Don't attempt to cache glyph metrics for FONT_INVALID_CODE

This was causing massive slowdown in redisplay when eg #xfe0f
(VARIATION SELECTOR-16) was present, as the cache ended up very large,
unused, and being recreated on every call to font_fill_lglyph_metrics
(Bug#39133).

* src/composite.c (fill_gstring_body): Hoist FONT_OBJECT_P check out
of loop.  Calculate glyph code and check for FONT_INVALID_CODE before
calling font_fill_lglyph_metrics.  Pass glyph code to it.

* src/font.c (font_fill_lglyph_metrics): Add code parameter, move
glyph code calculation up the call stack into fill_gstring_body.

* src/font.h: Adjust font_fill_lglyph_metrics prototype.

1 files changed, 1 insertions, 3 deletions

diff --git a/src/font.c b/src/font.c
index 2b90903c909..39ec1b3562a 100644
--- a/src/font.c
+++ b/src/font.c
@@ -4416,10 +4416,8 @@ DEFUN ("clear-font-cache", Fclear_font_cache, Sclear_font_cache, 0, 0, 0,
 
 
 void
-font_fill_lglyph_metrics (Lisp_Object glyph, Lisp_Object font_object)
+font_fill_lglyph_metrics (Lisp_Object glyph, struct font *font, unsigned int code)
 {
-  struct font *font = XFONT_OBJECT (font_object);
-  unsigned code = font->driver->encode_char (font, LGLYPH_CHAR (glyph));
   struct font_metrics metrics;
 
   LGLYPH_SET_CODE (glyph, code);