1. SWE 423: Multimedia Systems
Chapter 6: Computer-Based Animation

2. Outline Introduction Producing an Animation
Specifications of Animations
Methods of Controlling Animations
Display of Animations
Transmission of Animations
VRML

3. Introduction
An animation covers all changes that have a visual effect

4. Introduction
Computer-based animations are produced, edited and generated with the help of graphical tools to create visual effects
Multimedia API’s
Java3D
Constructs and renders 3D graphics
Provides a basic set of object primitives (cube, splines,...etc.)
An abstraction layer built on top of DirectX or OpenGL
DirectX
Windows API that supports video, images, audio, and 3D animation
Most widely used for Windows-based animations (video games)
OpenGL
Most popular 3D API in use today
Highly portable

5. Introduction
Computer-based animations are produced, edited and generated with the help of graphical tools to create visual effects
Rendering Tools
3D Studio Max
Character animation, game development and visual effects production (Sony Playstation)
Softimage XSI
For animation and special effects in movies
Maya
Softimage competitor
RenderMan
Excels in creating complex surface appearances and images
Has been used in many movies.
Simple/Quick Animation Generators
GIF Animation Packages
Looping through several GIF images creates an animation
Gifcon and GifBuilder (Windows) and animate (Linux)

6. Producing An Animation
Input Process
Drawings must be digitized or generated
Digitizing photos or drawings may require post-processing in order to remove any glitches
Composition Stage
Individual frames in a completed animation are generated by using image composition techniques to combine foreground and background elements
Trailer film is generated from placing low-resolution digitized frames in a grid.

7. Producing An Animation
InBetween Process
Interpolation methods are used to animate the movement from one position to another.
Linear interpolation (lerping) is the simplest but the most limited
E.g. the interpolation of animating throwing a ball using three points
Splines can be used to smoothly vary different parameters as a function of time, yet the problem is not completely solved (very complex)

8. Producing An Animation
Changing Colors
Uses the Color LookUp Table (CLUT) or (LUT) of the graphics memory and the double buffering method
Two parts of a frame are stored in different areas of graphic memory.
The graphic memory is divided into two fields, each having half as many bits per pixel.
The animation is generated by manipulating the CLUT.

9. Specification of Animations
Formal specifications that describe animations can be divided into three categories:
Linear-List Notations
High-Level Programming Language Notations
Graphical Languages

10. Linear List Notations
Each event is described by a beginning frame number, an end frame number and an action event that is to be performed.
Action events may accept input parameters
For example
42, 53, B, ROTATE “PALM”, 1, 30
This instruction means......
SCEne Format (Scefo) specification can be considered a superset of linear sets including groups and object hierarchies as well as transformation abstractions using high-level languages constructs. \

11. High-Level Programming Languages Notations
Values of variables can be used as parameters for animation routines.
For example, ASAS is a LISP extension that includes primitives such as vectors, colors, polygons, surfaces, groups, points of view, subworlds, and lighting aspects in addition to geometrical transformations operating on objects
For example
(grasp my-cube); cube is current object
(cw 0.05); small clock-wise rotation
(grasp camera); camera is current object
(right panning-speed); Move it to the right

12. Graphical Languages
Graphical actions cannot be easily described by and/or understood from textual scripts.
Hence, graphical animation languages describe animations in a visual manner.
GENESYS, DIAL and S-Dynamics System are examples of such systems.

13. Methods of Controlling Animations
Explicitly Declared
Procedural
Constraint-Based
Analyzing Live Action-Based
Kinematic and Dynamic

14. Explicitly Declared Control
All events that could occur in an animation are declared. This can be done at the
object level by specifying simple transformations (translations, rotations, scaling) to objects
frame level by specifying key frames and methods for interpolating between them.

15. Procedural Control
Based on communication among different objects whereby each object obtains knowledge about the static/dynamic properties of other objects.
Can be used to ensure consistency
For example ....

