Are there any game definition files that allow you to use GtkRadiant 1.4 to create maps for Q2W (1.4 and 1.5 use different file formats for the game packs)?
At one point, mattn committed a version of our configs to the ZeroRadiant repository at id Software. ZeroRadiant was based on 1.4, not 1.5. And so yes, somewhere out there, there are (very dated) files to allow working with Q2W in 1.4.
It might be easiest or most beneficial to just create them from scratch again, tho. Basically you would start with the Quake2 game profile, and modify a few surface and contents flags, and then optionally update/add/remove a few entity definitions.
