GL shaders have to be tweaked on every platform, and every device. The only thing that's consistent about them is that they're inconsistent everywhere. For ex

GL shaders have to be tweaked on every platform, and every device. The only thing that's consistent about them is that they're inconsistent everywhere. For example, certain drivers will reject shaders using integer literals where floats are expected, others won't; different GPUs will also behave different with respect to precision, or with how they handle a NaN in math.