The Blender Game Engine is a component of Blender, a free and open-source comprehensive 3D production suite, used for making real-time interactive content. The game engine was written from scratch in C++ as a mostly independent component, and includes support for features such as Python scripting and OpenAL 3D sound.
A shot from a little demo that I made.
I would love to learn how to write custom 2d filters with python... But where to start
Learn GLSL (especially the fragment shader part) as the filters are in GLSL and not in python. And then go for image filtering.