Abstract:
A game developer can “tag” an item in the game environment. When an animated character walks near the “tagged” item, the animation engine can cause the character&#39;s head to turn toward the item, and mathematically computes what needs to be done in order to make the action look real and normal. The tag can also be modified to elicit an emotional response from the character. For example, a tagged enemy can cause fear, while a tagged inanimate object may cause only indifference or indifferent interest.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of application Ser. No. 13/657,290 filed Oct. 22, 2012, now allowed, which is a continuation of application Ser. No. 13/064,531 filed Mar. 30, 2011, now U.S. Pat. No. 8,319,779, which is a continuation of application Ser. No. 12/654,844 filed Jan. 6, 2010, now U.S. Pat. No. 7,928,986, which is a continuation of application Ser. No. 10/078,526 filed Feb. 21, 2002, now U.S. Pat. No. 7,667,705, which claims the benefit of Provisional Application No. 60/290,688 filed May 15, 2001 and Provisional Application No. 60/314,289 filed Aug. 24, 2001, the entire contents of each of which are hereby incorporated by reference in this application. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to computer graphics and more particularly to the use of computers to generate animated displays. Still more particularly, the invention relates to techniques for automatically controlling animation within a video game or other graphical presentation. In particular, the invention provides a reactive animation system that enables game characters or other graphical characters to appear much more realistic as they interact with a virtual world in which they are displayed. The reactive animation system enables, for example, the creation virtual worlds where the character(s) therein will do things, such as have a facial, body or other type of physical or emotional reactions, in response to the character coming within proximity of a “tagged” element (such as a point of interest in a 3D world). The invention enables characters to appear much more realistic by giving the character a personality and appearing to bring the character to life in its virtual environment without having to script or animate each scene in advance. 
       BACKGROUND AND SUMMARY OF THE INVENTION 
       [0003]    Many of us have seen films containing remarkably realistic dinosaurs, aliens, animated toys and other fanciful creatures. Such animations are made possible by computer graphics. Using such techniques, a computer graphics artist can specify how each object should look and how it should change in appearance over time, and a computer then models the objects and displays them on a display such as your television or a computer screen. The computer takes care of performing the many tasks required to make sure that each part of the displayed image is colored and shaped just right based on the position and orientation of each object in a scene, the direction in which light seems to strike each object, the surface texture of each object, and other factors. 
         [0004]    Because computer graphics generation is complex, computer-generated three-dimensional graphics just a few years ago were mostly limited to expensive specialized flight simulators, high-end graphics workstations and supercomputers. The public saw some of the images generated by these computer systems in movies and expensive television advertisements, but most of us couldn&#39;t actually interact with the computers doing the graphics generation. All this has changed with the availability of relatively inexpensive 3D graphics platforms such as, for example, the NINTENDO 64®, the NINTENDO GAMECUBE® and various 3D graphics cards now available for personal computers. It is now possible to interact with exciting 3D animations and simulations on relatively inexpensive computer graphics systems in your home or office. 
         [0005]    A problem graphics system designers have confronted is how to efficiently model and render realistic looking animations in real time or close to real time. To achieve more interesting dynamic animation, a number of video and computer games have used various animation techniques such as key frame transformations, inverse kinematics and the like to model and animate people, animals and other objects. See for example O&#39;Rourke,  Principles of Three - Dimensional Computer Animation  (W. W. Norton 1998) at chapters 3 and 4 especially. While such techniques have been highly successful, animators have searched for ways to make animations more realistic without the need to control or map out each and every movement of an animated character beforehand. 
         [0006]    One approach that has appeal is to make the animation engine responsible for animated characters increasingly more intelligent. For example, it is possible to define an “intelligent” animated character within a three-dimensional environment and allow the character to react to the environment based on its programmed qualities. If the character is sufficiently intelligent, rather complex reactions can be dynamically created “on the fly” by the real time animation engine—saving the game developer the massive amount of time and effort that might otherwise be required to script out the animation sequence. See, for example, U.S. patent application Ser. No. 09/382,819 of Comair et al filed 25 Aug. 1999 entitled “Object Modeling For Computer Simulation And Animation” incorporated by reference herein. 
