ebitenutil: improve the performance of DebugPrint

Updates #1880

ebitenutil/debugprint.go

@@ -49,15 +49,11 @@ func DebugPrint(image *ebiten.Image, str string) {
 //
 // The available runes are in U+0000 to U+00FF, which is C0 Controls and Basic Latin and C1 Controls and Latin-1 Supplement.
 func DebugPrintAt(image *ebiten.Image, str string, x, y int) {
-	drawDebugText(image, str, x+1, y+1, true)
+	drawDebugText(image, str, x, y)
-	drawDebugText(image, str, x, y, false)
 }
 
-func drawDebugText(rt *ebiten.Image, str string, ox, oy int, shadow bool) {
+func drawDebugText(rt *ebiten.Image, str string, ox, oy int) {
 	op := &ebiten.DrawImageOptions{}
-	if shadow {
-		op.ColorM.Scale(0, 0, 0, 0.5)
-	}
 	x := 0
 	y := 0
 	w, _ := debugPrintTextImage.Size()

ebitenutil/gen.go

@@ -54,17 +54,26 @@ func run() error {
 		lines = append(lines, line)
 	}
 
+	dst := image.NewRGBA(image.Rect(0, 0, charWidth*32+1, lineHeight*8+1))
+	for i, clr := range []color.Color{color.RGBA{0, 0, 0, 0x80}, color.White} {
+		var offsetX int
+		var offsetY int
+		if i == 0 {
+			offsetX = 1
+			offsetY = 1
+		}
 		d := font.Drawer{
-		Dst:  image.NewRGBA(image.Rect(0, 0, charWidth*32, lineHeight*8)),
+			Dst:  dst,
-		Src:  image.NewUniform(color.White),
+			Src:  image.NewUniform(clr),
 			Face: bitmapfont.Face,
-		Dot:  fixed.P(dotX, dotY),
+			Dot:  fixed.P(dotX+offsetX, dotY+offsetY),
 		}
 		for _, line := range lines {
-		d.Dot.X = fixed.I(dotX)
+			d.Dot.X = fixed.I(dotX + offsetX)
 			d.DrawString(line)
 			d.Dot.Y += fixed.I(lineHeight)
 		}
+	}
 
 	f, err := os.Create("text.png")
 	if err != nil {
@@ -72,7 +81,7 @@ func run() error {
 	}
 	defer f.Close()
 
-	if err := png.Encode(f, d.Dst); err != nil {
+	if err := png.Encode(f, dst); err != nil {
 		return err
 	}