Really Basic OpenGL Post-Processing C++ Class for my Half-Life mod that can process multiple PP shaders

Hello.

I need a really basic post-processing class (C++ and OpenGL) for my Half-Life mod for multiple PP shaders with dynamic intensities.
If you need to hardcode them, grayscale and chromatic aberration. But shaders are optional, I just need the class. (An example shader for understanding/testing the system would be great)

Git Repo: https://github.com/edgarbarney/Trinity-renderer

Framebuffers are not present within the Half-Life engine itself, so rendering the screen to texture in the Half-Life engine can be found in this tutorial: https://twhl.info/wiki/page/VERC%3A_Real-Time_%22TRON_2.0%22_Glow_in_Half-Life

Ignore the obsolete CG stuff in the article and don’t use CG please. GLUT would be easier since it’s already used in the project.