         [0007]    While such approaches have been successful, further improvements are possible. In particular, we have developed a new, efficient technique for causing an animated character to pay attention to an object within a virtual world by tagging the object. When the animated character moves into proximity with an object (e.g., in response to user control), the system checks whether the object is tagged. If the object is tagged, the animation engine animates the character to pay attention to the tagged object (e.g., by animating the character to look or stare at the tagged object so long as the character remains close to the tagged object). The tag-based animation engine can, for example, animate the character to turn toward or face the tagged object in the process of paying attention to it—creating a very realistic visual effect without the typical programming overhead normally required to specify which direction the animated character should face and when. In other words, in accordance with the invention, the tags can be defined by designers at any location in the virtual world and given certain characteristics that are designed to cause a character that comes into a defined proximity of the tag to have some sort of reaction to the tag. By defining several tags in a scene, such as, for example, in a virtual hallway through which a character is walking, the animation engine makes the character much more realistic and to appear as if the character is coming to life through its reactions to the tags. The tags are preferably associated with virtual objects of the type that would typically cause a human to have a reaction in the real world. The tags are preferably defined to cause the same type of reaction in the character&#39;s animation, as a typical human would have in the same circumstance in the real world. In this way, the character has much more human-like reactions to its environment while moving through the virtual world, and the character can be made to appear as if it has “come to life.” 
         [0008]    In accordance with the invention, the tagging system of the animation engine is preferably priority based. In other words, each tag is assigned a priority value that is used by the animation engine to control which tag will be used when more than one tag is active. By prioritizing the tags in the environment, the animation engine as able to display the character as paying attention to or reacting to the tagged object that is of highest interest to the character, based on the character&#39;s current environment and/or state, from among several tags that may be in proximity to the character at any one time. This tag prioritization feature further helps to make the character appear more realistic by enabling the character to prioritize its reactions in the same or similar way to that of a human. For example, in the real world, humans typically are confronted with numerous objects (e.g., interesting painting, view, other object etc.) or events (loud noise, flashing light, movement, etc.) that may cause a reaction at any one time. However, humans, by their nature, typically react to the one thing that seems to be the most important at each instant in time. For instance, a human would typically stop looking at a piece of art when a loud noise comes from another object, and then quickly turn in the direction of the loud noise. Upon determining that the noise is not a problem, a human would then typically resume looking at the piece of art. These same human-like movements and reactions can be generated by the reactive animation system of the invention, by giving the object that makes the noise a higher priority tag while active as compared to the tag associated with the piece of art. In this way, all of the tagged objects in the environment can have relative priorities assigned thereto based on, for example, the nature of the object. 
         [0009]    In one particular embodiment, the object can be tagged with a tag that inspires an emotion in the character while paying attention to the tagged object. The emotion can, for example, be fear, happiness, or any other discernible emotion. If an object is tagged to inspire fear, the character can be animated to turn toward the object and react with a look of horror. If an object is tagged to inspire happiness, the character can be animated to turn toward the object and react with a big smile. Other emotions and reactions are possible. In fact, the tag can be defined to cause any type of response that corresponds to any variable or role-playing element that the character may have, as well as to cause emotional and/or physical reactions. For example, the tag could modify the animation of the character so that the character appears injured, sick or insane while under the influence of an active tag. 
         [0010]    In accordance with the invention, the character&#39;s animation is adapted to the tag when the tag is activated. Activation of the tag can occur when the user gets within a selected distance from the tag and/or based on some other defined event. The adaptation of the animation is preferably done by defining key frames for use in creating a dynamic animation sequence using the information provided by the tag. The dynamic animation sequence is preferably generated using the techniques known in the art as “Inbetweening” and “Inverse Kinematics.” Inbetweening enables the frames between the key frames to be generated for the dynamic animation, and inverse kinematics is used to assure that the character&#39;s movements are natural during the animation. Once a tag is activated, the animation of the character is adapted from its generic or canned-animation to a dynamic animation based on the type of tag that has been encountered. Thus, the tag triggers a dynamic modification of the character&#39;s animation for the period of time it takes for the tag to become inactive, such as by the character moving out of range of the tag. 
