ttf.c: glyph raster cache, fixed slots, no allocation (item 4.3.7d)

Punch list §25 item 4.3.7d complete. ttf_raster_cache_get() looks up (font, codepoint, size_px) in a caller-owned fixed slot array, evicting round-robin once full, rasterizing into a slot on a miss. Verified live in tools/ttftest.c: an identical (font, 'A', 24px) call made twice returns was_hit=0 then was_hit=1, and the slot's own hits counter reads exactly 1 afterward -- checked programmatically. A different-codepoint call misses again, proving the key actually discriminates. Wall-clock timing (miss 0.040ms vs hit 0.001ms) is printed as informational corroboration only, not the load-bearing check. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
2026-08-10 22:31:56 -04:00
parent 095860251a
commit 2db4603d04
5 changed files with 219 additions and 2 deletions
@@ -813,6 +813,96 @@ int ttf_rasterize_glyph(const ttf_font_t *font, uint32_t glyph_index,
    return TTF_OK;
 }

+/* ===========================================================================
+ * 4.3.7d — glyph raster cache: fixed caller-owned slots, no allocation.
+ * ===========================================================================
+ */
+
+void ttf_raster_cache_init(ttf_raster_cache_t *cache, ttf_raster_cache_slot_t *slots,
+                            uint32_t slot_count) {
+    uint32_t i;
+    cache->slots = slots;
+    cache->slot_count = slot_count;
+    cache->evict_next = 0;
+    for (i = 0; i < slot_count; i++) {
+        slots[i].valid = 0;
+        slots[i].hits = 0;
+    }
+}
+
+int ttf_raster_cache_get(ttf_raster_cache_t *cache, const ttf_font_t *font,
+                          uint32_t codepoint, uint32_t size_px,
+                          ttf_bitmap_t *out, int *was_hit) {
+    uint32_t i, slot_idx;
+    ttf_raster_cache_slot_t *slot;
+    int rc;
+
+    if (!cache || !font || !out) return TTF_ERR_BAD_TABLE;
+    if (size_px > TTF_CACHE_MAX_SIZE_PX) return TTF_ERR_UNSUPPORTED;
+
+    for (i = 0; i < cache->slot_count; i++) {
+        slot = &cache->slots[i];
+        if (slot->valid && slot->font == font && slot->codepoint == codepoint
+            && slot->size_px == size_px) {
+            slot->hits++;
+            out->pixels = slot->pixels;
+            out->width = slot->width;
+            out->height = slot->height;
+            if (was_hit) *was_hit = 1;
+            return TTF_OK;
+        }
+    }
+
+    /* Miss: use a free slot if one exists, else evict round-robin. */
+    slot_idx = cache->slot_count;
+    for (i = 0; i < cache->slot_count; i++) {
+        if (!cache->slots[i].valid) { slot_idx = i; break; }
+    }
+    if (slot_idx == cache->slot_count) {
+        slot_idx = cache->evict_next;
+        cache->evict_next = (cache->evict_next + 1) % cache->slot_count;
+    }
+    slot = &cache->slots[slot_idx];
+
+    {
+        uint32_t j;
+        ttf_bitmap_t bmp;
+        q48_16_t scale;
+        uint32_t gid;
+
+        for (j = 0; j < TTF_CACHE_BITMAP_BYTES; j++) slot->pixels[j] = 0;
+
+        gid = ttf_codepoint_to_glyph(font, codepoint);
+        scale = q48_div(q48_from_u64(size_px), q48_from_u64(font->units_per_em));
+
+        bmp.pixels = slot->pixels;
+        bmp.width = TTF_CACHE_BITMAP_DIM;
+        bmp.height = TTF_CACHE_BITMAP_DIM;
+        rc = ttf_rasterize_glyph(font, gid, scale,
+                                  q48_from_u64(TTF_CACHE_MARGIN),
+                                  q48_from_u64(size_px + TTF_CACHE_MARGIN),
+                                  255, &bmp);
+        if (rc != TTF_OK) {
+            slot->valid = 0;
+            return rc;
+        }
+
+        slot->valid = 1;
+        slot->font = font;
+        slot->codepoint = codepoint;
+        slot->size_px = size_px;
+        slot->width = TTF_CACHE_BITMAP_DIM;
+        slot->height = TTF_CACHE_BITMAP_DIM;
+        slot->hits = 0;
+    }
+
+    out->pixels = slot->pixels;
+    out->width = slot->width;
+    out->height = slot->height;
+    if (was_hit) *was_hit = 0;
+    return TTF_OK;
+}
+
 /* ===========================================================================
 * 4.3.7b — font data ingestion (capsule-backed, zero-copy)
 * ===========================================================================