examples/infinitescroll: Refactoring

examples/infinitescroll/main.go

@@ -20,7 +20,6 @@ import (
 	"fmt"
 	_ "image/png"
 	"log"
-	"math"
 
 	"github.com/hajimehoshi/ebiten"
 	"github.com/hajimehoshi/ebiten/ebitenutil"
@@ -32,10 +31,19 @@ const (
 )
 
 var (
-	theViewport     = &viewport{}
-	bgImage         *ebiten.Image
-	repeatedBgImage *ebiten.Image
-	groundImage     *ebiten.Image
+	bgImage *ebiten.Image
+)
+
+func init() {
+	var err error
+	bgImage, _, err = ebitenutil.NewImageFromFile(ebitenutil.JoinStringsIntoFilePath("_resources", "images", "tile.png"), ebiten.FilterNearest)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+var (
+	theViewport = &viewport{}
 )
 
 type viewport struct {
@@ -43,80 +51,48 @@ type viewport struct {
 	y16 int
 }
 
-func round(x float64) float64 {
-	return math.Floor(x + 0.5)
-}
-
 func (p *viewport) Move() {
 	w, h := bgImage.Size()
-	mx := w * 16
-	my := h * 16
+	maxX16 := w * 16
+	maxY16 := h * 16
 
 	p.x16 += w / 32
 	p.y16 += h / 32
-
-	for mx <= p.x16 {
-		p.x16 -= mx
-	}
-	for my <= p.y16 {
-		p.y16 -= my
-	}
-	for p.x16 < 0 {
-		p.x16 += mx
-	}
-	for p.y16 < 0 {
-		p.y16 += my
-	}
+	p.x16 %= maxX16
+	p.y16 %= maxY16
 }
 
 func (p *viewport) Position() (int, int) {
 	return p.x16, p.y16
 }
 
-func updateGroundImage(ground *ebiten.Image) {
-	ground.Clear()
-	x16, y16 := theViewport.Position()
-	op := &ebiten.DrawImageOptions{}
-	op.GeoM.Translate(float64(-x16)/16, float64(-y16)/16)
-	ground.DrawImage(repeatedBgImage, op)
-}
-
-func drawGroundImage(screen *ebiten.Image, ground *ebiten.Image) {
-	op := &ebiten.DrawImageOptions{}
-	screen.DrawImage(ground, op)
-}
-
 func update(screen *ebiten.Image) error {
 	theViewport.Move()
+
 	if ebiten.IsRunningSlowly() {
 		return nil
 	}
-	updateGroundImage(groundImage)
-	drawGroundImage(screen, groundImage)
 
-	msg := fmt.Sprintf("FPS: %0.2f", ebiten.CurrentFPS())
-	ebitenutil.DebugPrint(screen, msg)
-	return nil
-}
+	x16, y16 := theViewport.Position()
+	offsetX, offsetY := float64(-x16)/16, float64(-y16)/16
 
-func main() {
-	var err error
-	bgImage, _, err = ebitenutil.NewImageFromFile(ebitenutil.JoinStringsIntoFilePath("_resources", "images", "tile.png"), ebiten.FilterNearest)
-	if err != nil {
-		log.Fatal(err)
-	}
+	// Draw bgImage on the screen repeatedly.
+	const repeat = 3
 	w, h := bgImage.Size()
-	const repeat = 5
-	repeatedBgImage, _ = ebiten.NewImage(w*repeat, h*repeat, ebiten.FilterNearest)
 	for j := 0; j < repeat; j++ {
 		for i := 0; i < repeat; i++ {
 			op := &ebiten.DrawImageOptions{}
 			op.GeoM.Translate(float64(w*i), float64(h*j))
-			repeatedBgImage.DrawImage(bgImage, op)
+			op.GeoM.Translate(offsetX, offsetY)
+			screen.DrawImage(bgImage, op)
 		}
 	}
-	groundImage, _ = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterNearest)
 
+	ebitenutil.DebugPrint(screen, fmt.Sprintf("FPS: %0.2f", ebiten.CurrentFPS()))
+	return nil
+}
+
+func main() {
 	if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Infinite Scroll (Ebiten Demo)"); err != nil {
 		log.Fatal(err)
 	}