"FcDefaultSubstitute"("3") manual page

Name

FcDefaultSubstitute - Perform default substitutions in a pattern

#include <fontconfig.h>

void FcDefaultSubstitute (FcPattern *pattern);

Supplies default values for underspecified font patterns:

Patterns without a specified style or weight are set to Medium
Patterns without a specified style or slant are set to Roman
Patterns without a specified pixel size are given one computed from any specified point size (default 12), dpi (default 75) and scale (default 1).

Fontconfig version 2.3.2