mirror of
https://github.com/hajimehoshi/ebiten.git
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105 lines
3.3 KiB
Go
105 lines
3.3 KiB
Go
// Copyright 2018 The Ebiten Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package main
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import (
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"bytes"
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"image"
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_ "image/jpeg"
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"log"
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"github.com/hajimehoshi/ebiten/v2"
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"github.com/hajimehoshi/ebiten/v2/examples/resources/images"
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)
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const (
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screenWidth = 640
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screenHeight = 480
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)
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var (
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gophersImage *ebiten.Image
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)
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type Game struct{}
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func (g *Game) Update() error {
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return nil
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}
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func (g *Game) Draw(screen *ebiten.Image) {
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op := &ebiten.DrawImageOptions{}
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op.GeoM.Translate(0, 0)
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screen.DrawImage(gophersImage, op)
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// Box blur (7x7)
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// https://en.wikipedia.org/wiki/Box_blur
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//
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// Note that this is a fixed function implementation of a box blur - more
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// efficiency can be gained by using a separable blur
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// (blurring horizontally and vertically separately, or for large blurs,
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// even multiple horizontal or vertical passes), ideally combined with
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// doing the summing up in a fragment shader (Kage can be used here).
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//
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// So this implementation only serves to demonstrate use of alpha blending.
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layers := 0
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for j := -3; j <= 3; j++ {
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for i := -3; i <= 3; i++ {
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op := &ebiten.DrawImageOptions{}
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op.GeoM.Translate(float64(i), 244+float64(j))
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// This is a blur based on the source-over blend mode,
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// which is basically (GL_ONE, GL_ONE_MINUS_SRC_ALPHA). ColorM acts
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// on unpremultiplied colors, but all Ebitengine internal colors are
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// premultiplied, meaning this mode is regular alpha blending,
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// computing each destination pixel as srcPix * alpha + dstPix * (1 - alpha).
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//
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// This means that the final color is affected by the destination color when BlendSourceOver is used.
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// This blend mode is the default mode. See how this is calculated at the doc:
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// https://pkg.go.dev/github.com/hajimehoshi/ebiten/v2#Blend
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//
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// So if using the same alpha every time, the end result will sure be biased towards the last layer.
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//
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// Correct averaging works based on
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// Let A_n := (a_1 + ... + a_n) / n
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// A_{n+1} = (a_1 + ... + a_{n+1}) / (n + 1)
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// A_{n+1} = (n * A_n + a_{n+1)) / (n + 1)
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// A_{n+1} = A_n * (1 - 1/(n+1)) + a_{n+1} * 1/(n+1)
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// which is precisely what an alpha blend with alpha 1/(n+1) does.
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layers++
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op.ColorScale.ScaleAlpha(1 / float32(layers))
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screen.DrawImage(gophersImage, op)
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}
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}
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}
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func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
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return screenWidth, screenHeight
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}
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func main() {
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// Decode an image from the image file's byte slice.
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img, _, err := image.Decode(bytes.NewReader(images.FiveYears_jpg))
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if err != nil {
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log.Fatal(err)
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}
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gophersImage = ebiten.NewImageFromImage(img)
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ebiten.SetWindowSize(screenWidth, screenHeight)
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ebiten.SetWindowTitle("Blur (Ebitengine Demo)")
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if err := ebiten.RunGame(&Game{}); err != nil {
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log.Fatal(err)
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}
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}
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