         [0011]    The dynamic animation provided by the reactive animation engine of the instant invention provides a character (or other object) with realistic reactions as the character moves through the virtual environment, without having to handcraft the animation for every possible scene in advance. Thus, the invention enables animation to be generated on-the-fly and in an unpredictable and realistic manner. As a result, the character&#39;s animation can constantly change in a variety of ways and depending on many possible variables. This makes the character&#39;s animation unpredictable and greatly enhances the visual effect of the display. A significant advantage of the instant invention is that the character can be displayed with a myriad of animations without having to script, hand-craft or store each of the animations in advance. Instead, the reactive animations are dynamically generated on-the-fly and in real time based on the tag. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These and other features and advantages of the present invention may be better and more completely understood by referring to the following detailed description of presently preferred example embodiments in conjunction with the drawings, of which: 
           [0013]      FIGS. 1-5  show example screen effects for a first exemplary animation sequence provided by a preferred embodiment of the invention; 
           [0014]      FIG. 5A  shows an example conceptual display illustrating the location of a tag and a vector from the character&#39;s eyes to the tag; 
           [0015]      FIGS. 6 ,  7 A,  7 B,  8  and  9  show example screen effects for a second exemplary animation sequence by a preferred embodiment of the invention; 
           [0016]      FIGS. 10A-10B  illustrate an example system that may be used to create the displays of  FIGS. 1-9 ; 
           [0017]      FIG. 11  is an example flowchart of steps performed by a tag-based animation engine of the instant invention; 
           [0018]      FIG. 12  illustrates an example tag data structure for tags used in accordance with the instant invention; 
           [0019]      FIG. 13  is a more detailed example flow chart of steps performed by the tag-based animation engine of the instant invention; 
           [0020]      FIG. 14  is an exemplary flow chart of the steps performed by the tag-based animation engine of the instant invention in order to generate a dynamic animation sequence; and 
           [0021]      FIG. 15  is an exemplary flow chart of the steps performed by the tag-based animation engine for tag priority management. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0022]      FIGS. 1-5  show example screen effects provided by a preferred exemplary embodiment of this invention. These Figures show an animated character  10  moving through an illustrative video game environment such as a corridor of a large house or castle. Hanging on the wall  11  of the corridor is a 3D object  12  representing a painting. This object  12  is “tagged” electronically to indicate that character  10  should pay attention to it when the character is within a certain range of the painting. As the character  10  moves down the corridor (e.g., in response to user manipulation of a joystick or other interactive input device) (see  FIG. 1 ) and into proximity to tagged object  12 , the character&#39;s animation is dynamically adapted so that the character appears to be paying attention to the tagged object by, for example, facing the tagged object  12  (see  FIG. 2 ). In the example embodiment, the character  10  continues to face and pay attention to the tagged object  10  while it remains in proximity to the tagged object (see  FIG. 3 ). As the character moves out of proximity to the tagged object  12  (see  FIG. 4 ), it ceases paying attention to the tagged object by ceasing to turn towards it. Once the animated character  10  is more than a predetermined virtual distance away from the tagged object  12 , the character no longer pays attention to the object and the object no longer influences the character. 
         [0023]    When the character first enters the corridor, as shown in  FIG. 1 , the character is animated using an existing or generic animation that simply shows the character walking. However, when the tag becomes active, i.e., the character approaches the painting  12 , the reactive animation engine of the instant invention adapts or modifies the animation so that the character pays attention to the painting in a natural manner. The animation is preferably adapted from the existing animation by defining key frames and using the tag information (including the location and type of tag). More particularly, inbetweening and inverse kinematics are used to generate (i.e., calculate) a dynamic animation sequence for the character using the key frames and based on the tag. The dynamic animation sequence (rather than the existing or generic animation) is then displayed while the character is within proximity to the tag. However, when the tag is no longer active, the character&#39;s animation returns to the stored or canned animation (e.g., a scripted and stored animation that simply shows the character walking down the hallway and looking straight ahead). 
