Shader Coding - Best Practices

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Supported GLSL Versions

Note  Be aware that we currently _DO_NOT_ support glsl > 1.2x. Please don't mix '''glsl''' flavours: please stick to glsl 1.2x.(even though support for it is largely deprecated). The transition to OpenGL 3.0 / glsl >=1.3x is a very big undertaking, and not backward compatible. It is always a good idea to declare the expected GLSL version at the top of each file:
#version 120

Vertex Shaders

Note  For testing purposes, you can use a simple pass-through vertex shader:
#version 120
void main(void) {
        gl_Position = ftransform();

Fragment Shaders

Note  To check if your shader is working, use a trivial shader like this one or just add the last line to the end of the shader, it should turn all pixels black:
#version 120
void main() {
// turn all pixels into  black
gl_FragColor = vec4 (0.0,0.0,0.0,1.0);
Note  if4dnf: it's usually bad practice to do any kind of operations on gl_FragColor assignment. At most a vec4() swizzle is accepted, although even that one is treated differently based on the platform (some assign a temporary variable, some don't). Do wahtever you need in a separate vec4 variable and just assign it's value to gl_FragColor at the end.
Note  If the fragment isn't running, there should be an error message in the log file (I wish they'd still be written to the console). Might be that the texture isn't defined in the supporting framework for instance - the shader assumed that it is available, but you need to declare it in the matching C++ code/effect file first.
Note  This is how you can make a pixel darker:
gl_FragColor = color * 0.5;