Computer Graphics: Programming, Problem Solving, and Visual Communication Steve Cunningham California State University Stanislaus and Grinnell College PowerPoint Instructor’s Resource

Dynamics and Animation Using motion effectively in your work

An Animation Is… A sequence of individual images that are presented over time The images can either be –computed separately and assembled into the sequence later, or –computed in sequence and displayed as they are computed (real-time animation) The choice depends mostly on how complex the images are and whether you want to save the sequence for re-display

An Example Particle systems example: four frames showing progress This sequence shows how particles move

Procedural Animation Motion is built into the model so that objects are in different places with each display –Can be based on a meaningful parameter (such as time) or –Can just use frame-to-frame increments

Procedural Animation (2) Changes can be built into the model through the scene graph –Any component of the scene graph can use a parameter or can be changed with each display –Transformations (e.g. rotation or translation) –Geometry (e.g. number of objects or the particular shapes used) –Appearance (e.g. color, texture, alpha) –View (e.g. eyepoint, view direction)

Procedural Animation (3) Interpolations give us an important kind of procedural animation Points can be moved along spline curves using a parameter t that is the spline curve parameter These points can be eyepoints, geometry points, or can even be interpreted as directions or any other 3D value

Interpolation Examples Texture interpolation –From the left-hand texture to the right- hand one Geometry interpolation –From the left-hand geometry to the right- hand one

Interpolation Examples (2) Eyepoint animation: along a spline curve with control points shown in red

Problems with Animation Frame rates -- making the animation look smooth –Real-time animation speed can depend on the speed of the computer If your user has a newer computer, the animation may seem too fast –Some images are so complex that real-time animation cannot be done in acceptable time

Problems with Animation (2) Temporal aliasing -- sampling at discrete points in time –Common example is the moving spokes problem; a single frame is shown

Showing Motion in Static Frame Showing tracesAccumulation buffer

Non-Real Time Animation Computing frames individually and showing only finished frames avoids some of the problems with real-time animation Frames can be assembled with many kinds of movie-making tools Movie-showing software takes care of frame rates for you Extra work is involved in assembling the movie, however, and you cannot experiment with the animation

Non-Real Time Animation (2) There are other considerations if you want your animation to play on TV –For “normal” [non-HD] TV there are real issues with image size and the YIQ color system that will be used to transmit the picture –Look carefully at color choices and color bleeding problems