text/v2: add an example for font variations

Updates #2454

examples/fontvariation/LICENSE.md

@@ -0,0 +1,5 @@
+# `RobotoFlex.ttf`
+
+Open Font License 1.1
+
+https://github.com/googlefonts/roboto-flex/blob/main/OFL.txt

examples/fontvariation/main.go

@@ -0,0 +1,151 @@
+// 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 RobotoFlex.ttf
+var robotoFlexRegular []byte
+
+var robotoFlexFaceSource *text.GoTextFaceSource
+
+func init() {
+	s, err := text.NewGoTextFaceSource(bytes.NewReader(robotoFlexRegular))
+	if err != nil {
+		log.Fatal(err)
+	}
+	robotoFlexFaceSource = s
+}
+
+type Game struct {
+	// wght represents 'Weight'.
+	// https://learn.microsoft.com/en-us/typography/opentype/spec/dvaraxistag_wght
+	wght float32
+
+	// wdth represents 'Width'.
+	// https://learn.microsoft.com/en-us/typography/opentype/spec/dvaraxistag_wdth
+	wdth float32
+
+	// slnt represents 'Slant'.
+	// https://learn.microsoft.com/en-us/typography/opentype/spec/dvaraxistag_slnt
+	slnt float32
+}
+
+func NewGame() *Game {
+	return &Game{
+		wght: 400,
+		wdth: 100,
+		slnt: 0,
+	}
+}
+
+const (
+	minWght = 100
+	maxWght = 1000
+	minWdth = 30
+	maxWdth = 150
+	minSlnt = -10
+	maxSlnt = 0
+)
+
+func (g *Game) Update() error {
+	if inpututil.IsKeyJustPressed(ebiten.KeyQ) {
+		if g.wght > minWght {
+			g.wght -= 100
+		}
+	}
+	if inpututil.IsKeyJustPressed(ebiten.KeyW) {
+		if g.wght < maxWght {
+			g.wght += 100
+		}
+	}
+	if inpututil.IsKeyJustPressed(ebiten.KeyA) {
+		if g.wdth > minWdth {
+			g.wdth -= 10
+		}
+	}
+	if inpututil.IsKeyJustPressed(ebiten.KeyS) {
+		if g.wdth < maxWdth {
+			g.wdth += 10
+		}
+	}
+	if inpututil.IsKeyJustPressed(ebiten.KeyZ) {
+		if g.slnt > minSlnt {
+			g.slnt -= 1
+		}
+	}
+	if inpututil.IsKeyJustPressed(ebiten.KeyX) {
+		if g.slnt < maxSlnt {
+			g.slnt += 1
+		}
+	}
+	return nil
+}
+
+func (g *Game) Draw(screen *ebiten.Image) {
+	// Draw the instruction.
+	inst := fmt.Sprintf(`Press keys to adjust font variations.
+[Q, W]: wght (Weight): %0.0f [%d-%d]
+[A, S]: wdth (Width): %0.0f [%d-%d]
+[Z, X]: slnt (Slant): %0.0f [%d-%d]`, g.wght, minWght, maxWght, g.wdth, minWdth, maxWdth, g.slnt, minSlnt, maxSlnt)
+	op := &text.DrawOptions{}
+	op.GeoM.Translate(20, 20)
+	op.LineSpacingInPixels = 30
+	text.Draw(screen, inst, &text.GoTextFace{
+		Source: robotoFlexFaceSource,
+		Size:   20,
+	}, op)
+
+	// Draw the sample text.
+	const sampleText = `The quick brown fox jumps
+over the lazy dog.`
+	op = &text.DrawOptions{}
+	op.GeoM.Translate(20, screenHeight/2)
+	op.LineSpacingInPixels = 50
+	f := &text.GoTextFace{
+		Source: robotoFlexFaceSource,
+		Size:   40,
+	}
+	f.SetVariation(text.MustParseTag("wght"), g.wght)
+	f.SetVariation(text.MustParseTag("wdth"), g.wdth)
+	f.SetVariation(text.MustParseTag("slnt"), g.slnt)
+	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 Variation (Ebitengine Demo)")
+	if err := ebiten.RunGame(NewGame()); err != nil {
+		log.Fatal(err)
+	}
+}