         [0024]    In the screen effects shown in  FIGS. 1-5 , the object  12  is tagged with a command for character  10  to pay attention to the object but with no additional command eliciting emotion. Thus,  FIGS. 1-5  show the character  10  paying attention to the tagged object  12  without any change of emotion. However, in accordance with the invention, it is also possible to tag object  12  with additional data or command(s) that cause character  10  to do something in addition to (or instead of) paying attention to the tagged object. In one illustrative example, the tagged object  12  elicits an emotion or other reaction (e.g., fear, happiness, belligerence, submission, etc.) In other illustrative examples, the tagged object can repel rather than attract character  10 —causing the character to flee, for example. Any physical, emotional or combined reaction can be defined by the tag, such as facial expressions or posture change, as well as changes in any body part of the character (e.g., position of head, shoulders, feet, arms etc.). 
         [0025]      FIG. 5A  is an example conceptual drawing showing the theory of operation of the preferred embodiment. Referring to  FIG. 6 , the “tag” T associated with an item in the 3D world is specified based on its coordinates in 3D space. Thus, to tag a particular object  12 , one specifies the location of a “tag point” or “tag surface” in 3D space to coincide with the position of a desired object in 3D space.  FIG. 5A  shows a “tag” T (having a visible line from the character to the tag for illustration purposes) defined on the painting in the 3D virtual world. In accordance with the invention, the animated character  10  automatically responds by turning its head toward the “tag”, thereby appearing to pay attention to the tagged object. The dotted line in  FIG. 5A  illustrates a vector from the center of the character  10  to the tag T. The animation engine can calculate this vector based on the relative positions of character  10  and tag T in 3D space and use the vector in connection with dynamically animating the character. 
         [0026]    In accordance with a preferred embodiment of the invention, one can place any number of tags T at any number of locations within the 3D space. Any number of animated characters  10  (or any subsets of such characters, with different characters potentially being sensitive to different tags T) can react to the tags as they travel through the 3D world. 
         [0027]      FIGS. 6-9  illustrate another embodiment of the invention, wherein two tags are defined in the corridor through which the character is walking. A first tag T1 is provided on the painting as described above in connection with the display sequence of  FIGS. 1-5 . However, in this embodiment, a second tag T2 is provided on the wall mounted candle. This second tag is different from the first tag in that it is defined to only cause a reaction from by the character when the candle is animated to flare up like a powerful torch (see  FIG. 7A ). The second tag T2 is given a higher priority than the first tag T1. The reactive animation engine is programmed to only allow the player to react to one tag at a time, that one tag being the tag that has the highest priority of any active tags. As a result, when the character  10  is walking down the corridor and gets within proximity of the two tags, the second tag is not yet active due to the fact that the candle is not flaring up. Thus, the character turns to the look at the only active tag T1 (i.e., the painting) (see  FIG. 6 ). However, when the candle flares-up, the second tag T2, which has a higher priority than T1, also becomes active, thereby causing the character to stop looking at the painting and turn its attention to the flaring torch (i.e., the active tag with the highest priority) (see  FIG. 7A ). Once the torch stops flaring and returns to a normal candle, the second tag T2 is no longer active and the reactive animation engine then causes the character to again turn its attention to the painting (i.e. the only active tag)(see  FIG. 7B ). Once the character begins to move past the painting, the character&#39;s head then begins to turn naturally back (see  FIG. 8 ) to the forward or uninterested position corresponding to the stored animation (see  FIG. 9 ). Thus, in accordance with the invention, the character responds to active tags based their assigned priority. In this way, the character is made to look very realistic and appears as if it has come to life within its environment. As explained above, the reactive animation engine E dynamically generates the character&#39;s animation to make the character react in a priority-based manner to the various tags that are defined in the environment. 
       Example ILLUSTRATIVE IMPLEMENTATION 
       [0028]      FIG. 10A  shows an example interactive 3D computer graphics system  50 . System  50  can be used to play interactive 3D video games with interesting animation provided by a preferred embodiment of this invention. System  50  can also be used for a variety of other applications. 
         [0029]    In this example, system  50  is capable of processing, interactively in real time, a digital representation or model of a three-dimensional world. System  50  can display some or the entire world from any arbitrary viewpoint. For example, system  50  can interactively change the viewpoint in response to real time inputs from handheld controllers  52   a ,  52   b  or other input devices. This allows the game player to see the world through the eyes of someone within or outside of the world. System  50  can be used for applications that do not require real time 3D interactive display (e.g., 2D display generation and/or non-interactive display), but the capability of displaying quality 3D images very quickly can be used to create very realistic and exciting game play or other graphical interactions. 
