glGetUniformLocation unpredictable behavior

Question

I've defined a struct in my fragment shader, as below:

struct light_source{
    vec4 Ld, location;
    int type;
    float radii, specular_exponent;
};

And I'm using this uniform to access the struct members:
uniform light_source light_sources[5];

Now, from my C++ code, I'm getting the uniform locations like this:

Ld = glGetUniformLocation(Globals::ProgramId, "light_sources[0].Ld");
Ls = glGetUniformLocation(Globals::ProgramId, "light_sources[0].Ls");
location = glGetUniformLocation(Globals::ProgramId, "light_sources[0].location");
type = glGetUniformLocation(Globals::ProgramId, "light_sources[0].type");
radii = glGetUniformLocation(Globals::ProgramId, "light_sources[0].radii");
specular_exponent = glGetUniformLocation(Globals::ProgramId, "light_sources[0].specular_exponent");

When I print the above values, I find that the values are -1,1,2,-1,3,4 . So, I couldn't get locations for Ld and type . Similarly, if I add a new variable to the shader now , some times I get the location, and sometimes I get -1 .

I don't get the problem here. All the variable definitions are correct and there are no typos. Can this behavior be remedied?

are you using it? if the values aren't being used then they may be optimized out — ratchet freak
@ratchetfreak Thanks! Earlier, I added some dummy usages too for that. Like just assigning the light_sources[0].Ld to some new variable. But that new variable was also not being used anywhere (since it was just a dummy assignment). Now I added a proper usage for the variables, and I'm getting the locations. Thanks so much! — sanjeev mk

ratchet freak ratchet freak · Accepted Answer · 2014-10-22T23:51:38

When a uniform/attribute is not being used or has no effect on the output then the compiler/linker is free to remove it entirely which results in the getUniformLocation and glGetAttributeLocation returning invalid values.

glGetUniformLocation unpredictable behavior

1 Answers