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proper color mixing

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This commit is contained in:
Thomas Friedel 2019-04-17 13:12:57 +02:00
parent 4d0f41cc6b
commit ec3bde6374
1 changed files with 28 additions and 3 deletions
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31
backend/software/fill.go
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@ -3,6 +3,7 @@ package softwarebackend
import (
"image"
"image/color"
"math"
"github.com/tfriedel6/canvas/backend/backendbase"
)
@ -24,12 +25,36 @@ func (b *SoftwareBackend) Fill(style *backendbase.FillStyle, pts [][2]float64) {
if b.clip.AlphaAt(x, y).A == 0 {
return
}
b.Image.SetRGBA(x, y, style.Color)
b.Image.SetRGBA(x, y, mix(style.Color, b.Image.RGBAAt(x, y)))
})
})
}
func mix(col color.Color, alpha color.Alpha) color.RGBA {
func mix(src, dest color.Color) color.RGBA {
ir1, ig1, ib1, ia1 := src.RGBA()
r1 := float64(ir1) / 65535.0
g1 := float64(ig1) / 65535.0
b1 := float64(ib1) / 65535.0
a1 := float64(ia1) / 65535.0
ir2, ig2, ib2, _ := dest.RGBA()
r2 := float64(ir2) / 65535.0
g2 := float64(ig2) / 65535.0
b2 := float64(ib2) / 65535.0
r := (r1-r2)*a1 + r2
g := (g1-g2)*a1 + g2
b := (b1-b2)*a1 + b2
return color.RGBA{
R: uint8(math.Round(r * 255.0)),
G: uint8(math.Round(g * 255.0)),
B: uint8(math.Round(b * 255.0)),
A: 255,
}
}
func alphaColor(col color.Color, alpha color.Alpha) color.RGBA {
ir, ig, ib, _ := col.RGBA()
a2 := float64(alpha.A) / 255.0
r := float64(ir) * a2 / 65535.0
@ -53,7 +78,7 @@ func (b *SoftwareBackend) FillImageMask(style *backendbase.FillStyle, mask *imag
if a.A == 0 {
return
}
b.Image.SetRGBA(x, y, mix(style.Color, a))
b.Image.SetRGBA(x, y, alphaColor(style.Color, a))
})
}