examples/vector: add switching anti-alias

This change is a proof-of-concept of anti-alias with a pseudo MSAA
effect.

Updates #663

examples/vector/main.go

@@ -26,6 +26,7 @@ import (
 
 	"github.com/hajimehoshi/ebiten/v2"
 	"github.com/hajimehoshi/ebiten/v2/ebitenutil"
+	"github.com/hajimehoshi/ebiten/v2/inpututil"
 	"github.com/hajimehoshi/ebiten/v2/vector"
 )
 
@@ -46,7 +47,7 @@ const (
 	screenHeight = 480
 )
 
-func drawEbitenText(screen *ebiten.Image) {
+func drawEbitenText(screen *ebiten.Image, scale float32) {
 	var path vector.Path
 
 	// E
@@ -117,6 +118,8 @@ func drawEbitenText(screen *ebiten.Image) {
 	}
 	vs, is := path.AppendVerticesAndIndicesForFilling(nil, nil)
 	for i := range vs {
+		vs[i].DstX *= scale
+		vs[i].DstY *= scale
 		vs[i].SrcX = 1
 		vs[i].SrcY = 1
 		vs[i].ColorR = 0xdb / float32(0xff)
@@ -126,7 +129,7 @@ func drawEbitenText(screen *ebiten.Image) {
 	screen.DrawTriangles(vs, is, emptySubImage, op)
 }
 
-func drawEbitenLogo(screen *ebiten.Image, x, y int) {
+func drawEbitenLogo(screen *ebiten.Image, x, y int, scale float32) {
 	const unit = 16
 
 	var path vector.Path
@@ -157,6 +160,8 @@ func drawEbitenLogo(screen *ebiten.Image, x, y int) {
 	}
 	vs, is := path.AppendVerticesAndIndicesForFilling(nil, nil)
 	for i := range vs {
+		vs[i].DstX *= scale
+		vs[i].DstY *= scale
 		vs[i].SrcX = 1
 		vs[i].SrcY = 1
 		vs[i].ColorR = 0xdb / float32(0xff)
@@ -166,7 +171,7 @@ func drawEbitenLogo(screen *ebiten.Image, x, y int) {
 	screen.DrawTriangles(vs, is, emptySubImage, op)
 }
 
-func drawArc(screen *ebiten.Image, count int) {
+func drawArc(screen *ebiten.Image, count int, scale float32) {
 	var path vector.Path
 
 	path.MoveTo(350, 100)
@@ -185,6 +190,8 @@ func drawArc(screen *ebiten.Image, count int) {
 	}
 	vs, is := path.AppendVerticesAndIndicesForFilling(nil, nil)
 	for i := range vs {
+		vs[i].DstX *= scale
+		vs[i].DstY *= scale
 		vs[i].SrcX = 1
 		vs[i].SrcY = 1
 		vs[i].ColorR = 0x33 / float32(0xff)
@@ -198,7 +205,7 @@ func maxCounter(index int) int {
 	return 128 + (17*index+32)%64
 }
 
-func drawWave(screen *ebiten.Image, counter int) {
+func drawWave(screen *ebiten.Image, counter int, scale float32) {
 	var path vector.Path
 
 	const npoints = 8
@@ -228,6 +235,8 @@ func drawWave(screen *ebiten.Image, counter int) {
 	}
 	vs, is := path.AppendVerticesAndIndicesForFilling(nil, nil)
 	for i := range vs {
+		vs[i].DstX *= scale
+		vs[i].DstY *= scale
 		vs[i].SrcX = 1
 		vs[i].SrcY = 1
 		vs[i].ColorR = 0x33 / float32(0xff)
@@ -239,21 +248,57 @@ func drawWave(screen *ebiten.Image, counter int) {
 
 type Game struct {
 	counter int
+
+	aa        bool
+	offscreen *ebiten.Image
 }
 
 func (g *Game) Update() error {
 	g.counter++
+
+	// Switch anti-alias.
+	if inpututil.IsKeyJustPressed(ebiten.KeyA) {
+		g.aa = !g.aa
+	}
+
 	return nil
 }
 
 func (g *Game) Draw(screen *ebiten.Image) {
-	screen.Fill(color.White)
+	if g.offscreen != nil {
-	drawEbitenText(screen)
+		w, h := screen.Size()
-	drawEbitenLogo(screen, 20, 90)
+		if ow, oh := g.offscreen.Size(); ow != w || oh != h {
-	drawArc(screen, g.counter)
+			g.offscreen.Dispose()
-	drawWave(screen, g.counter)
+			g.offscreen = nil
+		}
+	}
+	if g.aa && g.offscreen == nil {
+		w, h := screen.Size()
+		g.offscreen = ebiten.NewImage(w*2, h*2)
+	}
 
-	ebitenutil.DebugPrint(screen, fmt.Sprintf("TPS: %0.2f\nFPS: %0.2f", ebiten.ActualTPS(), ebiten.ActualFPS()))
+	scale := float32(1)
+	dst := screen
+	if g.aa {
+		scale = 2
+		dst = g.offscreen
+	}
+
+	dst.Fill(color.White)
+	drawEbitenText(dst, scale)
+	drawEbitenLogo(dst, 20, 90, scale)
+	drawArc(dst, g.counter, scale)
+	drawWave(dst, g.counter, scale)
+
+	if g.aa {
+		op := &ebiten.DrawImageOptions{}
+		op.GeoM.Scale(0.5, 0.5)
+		op.Filter = ebiten.FilterLinear
+		screen.DrawImage(g.offscreen, op)
+	}
+
+	msg := fmt.Sprintf("TPS: %0.2f\nFPS: %0.2f\nPress A to switch anti-alias", ebiten.ActualTPS(), ebiten.ActualFPS())
+	ebitenutil.DebugPrint(screen, msg)
 }
 
 func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {