1. Week 7: Basic Ideas for Physical Simulations in Computer Graphics
Jack Tumblin
CS 395 Advanced Computer Graphics
Winter 2003

2. Recall Newton; New Notation
Newtonian Physics:
F = M a
Notation: time derivative as a dot
y ==
How does a spring work?
F = -K(x-x0) .
yt
OpenGL, local shading, MOST ray tracing
Make pictures ONLY from ‘single-bounce’ light: L->surf->eye + ‘ambient term’ for everything else.
Uses separate approximations for ‘shadows’—which are still just 1st-bounce paths from light to eye
Global Illum;
Make pictures for ALL paths through the scene between light sources and eye,

3. 1-D Spring-Mass Example
Given initial position y0 at time t=0, What is y for time t>0?
Position: y
Velocity: y = v
Accel: v = a
Newton says: F = Ma
Spring Force: F = GM -K(y - y0) solve.... y y0 . . K M G

4. 'State Variable' Form
'State' == A vector that holds everything you know about a particle
[or spring, or rigid object, or car, or body segment, or missile, or basketball or...]

5. How Do We Solve it?
Explicit Integration
Implicit Integration

6. Conclusion
Physically accurate (geometric optics only) simulation of light transport.
‘Ultimate Realism’? perceptual, not physical
Languished as tweak-hungry lab curiosity
Gradual adoption for multitexturing source, for mixing real/synthetic images, Ph.Ds, theatre/architectural lighting, archaeology,…
Growing interest for use in inverse rendering tasks: image-based rendering & modeling