a corresponding sound
track being played to simulate the character speaking the syllable "Ah". Figure
19A shows a structure 290 for the behavior which may include one or more time
frames 292 to ensure synchronization of the character with the behavior at each
key period. Following each time frame is the data about the movement of each
object in the character during that key period including the position change of
each object, the orientation change of each object and the scale change of each
object. Figure 19B illustrates a behavior object 294 for the "Ah" behavior
including links to each object (joint) in the mouth that is moved during the
Attorney Docket No. P0644-995100 -30- behavior. Figure 19C illustrates a sound track 296 associated with the "Ah"
behavior. In accordance with the invention, a behavior may also include a
plurality of behaviors which may be selected based on various factors including
a user's actions. Thus, the invention permits a class of behaviors to be
downloaded to the player at one time. Now, a method for streaming behaviors
in accordance with the invention will be described.
In accordance with the invention, it is desirable to being the animation of
the animated character including its behaviors as soon as possible so that the
user of the player application may begin viewing the animation as soon as
possible. When a large behavior file needs to be downloaded to the player
application, it is possible with conventional animation systems that the
animation of the animated character is delayed which is not acceptable. For
example, if a behavior contains a sound track, the sound data may be large
enough that the behavior takes as long to download as it does to play. On a
modem that transmits 28,800 bit per second, even compressed sound data
requires 13,000 bit per second to download the sound data and the behavior key
frames require the rest of the bandwidth. It is not reasonable to make a user wait
five minutes for the five minute long behavior to download before it is played.
In accordance with the invention, the animation system and in particular the
player application may start playing a behavior while the behavior is still being
downloaded to the player application which may be known as behavior
streaming.
-31-
Figure 20 is a flowchart illustrating a method 300 for streaming
behaviors in accordance with the invention. In step 302, the user may select a
behavior and/or start the execution of a behavior by, for example, clicking on a
button or an icon on a Web page. In step 304, the player application determines
if the behavior is a streaming behavior since each behavior associated with an
animated character may be identified as a streaming behavior or not. A behavior
may be identified as a streaming behavior when the behavior requires more than
a predetermined download time, such as when the behavior includes sound data.
If the behavior is not a streaming behavior, the method is completed. If the
behavior is a streaming behavior, the player application may download the
behavior objects, as described below, in step 306 and downloads the first
predetermined sized chunk of the behavior data in step 308. In a preferred
embodiment, the chunk of behavior data may be sufficient data for ten seconds
of the behavior. The rest of the behavior data may be downloaded
asynchronously as the player application is executing the previously
downloaded chunk of the behavior data. For a behavior that lasts a total of five
minutes, the streaming behavior beings playing after only ten seconds and the
rest of the behavior data may be downloaded as the behavior is being executed.
In accordance with the invention, the chunk being downloaded to the player
application may always be a predetermined number of seconds (ten seconds in a
preferred embodiment) ahead of the currently playing portion of the behavior.
In a preferred embodiment, the predetermined chunk of behavior data
downloaded before starting the behavior may be ten seconds of behavior time.
WO 00/77742 PCT/USOO/l
-32-
The downloading of the rest of the streaming behavior data may also be ten
seconds ahead of the currently playing behavior data. The ten second time takes
into account that the Internet sometimes suffers congestion and therefore is
delayed is delivering the behavior data. If the player application started playing
the streaming behavior as soon as it was downloaded, the user may experience
interruptions in the animation. Thus, the ten second interval provides a buffer of
data so that the system has some ability to compensate for when the Internet is
congested. For the streaming of the behavior data to work, the behavior data
must be compressed so that behavior data may be downloaded from the Internet
at least as fast as the player application plays the behavior data. For example, if
the user uses a modem to download the behavior data, the behavior data is
highly compressed so that it requires less than one second to download one
second worth of behavior data.
