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Technical Issues: Animation Technical Issues: Animation While graphical effects can visualize a game world, animation effects are what actually breathe life into it. Otherwise, you only have a static and motionless world.

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Technical Issues:Animation

  • While graphical effects can visualize a game world, animation effects are what actually breathe life into it.

    • Otherwise, you only have a static and motionless world.

  • Properly animating a game can be costly, but the results can be well worth it.

    • Hiring of animators and actors.

    • Purchase of modeling tools.

    • Purchase of motion data or motion capture sessions.

    • Additional software and hardware resources.


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Technical Issues:Animation

Screen shot and video of Unreal Tournament 2003. Some of the bestanimation effects in a video game ever.


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Animation Requirementsfor Video Games

  • Like graphics, animation is used to support the representation element of a video game.

    • Animation captures all motions and actions within a game and conveys this information to the player.

  • Animation has the same general requirements as graphics, plus a few more resulting from its dynamic nature.


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Animation Requirements:Be Smooth

  • Sudden or jerky motions in a game can be very distracting and very annoying.

    • This applies not only to any character or object animations, but also to any camera movement in the game.

  • Remember that the player identifies with the viewpoint of the game; sudden changes have been known to induce motion sickness!

  • Instead, animation should be as smooth and fluid as possible.


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Animation Requirements:Be Smooth

Screen shot from Mortal Kombat: Deadly Alliance. While graphically

impressive, this latest Mortal Kombat has been criticized for animation thatis best described as “stilted” and “choppy”. Not a good thing.


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Animation Requirements:Make Use of Ambient Effects

  • Animation should be used to bring life to ambient entities in the game world. This includes:

    • Non player characters.

    • Animals, birds, insects, and other critters.

    • Plant life.

    • Water, clouds, and other terrain effects.

    • Other game world entities including doors, furnishings, computers, and other objects.

  • By animating these entities, the game world will seem more vibrant and life-like.


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Animation Requirements:Make Use of Ambient Effects

Screen shot from the Legend of Zelda: The Ocarina of Time. The world is full of lively animated entities, including the characters wandering around, animals, and so on.


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Animation Requirements:Stage Action Properly

  • It is important to stage action properly for all animation in a game.

  • This includes:

    • Choosing a viewpoint that conveys the most information about events being animated.

    • Isolating events as much as possible so that only one thing at a time occupies the player’s attention.

  • If this staging is not done properly, the player can easily get confused or miss out on vital game information.


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Animation Requirements:Stage Action Properly

Screen shot from Killer Instinct Gold. TJ Combo’s level has interestinganimated effects. This includes a train that rumbles through every 10-20seconds. If that doesn’t distract you, I don’t know what will!


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Animation Requirements:Timing is Everything

  • The timing of animation is critically important to its success in a game.

  • If it is too slow or too fast, it will appear out of sync with the rest of the game.

    • This can be quite annoying and frustrating, especially if it has an impact on gameplay.

  • Sometimes, however, playing with timing can lead to some interesting special effects and gameplay situations.


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Animation Requirements:Timing is Everything

Screen shot from Max Payne. With its revolutionary “bullet time”, you canhave John Woo style animations with slow motion action, bullets zippingover your head, and so on. Just like the movies!


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Animation Requirements:Timing is Everything

Screen shot from Jet Li: Rise to Honor. A cool fighting game with lots of

features, including bullet time (that lets you change directions mid-flight).

Some have called this the “most flagrant abuse of bullet time ever seen”.


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Animation Requirements:Anticipate and Follow-through

  • Anticipation is an indication of action to come.

  • Follow-through is the reaction that happens after the action.

  • In most cases, realistic actions have both an anticipation and a follow-through.

    • For example, a character should bend its knees both before jumping and when landing.

  • The absence of anticipation and follow-through removes some of the realism and consistency of your game.


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Animation Requirements:Anticipate and Follow-through

Screen shot and animation from NBA Live. Jumping is done properly,

as one can see a player prepare to jump and also see them stickthe landing properly. Anticipation and follow-through are donenicely in this case.


