feature request: support older GLSL versions

This is exactly the kind of software that would shine on older hardware that is unable to run it because it requires a specific version of the OpenGL shading language. Lots of old laptops with intel gm45 graphics that would love to run this game in HD.

Start by locating the renderer and identifying the GLSL/OpenGL version currently required. Compare that requirement with the older Intel GM45 hardware described in the issue and determine the compatibility scope. Done means the game can run on the targeted older hardware without breaking current rendering behavior, with validation on an appropriate setup.

Written by the indexing model from the issue text.