- only disable clip planes on Windows, but not on Linux or macOS.
- If a driver reports full OpenGL 4.5 support, assume that all features are working properly.
Unfortunately the math behind the old clip planes is utterly impenetrable and so poorly documented that I have no idea how to set that up, so it is deactivated for now. It wasn't working anyway.
Regular skies need it off but SkyViewpoints need it on - and all others need to use the parent's setting.
So without engine side tracking we can end up rendering the sky with this setting off, resulting in omission of the fog layer.
- we need to check all GL versions when trying to get a context because some drivers only give us the version we request, leaving out newer features that are not exposed via extension.
- added some status info about uniform blocks.
- reactivate alpha testing per fixed function pipeline
- use the 'modern' way to define clip planes (GL_CLIP_DISTANCE). This is far more portable than the old glClipPlane method and a lot more robust than checking this in the fragment shader.
After thinking about it for a day or so I believe it's the best option to remove all compatibility code because it's a major obstacle for a transition to a core profile.
- Also fixed some very strange thing in the shader's desaturate function. For unknown reasons using the 'mix' function there did not work.
- fixed: The fog boundary special shader could not be used.
On GL 3.x+ this isn't needed at all and on older hardware it causes performance issues, in particular with hires textures due to impossibility of precaching.
In addition it forces some really awkward handling of lighting for things that have their own color, like stenciled sprites or particles.
With this special case gone it will be possible to handle this case in a saner manner than it is right now.
As compensation for older hardware a fullscreen blend will be drawn over the entire screen. This won't be 100% accurate but it's preferable to keeping the current method.
This means it won't work anymore on anything that doesn't support OpenGL 4.0, but I don't think this is a problem. On older NVidia cards performance gains could not be seen and on older AMDs using the vertex buffer was even worse as long as it got mixed with immediate mode rendering.
- removed gl_vid_compatibility. With the bump to 1.4 no hardware requiring this flag is supported anymore.
- disabled 16 bit framebuffers for the same reason. As a conseqence all code for rendering without stencil could also be removed.
