Detecting enabled state within shader

[kitfox]

Is there a way for a shader to determine if a particular light is enabled, or is fog is enabled, or similar?

[Kramer]

Pass it through as a boolean uniform parameter to your shaders from your main code.

[eteq]

Is that the only way? I find that GLSL is trouble in general for trying to find the state of the fixed functionality, in general - is there no way to access this kind of information without explicitly sending it to the shader?

[Kramer]

Actually, just checked the book and there is a built-in uniform variable that you can access from both types of shaders: gl_FogParameters

Found this reference: http://www.ce.chalmers.se/edu/course/EDA425/glsl_quickref.pdf

[darkprophet]

I had this discussion over at www.opengl.org about why the selection stack wasn’t available in GLSL, there were a few guesses until an ATI developer answered me, heres what he said:

The fixed-function state available to the GLSL is the state that GLSL subsumes. See section 7.5 of the language spec.

The GLSL vertex shader and fragment shader do not subsume selection. So you don’t get access to the bottom of the selection name stack. Just like you don’t get access to the display LIST_BASE. (Just an example of fixed-function state pulled out of a hat at random.)

Note - OpenGL ES 2.0 has a very elegant solution to what fixed-function state to provide to GLSL. It doesn’t provide any fixed-function state.

If you want a “selection name” accessable to your shader, you should send it as an attribute or uniform yourself.

GLSL subsumes (or takes over) a particular part of the pipeline, what states are enabled is actually none of its business…And with OpenGL ES 2.0, even gl_Light wont be available, its all going through uniforms and such…

Hope this helps,
DP

[eteq]

I was looking in a textbook I had, and I found there are ways to access the state of the fixed-functionality lights - gl_LightSource[i] accesses the ith light. The example shows use of gl_LightSource[i].position, gl_LightSource[i].diffuse, gl_LightSource[i].ambient, and gl_LightSource[i].specular, and I presume there’s more; I admit, this isn’t quite the same as checking the enabled state, but its part of the state, at least.