Notes for February 19 -- Phong shading

Note: I am not going to assign any homework on Tuesday Feb 19, because I think we need one more lecture before you are prepared to implement ray tracing to a sphere.

The next homework assignment will be given this Thursday, Feb 21.

Meanwhile, make sure you read through the notes for both ray tracing to a sphere and Phong shading very carefully, and that you understand everything.

We will be building on these notes in what follows next.

The first really interesting model for surface reflection was developed by Bui-Tong Phong in 1973. Before that, computer graphics surfaces were rendered using the simpler model of Gouraud shading, which used only diffuse lambert reflection, so it could not properly render shiny surfaces.
Phong's was the first model that accounted for specular highlights.
The Phong model begins by defining a reflection vector R, which is a reflection of the direction to the light source L about the surface normal N.
As we showed in class, and as you can see from the diagram on the right, it is given by:
R = 2 (N • L) N - L

Once R has been defined, then the Phong model approximates the specular component of surface reflectance as:
S_rgb max(0, E • R)^p )
where S_rgb is the color of specular reflection, p is a specular power, and E is the direction to the eye (in our case, E = -W, the reverse of the ray direction). The larger the specular power p, the "shinier" the surface will appear.
We can have more than one light. To get the complete Phong reflectance, we sum over the lights in the scene:
A_rgb + ∑_i lightColor_i ( D_rgb max(0, N • L_i) + S_rgb max(0, E • R) ^p )
where A_rgb, D_rgb and S_rgb are the ambient, diffuse and specular color, respectively, and p is the specular power.

At the end of the lecture we watched WORLD BUILDER by Bruce Branit