Add examples/particles

Fixes #826

examples/particles/main.go

@@ -0,0 +1,171 @@
+// Copyright 2019 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build example jsgo
+
+package main
+
+import (
+	"bytes"
+	"container/list"
+	"fmt"
+	"image"
+	"image/color"
+	_ "image/png"
+	"log"
+	"math"
+	"math/rand"
+	"time"
+
+	"github.com/hajimehoshi/ebiten"
+	"github.com/hajimehoshi/ebiten/ebitenutil"
+	"github.com/hajimehoshi/ebiten/examples/resources/images"
+)
+
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
+const (
+	screenWidth  = 640
+	screenHeight = 480
+)
+
+var smokeImage *ebiten.Image
+
+func init() {
+	// Decode image from a byte slice instead of a file so that
+	// this example works in any working directory.
+	// If you want to use a file, there are some options:
+	// 1) Use os.Open and pass the file to the image decoder.
+	//    This is a very regular way, but doesn't work on browsers.
+	// 2) Use ebitenutil.OpenFile and pass the file to the image decoder.
+	//    This works even on browsers.
+	// 3) Use ebitenutil.NewImageFromFile to create an ebiten.Image directly from a file.
+	//    This also works on browsers.
+	img, _, err := image.Decode(bytes.NewReader(images.Smoke_png))
+	if err != nil {
+		log.Fatal(err)
+	}
+	smokeImage, _ = ebiten.NewImageFromImage(img, ebiten.FilterDefault)
+}
+
+type sprite struct {
+	count    int
+	maxCount int
+	angle    float64
+
+	img   *ebiten.Image
+	scale float64
+	alpha float64
+}
+
+func (s *sprite) update() {
+	if s.count == 0 {
+		return
+	}
+	s.count--
+}
+
+func (s *sprite) terminated() bool {
+	return s.count == 0
+}
+
+func (s *sprite) draw(screen *ebiten.Image) {
+	if s.count == 0 {
+		return
+	}
+
+	const (
+		ox = screenWidth / 2
+		oy = screenHeight / 2
+	)
+	x := math.Cos(s.angle) * float64(s.maxCount-s.count)
+	y := math.Sin(s.angle) * float64(s.maxCount-s.count)
+
+	op := &ebiten.DrawImageOptions{}
+
+	sx, sy := s.img.Size()
+	op.GeoM.Translate(-float64(sx)/2, -float64(sy)/2)
+	op.GeoM.Scale(s.scale, s.scale)
+	op.GeoM.Translate(x, y)
+	op.GeoM.Translate(ox, oy)
+
+	rate := float64(s.count) / float64(s.maxCount)
+	alpha := 0.0
+	if rate < 0.2 {
+		alpha = rate / 0.2
+	} else if rate > 0.8 {
+		alpha = (1 - rate) / 0.2
+	} else {
+		alpha = 1
+	}
+	alpha *= s.alpha
+	op.ColorM.Scale(1, 1, 1, alpha)
+
+	op.Filter = ebiten.FilterLinear
+
+	screen.DrawImage(s.img, op)
+}
+
+func newSprite(img *ebiten.Image) *sprite {
+	c := rand.Intn(50) + 300
+	a := rand.Float64() * 2 * math.Pi
+	s := rand.Float64()*0.1 + 0.4
+	return &sprite{
+		img: img,
+
+		maxCount: c,
+		count:    c,
+		angle:    a,
+		scale:    s,
+		alpha:    0.5,
+	}
+}
+
+var sprites = list.New()
+
+func update(screen *ebiten.Image) error {
+	if sprites.Len() < 500 {
+		// Emit
+		sprites.PushBack(newSprite(smokeImage))
+	}
+
+	for e := sprites.Front(); e != nil; e = e.Next() {
+		s := e.Value.(*sprite)
+		s.update()
+		if s.terminated() {
+			defer sprites.Remove(e)
+		}
+	}
+
+	if ebiten.IsDrawingSkipped() {
+		return nil
+	}
+
+	screen.Fill(color.RGBA{0x99, 0xcc, 0xff, 0xff})
+	for e := sprites.Front(); e != nil; e = e.Next() {
+		s := e.Value.(*sprite)
+		s.draw(screen)
+	}
+
+	ebitenutil.DebugPrint(screen, fmt.Sprintf("TPS: %0.2f\nSprites: %d", ebiten.CurrentTPS(), sprites.Len()))
+	return nil
+}
+
+func main() {
+	if err := ebiten.Run(update, screenWidth, screenHeight, 1, "Particles (Ebiten demo)"); err != nil {
+		log.Fatal(err)
+	}
+}

examples/resources/generate.go

@@ -21,6 +21,7 @@
 //go:generate file2byteslice -package=images -input=./images/ebiten.png -output=./images/ebiten.go -var=Ebiten_png
 //go:generate file2byteslice -package=images -input=./images/fiveyears.jpg -output=./images/fiveyears.go -var=FiveYears_jpg
 //go:generate file2byteslice -package=images -input=./images/gophers.jpg -output=./images/gophers.go -var=Gophers_jpg
+//go:generate file2byteslice -package=images -input=./images/smoke.png -output=./images/smoke.go -var=Smoke_png
 //go:generate file2byteslice -package=images -input=./images/tile.png -output=./images/tile.go -var=Tile_png
 //go:generate file2byteslice -package=images -input=./images/runner.png -output=./images/runner.go -var=Runner_png
 //go:generate file2byteslice -package=images -input=./images/tiles.png -output=./images/tiles.go -var=Tiles_png

examples/resources/images/license.md

@@ -31,6 +31,14 @@ https://opengameart.org/content/runner-character
 CC0 1.0
 ```
 
+## smoke.png
+
+```
+https://opengameart.org/content/smoke-particle-assets
+
+CC0 1.0
+```
+
 ## tile.png
 
 ```