text: Cache GlyphAdvance result

text/advance.go

@@ -0,0 +1,38 @@
+// Copyright 2018 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package text
+
+import (
+	"golang.org/x/image/font"
+	"golang.org/x/image/math/fixed"
+)
+
+var glyphAdvanceCache = map[font.Face]map[rune]fixed.Int26_6{}
+
+func glyphAdvance(face font.Face, r rune) fixed.Int26_6 {
+	m, ok := glyphAdvanceCache[face]
+	if !ok {
+		m = map[rune]fixed.Int26_6{}
+		glyphAdvanceCache[face] = m
+	}
+
+	a, ok := m[r]
+	if !ok {
+		a, _ = face.GlyphAdvance(r)
+		m[r] = a
+	}
+
+	return a
+}

text/text.go

@@ -352,8 +352,7 @@ func Draw(dst *ebiten.Image, text string, face font.Face, x, y int, clr color.Co
 			if !g.char.empty() {
 				g.draw(dst, fx, fixed.I(y), clr)
 			}
-			a, _ := face.GlyphAdvance(c)
-			fx += a
+			fx += glyphAdvance(fa, c)
 		}
 		prevC = c
 	}