glDrawPixels isn't filling the window

I’m using GLFW on MacOS and I’m using some OpenGL calls to draw an image in the window. For some reason, glDrawPixels(…) isn’t filling the window. This is what I have:

#define IMAGE_WIDTH     800
#define IMAGE_HEIGHT    600

int main(int argc, const char * argv[])
    GLFWwindow* window;
    int nx = IMAGE_WIDTH;
    int ny = IMAGE_HEIGHT;

    // One time during setup.
    unsigned int data[ny][nx][3];
    for( size_t y = 0; y < ny; ++y )
        for( size_t x = 0; x < nx; ++x )
            data[y][x][0] = ( rand() % 256 ) * 256 * 256 * 256;
            data[y][x][1] = 0;
            data[y][x][2] = 0;

    // Initialize the library
    if (!glfwInit())
        return -1;

    /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(nx, ny, "FOO", NULL, NULL);
    if (!window)
        return -1;

    /* Make the window's context current */

    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
        /* Render here */
        glDrawPixels( nx, ny, GL_RGB, GL_UNSIGNED_INT, data );
        /* Swap front and back buffers */
        /* Poll for and process events */

    return 0;

I’ve tried to make it as clear as possible. The window dimensions and the pixel data should be based off the same provided dimensions, so it’s a little unclear to me why it seems to only fill a quarter of the screen. Here is a screencap of the window:

The window size is not measured in pixels. What you want for OpenGL operations is the framebuffer size. These may also change independently on macOS if a window moves between monitors with different scaling factors.

Also note that the window size may not match what you specified because the window manager may override it, so you should always query with glfwGetWindowSize or glfwGetFramebufferSize (or use the callbacks) to get the actual size.