108 lines
3.0 KiB
Go
108 lines
3.0 KiB
Go
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package main
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import (
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"image"
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"os"
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"time"
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_ "image/png"
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"github.com/faiface/pixel"
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"github.com/faiface/pixel/pixelgl"
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)
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func loadPicture(path string) (pixel.Picture, error) {
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file, err := os.Open(path)
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if err != nil {
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return nil, err
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}
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defer file.Close()
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img, _, err := image.Decode(file)
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if err != nil {
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return nil, err
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}
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return pixel.PictureDataFromImage(img), nil
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}
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const (
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windowWidth = 600
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windowHeight = 450
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foregroundHeight = 149
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// This is the scrolling speed (pixels per second)
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backgroundSpeed = 60
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foregroundSpeed = 120
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)
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type scrollingBackground struct {
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Pic pixel.Picture
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speed int
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}
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func run() {
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cfg := pixelgl.WindowConfig{
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Title: "Scrolling background demo",
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Bounds: pixel.R(0, 0, windowWidth, windowHeight),
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VSync: true,
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}
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win, err := pixelgl.NewWindow(cfg)
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if err != nil {
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panic(err)
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}
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// Pic must have double the width of the window, as it will scroll to the left
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picBackground, err := loadPicture("background.png")
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if err != nil {
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panic(err)
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}
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picForeground, err := loadPicture("foreground.png")
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if err != nil {
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panic(err)
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}
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// Backgrounds are made taking the left and right halves of the image
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background1 := pixel.NewSprite(picBackground, pixel.R(0, 0, windowWidth, windowHeight))
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background2 := pixel.NewSprite(picBackground, pixel.R(windowWidth, 0, windowWidth*2, windowHeight))
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foreground1 := pixel.NewSprite(picForeground, pixel.R(0, 0, windowWidth, foregroundHeight))
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foreground2 := pixel.NewSprite(picForeground, pixel.R(windowWidth, 0, windowWidth*2, foregroundHeight))
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// In the beginning, vector1 will put background1 filling the whole window, while vector2 will
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// put background2 just at the right side of the window, out of view
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backgroundVector1 := pixel.V(windowWidth/2, (windowHeight/2)+1)
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backgroundVector2 := pixel.V(windowWidth+(windowWidth/2), (windowHeight/2)+1)
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foregroundVector1 := pixel.V(windowWidth/2, (foregroundHeight/2)+1)
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foregroundVector2 := pixel.V(windowWidth+(windowWidth/2), (foregroundHeight/2)+1)
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bi, fi := 0., 0.
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last := time.Now()
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for !win.Closed() {
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dt := time.Since(last).Seconds()
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last = time.Now()
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// When one of the backgrounds has completely scrolled, we swap displacement vectors,
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// so the backgrounds will swap positions too regarding the previous iteration,
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// thus making the background endless.
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if bi <= -windowWidth {
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bi = 0
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backgroundVector1, backgroundVector2 = backgroundVector2, backgroundVector1
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}
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if fi <= -windowWidth {
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fi = 0
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foregroundVector1, foregroundVector2 = foregroundVector2, foregroundVector1
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}
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// This delta vector will move the backgrounds to the left
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db := pixel.V(-bi, 0)
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df := pixel.V(-fi, 0)
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background1.Draw(win, pixel.IM.Moved(backgroundVector1.Sub(db)))
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background2.Draw(win, pixel.IM.Moved(backgroundVector2.Sub(db)))
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foreground1.Draw(win, pixel.IM.Moved(foregroundVector1.Sub(df)))
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foreground2.Draw(win, pixel.IM.Moved(foregroundVector2.Sub(df)))
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bi -= backgroundSpeed * dt
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fi -= foregroundSpeed * dt
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win.Update()
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}
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}
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func main() {
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pixelgl.Run(run)
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}
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