How to create a full screen window on the current monitor with GLFW

Question

Creating a window with GLFW3 is done using glfwCreateWindow:

GLFWwindow* glfwCreateWindow ( int width,
                               int height,
                               const char *title,
                               GLFWmonitor *monitor,
                               GLFWwindow *share 
                             ) 

If the monitor parameter is not NULL, the window is created in full screen mode on the given monitor. One can receive the primary monitor by calling glfwGetPrimaryMonitor, or chose one of the results of glfwGetMonitors. But how can I create a full screen window on the current monitor, i.e. the monitor the window is currently running in windowed mode? There seems to be no way to receive the currently used monitor. There is glfwGetWindowMonitor, but it only returns the monitor in full screen mode, NULL in windowed mode.

Answer 1

You can find the current monitor with glfwGetWindowPos/glfwGetWindowSize. This function returns the monitor that contains the greater window area.

static int mini(int x, int y)
{
    return x < y ? x : y;
}

static int maxi(int x, int y)
{
    return x > y ? x : y;
}

GLFWmonitor* get_current_monitor(GLFWwindow *window)
{
    int nmonitors, i;
    int wx, wy, ww, wh;
    int mx, my, mw, mh;
    int overlap, bestoverlap;
    GLFWmonitor *bestmonitor;
    GLFWmonitor **monitors;
    const GLFWvidmode *mode;

    bestoverlap = 0;
    bestmonitor = NULL;

    glfwGetWindowPos(window, &wx, &wy);
    glfwGetWindowSize(window, &ww, &wh);
    monitors = glfwGetMonitors(&nmonitors);

    for (i = 0; i < nmonitors; i++) {
        mode = glfwGetVideoMode(monitors[i]);
        glfwGetMonitorPos(monitors[i], &mx, &my);
        mw = mode->width;
        mh = mode->height;

        overlap =
            maxi(0, mini(wx + ww, mx + mw) - maxi(wx, mx)) *
            maxi(0, mini(wy + wh, my + mh) - maxi(wy, my));

        if (bestoverlap < overlap) {
            bestoverlap = overlap;
            bestmonitor = monitors[i];
        }
    }

    return bestmonitor;
}