Speed up: avoid allocating

example/blocks/blocks/font.go

@@ -15,12 +15,12 @@
 package blocks
 
 import (
+	"errors"
 	"github.com/hajimehoshi/ebiten"
 	"github.com/hajimehoshi/ebiten/ebitenutil"
 	"image"
 	"image/color"
 	"math"
-	"strings"
 )
 
 var imageFont *ebiten.Image
@@ -41,11 +41,15 @@ func textWidth(str string) int {
 	return charWidth * len(str)
 }
 
+var fontImageParts = make([]ebiten.ImagePart, 0, 256)
+
 func drawText(rt *ebiten.Image, str string, ox, oy, scale int, c color.Color) error {
-	parts := make([]ebiten.ImagePart, len(strings.Replace(str, "\n", "", -1)))
+	if cap(fontImageParts) < len(str) {
+		return errors.New("str is too long")
+	}
+	parts := fontImageParts[:0]
 
 	locationX, locationY := 0, 0
-	i := 0
 	for _, c := range str {
 		if c == '\n' {
 			locationX = 0
@@ -55,9 +59,10 @@ func drawText(rt *ebiten.Image, str string, ox, oy, scale int, c color.Color) er
 		code := int(c)
 		x := (code % 16) * charWidth
 		y := ((code - 32) / 16) * charHeight
-		parts[i].Dst = image.Rect(locationX, locationY, locationX+charWidth, locationY+charHeight)
-		parts[i].Src = image.Rect(x, y, x+charWidth, y+charHeight)
-		i++
+		parts = append(parts, ebiten.ImagePart{
+			Dst: image.Rect(locationX, locationY, locationX+charWidth, locationY+charHeight),
+			Src: image.Rect(x, y, x+charWidth, y+charHeight),
+		})
 		locationX += charWidth
 	}
 

example/blocks/blocks/piece.go

@@ -143,17 +143,10 @@ const blockHeight = 10
 const fieldBlockNumX = 10
 const fieldBlockNumY = 20
 
+var blocksImageParts = make([]ebiten.ImagePart, 0, fieldBlockNumX*fieldBlockNumY)
+
 func drawBlocks(r *ebiten.Image, blocks [][]BlockType, x, y int, clr ebiten.ColorM) error {
-	l := 0
-	for _, blockCol := range blocks {
-		for _, block := range blockCol {
-			if block == BlockTypeNone {
-				continue
-			}
-			l++
-		}
-	}
-	parts := make([]ebiten.ImagePart, 0, l)
+	parts := blocksImageParts[:0]
 	for i, blockCol := range blocks {
 		for j, block := range blockCol {
 			if block == BlockTypeNone {

example/blocks/blocks/titlescene.go

@@ -33,10 +33,14 @@ func init() {
 
 type TitleScene struct {
 	count int
+	parts []ebiten.ImagePart
 }
 
 func NewTitleScene() *TitleScene {
-	return &TitleScene{}
+	w, h := imageBackground.Size()
+	return &TitleScene{
+		parts: make([]ebiten.ImagePart, (ScreenHeight/h+2)*(ScreenWidth/w+2)),
+	}
 }
 
 func (s *TitleScene) Update(state *GameState) error {
@@ -48,7 +52,7 @@ func (s *TitleScene) Update(state *GameState) error {
 }
 
 func (s *TitleScene) Draw(r *ebiten.Image) error {
-	if err := drawTitleBackground(r, s.count); err != nil {
+	if err := s.drawTitleBackground(r, s.count); err != nil {
 		return err
 	}
 	if err := drawLogo(r, "BLOCKS"); err != nil {
@@ -61,25 +65,24 @@ func (s *TitleScene) Draw(r *ebiten.Image) error {
 	return drawTextWithShadow(r, message, x, y, 1, color.NRGBA{0x80, 0, 0, 0xff})
 }
 
-func drawTitleBackground(r *ebiten.Image, c int) error {
+func (s *TitleScene) drawTitleBackground(r *ebiten.Image, c int) error {
 	w, h := imageBackground.Size()
 	dx := (-c / 4) % w
 	dy := (c / 4) % h
 
-	parts := []ebiten.ImagePart{}
+	index := 0
 	for j := -1; j < ScreenHeight/h+1; j++ {
 		for i := 0; i < ScreenWidth/w+1; i++ {
 			dstX := i*w + dx
 			dstY := j*h + dy
-			parts = append(parts, ebiten.ImagePart{
-				Dst: image.Rect(dstX, dstY, dstX+w, dstY+h),
-				Src: image.Rect(0, 0, w, h),
-			})
+			s.parts[index].Dst = image.Rect(dstX, dstY, dstX+w, dstY+h)
+			s.parts[index].Src = image.Rect(0, 0, w, h)
+			index++
 		}
 	}
 
 	return r.DrawImage(imageBackground, &ebiten.DrawImageOptions{
-		Parts: parts,
+		Parts: s.parts,
 	})
 }