text/v2: replace Rune and IndexInBytes with Start/EndIndexInBytes in Glyph

The relationships between runes and glyphs are n:m in general,
then Rune is not enough. Let Glyph have a range of a string.

Updates #2454

text/v2/layout.go

@@ -204,6 +204,7 @@ func appendGlyphs(glyphs []Glyph, text string, face Face, x, y float64, options
 		}
 	}
 
+	var indexOffset int
 	var originX, originY float64
 	var i int
 	for t := text; ; {
@@ -231,12 +232,13 @@ func appendGlyphs(glyphs []Glyph, text string, face Face, x, y float64, options
 			}
 		}
 
-		glyphs = face.appendGlyphs(glyphs, line, originX+offsetX+x, originY+offsetY+y)
+		glyphs = face.appendGlyphs(glyphs, line, indexOffset, originX+offsetX+x, originY+offsetY+y)
 
 		if !found {
 			break
 		}
 		t = rest
+		indexOffset += len(line) + 1
 		i++
 
 		// Advance the origin position in the secondary direction.

text/v2/std.go

@@ -18,6 +18,7 @@ import (
 	"image"
 	"runtime"
 	"sync/atomic"
+	"unicode/utf8"
 
 	"golang.org/x/image/font"
 	"golang.org/x/image/math/fixed"
@@ -92,7 +93,7 @@ func (s *StdFace) advance(text string) float64 {
 }
 
 // appendGlyphs implements Face.
-func (s *StdFace) appendGlyphs(glyphs []Glyph, text string, originX, originY float64) []Glyph {
+func (s *StdFace) appendGlyphs(glyphs []Glyph, text string, indexOffset int, originX, originY float64) []Glyph {
 	s.copyCheck()
 
 	origin := fixed.Point26_6{
@@ -109,9 +110,10 @@ func (s *StdFace) appendGlyphs(glyphs []Glyph, text string, originX, originY flo
 		if img != nil {
 			// Adjust the position to the integers.
 			// The current glyph images assume that they are rendered on integer positions so far.
+			_, size := utf8.DecodeRuneInString(text[i:])
 			glyphs = append(glyphs, Glyph{
-				Rune:         r,
+				StartIndexInBytes: indexOffset + i,
-				IndexInBytes: i,
+				EndIndexInBytes:   indexOffset + i + size,
 				Image:             img,
 				X:                 float64(imgX),
 				Y:                 float64(imgY),

text/v2/text.go

@@ -42,7 +42,7 @@ type Face interface {
 
 	advance(text string) float64
 
-	appendGlyphs(glyphs []Glyph, text string, originX, originY float64) []Glyph
+	appendGlyphs(glyphs []Glyph, text string, indexOffset int, originX, originY float64) []Glyph
 
 	direction() Direction
 
@@ -90,11 +90,14 @@ func adjustGranularity(x fixed.Int26_6) fixed.Int26_6 {
 
 // Glyph represents one glyph to render.
 type Glyph struct {
-	// Rune is a character for this glyph.
+	// StartIndexInBytes is the start index in bytes for the given string at AppendGlyphs.
-	Rune rune
+	StartIndexInBytes int
 
-	// IndexInBytes is an index in bytes for the given string at AppendGlyphs.
+	// EndIndexInBytes is the end index in bytes for the given string at AppendGlyphs.
-	IndexInBytes int
+	EndIndexInBytes int
+
+	// GID is an ID for a glyph of TrueType or OpenType font. GID is valid when the font is GoTextFont.
+	GID uint32
 
 	// Image is a rasterized glyph image.
 	// Image is a grayscale image i.e. RGBA values are the same.
@@ -110,9 +113,6 @@ type Glyph struct {
 	// The position is determined in a sequence of characters given at AppendGlyphs.
 	// The position's origin is the first character's origin position.
 	Y float64
-
-	// GID is an ID for a glyph of TrueType or OpenType font. GID is valid when the font is GoTextFont.
-	GID uint32
 }
 
 // Advance returns the advanced distance from the origin position when rendering the given text with the given face.

text/v2/text_test.go

@@ -0,0 +1,40 @@
+// 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_test
+
+import (
+	"regexp"
+	"strings"
+	"testing"
+
+	"github.com/hajimehoshi/bitmapfont/v3"
+
+	"github.com/hajimehoshi/ebiten/v2/text/v2"
+)
+
+func TestGlyphIndex(t *testing.T) {
+	const sampleText = `The quick brown fox jumps
+over the lazy dog.`
+
+	f := text.NewStdFace(bitmapfont.Face)
+	got := sampleText
+	for _, g := range text.AppendGlyphs(nil, sampleText, f, nil) {
+		got = got[:g.StartIndexInBytes] + strings.Repeat(" ", g.EndIndexInBytes-g.StartIndexInBytes) + got[g.EndIndexInBytes:]
+	}
+	want := regexp.MustCompile(`\S`).ReplaceAllString(sampleText, " ")
+	if got != want {
+		t.Errorf("got: %q, want: %q", got, want)
+	}
+}