In TapirEngine, the following lighting features are not used:
- global ambient
- directional lights
- specular lights
- rim lights
- fog
(The setters / getters for these parameters are still there, but they
don't affect rendering.)
This implementation disables those features in GLSL using #ifdefs. The C
code that sets up the lighting remains almost unchanged --
glGetUniformLocation() will return -1 if the specified uniform variable
name is not found, and glUniform*(-1, ...) will be no-op.