[shaping] adjust default cache size (#221)

Author: benoitkugler

shaping/lru.go

@@ -5,6 +5,10 @@ import (
 	"github.com/go-text/typesetting/harfbuzz"
 )
 
+// adjust the cache size of the zero value, used by default
+// in [HarfbuzzShaper]
+const defaultFontCacheSize = 32
+
 // fontEntry holds a single key-value pair for an LRU cache.
 type fontEntry struct {
 	next, prev *fontEntry
@@ -21,7 +25,9 @@ type fontLRU struct {
 	// https://git.sr.ht/~eliasnaur/gio/tree/e768fe347a732056031100f2c66987d6db258ea4/item/text/lru.go
 	m          map[*font.Font]*fontEntry
 	head, tail *fontEntry
-	maxSize    int
+
+	// the actual cache size is [maxSizeOffset] + [defaultFontCacheSize]
+	maxSizeOffset int
 }
 
 // Get fetches the value associated with the given key, if any.
@@ -47,7 +53,7 @@ func (l *fontLRU) Put(k *font.Font, v *harfbuzz.Font) {
 	val := &fontEntry{key: k, v: v}
 	l.m[k] = val
 	l.insert(val)
-	if len(l.m) > l.maxSize {
+	if len(l.m) > (defaultFontCacheSize + l.maxSizeOffset) {
 		oldest := l.tail.next
 		l.remove(oldest)
 		delete(l.m, oldest.key)

shaping/shaping.go

@@ -24,7 +24,7 @@ type HarfbuzzShaper struct {
 // It is safe to adjust the size after using the shaper, though shrinking
 // it may result in many evictions on the next shaping.
 func (h *HarfbuzzShaper) SetFontCacheSize(size int) {
-	h.fonts.maxSize = size
+	h.fonts.maxSizeOffset = size - defaultFontCacheSize
 }
 
 var _ Shaper = (*HarfbuzzShaper)(nil)