ebiten/examples/stars/main.go

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// Copyright 2021 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.
//go:build example
// +build example
package main
import (
"image/color"
"log"
"math/rand"
"time"
"github.com/hajimehoshi/ebiten/v2"
"github.com/hajimehoshi/ebiten/v2/ebitenutil"
)
const (
screenWidth = 640
screenHeight = 480
scale = 64
starsNum = 1024
)
func abs(a int) int {
if a < 0 {
return -a
}
return a
}
type Star struct {
fromx, fromy, tox, toy, brightness float64
}
func (s *Star) Init() {
s.tox = rand.Float64() * screenWidth * scale
s.fromx = s.tox
s.toy = rand.Float64() * screenHeight * scale
s.fromy = s.toy
s.brightness = rand.Float64() * 0xff
}
func (s *Star) Update(x, y float64) {
s.fromx = s.tox
s.fromy = s.toy
s.tox += (s.tox - x) / 32
s.toy += (s.toy - y) / 32
s.brightness += 1
if 0xff < s.brightness {
s.brightness = 0xff
}
if s.fromx < 0 || screenWidth*scale < s.fromx || s.fromy < 0 || screenHeight*scale < s.fromy {
s.Init()
}
}
func (s *Star) Draw(screen *ebiten.Image) {
color := color.RGBA{uint8(0xbb * s.brightness / 0xff),
uint8(0xdd * s.brightness / 0xff),
uint8(0xff * s.brightness / 0xff),
0xff}
ebitenutil.DrawLine(screen, s.fromx/scale, s.fromy/scale, s.tox/scale, s.toy/scale, color)
}
type Game struct {
stars [starsNum]Star
}
func NewGame() *Game {
g := &Game{}
for i := 0; i < starsNum; i++ {
g.stars[i].Init()
}
return g
}
func (g *Game) Update() error {
x, y := ebiten.CursorPosition()
for i := 0; i < starsNum; i++ {
g.stars[i].Update(float64(x*scale), float64(y*scale))
}
return nil
}
func (g *Game) Draw(screen *ebiten.Image) {
for i := 0; i < starsNum; i++ {
g.stars[i].Draw(screen)
}
}
func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
return screenWidth, screenHeight
}
func main() {
rand.Seed(time.Now().UnixNano())
ebiten.SetWindowSize(screenWidth*2, screenHeight*2)
ebiten.SetWindowTitle("Stars (Ebiten Demo)")
if err := ebiten.RunGame(NewGame()); err != nil {
log.Fatal(err)
}
}