Hi,

I am trying to use uniform variables in my shader but for some reason glGetUniformLocation always returns -1. I am mostly following Lazy Foo's tutorial. Here is the relevant code:

PointLineShader::PointLineShader() {
    GLuint vertexShaderId = loadShader("Shader/pointLine.vert", GL_VERTEX_SHADER);
    GLuint fragmentShaderId = loadShader("Shader/pointLine.frag", GL_FRAGMENT_SHADER);

    programId = glCreateProgram();
    glAttachShader(programId, vertexShaderId);
    glAttachShader(programId, fragmentShaderId);
    glLinkProgram(programId);

    glDetachShader(programId, vertexShaderId);
    glDetachShader(programId, fragmentShaderId);

    glDeleteShader(vertexShaderId);
    glDeleteShader(fragmentShaderId);

    positionLocation = glGetAttribLocation(programId, "in_Position");
    if (positionLocation == -1) {
        printf("%s is not a valid glsl program variable!\n", "in_Position");
    }

    colorLocation = glGetAttribLocation(programId, "in_Color");
    if (colorLocation == -1) {
        printf("%s is not a valid glsl program variable!\n", "in_Position");
    }

    // this doesn't work
    projectionMatrixLocation = glGetUniformLocation(programId, "projectionMatrix");
    if (projectionMatrixLocation == -1) {
        printf("%s is not a valid glsl program variable!\n", "projectionMatrix");
    }

    modelViewMatrixLocation = glGetUniformLocation(programId, "modelViewMatrix");
    if (modelViewMatrixLocation == -1) {
        printf("%s is not a valid glsl program variable!\n", "modelViewMatrix");
    }
}

And the vertex shader:

#version 400

uniform mat4 projectionMatrix;
uniform mat4 modelViewMatrix;

in vec2 in_Position;
in vec4 in_Color;
out vec4 ex_Color;
 
void main(void)
{
	gl_Position = gl_ProjectionMatrix * gl_ModelViewMatrix * vec4(in_Position.x, in_Position.y, 0.0, 1.0);
	//gl_Position = projectionMatrix * modelViewMatrix * vec4(in_Position.x, in_Position.y, 0.0, 1.0);
	ex_Color = in_Color;
}

To initialize openGL I am using SDL2 and glew. I noticed that I set the openGL version to 3.2 in SDL, but in the shaders I have "#version 400". If I change or remove it the shader won't compile.

I am not sure if it might be related, but textures also don't work right now even though I am using the same code as in my other program which uses SFML except for the image loading functions.

Call glUseProgram before getting the attributes. Also, "projectionMatrix", "modelViewMatrix", and possibly "in_Color" won't exist since they are being optimized out.

That didn't work

Also, I think the variables that are being optimized out are gl_ProjectionMatrix, etc. That is why I am trying to use my own variables.

Maybe I am doing something wrong with the initialization? This is how I create my openGL context:

    if (SDL_Init(SDL_INIT_VIDEO) < 0) // Initialize SDL's Video subsystem
        sdldie("Unable to initialize SDL"); // Or die on error

    // Request opengl 3.2 context.
    // SDL doesn't have the ability to choose which profile at this time of writing,
    // but it should default to the core profile
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);

    // Turn on double buffering with a 24bit Z buffer.
    // You may need to change this to 16 or 32 for your system
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);

    // Create our window centered at 512x512 resolution
    mainwindow = SDL_CreateWindow(PROGRAM_NAME, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
        screenWidth, screenHeight, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);
    if (!mainwindow) // Die if creation failed
        sdldie("Unable to create window");

    checkSDLError(__LINE__);

    // Create our opengl context and attach it to our window
    maincontext = SDL_GL_CreateContext(mainwindow);
    checkSDLError(__LINE__);


    // This makes our buffer swap syncronized with the monitor's vertical refresh
    SDL_GL_SetSwapInterval(1);

    GLenum status = glewInit();
    if(status != GLEW_OK) {
        fprintf(stderr, "INFO: glew couldn't be initialized. Exit\nGLEW Error: %s", glewGetErrorString(status));
        close();
    }

In your shader, using your own uniform is correct, don't use gl_*. Use #version 400 core and they should give compiler errors as they're removed from the language.

Anyway your problem seems to be this:

glDetachShader(programId, vertexShaderId);
glDetachShader(programId, fragmentShaderId);

Remove that code.

In your shader, using your own uniform is correct, don't use gl_*. Use #version 400 core and they should give compiler errors as they're removed from the language.

Anyway your problem seems to be this:

    glDetachShader(programId, vertexShaderId);
    glDetachShader(programId, fragmentShaderId);

Remove that code.

Ok, I figured it out. The problem was that I didn't use the variables so they were compiled out. Maybe that is what Geometrian meant. The detaching of the shader after linking should be okay: http://stackoverflow.com/questions/9113154/proper-way-to-delete-glsl-shader

But thanks for the #version 400 core tip. Now I only have to solve the texture problem.