diff --git a/examples/community/scrolling-background/README.md b/examples/community/scrolling-background/README.md new file mode 100644 index 0000000..5347004 --- /dev/null +++ b/examples/community/scrolling-background/README.md @@ -0,0 +1,5 @@ +# Infinite scrolling background demo + +Created by [Sergio Vera](https://github.com/svera) + +This example shows how to implement an infinite side scrolling background. diff --git a/examples/community/scrolling-background/gamebackground.jpg b/examples/community/scrolling-background/gamebackground.jpg new file mode 100644 index 0000000..050632d Binary files /dev/null and b/examples/community/scrolling-background/gamebackground.jpg differ diff --git a/examples/community/scrolling-background/main.go b/examples/community/scrolling-background/main.go new file mode 100644 index 0000000..b606b2f --- /dev/null +++ b/examples/community/scrolling-background/main.go @@ -0,0 +1,83 @@ +package main + +import ( + "image" + "os" + "time" + + _ "image/jpeg" + + "github.com/faiface/pixel" + "github.com/faiface/pixel/pixelgl" +) + +func loadPicture(path string) (pixel.Picture, error) { + file, err := os.Open(path) + if err != nil { + return nil, err + } + defer file.Close() + img, _, err := image.Decode(file) + if err != nil { + return nil, err + } + return pixel.PictureDataFromImage(img), nil +} + +const ( + windowWidth = 600 + windowHeight = 450 + // This is the scrolling speed + linesPerSecond = 60 +) + +func run() { + cfg := pixelgl.WindowConfig{ + Title: "Scrolling background demo", + Bounds: pixel.R(0, 0, windowWidth, windowHeight), + VSync: true, + } + win, err := pixelgl.NewWindow(cfg) + if err != nil { + panic(err) + } + + // Pic must have double the width of the window, as it will scroll to the left + pic, err := loadPicture("gamebackground.jpg") + if err != nil { + panic(err) + } + + // Backgrounds are made taking the left and right halves of the image + background1 := pixel.NewSprite(pic, pixel.R(0, 0, windowWidth, windowHeight)) + background2 := pixel.NewSprite(pic, pixel.R(windowWidth, 0, windowWidth*2, windowHeight)) + + // In the beginning, vector1 will put background1 filling the whole window, while vector2 will + // put background2 just at the right side of the window, out of view + vector1 := pixel.V(windowWidth/2, (windowHeight/2)+1) + vector2 := pixel.V(windowWidth+(windowWidth/2), (windowHeight/2)+1) + + i := float64(0) + last := time.Now() + for !win.Closed() { + dt := time.Since(last).Seconds() + last = time.Now() + // When one of the backgrounds has completely scrolled, we swap displacement vectors, + // so the backgrounds will swap positions too regarding the previous iteration, + // thus making the background endless. + if i <= -windowWidth { + i = 0 + vector1, vector2 = vector2, vector1 + } + // This delta vector will move the backgrounds to the left + d := pixel.V(-i, 0) + background1.Draw(win, pixel.IM.Moved(vector1.Sub(d))) + background2.Draw(win, pixel.IM.Moved(vector2.Sub(d))) + i -= linesPerSecond * dt + win.Update() + } +} + +func main() { + pixelgl.Run(run) +}