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<!DOCTYPE html>
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< meta charset = "utf-8" >
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< meta property = "og:image" itemprop = "image primaryImageOfPage" content = "https://hajimehoshi.github.io/ebiten/images/examples/masking.png" >
< meta name = "description" content = "Ebiten example - masking" >
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< title > Ebiten example - masking< / title >
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< main > < div class = "container" >
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< h2 > Ebiten example - masking< / h2 >
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< iframe src = "masking.content.html" width = "640" height = "480" > < / iframe >
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< div class = "card" > < pre class = "card-body" > < code class = "language-go" > // + build example
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package main
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import (
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" image"
" image/color"
_ " image/jpeg"
" log"
" math"
" github.com/hajimehoshi/ebiten"
" github.com/hajimehoshi/ebiten/ebitenutil"
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)
const (
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screenWidth = 320
screenHeight = 240
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)
var (
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bgImage *ebiten.Image
fgImage *ebiten.Image
maskedFgImage *ebiten.Image
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spotLightImage *ebiten.Image
spotLightX = 0
spotLightY = 0
spotLightVX = 1
spotLightVY = 1
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)
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func init() {
var err error
bgImage, _, err = ebitenutil.NewImageFromFile(" _resources/images/gophers.jpg" , ebiten.FilterNearest)
if err != nil {
log.Fatal(err)
}
fgImage, _, err = ebitenutil.NewImageFromFile(" _resources/images/fiveyears.jpg" , ebiten.FilterNearest)
if err != nil {
log.Fatal(err)
}
maskedFgImage, _ = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterNearest)
// Initialize the spot light image.
const r = 64
alphas := image.Point{r * 2, r * 2}
a := image.NewAlpha(image.Rectangle{image.ZP, alphas})
for j := 0; j < alphas.Y; j+ + {
for i := 0; i < alphas.X; i+ + {
// d is the distance between (i, j) and the (circle) center.
d := math.Sqrt(float64((i-r)*(i-r) + (j-r)*(j-r)))
// Alphas around the center are 0 and values outside of the circle are 0xff.
b := uint8(max(0, min(0xff, int(3*d*0xff/r)-2*0xff)))
a.SetAlpha(i, j, color.Alpha{b})
}
}
spotLightImage, _ = ebiten.NewImageFromImage(a, ebiten.FilterNearest)
}
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func update(screen *ebiten.Image) error {
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spotLightX + = spotLightVX
spotLightY + = spotLightVY
if spotLightX < 0 {
spotLightX = -spotLightX
spotLightVX = -spotLightVX
}
if spotLightY < 0 {
spotLightY = -spotLightY
spotLightVY = -spotLightVY
}
w, h := spotLightImage.Size()
maxX, maxY := screenWidth-w, screenHeight-h
if maxX < spotLightX {
spotLightX = -spotLightX + 2*maxX
spotLightVX = -spotLightVX
}
if maxY < spotLightY {
spotLightY = -spotLightY + 2*maxY
spotLightVY = -spotLightVY
}
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if ebiten.IsRunningSlowly() {
return nil
}
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// Reset the maskedFgImage.
maskedFgImage.Fill(color.White)
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op := & ebiten.DrawImageOptions{}
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op.CompositeMode = ebiten.CompositeModeCopy
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op.GeoM.Translate(float64(spotLightX), float64(spotLightY))
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maskedFgImage.DrawImage(spotLightImage, op)
// Use ' source-in' composite mode so that the source image (fgImage) is used but the alpha
// is determined by the destination image (maskedFgImage).
//
// The result image is the source image with the destination alpha. In maskedFgImage, alpha
// values in the hole is 0 and alpha values in other places are 0xff. As a result, the
// maskedFgImage draws the source image with a hole that shape is spotLightImage. Note that
// RGB values in the destination image are ignored.
//
// See also https://www.w3.org/TR/compositing-1/#porterduffcompositingoperators_srcin.
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op = & ebiten.DrawImageOptions{}
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op.CompositeMode = ebiten.CompositeModeSourceIn
maskedFgImage.DrawImage(fgImage, op)
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screen.Fill(color.RGBA{0x00, 0x00, 0x80, 0xff})
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screen.DrawImage(bgImage, & ebiten.DrawImageOptions{})
screen.DrawImage(maskedFgImage, & ebiten.DrawImageOptions{})
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return nil
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}
func max(a, b int) int {
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if a < b {
return b
}
return a
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}
func min(a, b int) int {
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if a < b {
return a
}
return b
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}
func main() {
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if err := ebiten.Run(update, screenWidth, screenHeight, 2, " Masking (Ebiten Demo)" ); err != nil {
log.Fatal(err)
}
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}
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< / code > < / pre > < / div >
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< / div > < / main >
< footer > < div class = "container" >
< p > © 2013 Hajime Hoshi< / p >
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< p > Code is licensed under < a href = "https://github.com/hajimehoshi/ebiten/blob/master/LICENSE" > the Apache License 2.0< / a > .< / p >
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< p > The content of this page is licensed under < a href = "https://creativecommons.org/licenses/by/4.0/" > the Creative Commons Attribution 4.0 License< / a > .< / p >
< / div > < / footer >
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< script src = "../scripts/highlight.pack.js" > < / script >
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< script > hljs . initHighlightingOnLoad ( ) ; < / script >
