Announcements

Plan

Lighting and Material intro
- Demo of TeddyBearLit
- The Phong Model
- 33 parameters: tutors/lightmaterial
- 22 parameters: the tw/demos/materialTutor2 (if possible)
lab exercise on material and lighting: the orange ring

Let's put up the equation and the parameters and see what everything means.

The pytw/demos/material-and-lighting/TeddyBearLit.py is simple way to see lighting for an object that uses material. We'll have to look at pytw/TW.py to see how the material for the twTeddyBear is done. We can even how twColor is implemented, as well.
The tw/tutors/lightmaterial.cc is an interactive way to try the OpenGL API for material and lighting.
The pytw/demos/material-and-lighting/materialTutor2.py is an interactive way to try the restricted TW API for material and lighting.

TW has several simplifications that help in certain simple situations:

void twGrayLight(GLint lightId, GLfloat* pos, GLfloat a, GLfloat d, GLfloat s) assumes you don't want colored lights, so the RGB values for each kind of light are equal. For example, 50% gray light for the ambient would be
```
GLfloat gray50 = (0.5, 0.5, 0.5)
glLightfv(GL_LIGHT0,GL_LIGHT_AMBIENT,gray50)
```
This means that for each kind of light, you only have to supply 1 number instead of 3. That reduces the 9 parameters to 3, and those parameters can be supplied just to twGrayLight. The following specifies a light at (1,2,3) with 0.3 for ambient, 0.4 diffuse and 0.5 specular:
```
GLfloat lightPos = ( 1, 2, 3, 1 )
twGrayLight(GL_LIGHT0, lightPos, 0.3, 0.4, 0.5)
```
void twColor(twTriple color, GLfloat spec, GLfloat shininess) assumes that you want the same RGB values for ambient as for diffuse, and that you want a gray color for the specular reflection. Thus, you can give a matrix of 3 values for the ambient and diffuse material, one value for the specular, and one value for the shininess (on the 0-128 scale):
```
    twTriple objColor = (0.2, 0.3, 0.4)
    twColor(objColor,0.9,20)
```

Today, let's try to replicate the orange ring, using the tutors, and then, if possible, an OpenGL program.

Next time, we'll look at the following issues and demos:

demos/material-and-lighting/DiffuseVsSpecular.cc A demo of the difference between diffuse and specular light, falling on the same material. The left ball only gets specular light, the right ball only gets diffuse light. Both light sources have full ambient light. I suggest looking at the balls from above ('Y' keyboard callback) and using the menu to "show lights."
demos/material-and-lighting/JewelAndBall.cc A demo of the difference between flat and smooth shading, using the same material. The left ball uses flat shading, looking like a jewel, and the right one uses smooth shading, looking like a ball. Slices and stacks are the same!
demos/material-and-lighting/PointVsDirLights.cc A demo of the difference between directional light (on the left) and point sources (on the right)

Front View

Top View
demos/material-and-lighting/Moon.cc A demo of the moon, showing zero ambient light. It's cool to rotate this.
demos/material-and-lighting/SpotlightDemo.cc An interactive demo of lighting a large quad using a spotlight.

It's important to interact with this:
- + increases the number of squares
- - decreases the number of squares
- h hides the lines
- d draws the lines
- f flat shading
- s smooth shading
- w widens the cutoff angle
- n narrows the cutoff angle

Written by Scott D. Anderson
scott.anderson@acm.org

This work is licensed under a Creative Commons License.