docs: provide a primer on the fontconfig format #563

dnkl commented 2025年05月24日 09:49:33 +02:00

This section is not factually correct, though I can see how one would arrive at this conclusion.

I looked at fcft's documentation, and it's too ambiguous as well. Foot's docs are the best, but could probably be improved as well:

The fallback fonts are searched in the order they appear. If a glyph cannot be found in any of the fallback fonts, the dynamic fallback list from fontconfig (for the primary font) is searched.

To expand on this; fontconfig always returns "something" (unless you don't have any fonts installed), regardless of what font name you give it (try fc-match foobar). It's also almost always a list of fonts (unless you only have a single font installed (try fc-match -s foobar).

This is what foot's documentation refers to as the dynamic fallback list from fontconfig.

The fallback list in foot and fuzzel is an fcft feature, where fcft will search the "explicit" fallbacks first, whenever a glyph cannot be found in the primary font. When it cannot find a glyph in any of the explicit fallbacks, then it searches the fontconfig fallbacks (of the primary font only, i.e. the first font in the foot/fuzzel list).

Why do we allow this? First, to allow a custom fallback sequence. Second, and perhaps more importantly, it allows you to specify custom font options for each fallback font, something not possible with the fontconfig fallbacks. This includes everything, from size, style, weight, to limiting the codepoint range etc.

This section is not factually correct, though I can see how one would arrive at this conclusion. I looked at fcft's documentation, and it's too ambiguous as well. Foot's docs are the best, but could probably be improved as well: > The fallback fonts are searched in the order they appear. If a glyph cannot be found in any of the fallback fonts, the dynamic fallback list from fontconfig (for the primary font) is searched. To expand on this; fontconfig **always** returns "something" (unless you don't have any fonts installed), regardless of what font name you give it (try `fc-match foobar`). It's also almost always a list of fonts (unless you only have a single font installed (try `fc-match -s foobar`). This is what foot's documentation refers to as _the dynamic fallback list from fontconfig_. The fallback list in foot and fuzzel is an fcft feature, where fcft will search the "explicit" fallbacks first, whenever a glyph cannot be found in the primary font. When it cannot find a glyph in any of the explicit fallbacks, then it searches the fontconfig fallbacks (of the primary font only, i.e. the first font in the foot/fuzzel list). Why do we allow this? First, to allow a custom fallback sequence. Second, and perhaps more importantly, it allows you to specify custom font options for each fallback font, something not possible with the fontconfig fallbacks. This includes everything, from size, style, weight, to limiting the codepoint range etc.

dnkl commented 2025年05月24日 09:52:10 +02:00

Finally, this also means that we will not use the fallback font only, if the primary font doesn't exist. FontConfig will still give us "a" font for the primary font, but it may not be the "correct" font.

Finally, this also means that we will **not** use the fallback font only, if the primary font doesn't exist. FontConfig will still give us "a" font for the primary font, but it may not be the "correct" font.