Ebiten example - mosaic

package main

import (
    "github.com/hajimehoshi/ebiten"
    "github.com/hajimehoshi/ebiten/ebitenutil"
    _ "image/jpeg"
    "log"
)

const (
    screenWidth  = 320
    screenHeight = 240
)

const mosaicRatio = 16

var (
    gophersImage        *ebiten.Image
    gophersRenderTarget *ebiten.Image
)

func update(screen *ebiten.Image) error {
    op := &ebiten.DrawImageOptions{}
    op.GeoM.Scale(1.0/mosaicRatio, 1.0/mosaicRatio)
    gophersRenderTarget.DrawImage(gophersImage, op)
    op = &ebiten.DrawImageOptions{}
    op.GeoM.Scale(mosaicRatio, mosaicRatio)
    screen.DrawImage(gophersRenderTarget, op)
    return nil
}

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