SDL_Init(SDL_INIT_EVERYTHING);
SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);        // red: 8 bits
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);      // green: 8 bits
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);       // blue: 8 bits
SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);      // alpha: 8 bits
SDL_GL_SetAttribute(SDL_GL_BUFFER_SIZE, 32);    // r + g + b + a = 32 bits
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
graphWindow = SDL_CreateWindow(title, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, width, height, SDL_WINDOW_OPENGL);

typedef struct {
    float r;
    float g;
    float b;
    float a;
} Pixel;

// ...

void main(void) {
    Pixel *pixels;
    // ...
    pixels = malloc(width * height * sizeof(Pixel));
    // ...

    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    while (graphNotClosed) {
        glDrawPixels(width, height, GL_RGBA, GL_FLOAT, pixels);
        // do some number cruching and change some elements of array "pixels"
        // ...
        SDL_GL_SwapWindow(graphWindow);
    }
}