These are some of the engines that I briefly checked out. The links lead to the part of the codetrees that contain OS specific support, not the root of the codetrees. There're many other engines, but I left out engines who either did not have code repositories online, were for specifically for mobile games, were not primarily coded in C/C++, or did not have any Unix support.
Torque3D engine: https://github.com/GarageGames/Torque3D/tree/development/Engine/source/platformX86UNIX
Has at least some FreeBSD support, but I'm not sure how well it's been exercised.
GoDot engine: https://github.com/godotengine/godot/tree/master/platform
Doesn't have FreeBSD support, but has Haiku support. How'd we get beat by an OS that doesn't even have a real release???
Ogre3D (rendering ONLY): https://github.com/OGRECave/ogre/tree/master/OgreMain/src
Has some support for GLX. It might actually work great.
Panda3d engine: https://github.com/panda3d/panda3d/tree/master/panda/src
Has some support for GLX. It might actually work great.
Irrlicht engine: https://sourceforge.net/p/irrlicht/code/HEAD/tree/trunk/source/Irrlicht/
Has some support for GLX. It might actually work great.
Delta3D engine: https://sourceforge.net/p/delta3d/code/HEAD/tree/trunk/delta3d/src/
Has some X11 support. Not sure of how functional it is.
Quake2 engine: https://github.com/id-Software/Quake-2
Has native Linux & native Irix code, but doesn't have native FreeBSD code. Has generic Unix code, so maybe that could be used as a basis for creating native code for FreeBSD.
Torque3D engine: https://github.com/GarageGames/Torque3D/tree/development/Engine/source/platformX86UNIX
Has at least some FreeBSD support, but I'm not sure how well it's been exercised.
GoDot engine: https://github.com/godotengine/godot/tree/master/platform
Doesn't have FreeBSD support, but has Haiku support. How'd we get beat by an OS that doesn't even have a real release???
Ogre3D (rendering ONLY): https://github.com/OGRECave/ogre/tree/master/OgreMain/src
Has some support for GLX. It might actually work great.
Panda3d engine: https://github.com/panda3d/panda3d/tree/master/panda/src
Has some support for GLX. It might actually work great.
Irrlicht engine: https://sourceforge.net/p/irrlicht/code/HEAD/tree/trunk/source/Irrlicht/
Has some support for GLX. It might actually work great.
Delta3D engine: https://sourceforge.net/p/delta3d/code/HEAD/tree/trunk/delta3d/src/
Has some X11 support. Not sure of how functional it is.
Quake2 engine: https://github.com/id-Software/Quake-2
Has native Linux & native Irix code, but doesn't have native FreeBSD code. Has generic Unix code, so maybe that could be used as a basis for creating native code for FreeBSD.