text/v2: add an example for font features

Updates #2454

examples/fontfeature/LICENSE.md

@@ -0,0 +1,5 @@
+# `FiraSans-Regular.ttf`
+
+Open Font License 1.1
+
+https://github.com/mozilla/Fira/blob/master/LICENSE

examples/fontfeature/main.go

@@ -0,0 +1,140 @@
+// 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 main
+
+import (
+	"bytes"
+	_ "embed"
+	"fmt"
+	"log"
+
+	"github.com/hajimehoshi/ebiten/v2"
+	"github.com/hajimehoshi/ebiten/v2/inpututil"
+	"github.com/hajimehoshi/ebiten/v2/text/v2"
+)
+
+const (
+	screenWidth  = 640
+	screenHeight = 480
+)
+
+//go:embed FiraSans-Regular.ttf
+var firaSansRegular []byte
+
+var firaSansFaceSource *text.GoTextFaceSource
+
+func init() {
+	s, err := text.NewGoTextFaceSource(bytes.NewReader(firaSansRegular))
+	if err != nil {
+		log.Fatal(err)
+	}
+	firaSansFaceSource = s
+}
+
+type Game struct {
+	// liga represents 'Standard Ligatures'.
+	// https://learn.microsoft.com/en-us/typography/opentype/spec/features_ko#tag-liga
+	liga uint32
+
+	// tnum represents 'Tabular Figures'.
+	// https://learn.microsoft.com/en-us/typography/opentype/spec/features_pt#tag-tnum
+	tnum uint32
+
+	// smcp represents 'Small Capitals'.
+	// https://learn.microsoft.com/en-us/typography/opentype/spec/features_pt#tag-smcp
+	smcp uint32
+
+	// zero represents 'Slashed Zero'.
+	// https://learn.microsoft.com/en-us/typography/opentype/spec/features_uz#tag-zero
+	zero uint32
+}
+
+func (g *Game) Update() error {
+	if inpututil.IsKeyJustPressed(ebiten.KeyL) {
+		if g.liga == 0 {
+			g.liga = 1
+		} else {
+			g.liga = 0
+		}
+	}
+	if inpututil.IsKeyJustPressed(ebiten.KeyT) {
+		if g.tnum == 0 {
+			g.tnum = 1
+		} else {
+			g.tnum = 0
+		}
+	}
+	if inpututil.IsKeyJustPressed(ebiten.KeyS) {
+		if g.smcp == 0 {
+			g.smcp = 1
+		} else {
+			g.smcp = 0
+		}
+	}
+	if inpututil.IsKeyJustPressed(ebiten.KeyZ) {
+		if g.zero == 0 {
+			g.zero = 1
+		} else {
+			g.zero = 0
+		}
+	}
+	return nil
+}
+
+func (g *Game) Draw(screen *ebiten.Image) {
+	// Draw the instruction.
+	inst := fmt.Sprintf(`Press keys to toggle font features.
+[L] 'liga' (Standard Ligatures) (%d)
+[T] 'tnum' (Tabular Figures) (%d)
+[S] 'smcp' (Small Capitals) (%d)
+[Z] 'zero' (Slashed Zero) `, g.liga, g.tnum, g.smcp)
+	op := &text.DrawOptions{}
+	op.GeoM.Translate(20, 20)
+	op.LineSpacingInPixels = 30
+	text.Draw(screen, inst, &text.GoTextFace{
+		Source: firaSansFaceSource,
+		Size:   20,
+	}, op)
+
+	// Draw the sample text.
+	const sampleText = `0 (number) / O (alphabet)
+ffi
+3.14
+2.71`
+	op = &text.DrawOptions{}
+	op.GeoM.Translate(20, screenHeight/2)
+	op.LineSpacingInPixels = 50
+	f := &text.GoTextFace{
+		Source: firaSansFaceSource,
+		Size:   40,
+	}
+	f.SetFeature(text.MustParseTag("liga"), g.liga)
+	f.SetFeature(text.MustParseTag("tnum"), g.tnum)
+	f.SetFeature(text.MustParseTag("smcp"), g.smcp)
+	f.SetFeature(text.MustParseTag("zero"), g.zero)
+	text.Draw(screen, sampleText, f, op)
+}
+
+func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
+	return screenWidth, screenHeight
+}
+
+func main() {
+	ebiten.SetWindowSize(screenWidth, screenHeight)
+	ebiten.SetWindowTitle("Font Feature (Ebitengine Demo)")
+	if err := ebiten.RunGame(&Game{}); err != nil {
+		log.Fatal(err)
+	}
+}