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slicedpan's picture

Can't get uniform locations using GL.GetUniformLocation

Posted Thursday, 30 June, 2011 - 00:03 by slicedpan in

Hi, I am using the following code to load a vertex and fragment shader from files and then link them into a shader program.
The compiling/linking doesn't raise any errors, however I can't get the location of any of the uniforms defined in the shaders.

GL.CompileShader(vertexHandle);	
GL.CompileShader(fragHandle);
 
_glHandle = GL.CreateProgram();
GL.AttachShader(_glHandle, vertexHandle);
GL.AttachShader(_glHandle, fragHandle);
GL.LinkProgram(_glHandle);
 
Console.WriteLine(GL.GetProgramInfoLog(_glHandle));	//this does not generate any error message
 
GL.UseProgram(_glHandle);
 
int count;
GL.GetProgram(_glHandle, ProgramParameter.ActiveUniforms, out count);
Console.WriteLine(count.ToString() + " active uniforms");
 
int uniformLocation = GL.GetUniformLocation(_glHandle, "blah");
if (uniformLocation < 0)
	throw new Exception("couldn't get uniform location!");    //this exception gets thrown every time

The shader in question looks like this:

#version 330
 
layout(location = 0) in vec3 Position;
layout(location = 1) in vec3 Normal;
layout(location = 2) in vec2 TexCoord;
 
uniform float blah;
 
out vec3 out_Color;
 
void main()
{
    gl_Position = vec4(Position, 1);        
}
‹ Anisotropic Filtering in OpenGL 3.2 Conceptual question about GL.ActiveTexture ›

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c2woody's picture

Re: Can't get uniform locations using GL.GetUniformLocation

Posted Thursday, 30 June, 2011 - 07:52 by c2woody

Depending on the shader compiler the "blah" uniform may be optimized away so the location is not accessible.

tksuoran's picture

Re: Can't get uniform locations using GL.GetUniformLocation

Posted Thursday, 30 June, 2011 - 09:36 by tksuoran

Unused uniforms will not get location assigned to them.

You can use following code to see what uniforms you have:

int size;
ActiveUniformType type;
int uniformCount;
 
GL.GetProgram(ProgramObject, ProgramParameter.ActiveUniforms, out uniformCount);
for(int i = 0; i < uniformCount; ++i)
{
    string  name = GL.GetActiveUniform(ProgramObject, i, out size, out type);
    int slot = GL.GetUniformLocation(ProgramObject, name);
}
slicedpan's picture

Re: Can't get uniform locations using GL.GetUniformLocation

Posted Thursday, 30 June, 2011 - 10:03 by slicedpan

Thanks guys!

It actually was being optimized away since I didn't actually use the uniform in the shaders.
Thanks for the code tksuoran, some of that might end up in my project!