BLF: Do Not Cache Unused Rendered Glyphs

The loading of a font size or style renders bitmaps of the characters
0-255 and stores them in a cache. But glyphs 128-255 in this cache are
not accessible. What used to be ansi high-bit characters are now multi-
byte UTF-8 sequences.

Therefore this patch reduces the glyph_ascii_table size to 128 and
only caches characters 32-127, the visible portion of ASCII, which
greatly reduces the time to load a font.

See D12189 for more details.

Differential Revision: https://developer.blender.org/D12189

Reviewed by Campbell Barton

source/blender/blenfont/intern/blf_font.c

@@ -317,7 +317,8 @@ static GlyphBLF **blf_font_ensure_ascii_table(FontBLF *font, GlyphCacheBLF *gc)
   /* build ascii on demand */
   if (glyph_ascii_table['0'] == NULL) {
     GlyphBLF *g;
-    for (uint i = 0; i < 256; i++) {
+    /* Skip control characters and just cache rendered glyphs for visible ASCII range. */
+    for (uint i = 32; i < 128; i++) {
       g = blf_glyph_search(gc, i);
       if (!g) {
         FT_UInt glyph_index = FT_Get_Char_Index(font->face, i);

source/blender/blenfont/intern/blf_internal_types.h

@@ -71,7 +71,7 @@ typedef struct GlyphCacheBLF {
   ListBase bucket[257];
 
   /* fast ascii lookup */
-  struct GlyphBLF *glyph_ascii_table[256];
+  struct GlyphBLF *glyph_ascii_table[128];
 
   /* texture array, to draw the glyphs. */
   GPUTexture *texture;