Very strange behaviour with sampler handling using OpenGL and GLSL

Question

I have implemented cubemap shadow mapping successfully with just one point light.

To render this scene I use in the first render pass geometry shaders to dispatch the 6 frustrums. In the second render pass I use samplerCubeShadow in the fragment shader to computer the shadow factor.

I have OpenGL/GLSL version 4.40 with NVIDIA GeForce GTX 780M.

Here's a screenshot:

But now I want to implement multiple cubemap shadow mapping to render shadows using several point lights.

Here's some peace of code from my fragment shader:

[...]

/*
** Shadow Cube sampler array.
*/
uniform samplerCubeShadow ShadowCubeSampler[5]; //Max point light by scene = 5

[...]

float ConvertDistToClipSpace(vec3 lightDir_ws)
{
    vec3 AbsVec = abs(lightDir_ws);
    float LocalZcomp = max(AbsVec.x, max(AbsVec.y, AbsVec.z));

    float NormZComp = (NearFar.y + NearFar.x)/(NearFar.y - NearFar.x)
        - (2.0f * NearFar.y * NearFar.x)/(LocalZcomp * NearFar.y - NearFar.x);

    return ((NormZComp + 1) * 0.5f);
}

float GetCubeShadowFactor(vec3 vertexPosition_ws, float shadowFactor, int idx)
{
    vec3 lightToVertexDir_ws = vertexPosition_ws - LightPos_ws.xyz;
    float LightToVertexClipDist = ConvertDistToClipSpace(lightToVertexDir_ws);

    float LightToOccluderClipDist = texture(
        ShadowCubeSampler[idx], vec4(lightToVertexDir_ws, LightToVertexClipDist));

    if (LightToOccluderClipDist < LightToVertexClipDist)
    {
        shadowFactor = 0.0f;
    }
    return (shadowFactor);
}

void main(void)
{
    [...]

    for (int idx = 0; idx < 1; idx++) //Test first with 1 point light
    {
        float ShadowFactor = GetCubeShadowFactor(Position_ws.xyz, ShadowFactor, idx);
    }
    [...]
}

The problem is I have the error 1282 (INVALID_OPERATION). To resume the situation here, I want to display exactly the same scene like in the picture above with a SINGLE point light but this time using an array of samplerCubeShadow. What is amazing is if I replace the first parameter of the function 'texture' 'ShadowCubeSampler[idx]' by 'ShadowCubeSampler[0]' is works! However the value of 'idx' is always '0'. I tried the following code without success:

int toto = 0;

float LightToOccluderClipDist = texture(ShadowCubeSampler[toto], vec4(lightToVertexDir_ws, LightToVertexClipDist));

I already have the error 1282! The type of the index is the same (int)!

I have already use arrays of 'sampler2DShadow' or 'sampler2D' without problem.

So, Why it does not work correctly using 'samplerCubeShadow' and the solution 'ShadowCubeSampler[0]' works and not the others ?

PS: If I define an array of 2 and if I use 2 cubemaps so 2 point lights, it works. So, if I load a number of cubemaps inferior to the number specified in the fragment shader it fails!

I have no compilation error and no linkage error. Here's the code I use to check shader programs state:

void video::IEffectBase::Log(void) const
{
    GLint errorLink = 0;

    glGetProgramiv(this->m_Handle, GL_LINK_STATUS, &errorLink);

    if (errorLink != GL_TRUE)
    {
        GLint sizeError = 0;

        glGetProgramiv(this->m_Handle, GL_INFO_LOG_LENGTH, &sizeError);

        char *erreur = new char[sizeError + 1];

        glGetShaderInfoLog(this->m_Handle, sizeError, &sizeError, erreur);

        erreur[sizeError] = '\0';

        std::cerr << erreur << std::endl;

        glDeleteProgram(this->m_Handle);

        delete[] erreur;
    }
}

And about the texture unit limits:

std::cout << GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS << std::endl;
std::cout << GL_MAX_TEXTURE_IMAGE_UNITS << std::endl;

$> 35660
$> 34930

If I use 'ShadowCubeSampler[0]', '0' written directly in the code I have the same display like the picture a the beginning of the my post without error. If I use 'ShadowCubeSampler[idx]' with idx = 0 I have the following display:

As you can see, all the geometry sharing this shader has not been rendered. However I don't have any linkage error. How can you explain that ? Is it possible the system unlink the shader program?

UPDATE

Let's suppose my array of samplerCubeShadow can contain 2 maximum samplers (uniform samplerCubeShadow tex_shadow2).

I noticed if I load just one point light, so one cubemap:

CASE 1

uniform samplerCubeShadow tex_shadow[1]; //MAX POINT LIGHT = 1
for (int i=0; i < 1; i++) {tex_shadow[i];} //OK
for (int i=0; i < 1; i++) {texture(tex_shadow[i], ...);} //OK
for (int i=0; i < 1; i++) {texture(tex_shadow[0], ...);} //OK

CASE 2

uniform samplerCubeShadow tex_shadow[2]; //MAX POINT LIGHT = 2
for (int i=0; i < 1; i++) {tex_shadow[i];} //NOT OK - 1282
for (int i=0; i < 1; i++) {texture(tex_shadow[i], ...);} //NOT OK - 1282
for (int i=0; i < 1; i++) {texture(tex_shadow[0], ...);} //OK

CASE 3

uniform samplerCubeShadow tex_shadow[2]; //MAX POINT LIGHT = 2
for (int i=0; i < 2; i++) {tex_shadow[i];} //OK
for (int i=0; i < 2; i++) {texture(tex_shadow[i], ...);} //OK
for (int i=0; i < 2; i++) {texture(tex_shadow[0], ...);} //OK

Conclusion: if the max number of sampler is equal to the number of sampler loaded, I can loop over the samplers contained in my array. If the number is inferior, it does not work! I can use a maximum of 32 texture units for each use of shader program. I have the same problem using the samplerCube keyword.

It's very strange because I don't have any problem using sampler2D or sampler2DShadow for spot light shadow computation.

I check with NSight where I put a break point in the fragment shader file and of course the break point is neaver reached. It's like the shader program is not linked but it's not the case.

Do you think it could be a problem concerning cubeMap samplers in general or the problem comes from the cubemap initialization ?

Does anyone can help me?

Answer 1

i have never use an array inside of glsl and infortuntly i dont have the equipments now to do so, but have you tried using an unsigned int uint in glsl.

float GetCubeShadowFactor(vec3 vertexPosition_ws, float shadowFactor, uint idx) {
....
}

also note that you cannot use infinite samplers in you shaders.