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Animation Requirements:Secondary Motion

  • When animating a character, you should first focus on animating its primary motion, such as arms and legs moving.

  • Be sure, however, not to ignore a character’s secondary motions.

    • This includes things such as hair and clothing movement, and so on.

  • While this can take lots of time to do, it can be well worth it in the end.


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Animation Requirements:Secondary Motion

Screen shot from Dead or Alive 3. A lot of attention is paid to animating secondary motion of hair, clothing, and so on.


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Animation Requirements:Be Representative

  • The animations of a character or an object should reveal or reflect their various properties and behaviours.

    • For example, a rubber ball would distort when bounced on the floor, whereas a metal ball would perhaps only wobble or resonate.

  • This helps reinforce consistency and immersion in a game, as characters and objects would act in a way that is fitting and suitable to themselves.


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Animation Requirements:Be Representative

Screen shot and video from Dead or Alive 3. The animation of each character, including Brad Wong above, reflects their personality, behaviour,

and fighting style in the game.


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Animation Requirements:Obey Appropriate Laws

  • It is important for animation to follow appropriate laws of physics and nature according to the type of game being played.

    • This includes gravity, friction, momentum, skeletal mechanics, acceleration, force transfer, and so on.

  • It does not matter whether these laws are realistic or not, as long as they are in sync with the player’s expectations of the game.

    • Depending on the genre and style of game, physics and natural laws can be realistic or more cartoonish.

    • Supporting player expectations is the key!


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Animation Requirements:Obey Appropriate Laws

Screen shot from Oni. Despite being unconscious, the guard has absolutelyno difficulty in keep his legs in the air. Such disrespect for the law ofgravity is quite noticeable to the player.


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Animation Requirements:Obey Appropriate Laws

Video from Unreal Tournament 2003. Note the realistic skeletal

mechanics when you fall and die. Bodies will shape themselves toterrain quite naturally.


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Animation Requirements:Obey Appropriate Laws

Videos produced using the Havok 2 game engine. These showsome really nice animation effects based on physics and accurate modelsof the game characters. This engine is used in Max Payne 2, Half Life 2,and Deus Ex, Invisible War.


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Animation Techniques

  • There are a variety of different techniques for providing animation in video games.

  • Among these are the following:

    • Simple animation effects.

    • Rigid body animation.

    • Articulated structure animation.

    • Dynamic simulation.

    • Particle animation.

    • Behavioural animation.


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Simple Animation Effects

  • There are several simple animation tricks that can be done in real-time.

    • These are some of the first techniques, and are therefore hardware based.

  • Palette or colour map animation:

    • Simple animation effects are achieved by manipulating the palette or colour map of a bitmap or texture (also known as look-up-table animation).

  • Hardware based sprite animation:

    • Some graphics hardware has support for sprites, and allows motion and other manipulations. (In some cases, this is how mouse cursors are implemented.)


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Simple Animation Effects

A simple example of palette animation. This is simple colour cycling,

where colours of the palette are merely shifted to produce an animation.

Similar techniques can be used to produce waterfalls, waves, and so on.


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Simple Animation Effects

A more impressive demonstration of palette animation. It can be usedto create a variety of effects with minimal difficulty.


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Rigid Body Animation

  • Rigid body animation is a relatively simple form of animation that is an extension of existing rendering techniques.

    • Animated scenes can be produced simply by rendering a scene with objects in different positions and orientations.

    • The problem is, however, how do we specify and control the movement of objects in a scene?

  • There are two main approaches to doing this:

    • Keyframing or interpolation.

    • Explicit scripting.


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Rigid Body Animation:Keyframing or Interpolation

  • Keyframing systems are based on a well-known production technique in traditional animation.

    • To cope with lengthy animations, companies adopted a hierarchical system in which lead animators specify a sequence by drawing keyframes at certain intervals.

    • Other animators would then draw the intermediate frames to complete the animation.

