Lighting with Shaders

• I am continuing with the red book.
• A note on normals
  • Normals are not usually stored in homogenious coordinates
    • Normals are not translated
    • Normals are not projected
  • If a surface gets stretched in a non uniform way, the normal moves in the opposite direction.
    • Let M be the transformation matrix from model coordinates to eye coordinates.
    • let n be the normal at a point
    • n' = M^-1T n
    • But this is only necessary if you do shape changing transformations (like non-uniform scale)
• My last program to lights
  • Added the depth buffer and double buffer stuff.
  • And turned on filled polygons
  • 
• A little ambient lighting.
  • I did something flakey to select different shaders at the command line.

  • // in the global space
    ShaderInfo noLight[] = {
        { GL_VERTEX_SHADER, "move.vert" },
        { GL_FRAGMENT_SHADER, "move.frag"},
        { GL_NONE, NULL}
    };
    
    ShaderInfo ambient[] = {
        { GL_VERTEX_SHADER, "move.vert" },
        { GL_FRAGMENT_SHADER, "ambient.glsl"},
        { GL_NONE, NULL}
    };
    
    
    // in setup
       switch (ShaderNumber) {
          case 1:
             Program = LoadShaders(ambient);
             break;
          case 0:
          default:
             Program = LoadShaders(noLight);
             break;
       }
    ...
    if (ShaderNumber > 0) {
        AmbientLoc = glGetUniformLocation(Program, "Ambient");
    }
    
    // in main
       if (argc > 1) {
           ShaderNumber = atoi(argv[1]);
        } else {
           ShaderNumber = 0;
        }
    
    
            

  • A new uniform vector in the shader, Ambient.
  • Look at the new shader (ambient.glsl)
  • 
  • Additional code

    // in display
    vec4 ambient = vec4(0.3, 0.3, 0.3, 1.0);
    
    if (ShaderNumber > 0) {
        glUniform4fv(AmbientLoc, 1, ambient);
    }