One common request is to use Pango with a custom font. The way I recommend doing that is by creating a custom FcConfig and adding custom fonts to it and using pango against that config.
However, currently only fonts on disk can be added to a config. Lets fix that to either get a memory buffer, or a FT_Face, similar to FcFreeTypeQueryFace. We probably need to add a FcFileScan() variant too.
Perhaps better to add Memory() version to avoid FreeType dependency in non fcfreetype.h API.
Humm. A version that takes FT_Face is useful regardless. So perhaps we can add FcFreeTypeConfigAppFontAddFace() as well as FcConfigAppFontAddMemory().
This might be tricky. Clients of fontconfig currently only expect FC_FILE/FC_INDEX. We would need to update them all to check for the FC_FT_FACE as well...
Taking FT_Face might not be a good idea. Taking memory and creating a FT_FACE every time works.
Alternatively, we can use modern Linux APIs to assign to a piece of memory a file name. That might be the least portable but most useful.
For reference, I discussed using custom fonts with pango in detail here:
on Mar 24, 2017 at 04:20:27.
(provided by the Example extension).