ebiten/examples/blur/main.go
2022-09-17 23:27:45 +09:00

108 lines
3.3 KiB
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.
//go:build example
// +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
//
// Note that this is a fixed function implementation of a box blur - more
// efficiency can be gained by using a separable blur
// (blurring horizontally and vertically separately, or for large blurs,
// even multiple horizontal or vertical passes), ideally combined with
// doing the summing up in a fragment shader (Kage can be used here).
//
// So this implementation only serves to demonstrate use of alpha blending.
layers := 0
for j := -3; j <= 3; j++ {
for i := -3; i <= 3; i++ {
op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(float64(i), 244+float64(j))
// This is a blur based on the CompositerModeSourceOver composition mode,
// which is basically (GL_ONE, GL_ONE_MINUS_SRC_ALPHA). ColorM acts
// on unpremultiplied colors, but all Ebitengine internal colors are
// premultiplied, meaning this mode is regular alpha blending,
// computing each destination pixel as srcPix * alpha + dstPix * (1 - alpha).
//
// This means that the final color is affected by the destination color 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
//
// So if using the same alpha every time, the end result will sure be biased towards the last layer.
//
// Correct averaging works based on
// Let A_n := (a_1 + ... + a_n) / n
// A_{n+1} = (a_1 + ... + a_{n+1}) / (n + 1)
// A_{n+1} = (n * A_n + a_{n+1)) / (n + 1)
// A_{n+1} = A_n * (1 - 1/(n+1)) + a_{n+1} * 1/(n+1)
// which is precisely what an alpha blend with alpha 1/(n+1) does.
layers++
op.ColorM.Scale(1, 1, 1, 1.0/float64(layers))
screen.DrawImage(gophersImage, op)
}
}
}
func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
return screenWidth, screenHeight
}
func main() {
// Decode an image from the image file's byte slice.
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 (Ebitengine Demo)")
if err := ebiten.RunGame(&Game{}); err != nil {
log.Fatal(err)
}
}