Ebiten example - rotate

package main

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

    "github.com/hajimehoshi/ebiten"
    "github.com/hajimehoshi/ebiten/examples/common"
)

const (
    screenWidth  = 320
    screenHeight = 240
)

var (
    count        int
    gophersImage *ebiten.Image
)

func update(screen *ebiten.Image) error {
    count++
    w, h := gophersImage.Size()
    op := &ebiten.DrawImageOptions{}
    op.GeoM.Translate(-float64(w)/2, -float64(h)/2)
    op.GeoM.Rotate(float64(count%360) * 2 * math.Pi / 360)
    op.GeoM.Translate(screenWidth/2, screenHeight/2)
    if err := screen.DrawImage(gophersImage, op); err != nil {
        return err
    }
    return nil
}

func main() {
    var err error
    gophersImage, _, err = common.AssetImage("gophers.jpg", ebiten.FilterNearest)
    if err != nil {
        log.Fatal(err)
    }
    if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Rotate (Ebiten Demo)"); err != nil {
        log.Fatal(err)
    }
}