Ebiten example - perspective

// +build example

package main

import (
        "image"
        _ "image/jpeg"
        "log"

        "github.com/hajimehoshi/ebiten"
        "github.com/hajimehoshi/ebiten/ebitenutil"
)

const (
        screenWidth  = 320
        screenHeight = 240
)

var (
        gophersImage *ebiten.Image
)

func update(screen *ebiten.Image) error {
        if ebiten.IsRunningSlowly() {
                return nil
        }
        op := &ebiten.DrawImageOptions{}
        w, h := gophersImage.Size()
        for i := 0; i < h; i++ {
                op.GeoM.Reset()
                width := w + i*3/4
                x := ((h - i) * 3 / 4) / 2
                op.GeoM.Scale(float64(width)/float64(w), 1)
                op.GeoM.Translate(float64(x), float64(i))
                maxWidth := float64(w) + float64(h)*3/4
                op.GeoM.Translate(-maxWidth/2, -float64(h)/2)
                op.GeoM.Translate(screenWidth/2, screenHeight/2)
                r := image.Rect(0, i, w, i+1)
                op.SourceRect = &r
                screen.DrawImage(gophersImage, op)
        }
        return nil
}

func main() {
        var err error
        gophersImage, _, err = ebitenutil.NewImageFromFile("_resources/images/gophers.jpg", ebiten.FilterNearest)
        if err != nil {
                log.Fatal(err)
        }
        if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Perspective (Ebiten Demo)"); err != nil {
                log.Fatal(err)
        }
}