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I want to block font substitution in specific apps on Linux, but my research indicates that it might be controlled only at the system level, probably with fontconfig. I have found some discussion of how to direct fontconfig to substitute particular fonts, but nothing on how to competely turn off the feature.
The best answer would be how to disable glyph fallback for individual apps, but doing it system wide would be better than nothing.
There appears to be absolutely no way to disable font fallback. If you have fontconfig installed, the font substitution mechanism will always be active.
I have discovered two narrow ways to limit fallback. First, to block fallback in applications that use Pango, you can use the Pango fallback attribute to compile a special version that doesn't use fallback fonts. (Edit: Someone suggested to me that it may also be possible to do this by modifying the GtkTextLayout and GtkTextView within an app.)
Second, you can restrict the fontconfig search path to a directory with just the font(s) you want.
