image/draw: add CMYK fast path.

Change-Id: I9582aff7ca141a8aead5692af74b9c708b1700cc
Reviewed-on: https://go-review.googlesource.com/5020
Reviewed-by: Rob Pike <r@golang.org>

diff --git a/src/image/draw/draw.go b/src/image/draw/draw.go
index b1fc979a7dc8e7a7c548e8cd44b2adf9525c6c7b..7f9127168e666f4f4b4ff6b657b40801bfdbf1c9 100644 (file)
--- a/src/image/draw/draw.go
+++ b/src/image/draw/draw.go
@@ -127,6 +127,9 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
                                        if drawYCbCr(dst0, r, src0, sp) {
                                                return
                                        }
+                               case *image.CMYK:
+                                       drawCMYK(dst0, r, src0, sp)
+                                       return
                                }
                        } else if mask0, ok := mask.(*image.Alpha); ok {
                                switch src0 := src.(type) {
@@ -151,6 +154,9 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
                                        if drawYCbCr(dst0, r, src0, sp) {
                                                return
                                        }
+                               case *image.CMYK:
+                                       drawCMYK(dst0, r, src0, sp)
+                                       return
                                }
                        }
                }
@@ -462,6 +468,28 @@ func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Po
        return true
 }
 
+func drawCMYK(dst *image.RGBA, r image.Rectangle, src *image.CMYK, sp image.Point) {
+       // An image.CMYK is always fully opaque, and so if the mask is implicitly nil
+       // (i.e. fully opaque) then the op is effectively always Src.
+       i0 := (r.Min.X - dst.Rect.Min.X) * 4
+       i1 := (r.Max.X - dst.Rect.Min.X) * 4
+       si0 := (sp.X - src.Rect.Min.X) * 4
+       yMax := r.Max.Y - dst.Rect.Min.Y
+
+       y := r.Min.Y - dst.Rect.Min.Y
+       sy := sp.Y - src.Rect.Min.Y
+       for ; y != yMax; y, sy = y+1, sy+1 {
+               dpix := dst.Pix[y*dst.Stride:]
+               spix := src.Pix[sy*src.Stride:]
+
+               for i, si := i0, si0; i < i1; i, si = i+4, si+4 {
+                       dpix[i+0], dpix[i+1], dpix[i+2] =
+                               color.CMYKToRGB(spix[si+0], spix[si+1], spix[si+2], spix[si+3])
+                       dpix[i+3] = 255
+               }
+       }
+}
+
 func drawGlyphOver(dst *image.RGBA, r image.Rectangle, src *image.Uniform, mask *image.Alpha, mp image.Point) {
        i0 := dst.PixOffset(r.Min.X, r.Min.Y)
        i1 := i0 + r.Dx()*4