OpenGL allows you to change the way textures are drawn. This process is called blending and it's often used when combining multiple textures. However, blending can also be applied to texture rendering on screen. OpenGL uses a so-called "blending function" to define the mathematical function that calculates the final color value. For example, the
GL_FUNC_ADD blending function defines additive blending, which is used when mixing colored lights in a scene.
This function uses two values: