How to send const data to shaders?

Question

I want to send const int variable from CPU side to shader so I could initialize the array in the shader conveniently.

But if sending with usual glUniform1ui(programm, N) shader compiler says that N must be const.

#version 450 core
uniform const int N;
int myArray[N];

void main() {
//...
}

Is this possible ? If yes what are the workarounds ?

p.s. I know that this is not related to the definition of uniform variables which clarifies that uniforms are immutable per shaders executing

Answer 1

A constant is as the name says constant and cannot be changed from outside via one of the glUniform methods and is NOT a uniform.

If you want to change the constant value, you've to recompile the hole shader and changing the shaders text before.

Sample ( Pseudocode )

GLchar** shaderSources = new GLChar*[3];
shaderSources[0] = "#version 450 core\n";
shaderSources[1] = "#define ARRAY_LENGTH 5\n";
shaderSources[2] = myShaderCode;
glShaderSource(shader, 2, shaderSources, LENGTH_OF_EACH(shaderSources, 2));

Shader:

int myArray[ARRAY_LENGTH];
void main()
{
    for (int i = 0; i < ARRAY_LENGTH; i++) myArray[i] ....;
}

A different approach is using textures ( or SSBO ) instead of arrays and get values of the texture without interpolation between the values.