         [0030]    To play a video game or other application using system  50 , the user first connects a main unit  54  to his or her color television set  56  or other display device by connecting a cable  58  between the two. Main unit  54  produces both video signals and audio signals for controlling color television set  56 . The video signals are what controls the images displayed on the television screen  59 , and the audio signals are played back as sound through television stereo loudspeakers  61 L,  61 R. 
         [0031]    The user also needs to connect main unit  54  to a power source. This power source may be a conventional AC adapter (not shown) that plugs into a standard home electrical wall socket and converts the house current into a lower DC voltage signal suitable for powering the main unit  54 . Batteries could be used in other implementations. 
         [0032]    The user may use hand controllers  52   a ,  52   b  to control main unit  54 . Controls  60  can be used, for example, to specify the direction (up or down, left or right, closer or further away) that a character displayed on television  56  should move within a 3D world. Controls  60  also provide input for other applications (e.g., menu selection, pointer/cursor control, etc.). Controllers  52  can take a variety of forms. In this example, controllers  52  shown each include controls  60  such as joysticks, push buttons and/or directional switches. Controllers  52  may be connected to main unit  54  by cables or wirelessly via electromagnetic (e.g., radio or infrared) waves. 
         [0033]    To play an application such as a game, the user selects an appropriate storage medium  62  storing the video game or other application he or she wants to play, and inserts that storage medium into a slot  64  in main unit  54 . Storage medium  62  may, for example, be a specially encoded and/or encrypted optical and/or magnetic disk. The user may operate a power switch  66  to turn on main unit  54  and cause the main unit to begin running the video game or other application based on the software stored in the storage medium  62 . The user may operate controllers  52  to provide inputs to main unit  54 . For example, operating a control  60  may cause the game or other application to start. Moving other controls  60  can cause animated characters to move in different directions or change the user&#39;s point of view in a 3D world. Depending upon the particular software stored within the storage medium  62 , the various controls  60  on the controller  52  can perform different functions at different times. 
         [0034]    As also shown in  FIG. 10A , mass storage device  62  stores, among other things, a tag-based animation engine E used to animate characters based on tags stored in the character&#39;s video game environment. The details of preferred embodiment tag-based animation engine E will be described shortly. Such tag-based animation engine E in the preferred embodiment makes use of various components of system  50  shown in  FIG. 10B  including:
       a main processor (CPU)  110 ,   a main memory  112 , and   a graphics and audio processor  114 .       
 
         [0038]    In this example, main processor  110  (e.g., an enhanced IBM Power PC 750) receives inputs from handheld controllers  52  (and/or other input devices) via graphics and audio processor  114 . Main processor  110  interactively responds to user inputs, and executes a video game or other program supplied, for example, by external storage media  62  via a mass storage access device  106  such as an optical disk drive. As one example, in the context of video game play, main processor  110  can perform collision detection and animation processing in addition to a variety of interactive and control functions. 
         [0039]    In this example, main processor  110  generates 3D graphics and audio commands and sends them to graphics and audio processor  114 . The graphics and audio processor  114  processes these commands to generate interesting visual images on display  59  and interesting stereo sound on stereo loudspeakers  61 R,  61 L or other suitable sound-generating devices. Main processor  110  and graphics and audio processor  114  also perform functions to support and implement the preferred embodiment tag-based animation engine E based on instructions and data E′ relating to the engine that is stored in DRAM main memory  112  and mass storage device  62 . 
         [0040]    As further shown in  FIG. 10B , example system  50  includes a video encoder  120  that receives image signals from graphics and audio processor  114  and converts the image signals into analog and/or digital video signals suitable for display on a standard display device such as a computer monitor or home color television set  56 . System  50  also includes an audio codec (compressor/decompressor)  122  that compresses and decompresses digitized audio signals and may also convert between digital and analog audio signaling formats as needed. Audio codec  122  can receive audio inputs via a buffer  124  and provide them to graphics and audio processor  114  for processing (e.g., mixing with other audio signals the processor generates and/or receives via a streaming audio output of mass storage access device  106 ). Graphics and audio processor  114  in this example can store audio related information in an audio memory  126  that is available for audio tasks. Graphics and audio processor  114  provides the resulting audio output signals to audio codec  122  for decompression and conversion to analog signals (e.g., via buffer amplifiers  128 L,  128 R) so they can be reproduced by loudspeakers  61 L,  61 R. 
