Its a very good idea to use a 2D Shader with Black Materials and Textures that render in front of your game. Seperate from the Shader you use to render your game scene.

Steps:

1. Get the windows height and width variables:

GLFWVidMode vidmode = glfwGetVideoMode(glfwGetPrimaryMonitor());

float screenwidth = vidmode.width(); float screenheight = vidmode.height();

2. Make a 2D Shader seperate from your InGame Vertex Shader

3. Convert the screen coordinates to 2D OpenGL Coordinates

4. With the 2D Shader. Make 2 Black Rectangles. Compared to the width and height of the screen