From 7fa1f9096f2dc857e28e39f8073e2efcb3591dde Mon Sep 17 00:00:00 2001
From: Thomas Friedel <tomee6@gmail.com>
Date: Tue, 16 Apr 2019 16:33:55 +0200
Subject: [PATCH] implemented FillImageMask in software backend

---
 backend/backendbase/base.go |  2 +-
 backend/gogl/fill.go        |  2 +-
 backend/software/fill.go    | 30 ++++++++++++++++++++++++++++++
 backend/xmobile/fill.go     |  2 +-
 shadows.go                  |  4 +++-
 text.go                     |  2 +-
 6 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/backend/backendbase/base.go b/backend/backendbase/base.go
index 5b26030..3cb678c 100644
--- a/backend/backendbase/base.go
+++ b/backend/backendbase/base.go
@@ -20,7 +20,7 @@ type Backend interface {
 	Clear(pts [4][2]float64)
 	Fill(style *FillStyle, pts [][2]float64)
 	DrawImage(dimg Image, sx, sy, sw, sh float64, pts [4][2]float64, alpha float64)
-	FillImageMask(style *FillStyle, mask *image.Alpha, pts [][2]float64) // pts must have four points
+	FillImageMask(style *FillStyle, mask *image.Alpha, pts [4][2]float64) // pts must have four points
 
 	ClearClip()
 	Clip(pts [][2]float64)
diff --git a/backend/gogl/fill.go b/backend/gogl/fill.go
index 125321d..68e5c58 100644
--- a/backend/gogl/fill.go
+++ b/backend/gogl/fill.go
@@ -146,7 +146,7 @@ func (b *GoGLBackend) Fill(style *backendbase.FillStyle, pts [][2]float64) {
 	}
 }
 
-func (b *GoGLBackend) FillImageMask(style *backendbase.FillStyle, mask *image.Alpha, pts [][2]float64) {
+func (b *GoGLBackend) FillImageMask(style *backendbase.FillStyle, mask *image.Alpha, pts [4][2]float64) {
 	b.activate()
 
 	w, h := mask.Rect.Dx(), mask.Rect.Dy()
diff --git a/backend/software/fill.go b/backend/software/fill.go
index 89a46a1..77c63a1 100644
--- a/backend/software/fill.go
+++ b/backend/software/fill.go
@@ -1,6 +1,7 @@
 package softwarebackend
 
 import (
+	"image"
 	"image/color"
 
 	"github.com/tfriedel6/canvas/backend/backendbase"
@@ -28,6 +29,35 @@ func (b *SoftwareBackend) Fill(style *backendbase.FillStyle, pts [][2]float64) {
 	})
 }
 
+func mix(col color.Color, alpha color.Alpha) color.RGBA {
+	ir, ig, ib, ia := col.RGBA()
+	a2 := float64(alpha.A) / 255.0
+	r := float64(ir) * a2 / 65535.0
+	g := float64(ig) * a2 / 65535.0
+	b := float64(ib) * a2 / 65535.0
+	a := float64(ia) * a2 / 65535.0
+	return color.RGBA{
+		R: uint8(r * 255.0),
+		G: uint8(g * 255.0),
+		B: uint8(b * 255.0),
+		A: uint8(a * 255.0),
+	}
+}
+
+func (b *SoftwareBackend) FillImageMask(style *backendbase.FillStyle, mask *image.Alpha, pts [4][2]float64) {
+	mw := float64(mask.Bounds().Dx())
+	mh := float64(mask.Bounds().Dy())
+	b.fillQuad(pts, func(x, y int, sx2, sy2 float64) {
+		sxi := int(mw*sx2 + 0.5)
+		syi := int(mh*sy2 + 0.5)
+		a := mask.AlphaAt(sxi, syi)
+		if a.A == 0 {
+			return
+		}
+		b.Image.SetRGBA(x, y, mix(style.Color, a))
+	})
+}
+
 func (b *SoftwareBackend) ClearClip() {
 	p := b.clip.Pix
 	for i := range p {
diff --git a/backend/xmobile/fill.go b/backend/xmobile/fill.go
index fe7a217..8f27cba 100755
--- a/backend/xmobile/fill.go
+++ b/backend/xmobile/fill.go
@@ -146,7 +146,7 @@ func (b *XMobileBackend) Fill(style *backendbase.FillStyle, pts [][2]float64) {
 	}
 }
 
-func (b *XMobileBackend) FillImageMask(style *backendbase.FillStyle, mask *image.Alpha, pts [][2]float64) {
+func (b *XMobileBackend) FillImageMask(style *backendbase.FillStyle, mask *image.Alpha, pts [4][2]float64) {
 	b.activate()
 
 	w, h := mask.Rect.Dx(), mask.Rect.Dy()
diff --git a/shadows.go b/shadows.go
index 8b153d6..3944335 100644
--- a/shadows.go
+++ b/shadows.go
@@ -34,7 +34,9 @@ func (cv *Canvas) drawShadow(pts [][2]float64, mask *image.Alpha) {
 		if len(cv.shadowBuf) != 4 {
 			panic("invalid number of points to fill with mask, must be 4")
 		}
-		cv.b.FillImageMask(&style, mask, cv.shadowBuf)
+		var quad [4][2]float64
+		copy(quad[:], cv.shadowBuf)
+		cv.b.FillImageMask(&style, mask, quad)
 	} else {
 		cv.b.Fill(&style, cv.shadowBuf)
 	}
diff --git a/text.go b/text.go
index c010423..adaa673 100644
--- a/text.go
+++ b/text.go
@@ -218,7 +218,7 @@ func (cv *Canvas) FillText(str string, x, y float64) {
 	cv.drawShadow(pts[:], mask)
 
 	stl := cv.backendFillStyle(&cv.state.fill, 1)
-	cv.b.FillImageMask(&stl, mask, pts[:])
+	cv.b.FillImageMask(&stl, mask, pts)
 }
 
 // StrokeText draws the given string at the given coordinates