This was done to clean up the license and to ensure that any commercial fork of the engine has to obey the far stricter requirements concerning source distribution. The old license was compatible with GPLv2 whereas combining GPLv2 and LGPLv3 force a license upgrade to GPLv3. The license of code that originates from ZDoomGL has not been changed.
Both of these were inherited from ZDoomGL and in terms of light design in maps it makes absolutely no sense to have them user configurable. They should have been removed 11 years ago.
- restricted gl_lights_additive to legacy code and removed menu entry for this.
For modern hardware this setting is completely pointless, it offers no advantage and degrades visual quality. Its only reason for existence was that drawing additive lights with textures is a lot faster, and that's all it's being used for now.
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.
