text/v2: add LimitedFace

Closes #2857

examples/mixedfont/main.go

@@ -57,19 +57,24 @@ type Game struct {
 
 func (g *Game) Update() error {
 	if g.face == nil {
-		g.face = text.NewMultiFace([]text.Face{
 		// goregular.TTF is used primarily. If a glyph is not found in this font, the second font is used.
-			&text.GoTextFace{
+		// Use text.LimitedFace to limit the glyphs.
+		en := text.NewLimitedFace(&text.GoTextFace{
 			Source: goRegularFaceSource,
 			Size:   24,
-			},
+		})
+		// Limit the glyphs for ASCII and Latin-1 characters for this face.
+		// This means that, for example, '…' (U+2026) is not rendered by this face.
+		en.AddUnicodeRange('\u0020', '\u00ff')
+
 		// M+ Font is the second font.
 		// Use a relatively big size to see different-sized faces are well mixed.
-			&text.GoTextFace{
+		ja := &text.GoTextFace{
 			Source: mplusFaceSource,
 			Size:   32,
-			},
-		})
+		}
+
+		g.face = text.NewMultiFace([]text.Face{en, ja})
 	}
 	return nil
 }
@@ -78,7 +83,7 @@ func (g *Game) Draw(screen *ebiten.Image) {
 	op := &text.DrawOptions{}
 	op.GeoM.Translate(20, 20)
 	op.LineSpacingInPixels = 48
-	text.Draw(screen, "HelloこんにちはWorld世界\n日本語とEnglish", g.face, op)
+	text.Draw(screen, "HelloこんにちはWorld世界\n日本語とEnglish…", g.face, op)
 }
 
 func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {

text/v2/limited.go

@@ -0,0 +1,112 @@
+// Copyright 2023 The Ebitengine 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 (
+	"github.com/hajimehoshi/ebiten/v2/vector"
+)
+
+var _ Face = (*LimitedFace)(nil)
+
+type LimitedFace struct {
+	face          Face
+	unicodeRanges unicodeRanges
+}
+
+// NewLimitedFace creates a new LimitedFace from the given face.
+// In the default state, glyphs for any runes are limited and not rendered.
+// You have to call AddUnicodeRange to add allowed glyphs.
+func NewLimitedFace(face Face) *LimitedFace {
+	return &LimitedFace{
+		face: face,
+	}
+}
+
+// AddUnicodeRange adds a rune range for rendered glyphs.
+// A range is inclusive, which means that a range contains the specified rune end.
+func (l *LimitedFace) AddUnicodeRange(start, end rune) {
+	l.unicodeRanges.add(start, end)
+}
+
+// Metrics implements Face.
+func (l *LimitedFace) Metrics() Metrics {
+	return l.face.Metrics()
+}
+
+// advance implements Face.
+func (l *LimitedFace) advance(text string) float64 {
+	return l.face.advance(l.unicodeRanges.filter(text))
+}
+
+// hasGlyph implements Face.
+func (l *LimitedFace) hasGlyph(r rune) bool {
+	return l.unicodeRanges.contains(r) && l.face.hasGlyph(r)
+}
+
+// appendGlyphsForLine implements Face.
+func (l *LimitedFace) appendGlyphsForLine(glyphs []Glyph, line string, indexOffset int, originX, originY float64) []Glyph {
+	return l.face.appendGlyphsForLine(glyphs, l.unicodeRanges.filter(line), indexOffset, originX, originY)
+}
+
+// appendVectorPathForLine implements Face.
+func (l *LimitedFace) appendVectorPathForLine(path *vector.Path, line string, originX, originY float64) {
+	l.face.appendVectorPathForLine(path, l.unicodeRanges.filter(line), originX, originY)
+}
+
+// direction implements Face.
+func (l *LimitedFace) direction() Direction {
+	return l.face.direction()
+}
+
+// private implements Face.
+func (l *LimitedFace) private() {
+}
+
+type unicodeRange struct {
+	start rune
+	end   rune
+}
+
+type unicodeRanges struct {
+	ranges []unicodeRange
+}
+
+func (u *unicodeRanges) add(start, end rune) {
+	u.ranges = append(u.ranges, unicodeRange{
+		start: start,
+		end:   end,
+	})
+}
+
+func (u *unicodeRanges) contains(r rune) bool {
+	for _, rg := range u.ranges {
+		if rg.start <= r && r <= rg.end {
+			return true
+		}
+	}
+	return false
+}
+
+func (u *unicodeRanges) filter(str string) string {
+	var rs []rune
+	for _, r := range str {
+		if !u.contains(r) {
+			// U+FFFD is "REPLACEMENT CHARACTER".
+			r = '\ufffd'
+		}
+		rs = append(rs, r)
+	}
+	return string(rs)
+}