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examples/masking: Rename variables

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This commit is contained in:
Hajime Hoshi 2018-01-29 02:47:38 +09:00
parent 9730af7976
commit 023315c256
1 changed files with 11 additions and 11 deletions
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22
examples/masking/main.go
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@ -35,7 +35,7 @@ const (
var (
bgImage *ebiten.Image
fgImage *ebiten.Image
maskImage *ebiten.Image
maskedFgImage *ebiten.Image
spotLightImage *ebiten.Image
spotLightX = 0
spotLightY = 0
@ -55,7 +55,7 @@ func init() {
log.Fatal(err)
}
maskImage, _ = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterNearest)
maskedFgImage, _ = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterNearest)
// Initialize the spot light image.
const r = 64
@ -100,30 +100,30 @@ func update(screen *ebiten.Image) error {
return nil
}
maskImage.Clear()
maskedFgImage.Clear()
op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(float64(spotLightX), float64(spotLightY))
maskImage.DrawImage(spotLightImage, op)
maskedFgImage.DrawImage(spotLightImage, op)
// Use 'source-out' composite mode so that the source image (fgImage) is used but the alpha
// is determined by the destination image (maskImage). With source-out, the destination image
// values are not used at the result image.
// is determined by the destination image (maskedFgImage). With source-out, the destination
// image values are not used at the result image.
//
// If the alpha value of the destination is 0xff, the source at the point is not adopted.
// In the opposite way, if the alpha value of the destination is 0, the source at the point
// is fully adopted. As alpha values outside of the spot light image are 0, the source values
// are fully adopted there. As a result, the maskImage draws the source image with a hole
// that shape is spotLightImage.
// is fully adopted. As alpha values outside of the spot light image are 0, the source
// values are fully adopted there. As a result, the maskedFgImage draws the source image
// with a hole that shape is spotLightImage.
//
// See also https://www.w3.org/TR/compositing-1/#porterduffcompositingoperators_srcout.
op = &ebiten.DrawImageOptions{}
op.CompositeMode = ebiten.CompositeModeSourceOut
maskImage.DrawImage(fgImage, op)
maskedFgImage.DrawImage(fgImage, op)
screen.Fill(color.RGBA{0x00, 0x00, 0x80, 0xff})
screen.DrawImage(bgImage, &ebiten.DrawImageOptions{})
screen.DrawImage(maskImage, &ebiten.DrawImageOptions{})
screen.DrawImage(maskedFgImage, &ebiten.DrawImageOptions{})
return nil
}