TILO_FONT_CATALOG: the catalog to read instead of the compiled-in
checkout path, for a binary built somewhere else and run here. Without it
such a run silently sets every frame in the host’s faces, which looks
almost right and is wrong in a way that only shows up in the review of a
screenshot. The toolkit reads it into HostPaths::font_catalog, which is
where a reader takes it from.
The root a capture would set text from, without reading a font: the roots
[bundled_font_system] tries, checked for a manifest this build pins. A
run whose answer is None would render every frame in the host’s faces,
which is not the product, so a capture asks this before it draws anything.
The catalog this build prepared from the source checkout, in this crate’s
OUT_DIR: it is part of the build’s output, so wherever the build is
reused the catalog is too. The build names it from its profile directory,
which holds the running program (or its deps/examples), so it is found
above the program; the build directory’s path is not compiled in.