Returning to the flowchart, after the initial chunk of behavior data is
downloaded, the player application may execute the behavior in step 310. While
the initial chunk of behavior is being executed, the player application may
determine if the downloaded behavior data is more than a predetermined number
of seconds (twenty seconds in a preferred embodiment) ahead of the behavior
data currently being played in step 312. If the downloaded behavior data is
more than twenty seconds ahead of the currently played behavior data, the
player application may stop further downloads in step 314 until the new
behavior data is less than a predetermined time (ten seconds in a preferred
embodiment) ahead of the currently playing behavior data. Then, in step 316,
-33- the player application may download the next chunk of behavior data. In step
318, the player application may determine if there is more behavior data to
download and either loop back to step 308 to download a next chunk of behavior
data or complete the method if there is no more behavior data to be downloaded.
Now, the streaming behavior files in accordance with the invention will be
described.
Figure 21 is a diagram illustrating a stream file 330 in accordance with
the invention. In particular, the creator described above, may generate special
files for streaming behaviors known as stream files. The stream files 330 may
include behavior objects 332 and one or more chunks of key frame and sound
data 334. The behavior objects may include all of the data that describes the
components of the behavior, such as the geometry and the movement of each
joint in the animated character during the behavior. The behavior objects does
not contain any key frames of behavior data, such as sound data. Each of the
one or more chunks of behavior data 334 may contain a predetermined amount
of behavior data (such as two seconds of behavior data in a preferred
embodiment). For example, the first chunk of behavior data may contain all of
the keyframes from all of the behavior tracks which occur during the first
predetermined time interval along with the sound data that plays during the first
predetermined time interval of the behavior. Each chunk of behavior data starts
at the same time as the corresponding time in the behavior so that the initial
chunk starts at the start of the behavior. Now, an example of the structure for
each chunk of behavior data will be described.
Figure 22 is a diagram illustrating an example of the structure of each
chunk of behavior data 334. Each chunk 334 may be divided into one or more
tracks 336 wherein each track contains data about a particular portion of the
animated character. In this example, there is a head track 338, a torso track 340
and a knee track 342 as shown in Figure 22 which are respectively associated
with the head, torso and knee of the animated character geometry. As shown,
the chunk also include the sound data 344 for that particular portion of the
behavior data.
Figure 23 is a diagram illustrating more details of the chunk 334 of
behavior data. In particular, the chunk of behavior data includes the tracks 338,
340 and a timestamp 350. The timestamp may indicate the time of the chunk
within the behavior, such as that the chuck covers time t to time t+2 seconds of
the behavior. Each track 338, 340 may include an identifier 352 that identifies
the behavior object with which the particular track is associated, a length of data
field 354 (len) indicating that length of the data in the track and a data field 356
containing the keyframe and behavior data for that track. Each chunk 334 may
end with a track identification of zero (id-0) indicating the end of the particular
chunk of behavior data. Now, the operation of the player will be described.
Figures 24 and 25 are flowcharts illustrating the operation of the player
in accordance with the invention. Figure 24 is a flowchart illustrating the
operation 400 of the player for each frame of images being displayed to the user
of the client computer. In step 402, the player may read any user inputs and
react according to those user inputs. Next, the player may determine any
-35- geometry changes in the character in step 404 based on any currently executing
behaviors. Next, the player may generate the polygons of the character in step
406 based on the above determined changes in the geometry and the morphlinks
as described above. Once the polygons are generated, the data about the
polygons of the character may be scan converted in step 408 so that the
character and the polygons may be displayed on a display screen. In step 410,
the character may be transferred to the display memory, such as by using a well
known BLTBLK routine, so that it may be displayed to the user. Now, the
details about determining the geometry changes will be described.
Figure 25 is a flowchart illustrating a method 420 for determining
geometry changes in accordance with the invention. In step 422, the player may
call any update scripts which may include commands about the current behavior
being executed. If there are no other behaviors being executed, the player may
execute the idle behavior. In step 424, the player may determine if the update
scripts contain any new behaviors and request the download of the new behavior
in step 426 if a new behavior is needed. Next, in step 428, the player determines
the geometry changes for the character based on the currently executing
behavior.
While the foregoing has been with reference to a particular embodiment
of the invention, it will be appreciated by those skilled in the art that changes in
this embodiment may be made without departing from the principles and spirit
of the invention, the scope of which is defined by the appended claims.