cairo_user_scaled_font_init_func_t
for details of how the callback
works.cairoUserFontFaceSetInitFunc(font.face, init.func)
font.face
CairoFontFace
] A user font faceinit.func
NULL
CAIRO_STATUS_USER_FONT_IMMUTABLE
error will occur. A user font-face is immutable as soon as a scaled-font
is created from it.
Since 1.8