opengl - GLSL fixed function fragment program replacement

Question

When using the OpenGL fixed function pipeline for vertex setup, how a fragment program looks like that is compatible to the fixed function vertex setup? I guess that usually depends on the number of light sources and texture layers etc.. So for example how does a simple non-texture one-lightsource goraud shading fragment program look like that replaces GL's fixed function shader?

Answer 1

You might be interested in having a look at ShaderGen. From the description:

ShaderGen is a program that can automatically produce shaders that mimic the results of a set of fixed function state. This tool was used to verify the fixed function shader code that is described in Chapter 9.

By the way, you will most likely encounter subtle driver problems if you mix fixed function and GLSL. This is not the "most used way" to do shading so it has a good change of having bugs (at least it did when I tried it). If what you need works, great! Otherwise, you're likely much better off writing the vertex and fragment shaders in GLSL. From what I heard, the driver of modern GPUs uses shaders under the hood anyway to do fixed function.