// +build example jsgo

package main

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

        "github.com/hajimehoshi/ebiten"
        "github.com/hajimehoshi/ebiten/examples/resources/images"
)

const (
        screenWidth  = 320
        screenHeight = 240
)

var (
        count        = 0
        gophersImage *ebiten.Image
)

func update(screen *ebiten.Image) error {
        count++
        if ebiten.IsRunningSlowly() {
                return nil
        }
        w, h := gophersImage.Size()
        op := &ebiten.DrawImageOptions{}

        // Move the image's center to the screen's upper-left corner.
        // This is a prepartion for rotating. When geometry matrices are applied,
        // the origin point is the upper-left corner.
        op.GeoM.Translate(-float64(w)/2, -float64(h)/2)

        // Rotate the image. As a result, the anchor point of this rotate is
        // the center of the image.
        op.GeoM.Rotate(float64(count%360) * 2 * math.Pi / 360)

        // Move the image to the screen's center.
        op.GeoM.Translate(screenWidth/2, screenHeight/2)
        screen.DrawImage(gophersImage, op)
        return nil
}

func main() {
        // Decode image from a byte slice instead of a file so that
        // this example works in any working directory.
        // If you want to use a file, there are some options:
        // 1) Use os.Open and pass the file to the image decoder.
        //    This is a very regular way, but doesn't work on browsers.
        // 2) Use ebitenutil.OpenFile and pass the file to the image decoder.
        //    This works even on browsers.
        // 3) Use ebitenutil.NewImageFromFile to create an ebiten.Image directly from a file.
        //    This also works on browsers.
        img, _, err := image.Decode(bytes.NewReader(images.Gophers_jpg))
        if err != nil {
                log.Fatal(err)
        }
        gophersImage, _ = ebiten.NewImageFromImage(img, ebiten.FilterDefault)

        if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Rotate (Ebiten Demo)"); err != nil {
                log.Fatal(err)
        }
}