Question

I am writing a GLSL program as part of a plugin running inside of Maya, a closed-source 3D application. Maya uses the fixed function pipeline to define it’s lights, so my program has to get it’s light information from the gl_LightSource array using the compatibility profile. My light evaluation is working fine (thanks Nicol Bolas) except for one thing, I cannot figure out how to determine if a particular light in the array is enabled or disabled. Here is what I have so far:

#version 410 compatibility

vec3 incidentLight (in gl_LightSourceParameters light, in vec3 position)
{
    if (light.position.w == 0) {
        return normalize (-light.position.xyz);
    } else {
        vec3 offset = position - light.position.xyz;
        float distance = length (offset);
        vec3 direction = normalize (offset);
        float intensity;
        if (light.spotCutoff <= 90.) {
            float spotCos = dot (direction, normalize (light.spotDirection));
            intensity = pow (spotCos, light.spotExponent) *
                    step (light.spotCosCutoff, spotCos);
        } else {
            intensity = 1.;
        }
        intensity /= light.constantAttenuation +
                light.linearAttenuation * distance +
                light.quadraticAttenuation * distance * distance;
        return intensity * direction;
    }
}

void main ()
{
    for (int i = 0; i < gl_MaxLights; ++i) {
        if (/* ??? gl_LightSource[i] is enabled ??? */ 1) {
            vec3 incident = incidentLight (gl_LightSource[i], position);
            <snip>
        }
    }
    <snip>
}

When Maya enables new lights my program works as expected but when Maya disables a previously enabled light, presumably using glDisable (GL_LIGHTi), it’s parameters are not reset in the gl_LightSource array and gl_MaxLights obviously does not change, so my program continues to use that stale light information in it’s shading computation. Although I am not showing it above, the light colors, for example gl_LightSource[i].diffuse, also continue to have stale non-zero values after they are disabled.

Maya draws all other geometry using the fixed-function pipline (no GLSL) and those objects correctly ignore disabled lights, how can I mimic this behavior in GLSL?

Answer 1

Unfortunately I looked at the GLSL spec and I don’t see anything that provides this information. I also saw another thread which seemed to come to the same conclusion.

Is there any way you can modify the light values in your plugin, or add an extra uniform that can be used as an enable/disable flag?