1. Create a FBO of a certain width and height in Game::Initialise()
2. Set the viewport and perspective projection matrix based on the FBO size
3. Bind the FBO and render the scene a first time

    m_pFBO->Bind(); // Render to texture
    RenderScene(0); // pass 0 – don’t render TV screen

4. Reset the viewport and perspective projection matrix based on the window size
5. Go back to rendering to the default framebuffer, and render the scene again.

    glBindFramebuffer(GL_FRAMEBUFFER, 0); // Render to window
    RenderScene(1); // pass 1 – render scene including TV screen

6. Bind the texture in the FBO and render an object not present in first pass (e.g., TV screen)

    m_pFBO->BindTexture(0); // draw TV screen using the framebuffer texture

7. Swap buffers

High

Example from Portal