ebiten: add FilterPixelated

Closes #2826

Author: hajimehoshi

examples/filter/main.go

@@ -19,6 +19,7 @@ import (
 	"image"
 	_ "image/png"
 	"log"
+	"math"
 
 	"github.com/hajimehoshi/ebiten/v2"
 	"github.com/hajimehoshi/ebiten/v2/ebitenutil"
@@ -35,27 +36,40 @@ var (
 )
 
 type Game struct {
+	counter int
 }
 
 func (g *Game) Update() error {
+	g.counter++
 	return nil
 }
 
 func (g *Game) Draw(screen *ebiten.Image) {
-	ebitenutil.DebugPrint(screen, "Nearest Filter (default) VS Linear Filter")
+	scale := 2*math.Sin(float64(g.counter%360)*math.Pi/180) + 4
+
+	ebitenutil.DebugPrintAt(screen, "Nearest Filter (default) and Linear Filter", 16, 16)
 
 	op := &ebiten.DrawImageOptions{}
-	op.GeoM.Scale(4, 4)
+	op.GeoM.Scale(scale, scale)
 	op.GeoM.Translate(64, 64)
 	// By default, nearest filter is used.
 	screen.DrawImage(ebitenImage, op)
 
 	op = &ebiten.DrawImageOptions{}
-	op.GeoM.Scale(4, 4)
-	op.GeoM.Translate(64, 64+240)
+	op.GeoM.Scale(scale, scale)
+	op.GeoM.Translate(64+240, 64)
 	// Specify linear filter.
 	op.Filter = ebiten.FilterLinear
 	screen.DrawImage(ebitenImage, op)
+
+	ebitenutil.DebugPrintAt(screen, "Pixelated Filter", 16, 16+200)
+
+	op = &ebiten.DrawImageOptions{}
+	op.GeoM.Scale(scale, scale)
+	op.GeoM.Translate(64, 64+200)
+	// Specify pixelated filter.
+	op.Filter = ebiten.FilterPixelated
+	screen.DrawImage(ebitenImage, op)
 }
 
 func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {

gameforui.go

@@ -15,10 +15,8 @@
 package ebiten
 
 import (
-	"fmt"
 	"image"
 	"math"
-	"sync"
 	"sync/atomic"
 
 	"github.com/hajimehoshi/ebiten/v2/internal/atlas"
@@ -131,25 +129,12 @@ func (g *gameForUI) DrawFinalScreen(scale, offsetX, offsetY float64) {
 	DefaultDrawFinalScreen(g.screen, g.offscreen, geoM)
 }
 
-var (
-	theScreenShader     *Shader
-	theScreenShaderOnce sync.Once
-)
-
 // DefaultDrawFinalScreen is the default implementation of [FinalScreenDrawer.DrawFinalScreen],
 // used when a [Game] doesn't implement [FinalScreenDrawer].
 //
 // You can use DefaultDrawFinalScreen when you need the default implementation of [FinalScreenDrawer.DrawFinalScreen]
 // in your implementation of [FinalScreenDrawer], for example.
 func DefaultDrawFinalScreen(screen FinalScreen, offscreen *Image, geoM GeoM) {
-	theScreenShaderOnce.Do(func() {
-		s, err := newShader([]byte(builtinshader.ScreenShaderSource), "screen")
-		if err != nil {
-			panic(fmt.Sprintf("ebiten: compiling the screen shader failed: %v", err))
-		}
-		theScreenShader = s
-	})
-
 	scale := geoM.Element(0, 0)
 	switch {
 	case !screenFilterEnabled.Load(), math.Floor(scale) == scale:
@@ -166,6 +151,7 @@ func DefaultDrawFinalScreen(screen FinalScreen, offscreen *Image, geoM GeoM) {
 		op.Images[0] = offscreen
 		op.GeoM = geoM
 		w, h := offscreen.Bounds().Dx(), offscreen.Bounds().Dy()
-		screen.DrawRectShader(w, h, theScreenShader, op)
+		screenShader := builtinShader(builtinshader.FilterPixelated, builtinshader.AddressUnsafe, false)
+		screen.DrawRectShader(w, h, screenShader, op)
 	}
 }

graphics.go

@@ -28,6 +28,10 @@ const (
 
 	// FilterLinear represents linear filter
 	FilterLinear Filter = Filter(builtinshader.FilterLinear)
+
+	// FilterPixelated represents a pixelated filter.
+	// FilterPixelated is similar to FilterNearest, but it preserves the pixelated appearance even when scaled to non-integer sizes.
+	FilterPixelated Filter = Filter(builtinshader.FilterPixelated)
 )
 
 // GraphicsLibrary represents graphics libraries supported by the engine.