Ebiten example - alphablending

package main

import (
    "image/color"
    _ "image/png"
    "log"

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

const (
    screenWidth  = 320
    screenHeight = 240
)

var (
    count           int
    tmpRenderTarget *ebiten.Image
    ebitenImage     *ebiten.Image
    saved           bool
)

func update(screen *ebiten.Image) error {
    count++
    count %= 600
    diff := float64(count) * 0.2
    switch {
    case 480 < count:
        diff = 0
    case 240 < count:
        diff = float64(480-count) * 0.2
    }

    if err := tmpRenderTarget.Clear(); err != nil {
        return err
    }
    for i := 0; i < 10; i++ {
        op := &ebiten.DrawImageOptions{}
        op.GeoM.Translate(15+float64(i)*diff, 20)
        op.ColorM.Scale(1.0, 1.0, 1.0, 0.5)
        if err := tmpRenderTarget.DrawImage(ebitenImage, op); err != nil {
            return err
        }
    }

    screen.Fill(color.NRGBA{0x00, 0x00, 0x80, 0xff})
    for i := 0; i < 10; i++ {
        op := &ebiten.DrawImageOptions{}
        op.GeoM.Translate(0, float64(i)*diff)
        if err := screen.DrawImage(tmpRenderTarget, op); err != nil {
            return err
        }
    }

    return nil
}

func main() {
    var err error
    ebitenImage, _, err = ebitenutil.NewImageFromFile("images/ebiten.png", ebiten.FilterNearest)
    if err != nil {
        log.Fatal(err)
    }
    tmpRenderTarget, err = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterNearest)
    if err != nil {
        log.Fatal(err)
    }
    if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Alpha Blending (Ebiten Demo)"); err != nil {
        log.Fatal(err)
    }
}