Counts the number unknown glyphs in @layout. That is, zero if
glyphs for all characters in the layout text were found, or more
than zero otherwise.
This function can be used to determine if there are any fonts
available to render all characters in a certain string, or when
used in combination with %PANGO_ATTR_FALLBACK, to check if a
certain font supports all the characters in the string.
Counts the number unknown glyphs in @layout. That is, zero if glyphs for all characters in the layout text were found, or more than zero otherwise.
This function can be used to determine if there are any fonts available to render all characters in a certain string, or when used in combination with %PANGO_ATTR_FALLBACK, to check if a certain font supports all the characters in the string.