SE 134

1. SE 134 Video Game Animation Ali Parandian Chad Quan George Chan

2. Topics • Goal of computer game animation • Animation techniques • Past (2D Animation) • Sprites • Morphing • Embedding • Present (3D Animation) • Modeling • Articulated Model and Skinning • Particle System • Deformed Objects • Rendering • Animation • Keyframing • Inverse Kinematics • Motion Capture • Procedural Algorithms

3. Goal • To create a realistic animated game character.

4. Animation Techniques- PastSprites • A sprite is a bitmap image or a series of images. • Rapid replacement of sprites with successive images. • Sequence of images composite one image per frame. • Disadvantage: sprites comes from a fixed library. • Changes to the depth and lighting impossible.

5. Animation Techniques- PastMorphing • An image is metamorphosed to another image. • Provides a clean transition from one picture to another. • Expensive and hard to implement.

6. Animation Techniques- PastEmbedding • Objects can be added or removed from a scene. • Popular technique for many digital cinema. • Difficult to implement for moving scenes.

7. Animation Techniques- Present • Movement towards 3D animation • Problem? • “Jointed” animated characters • Each limb was a rigid object • Interpenetration at joints!

8. Animation Techniques- Present3D Animation • Virtual world where objects and characters can interact with one another. • 3 Main components of 3D Animation. • Model, describing the elements of a scene. • Animate, specifies how the objects move in the environment. • Render, coverts the information (object and their motion) into images.

9. Animation TechniquesModeling – Articulated Model • Collection of objects connected together by joints. • The collection of joints resembles a Hierarchy tree-like structure. • Moving the elbow would affect the location of the wrist’s position.

10. Animation TechniquesModeling – Particle System • Collection of points in space. • Particles move or collide with each other is decided by a set motion. • A set motion is determined by a set of rules, i.e.: The laws of physics. • Examples are watersplash, smoke, a flock of birds flying.

11. Animation TechniquesModeling – Deformable Objects • Models similar to articulated but without the defined joints. • The structure of the object is too great to implement joints. • Examples: water, hair, rocks, ground.

12. Animation TechniquesModeling The diver represents an articulated object The body of water is a deformed object. The splash of course would be a particle system

13. Animation TechniquesRendering • The process of generating a visual representation of the objects in 3D animation. • Adds the collection of bitmap textures its light attributes to create a complete image. • Some popular rendering algorithms are: rasterisation, ray casting, radiosity, and ray tracing.

14. Animation TechniquesAnimation • Challenge of creating realistic motion. • Need a balance between automation and control.

15. Keyframe Animation • A simple yet effective way to animate 3D objects • Each frame represents a position for the object • Number of frames are limited, so object may appear to “jump” when going from one frame to another

16. Keyframe Animation • One solution is to just manually make more keyframes • This takes time, and the programmer may not want to do it

17. Keyframe Animation • Instead of making them manually, use interpolation to create new frames • Interpolation is creating a new position between existing positions

18. Linear Interpolation • The easiest form of interpolation • Given the same point in two different keyframes, a line is drawn between them • The new point exists somewhere on this line

19. Linear Interpolation • Where the point exists depends on three things: • Total number of keyframes in animation • Total time of animation • Desired time of the new Position

20. Linear Interpolation • see page 466-467 for formulas • Done for every point and combined to make a new keyframe • Disadvantage: the formula doesn’t always give a good approximation of the points

21. Hermite Spline Interpolation • This method shares the same idea as linear interpolation • Considers two frames before and after the desired new frame, instead of one before and after • Point approximation is more accurate than linear interpolation • see page 468-469 for calculations

22. Kinematics • Determines parameters needed for a jointed, flexible object to achieve a pose • Factors in maintaining balance, joint angle limitations, and collisions between the body and limbs. • Two ways of doing this

23. Inverse Kinematics • Inverse Kinematics: figure out what angles joints will need in order to achieve a pose, given the desired configuration based on a hierarchy. • Specify the position of one object and every object above it in the hierarchy. Motion is inherited up. • To perform one action must be able to move multiple joints. • Example: to move the arm and torso to one position, the algorithm can figure the position of where the shoulder and elbow should be. • Factors in maintaining balance, joint angle limitations, and collisions between the body and limbs. • Disadvantage: There is no general analytical solution • Must be solved through non-linear programming techniques

24. Forward Kinematics • Forward Kinematic Animation: given desired angle changes for the figure’s joints will result in a pose. • Motion is inherited down the hierarchy. • Easier than inverse kinematics

25. Motion Capture • A person wears sensors near each joint • Computer software records positions, angles, velocities, accelerations, and impulses for all sensors • Typically captures sub-millimeter positions

26. Motion Capture • Advantages: • Faster than manually creating animations • Can have much more natural looking motions and catch subtleties of the object. • Disadvantages: • Can’t do anatomically impossible motions • Motion is restricted to the laws of physics. • Sensors attached to the skin can shift out of position during human movement causing real performance to differ from data recorded.

27. Procedural Animations • Algorithm used to generate animation in real-time • Can be used for both simple and complex motions • Most popular method is the Physically Based Simulation. • Flocking is another example of procedural methods. • Advantages: • Easy to generate similar motions. • Generate interactive behavior that responds to the user by computing a response in real time. • Ideal for models like the particle system. • Disadvantages: • Can be very expensive to compute during real time scenes • Cannot control fine detail in animation.

28. Procedural Animation • One example of an application is creating death animations for characters • The body can react to the environment while falling/fallen more realistically than other animation techniques • Other examples: smoke, fire, water, clothing, hair.

29. References • Cybulski, Krys. Computer Graphics & Animation. http://www.bergen.org/AAST/ComputerAnimation/CompAn_Graphix.html • DeLoura, Mark. Game Programming Gems. Charles River Media. 2001. • Hodgins, Jessica. Computer Animation. College of Computing and Graphics, Visualization, and Usability Center. • Wikipedia. Computer Animation. http://en.wikipedia.org/wiki/Computer_animation • Animation in video games by Jason Gregory