BLF: Perf: Add a kerning cache table for ascii chars.

This adds less than a megabyte of mem usage.
FT_Get_Kerning was the 2nd hotspot when profilling. This commit completly
remove this cost.

One concern though: I don't know if the kerning data is constant for every
sizes but it seems to be the case. I tested different fonts at different
dpi scalling and saw no differences.

1 files changed, 55 insertions, 0 deletions

diff --git a/source/blender/blenfont/intern/blf_glyph.c b/source/blender/blenfont/intern/blf_glyph.c
index d472825e940..f5a645af5e0 100644
--- a/source/blender/blenfont/intern/blf_glyph.c
+++ b/source/blender/blenfont/intern/blf_glyph.c
@@ -65,6 +65,61 @@
 #include "BLI_strict_flags.h"
 #include "BLI_math_vector.h"
 
+KerningCacheBLF *blf_kerning_cache_find(FontBLF *font)
+{
+	KerningCacheBLF *p;
+
+	p = (KerningCacheBLF *)font->kerning_caches.first;
+	while (p) {
+		if (p->mode == font->kerning_mode)
+			return p;
+		p = p->next;
+	}
+	return NULL;
+}
+
+/* Create a new glyph cache for the current kerning mode. */
+KerningCacheBLF *blf_kerning_cache_new(FontBLF *font)
+{
+	KerningCacheBLF *kc;
+
+	kc = (KerningCacheBLF *)MEM_callocN(sizeof(KerningCacheBLF), "blf_kerning_cache_new");
+	kc->next = NULL;
+	kc->prev = NULL;
+	kc->mode = font->kerning_mode;
+
+	unsigned int i, j;
+	for (i = 0; i < 0x80; i++) {
+		for (j = 0; j < 0x80; j++) {
+			GlyphBLF *g = blf_glyph_search(font->glyph_cache, i);
+			if (!g) {
+				FT_UInt glyph_index = FT_Get_Char_Index(font->face, i);
+				g = blf_glyph_add(font, glyph_index, i);
+			}
+			/* Cannot fail since it has been added just before. */
+			GlyphBLF *g_prev = blf_glyph_search(font->glyph_cache, j);
+
+			FT_Vector delta = {.x = 0, .y = 0};
+			if (FT_Get_Kerning(font->face, g_prev->idx, g->idx, kc->mode,
+			                   &delta) == 0) {
+				kc->table[i][j] = (int)delta.x >> 6;
+			}
+			else {
+				kc->table[i][j] = 0;
+			}
+		}
+	}
+
+	BLI_addhead(&font->kerning_caches, kc);
+	return kc;
+}
+
+void blf_kerning_cache_clear(FontBLF *font)
+{
+	font->kerning_cache = NULL;
+	BLI_freelistN(&font->kerning_caches);
+}
+
 GlyphCacheBLF *blf_glyph_cache_find(FontBLF *font, unsigned int size, unsigned int dpi)
 {
 	GlyphCacheBLF *p;