As promised, here's a .map exporter for Blender 2.80

Exports either individual faces as pyramids, or objects as convex brushes. Uses material names for texture assignment and material image size for scaling. Supports UVs both in standard Quake and in Valve220 format (adapted from EricW's implementation for OBJ2MAP). Offers custom grid. Allows saving to clipboard.

The exporter ensures that the brushes are convex and the faces planar. You don't have to triangulate the meshes in advance, but in some cases it can help with UVs (e.g. with mid-edge vertices). There's room for improvement, but it should work fine as is.

Standard format UV export is lossy (no shearing). I don't really expect anyone to be using it over Valve220 anyway, but it should produce decent results for id1-style detailing. Single-axis curves should be fine, no miracles though.

Only tested in Trenchbroom for now. Might need to change precision for other editors. Let me know if it works/breaks elsewhere. 

That is an amazing plugin, Chedap! Thank you so much for what you do. It works really really well! 

Installing the .py file through the plugin menu in Blender 2.80 or 2.91 like normal and it doesn't show up. Does this not work anymore? 

Hi, I'm trying to convert a level from Unreal Gold and it's full of Infinities and NaNs.
https://mega.nz/file/ADYmXZJB#NIogY6csRsOdwGfK4VElcPpt0rGouUfI3JOWNHFi5oQ

Blender plugin needs "division by zero" protection in one place. 

https://mega.nz/file/dSZ2HTKY#XcH68aNshH49Pr26Mtgk2L7d7RGrgIKUzNjUwaskPfg 

@Tintin: the plugin is a single python script. That's what you should download (rather than a .zip) and point to in the Blender's "Install..." dialog.

@crystallize: I have added a check for missing images. This prevents the error, but you should not expect sane UVs on export, since without the files there's no way for the exporter to determine the scale.