  • This same approach can be taken for animation in video games.

    • The participants, however, are different.


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Rigid Body Animation:Keyframing or Interpolation

  • In this case, animators specify the keyframes themselves, and a computer will generate the intermediate frames.

  • Usually, this generation uses some form of mathematical interpolation.

    • Linear interpolation is simple, but this approach on its own is often inadequate.

    • Non linear interpolation (for example, with splines) can sometimes provide better, or more realistic results.

  • Sometimes, however, interpolation still does not produce what the animator is looking for.


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Rigid Body Animation:Keyframing or Interpolation

Original keyframes fora bouncing ballanimation sequence.

Animation pathgenerated usinglinear interpolation(not very realistic).

Animation pathgenerated usingnon linear interpolation. The bounce is morerealistic this time.


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Rigid Body Animation:Explicit Scripting

  • Explicit scripting is a process that allows animators to specify the complete animation path of objects.

  • This includes:

    • Changes in object position, orientation, and other characteristics.

    • Changes in object velocity and acceleration.

  • Scripting can be done in a graphical or mathematical fashion.


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Rigid Body Animation:Explicit Scripting

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Animation path of an object (left) along with its velocity curve (right).

Combining the two together, the position of the object in its animationcan be determined quite easily using this simple scripting.


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Articulated Structure Animation

  • The premise behind articulated structure animation is that many objects have an underlying structure that dictates the kinds of motions the object is capable of.

  • This includes a variety of game elements:

    • Game characters.

    • Animal and plant life.

    • Non rigid composite objects.

  • Because of this underlying structure, special considerations are necessary.


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Articulated Structure Animation

  • To support this kind of animation, the underlying structure of an object must be defined in addition to any surface modeling.

    • This structure is a collection of rigid objects connected by joints which enable the parts of the structure to move with respect to one another.

    • For example, the skeleton of a game character must be provided in addition to a polygonal mesh for realistic animation.


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Articulated Structure Animation

Sample skeleton model for a game character. By defining a skeleton,and attaching surface polygons, we have a fully articulated modelsuitable for animation purposes.


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Articulated Structure Animation

  • Animation with these articulated structures is accomplished using similar approaches to rigid body systems:

    • Keyframing or interpolation.

    • Explicit scripting.

  • This time, animation is defined in terms of joint movement in the structures.

    • Corresponding polygons attached to the structure move accordingly.

    • When rendered in the game with textures, the animation is complete.


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Articulated Structure Animation

Sample animations of a game character running (left) and jumping (right).

By manipulating the underlying articulated structure, it is possibleto generate some reasonably realistic animation.


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Articulated Structure Animation

Sample completed animation with polygonal model, shading, and

texturing complete.


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Articulated Structure Animation

Another completed example, where you can view the skeleton, joints,

wireframe, and the final textured and shaded result.


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Dynamic Simulation

  • The previous animation techniques involve specifying the motion of game entities with little regard for the laws of the game world.

  • Dynamic simulation involves the rigorous application of physical and natural laws to simulate motion for animation.

    • The basic premise is that adherence to these laws should produce more realistic or natural animation than more traditional techniques.

    • The problem is, however, that doing this removes artistic control from the animator.


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Dynamic Simulation

  • The general approach to dynamic simulation animation is:

    • Determine which laws you wish to apply to the game world and all of its objects.

    • Define the game world and its objects, ensuring you have all of the required attributes and information.

    • Identify the motions you want the objects to exhibit.

    • Simulate the motions and save the results.

  • If this does not produce the desired animation, game world and object data may need tuning, or artistic intervention is necessary.


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Dynamic Simulation

Sample pictures and animations of aliens using dynamic simulation, as

well as more traditional techniques.


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Particle Animation

  • Particle animation refers to the animation of a large population of independent particles to simulate some phenomenon.

    • This phenomenon is viewed as the overall movement of the collection of particles.

  • This form of animation can be used to model several different kinds of effects:

    • Smoke, clouds, fire, explosions, sparks, debris, tornados, sand storms, and so on.


