This is still very much Work in Progress and not supported by the official TrenchBroom yet.

The goal of TrenchBroomBFG is to make mapping for Doom 3 (BFG) as easy as it is for Quake.

Doom 3 also requires some extensions in order to work with TrenchBroom. The Quake 1/2/3 communities already adopted the Valve 220 .map format in the BSP compilers and I did the same with dmap in RBDOOM-3-BFG. I usually develop these things for RBDOOM-3-BFG but I created a separated branch for vanilla Doom 3 so everybody can adopt TrenchBroom and the new Doom 3 (Valve) .map support. You can find all relevant code snippets by looking for TrenchBroom in the comments

https://github.com/RobertBeckebans/DOOM-3/tree/506-TrenchBroom-interop

TrenchBroomBFG's abilities for Doom 3 are still limited at the moment and it works best with RBDOOM-3-BFG.

You can only save maps to the Doom 3 (Valve) format but you can copy paste from the vanilla Doom 3 .map format into the Doom 3 (Valve)configuration and reset your texture alignment as you want.

RBDOOM-3-BFG >= 1.4 also has the console command convertMaptoValve220 <mapname> which lets you easily convert any original Doom 3 (and BFG) .map and saves it with the _valve220.map suffix. This command prepares Doom 3 maps for editing in TrenchBroom and saves a lot of additional work in this TrenchBroomBFG fork. In addition the RBDOOM-3-BFG engine framework and ingame light editor can also save light settings, new entities or placed ragdolls back to the new Doom 3 (Valve) .map format so both programs interop with each other.

Here is an overview of the changes made to TrenchBroom:

• Doom 3 .map parser with brushDef3, patchDef2, patchDef3 primitives
• Doom 3 Valve .map configuration
• Quake 3 .shader parser adopted to support .mtr materials. It includes support for Doom 3 diffuse stages and the lookup for them is like in idMaterial::GetEditorImage()
• New Doom 3 OBJ parser. My TB Interop branch automatically creates OBJ files to work with TB and it also allows seamless interop with Blender 2.8x - 3.x without the need of additional model formats
• RBDOOM-3-BFG >= 1.4 ships with TB specific helper entities like misc_model or func_rotating_model to reflect TrenchBroom's clean architecture and differentiation between Brush Entities and Point Entities
• Game FGDs for Doom 3 and Doom 3 BFG
• Custom PNG icons for special entities like lights, speakers, particle emitters, info_location, target_* and so on
• After loading a map TrenchBroomBFG generates unique entity names and also fixes missing or bad "model" keys for brush based entitites
• Creating new entities like a light will automatically receive unique names like light_2
• Changed Rotation Tool behaviour to use "angles" by default
• Translucent materials that might cause BSP leaks have a purple rectangle border in the Texture Browser
• Changed OBJ exporter so exported models can be easier reimported by RBDOOM-3-BFG

• It doesn't allow to create bezier patches at the moment so you won't be able to edit existing Doom 3 maps
• TrenchBroomBFG doesn't support brush primitives like in D3Radiant or DarkRadiant. Use the Valve 220 .map format instead
• It has no support for BFG .resource files and .bimage files. You need to call exportImagesToTrenchBroom in RBDoom's console once to have all images available in base/_tb/textures/ as PNG format.
• Many entities work differently in Doom 3 if they have an origin. Brush work in D3 is usually stored in entity space and not world space. This is a major issue and not solved within TrenchBroomBFG. However as a workaround you can use the convertMapToValve220 engine command to prepare a Doom 3 map for the TrenchBroom Doom 3 (Valve) configuration.
• Doom 3's primary model formats are LWO and ASE. Assimp has problems to convert them into the Quake/Doom coordinates. (not an issue with the BFG edition)
• Some ASE models can't be loaded and materials are usually all wrong if loaded (not an issue with the BFG edition)
• TrenchBroomBFG doesn't support the "rotation" keyword and many models have the wrong orientation (not an issue with the BFG edition)
• TrenchBroomBFG breaks compatibility for other id Tech engines, e.g. entity links work between "target[num]" and "name" and not "targetname"
• Linked groups do not work yet with id Tech 4 due to name conflicts

• Binary builds are bundled with RBDOOM-3-BFG available from Mod DB releases. You can find this customized version under tools/trenchbroom/.

For feedback, questions and support join the id Tech 4 Discord: https://discord.gg/Q3E9rUFnnP , #rbdoom3bfg

You can also find weekly or monthly snapshots of this TrenchBroom version in the pinned messages of #rbdoom3bfg