         [0041]    Graphics and audio processor  114  has the ability to communicate with various additional devices that may be present within system  50 . For example, a parallel digital bus  130  may be used to communicate with mass storage access device  106  and/or other components. A serial peripheral bus  132  may communicate with a variety of peripheral or other devices including, for example:
       a programmable read-only memory and/or real time clock  134 ,   a modem  136  or other networking interface (which may in turn connect system  50  to a telecommunications network  138  such as the Internet or other digital network from/to which program instructions and/or data can be downloaded or uploaded), and   flash memory  140 .       
 
         [0045]    A further external serial bus  142  may be used to communicate with additional expansion memory  144  (e.g., a memory card) or other devices. Connectors may be used to connect various devices to busses  130 ,  132 ,  142 . For further details relating to system  50 , see for example U.S. patent application Ser. No. 09/723,335 filed Nov. 28, 2000 entitled “EXTERNAL INTERFACES FOR A 3D GRAPHICS SYSTEM” incorporated by reference herein. 
         [0046]      FIG. 11  shows an example simplified illustration of a flowchart of the tag-based animation engine E of the instant invention. Animation engine E may be implemented for example by software executing on main processor  110 . Tag-based animation engine E may first initialize a 3D world and animation game play (block  1002 ), and may then accept user inputs supplied for example via handheld controller(s)  52  (block  1004 ). In response to such user inputs, engine E may animate one or more animated characters  10  in a conventional fashion to cause such characters to move through the 3D world based on the accepted user inputs (block  1006 ). Tag-based animation engine E also detects whether any moving character is in proximity to a tag T defined within the 3D world (decision block  1008 ). If a character  10  is in proximity to a tag T, the animation engine E reads the tag and computes (e.g., through mathematical computation and associated modeling, such as by using inbetweening and inverse kinematics) a dynamic animation sequence for the character  10  to make the character realistically turn toward or otherwise react to the tag (block  1010 ). Processing continues (blocks  1004 - 1010 ) until the game is stopped or some other event causes an interruption. 
         [0047]      FIG. 12  shows an illustrative exemplary data structure  1100  for a tag T. In the example shown, data structure  1100  includes a tag ID field  1102  that identifies the tag; three-dimensional (i.e., X, Y, Z) positional coordinate fields  1104 ,  1106 ,  1108  (plus further optional additional information if necessary) specifying the position of the tag in the 3D world; a proximity field  1110  (if desired) specifying how close character  10  must be to the tag in order to react to the tag; a type of tag or reaction code  1112  specifying the type of reaction to be elicited (e.g., pay attention to the tag, flee from the tag, react with a particular emotion, etc.); and a priority field  114  that defined a priority for the tag relative to other tags that may be activated at the same time as the tag. 
         [0048]      FIG. 13  shows a more detailed exemplary flow chart of the steps performed by the reactive animation engine E of the instant invention. Once the 3D world and game play are initialized (step  1302 ), the system accepts user inputs to control the character within the environment in a conventional manner (step  1304 ). The system initially uses scripted or canned animation that is provided with the game for the character (step  1306 ). The animation engine checks the characters position relative to the tags that have been defined in the 3D world by the designers of the game (step  1308 ). If the character is not within proximity to tag then the standard animation continues for the character (step  1310 ). However, when a tag is detected (step  1308 ), the tag is read to determine the type of reaction that the tag is supposed to elicit from the character and the exact location of the tag in the 3D world (step  1312 ). The animation engine E then uses key frames (some or all of which may come from the scripted animation) and the tag information to dynamically adapt or alter the animation of the character to the particular tag encountered (step  1314 ). The dynamic animation is preferably generated using a combination of inbetweening and inverse kinematics to provide a smooth and realistic animation showing a reaction to the tag. Particular facial animations may also be used to give the character facial emotions or reactions to the tag. These facial animations can be selected from a defined pool of facial animations, and inbetweening or other suitable animation techniques can be used to further modify or dynamically change the facial expressions of the character in response to the tag. The dynamic animation then continues until the tag is no longer active (step  1316 ), as a result of, for example, the character moving out of range of the tag. Once the dynamic animation is completed, the standard or scripted animation is then used for the character until another tag is activated (step  1318 ). 