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Particle Animation

  • Each particle behaves relatively independently, according to some kind of scripted behaviour.

  • Each frame of a particle animation is generally constructed as follows:

    • New particles are generated and injected into the current system.

    • Each new particle is assigned its individual attributes.

    • Any particles that have exceeded their lifetime are extinguished.

    • The current particles are moved according to their scripted behaviour.

    • The current particles are then rendered.


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Particle Animation

Particle animation can add greatly to the special effects in a game, as shown in this image and demo.


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Behavioural Animation

  • Behavioural animation means modeling the behaviour of game world objects.

    • This is more complex than just basic movement.

    • This depends on certain behavioural rules and attributes defined for each object.

    • This may also depend upon the behaviour of nearby objects as well.

  • A collection of entities in behavioural animation evolve according to the behaviour of neighbours in the population.

    • The goal is to make the collection look realistic.


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Behavioural Animation

Screen shot and video from Dead or Alive 3. The animation of each character, including Brad Wong above, reflects their personality, behaviour,

and fighting style in the game.


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Behavioural Animation

Screen shots from several flocking

programs with different behaviours.

(Go back to our artificial life/flockingdiscussion for more information.)


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Motion Capture: Acquiring Data for Animation

  • Where does data come from to create realistic animations in games?

  • Typically, such data is the result of some kind of motion capture process.

    • This technique is growing in popularity, and is now in use in many video games.

    • It has been around since at least 1915, when rotoscoping was invented to assist in cartoon production.


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Motion Capture: Acquiring Data for Animation

Clip from the Simpsons. No one does motion capture better than Homer!


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Motion Capture Techniques

  • Motion capture data can be collected in a variety of different ways.

  • Rotoscoping:

    • Traditional video of motion is projected onto paper or a computer screen, one frame at a time, where it is traced for use in character animations.

  • Optical motion capture:

    • Reflective markers at key points on the subject are captured by several cameras; this data is fed into and analyzed by computers to produce the motion capture data.


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Motion CaptureTechniques

Screen shot of Karateka. Created in 1986, this is perhaps the first video game to use motion capture, with all character animationscreated with the help of rotoscoping.


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Motion Capture Techniques

Images from a motion capture session of Roger Clemens for 989 Sports’ MLB 2002. On the left is Clemens suited for optical motion capture; on the

right are the generated skeletal models and final textured representation.


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Motion Capture Techniques

  • Electromagnetic trackers:

    • The subject is fitted with several sensors that measure their spatial relationship to a nearby transmitter generating an electromagnetic field; their data is then fed into a computer.

  • Electromechanical suits:

    • The suit is composed of a group of structures linked by some form of angular measurement devices located at the major joints of the subject. The suit is driven by the subject’s actions, with all data from the measurement devices recorded by a computer.


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Motion Capture Techniques

Pictures of an electromagnetic tracking system (left) and anelectromechanical suit (right) for motion capture.


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Motion Capture Techniques

  • Digital armatures:

    • These are posable models constructed out of rigid modules connected by joints whose rotations are measured by angular sensors.

    • There are two kinds of armatures: stop-motion armatures (used in keyframing) and puppeteering armatures (used in real-time).

  • The motion capture techniques listed on these last few slides vary in expense, resolution and sampling capabilities, and general availability.

    • It is important to weigh the various factors in choosing which motion capture is right for you.


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Motion Capture Techniques

Picture of the Monkey 2 modular digital armature.


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Motion Capture Issues

  • The following are issues to consider when considering motion capture for a game:

    • Do you want realistic motion?

    • Can the desired data be successfully captured?

    • Do you have the budget and time to afford motion capture for the project?

    • Do you have the budget to hire the talent (actors, athletes, and so on) for the session?

    • How do you choose and locate the talent to use?

    • Which actions do you want captured and which will you use traditional techniques on?

    • Do you have the software tools and skills on your development team to effectively use the data once it has been captured?


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