16. Constraint-Based Control
Many objects movements in the real world are determined by other objects which they come in contact with
E.g. presence of strong wind or fast moving large objects
Instead of explicit declaration, constraints based on the environment can be used to control objects’ motion.
Example Systems: Sketchpad and ThingLab.

17. Analyzing Live Action-Based Control
Control is achieved by examining the motions of objects in the real world.
Rotoscoping: is a technique where animators trace live action movement, frame by frame, for use in animated films.
Originally, pre-recorded live-film images were projected onto a frosted glass panel and redrawn by an animator.
This projection equipment is called a Rotoscope.
Another way is to attach indicators to key points on the body of a human actor.
For example the data glove [gesture language for hearing-impaired people]

18. Kinematic and Dynamic Control
Kinematics refer to the position and velocity of points
“The cube is at the origin at time t = 0. Thereafter, it moves with constant acceleration in the direction (1 meter, 1 meter, 5 meters)”
Dynamics takes into account the physical laws that govern kinematics
Newton laws for the movement of large objects
Euler-Lagrange equations for fluids
A particle moves with an acceleration proportional to the forces acting on it.
For example: “At time t = 0, the cube is at position (0 meter, 100 meter, 0 meter). The cube has a mass of 100 grams. The force of gravity acts on the cube.”

19. Display of Animation
To display animations with raster systems, the animated objects must be scan-converted and stored as pixmap in the frame buffer.
Scan conversion must be done at least 10 times per second to ensure smooth visual effects.
The actual scan-conversion must take a small portion of 10 times/second in order to avoid distracting ghost effect
Double buffering is used to avoid the ghost effect

20. Display of Animation Example
Load CLUT to display values as background color;
Scan-convert object into image0
Load CLUT to display only image0
Repeat
Scan-convert object into image1
Load CLUT to display only image1
Rotate object data structure description
Until (termination condition)

21. Transmission of Animation
Two forms of transmission
Symbolic representation of an animation is transmitted together with the operations performed on the object.
The receiver displays the animation.
Transmission is fast since text is much smaller than pixmaps
Display is slow since the pixmap has to be generated from their descriptions.
The pixmap representations are transmitted and displayed
Transmission time is longer.
Display is faster.

22. VRML Virtual Reality Modeling Language
Describes 3D interactive worlds and objects that can be used together with the World Wide Web.
Illustrations, product definitions or virtual reality presentations can be generated on the Web.
History of VRML
May 1994: At the first Int. Conf. on the WWW, the idea of a platform-independent standard for 3-D WWW applications originated
October 1994: VRML 1.0 was presented at the second Int. Conf. on the WWW.
VRML 1.0 defined the parameters for creating 3D objects that can travel across the Internet.
August 1995: VAG (Vrml Architecture Group) was established

23. VRML
History of VRML
January 1996: VAG called for proposals for VRML 2.0. Each of the following submitted their own
Apple: “Out of this World”
Sun: “Holoweb”
German National Research Center for Information Technology (GMD) and others: “Dynamic Worlds”
IBM Japan: “Reactive Virtual Environment”
Microsoft: “Active VRML”
Silicon Graphics Inc. (SGI), Sony, and others “Moving Worlds”
August 1996: VRML 2.0 in its final form was presented in SIGGRAPH 96.

24. VRML Capabilities
VRML is capable of representing static and animated objects as well as hyperlinks to other media such as sound, motion pictures and still pictures
There are three ways of navigating though a virtual world:
Walk: Movement over the ground at eye-level
Fly: Movement at any height
Examine: Rotating an object in order to closely examine it.

25. VRML Example Color interpolator
This example interpolates in a 10-second long cycle from red to green to blue
DEF myColor ColorInterpolator{
key [0.0, 0.5, 1.0]
keyValue [1 0 0, 0 1 0, 0 0 1] # red, green, blue }
DEF myClock TimeSensor {
cycleInterval 10.0 # 10 second animation
loop TRUE # animation in endless loop