1. CS 431/636 Advanced Rendering Techniques
Dr. David Breen
Matheson 308
Thursday 6PM  8:50PM
Presentation 3
4/18/06

2. Logistics Read research paper and prepare written summary and question
L.M. Sobierajski and A.E. Kaufman, "Volumetric Ray Tracing," 1994 Symposium on Volume Visualization Proceedings, Oct. 1994, pp
Art Widmann presents next week
Assignment due dates
Making Effective Artistic Renderings - Doug DeCarlo; UCross 153; Friday 2PM

3. Slide Credits Jonathan Cohen - Johns Hopkins
Yizhou Yu - University of Illinois
Kevin Suffern -University of Technology, Sydney, Australia
G. Drew Kessler, Larry Hodges - Georgia Institute of Technology

4. Color Models

5. Light Models

6. Spot Light Specified by L = Pl - Ps if  >  else
Position, Direction
Cone angle, sharpness
L = Pl - Ps
if  > 
IL= 0
else
IL= cosn((/2)(/)) Dl Pl Ps  

7. Shading Models

14. Calculating the Reflected Ray
r = (2  (n · L)  n) - L
Derivation left for the students
Clamp all dot products to zero. They shouldn’t be negative, but they can be
MAX (0, n · L)

23. Including Surface Color
for all lights {
ILkd  C  cos() + ILks  C  cosn() }     + Iaka  C
C - RGB surface color
Could define Cd, Cs and Ca, but you don’t have to

24. Calculating Normals
Create vector structure (for normals) same size as vertex structure
For each face
Calculate unit normal
Add to normal structure using vertex index
Normalize all the normals
N(,,)= Na+ Nb+ Nc v v v v v v v v
f 1 3 4
f 1 4 2
f 5 6 8
f 5 8 7
f 1 2 6
f 1 6 5
f 3 7 8
f 3 8 4
f 1 5 7
f 1 7 3
f 2 4 8
f 2 8 6
vertices
triangles

25. Shading Pixels Overview
for (i=0; i++; i < hres)
for (j=0; j++; j < vres) {
Calculate Ray
for (k=0; k++; k < NumObject) {
Attempt to intersect Ray with Objectk
for all intersections
Save t, ObjectID & xsect pt/param }
Perform shading calculation on closest point
(intersection with the lowest non-negative t)
Set pixel value at Image[i,j]

26. Supersample & Average Image
hres and vres are even
for (i=0; i++; i < hres/2)
for (j=0; j++; j < vres/2) {
offset = 2  [i,j];
newImage[i,j] = (oldImage[offset] + oldImage[offset + [0,1]] +
oldImage[offset + [1,0]] +
oldImage[offset + [1,1]])/4; }

27. Wrap Up Discuss next week’s programming assignment
Add point lights with color
Add color, shading parameters and normals to models
Phong shading
Supersample image
Discuss status/problems/issues with this week’s programming assignment