ebiten/examples/blur/main.go

// Copyright 2018 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// +build example

package main

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

	"github.com/hajimehoshi/ebiten/v2"
	"github.com/hajimehoshi/ebiten/v2/examples/resources/images"
)

const (
	screenWidth  = 640
	screenHeight = 480
)

var (
	gophersImage *ebiten.Image
)

type Game struct{}

func (g *Game) Update() error {
	return nil
}

func (g *Game) Draw(screen *ebiten.Image) {
	op := &ebiten.DrawImageOptions{}
	op.GeoM.Translate(0, 0)
	screen.DrawImage(gophersImage, op)

	// Box blur (7x7)
	// https://en.wikipedia.org/wiki/Box_blur
	for j := -3; j <= 3; j++ {
		for i := -3; i <= 3; i++ {
			op := &ebiten.DrawImageOptions{}
			op.GeoM.Translate(float64(i), 244+float64(j))
			// Alpha scale should be 1.0/49.0, but accumulating 1/49 49 times doesn't reach to 1, because
			// the final color is affected by the destination alpha when CompositeModeSourceOver is used.
			// This composite mode is the default mode. See how this is calculated at the doc:
			// https://pkg.go.dev/github.com/hajimehoshi/ebiten/v2#CompositeMode
			//
			// Use a higher value than 1.0/49.0. Here, 1.0/25.0 here to get a reasonable result.
			op.ColorM.Scale(1, 1, 1, 1.0/25.0)
			screen.DrawImage(gophersImage, op)
		}
	}
}

func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
	return screenWidth, screenHeight
}

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.FiveYears_jpg))
	if err != nil {
		log.Fatal(err)
	}
	gophersImage = ebiten.NewImageFromImage(img)

	ebiten.SetWindowSize(screenWidth, screenHeight)
	ebiten.SetWindowTitle("Blur (Ebiten Demo)")
	if err := ebiten.RunGame(&Game{}); err != nil {
		log.Fatal(err)
	}
}