Lighting in OpenGL

CS 481/681 2007 Lecture, Dr. Lawlor

Kinds of Light that Reflect off Surfaces

Diffuse: light that reflects off the surface equally in all directions. Also known as Lambertian.
Specular: light that glances off the surface mostly in the mirror-reflection direction. "Shininess"
Indirect: light arriving from other nearby surfaces. Not yet easy to compute in realtime!
Ambient: constant approximation of indirect light.

Examples of Lighting

To actually render lighting, you need a zillion unit-length direction vectors starting at the point on the surface you're shading:

	vec3 N = normalize(normal); // Points away from surface
	vec3 L1 = normalize(vec3(0,1,0)); // Points toward light 1
	vec3 C = normalize(vec3(cameraloc)-position); // Points toward camera
	vec3 H1 = normalize(C+L1); // Blinn's "halfway vector" for light 1

Then you need to compute (clamped) dot products between them:

	float A=0.2; // Ambient illumination
	float D=clamp(dot(N,L1),0.0,1.0); // Diffuse light fraction
	float S=pow(clamp(dot(N,H1),0.0,1.0),50.0); // Specular fraction.  Constant controls highlight size

And finally you just combine these together--you can get lots of different effects by combining them in different ways. Here I've added in "M" for the object ("Material") color, and "K" for a checkerboard pattern.