ebiten/examples/particles/main.go

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// 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
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dir float64
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img *ebiten.Image
scale float64
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angle float64
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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
)
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x := math.Cos(s.dir) * float64(s.maxCount-s.count)
y := math.Sin(s.dir) * float64(s.maxCount-s.count)
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op := &ebiten.DrawImageOptions{}
sx, sy := s.img.Size()
op.GeoM.Translate(-float64(sx)/2, -float64(sy)/2)
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op.GeoM.Rotate(s.angle)
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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)
screen.DrawImage(s.img, op)
}
func newSprite(img *ebiten.Image) *sprite {
c := rand.Intn(50) + 300
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dir := rand.Float64() * 2 * math.Pi
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a := rand.Float64() * 2 * math.Pi
s := rand.Float64()*0.1 + 0.4
return &sprite{
img: img,
maxCount: c,
count: c,
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dir: dir,
angle: a,
scale: s,
alpha: 0.5,
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}
}
var sprites = list.New()
func update(screen *ebiten.Image) error {
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if sprites.Len() < 500 && rand.Intn(4) < 3 {
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// 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)
}
}