1 files changed, 123 insertions, 3 deletions
diff --git a/libgo/go/image/ycbcr.go b/libgo/go/image/ycbcr.go
index 93c354b33b4..71c0518a818 100644
--- a/libgo/go/image/ycbcr.go
+++ b/libgo/go/image/ycbcr.go
@@ -138,9 +138,8 @@ func (p *YCbCr) Opaque() bool {
 	return true
 }
 
-// NewYCbCr returns a new YCbCr with the given bounds and subsample ratio.
-func NewYCbCr(r Rectangle, subsampleRatio YCbCrSubsampleRatio) *YCbCr {
-	w, h, cw, ch := r.Dx(), r.Dy(), 0, 0
+func yCbCrSize(r Rectangle, subsampleRatio YCbCrSubsampleRatio) (w, h, cw, ch int) {
+	w, h = r.Dx(), r.Dy()
 	switch subsampleRatio {
 	case YCbCrSubsampleRatio422:
 		cw = (r.Max.X+1)/2 - r.Min.X/2
@@ -162,6 +161,13 @@ func NewYCbCr(r Rectangle, subsampleRatio YCbCrSubsampleRatio) *YCbCr {
 		cw = w
 		ch = h
 	}
+	return
+}
+
+// NewYCbCr returns a new YCbCr image with the given bounds and subsample
+// ratio.
+func NewYCbCr(r Rectangle, subsampleRatio YCbCrSubsampleRatio) *YCbCr {
+	w, h, cw, ch := yCbCrSize(r, subsampleRatio)
 	i0 := w*h + 0*cw*ch
 	i1 := w*h + 1*cw*ch
 	i2 := w*h + 2*cw*ch
@@ -176,3 +182,117 @@ func NewYCbCr(r Rectangle, subsampleRatio YCbCrSubsampleRatio) *YCbCr {
 		Rect:           r,
 	}
 }
+
+// NYCbCrA is an in-memory image of non-alpha-premultiplied Y'CbCr-with-alpha
+// colors. A and AStride are analogous to the Y and YStride fields of the
+// embedded YCbCr.
+type NYCbCrA struct {
+	YCbCr
+	A       []uint8
+	AStride int
+}
+
+func (p *NYCbCrA) ColorModel() color.Model {
+	return color.NYCbCrAModel
+}
+
+func (p *NYCbCrA) At(x, y int) color.Color {
+	return p.NYCbCrAAt(x, y)
+}
+
+func (p *NYCbCrA) NYCbCrAAt(x, y int) color.NYCbCrA {
+	if !(Point{X: x, Y: y}.In(p.Rect)) {
+		return color.NYCbCrA{}
+	}
+	yi := p.YOffset(x, y)
+	ci := p.COffset(x, y)
+	ai := p.AOffset(x, y)
+	return color.NYCbCrA{
+		color.YCbCr{
+			Y:  p.Y[yi],
+			Cb: p.Cb[ci],
+			Cr: p.Cr[ci],
+		},
+		p.A[ai],
+	}
+}
+
+// AOffset returns the index of the first element of A that corresponds to the
+// pixel at (x, y).
+func (p *NYCbCrA) AOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.AStride + (x - p.Rect.Min.X)
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *NYCbCrA) SubImage(r Rectangle) Image {
+	r = r.Intersect(p.Rect)
+	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
+	// either r1 or r2 if the intersection is empty. Without explicitly checking for
+	// this, the Pix[i:] expression below can panic.
+	if r.Empty() {
+		return &NYCbCrA{
+			YCbCr: YCbCr{
+				SubsampleRatio: p.SubsampleRatio,
+			},
+		}
+	}
+	yi := p.YOffset(r.Min.X, r.Min.Y)
+	ci := p.COffset(r.Min.X, r.Min.Y)
+	ai := p.AOffset(r.Min.X, r.Min.Y)
+	return &NYCbCrA{
+		YCbCr: YCbCr{
+			Y:              p.Y[yi:],
+			Cb:             p.Cb[ci:],
+			Cr:             p.Cr[ci:],
+			SubsampleRatio: p.SubsampleRatio,
+			YStride:        p.YStride,
+			CStride:        p.CStride,
+			Rect:           r,
+		},
+		A:       p.A[ai:],
+		AStride: p.AStride,
+	}
+}
+
+// Opaque scans the entire image and reports whether it is fully opaque.
+func (p *NYCbCrA) Opaque() bool {
+	if p.Rect.Empty() {
+		return true
+	}
+	i0, i1 := 0, p.Rect.Dx()
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for _, a := range p.A[i0:i1] {
+			if a != 0xff {
+				return false
+			}
+		}
+		i0 += p.AStride
+		i1 += p.AStride
+	}
+	return true
+}
+
+// NewNYCbCrA returns a new NYCbCrA image with the given bounds and subsample
+// ratio.
+func NewNYCbCrA(r Rectangle, subsampleRatio YCbCrSubsampleRatio) *NYCbCrA {
+	w, h, cw, ch := yCbCrSize(r, subsampleRatio)
+	i0 := 1*w*h + 0*cw*ch
+	i1 := 1*w*h + 1*cw*ch
+	i2 := 1*w*h + 2*cw*ch
+	i3 := 2*w*h + 2*cw*ch
+	b := make([]byte, i3)
+	return &NYCbCrA{
+		YCbCr: YCbCr{
+			Y:              b[:i0:i0],
+			Cb:             b[i0:i1:i1],
+			Cr:             b[i1:i2:i2],
+			SubsampleRatio: subsampleRatio,
+			YStride:        w,
+			CStride:        cw,
+			Rect:           r,
+		},
+		A:       b[i2:],
+		AStride: w,
+	}
+}