FontManager.resolve_font silently returns the default face for any .bdf

[ChuckBuilds]

Summary

FontManager.resolve_font() cannot load a bitmap (.bdf) font at anything other than its own pixel size, and when it fails it returns the default face without signalling it. Callers cannot tell a successful load from a silent fallback, so a plugin offering a .bdf in its font picker appears to ignore the setting.

Why it is invisible

A .bdf exists at exactly one pixel size. FreeType raises OSError: invalid pixel size for any other, so ImageFont.truetype(path, size) fails whenever the requested size differs from the file's PIXEL_SIZE. resolve_font then falls back — and in current Pillow the default face is itself a FreeTypeFont, so the returned type gives no hint that anything went wrong.

common_fonts carries five_by_seven → assets/fonts/5x7.bdf, which is native 7px. Any caller asking for it at the usual 8 gets the default face back and no error.

Impact seen in plugins

This has now surfaced in five plugins in ledmatrix-plugins, each with its own copy of the loader:

Plugin	Symptom
clock-simple	5x7.bdf and 4x6.bdf rendered byte-identical to the default
countdown	five_by_seven fell back even though the plugin had its own working loader — the catalog has the family, so the plugin trusted the core's answer
news	both .bdf faces fell back
tide-display	4x6.bdf worked and 5x7.bdf did not, purely because the default font_size of 6 happened to match one of them
mqtt-notifications, youtube-stats	same loader, same behaviour

The countdown case is the one that argues for fixing it here: the plugin only consulted its own loader when the catalog missed a family, so a family the core claims-and-then-degrades is worse than one it does not know about.

Suggested fix

In the loader, on OSError, read PIXEL_SIZE from the .bdf header and retry at that size before giving up:

try:
    return ImageFont.truetype(path, size_px)
except OSError:
    native = _bdf_pixel_size(path)
    if native is None or native == size_px:
        raise
    return ImageFont.truetype(path, native)

That is the fix applied per-plugin in ChuckBuilds/ledmatrix-plugins#362, #369 and #370; doing it in FontManager would let those copies drop it.

Failing that, having resolve_font signal the fallback — a return value, or a warning naming the family — would at least make it diagnosable rather than looking like a plugin bug.

Environment

Pillow 11.3.0. The .bdf size constraint is a FreeType property rather than a Pillow-version one, so I would expect this to reproduce broadly, but I have only verified it here.