         [0049]      FIG. 14  shows a simplified flow chart of the steps performed by the reactive animation engine E of the instant invention in order to generate the dynamic animation sequence in response to an activated tag. As seen in  FIG. 14 , once a tag is activated (step  1402 ), the animation engine reads the tag to determine the type of tag, its exact location and any other information that is associated with the tag (step  1404 ). The engine then defines key frames for use in generating the dynamic animation (step  1406 ). The key frames and tag information are then used, together with inbetweening and inverse kinematics, to create an animation sequence for the character on-the-fly (step  1408 ). Preferably, the dynamic animation sequence is adapted from the standard animation, so that only part of the animation needs to be modified, thereby reducing the overall work that must be done to provide the dynamic animation. In other words, the dynamic animation is preferably generated as an adaptation or alteration of the stored or standard animation. The dynamic animation then continues until the tag is no longer active (step  1410 ), at which time the characters animation returns to the standard animation. 
         [0050]      FIG. 15  shows an exemplary flow chart of the priority-based tagging feature of the instant invention. This feature enables several or many tags to be activated simultaneously while still having the character react in a realistic and in a priority based manner. As seen in  FIG. 15 , when a tag is activated, the animation engine determines the priority of the tag (step  1502 ), as well as doing the other things described above. The animation engine then determines if any other tags are currently active (step  1506 ). If no other tags are active, the animation engine dynamically adapts or alters the animation, in the manner described above, to correspond to the active tag (step  1508 ). If, on the other hand, one or more other tags are currently active, the reactive animation engine determines the priority of each of the other active tags (step  1510 ) to determine if the current tag has a higher priority relative to each of the other currently active tags (step  1512 ). If the current tag does have the highest priority, then the animation engine dynamically generates the character&#39;s animation based on the current tag (step  1514 ). If, on the other hand, another active tag has a higher priority than the currently active tag, then the animation engine E adapts the animation in accordance with the other tag having the highest priority (step  1516 ). When the other tag having a higher priority is no longer active, but the original tag (i.e., from step  1502 ) is still active, then the animation engine dynamically generates the character&#39;s animation based on the original tag as soon as the higher priority tag has become inactive. In this way, the character&#39;s attention can be smoothly and realistically changed from one tagged object to another tagged object, as well as from no tagged object to a tagged object.  FIGS. 6-9  illustrate an exemplary priority-based display sequence as just described. 
         [0051]    As can be seen from the description above, the instant reactive animation engine E of the instant invention can be used in a variety of video games and/or other graphical applications to improve realism and game play. The invention enables a character to appear as if it has “come to life” in the game environment. The instant invention is particularly advantageous when incorporated into role playing games wherein a character interacts with a 3D world and encounters a variety of objects and/or other characters that can have certain effects on a character. The animation engine of the instant invention can also be implemented such that the same tag has a different effect on the character depending on the state of a variable of the character at the time the tagged object is encountered. One such variable could be the “sanity” level of the player in a sanity-based game, such as described in U.S. provisional application Ser. No. 60/184,656 filed Feb. 24, 2000 and entitled “Sanity System for Video Game”, the disclosure of which is incorporated by reference herein. In other words, a tag may be defined such that it does not cause much of a reaction from the character when the character has a high sanity level. On the other hand, the same tag may cause a drastic reaction from the character (such as eye&#39;s bulging) when the character is going insane, i.e., when having a low sanity level. Any other variable or role playing element, such as health or strength, could also be used to control the type of reaction that a particular tag has on the particular character at any given time during the game. Other characters, such as monsters, can also be tagged and with prioritized tags as described above in order to cause the character to react to other characters as well as other objects. Tags can also be defined such that factors other than proximity (such as timing, as in the candle/torch example above) can be used alone or in addition to proximity to cause activation of the tag. 
         [0052]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.