// DrawMask将dst上的r.Min，src上的sp，mask上的mp对齐，然后对dst上的r型矩阵区域执行Porter-Duff合并操作。
// mask设置为nil就代表完全不透明。
func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op) {
clip(dst, &r, src, &sp, mask, &mp)
if r.Empty() {
return
}
// Fast paths for special cases. If none of them apply, then we fall back to a general but slow implementation.
switch dst0 := dst.(type) {
case *image.RGBA:
if op == Over {
if mask == nil {
switch src0 := src.(type) {
case *image.Uniform:
drawFillOver(dst0, r, src0)
return
case *image.RGBA:
drawCopyOver(dst0, r, src0, sp)
return
case *image.NRGBA:
drawNRGBAOver(dst0, r, src0, sp)
return
case *image.YCbCr:
// An image.YCbCr is always fully opaque, and so if the
// mask is nil (i.e. fully opaque) then the op is
// effectively always Src. Similarly for image.Gray and
// image.CMYK.
if imageutil.DrawYCbCr(dst0, r, src0, sp) {
return
}
case *image.Gray:
drawGray(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) {
case *image.Uniform:
drawGlyphOver(dst0, r, src0, mask0, mp)
return
}
}
} else {
if mask == nil {
switch src0 := src.(type) {
case *image.Uniform:
drawFillSrc(dst0, r, src0)
return
case *image.RGBA:
drawCopySrc(dst0, r, src0, sp)
return
case *image.NRGBA:
drawNRGBASrc(dst0, r, src0, sp)
return
case *image.YCbCr:
if imageutil.DrawYCbCr(dst0, r, src0, sp) {
return
}
case *image.Gray:
drawGray(dst0, r, src0, sp)
return
case *image.CMYK:
drawCMYK(dst0, r, src0, sp)
return
}
}
}
drawRGBA(dst0, r, src, sp, mask, mp, op)
return
case *image.Paletted:
if op == Src && mask == nil && !processBackward(dst, r, src, sp) {
drawPaletted(dst0, r, src, sp, false)
return
}
}
x0, x1, dx := r.Min.X, r.Max.X, 1
y0, y1, dy := r.Min.Y, r.Max.Y, 1
if processBackward(dst, r, src, sp) {
x0, x1, dx = x1-1, x0-1, -1
y0, y1, dy = y1-1, y0-1, -1
}
var out color.RGBA64
sy := sp.Y + y0 - r.Min.Y
my := mp.Y + y0 - r.Min.Y
for y := y0; y != y1; y, sy, my = y+dy, sy+dy, my+dy {
sx := sp.X + x0 - r.Min.X
mx := mp.X + x0 - r.Min.X
for x := x0; x != x1; x, sx, mx = x+dx, sx+dx, mx+dx {
ma := uint32(m)
if mask != nil {
_, _, _, ma = mask.At(mx, my).RGBA()
}
switch {
case ma == 0:
if op == Over {
// No-op.
} else {
dst.Set(x, y, color.Transparent)
}
case ma == m && op == Src:
dst.Set(x, y, src.At(sx, sy))
default:
sr, sg, sb, sa := src.At(sx, sy).RGBA()
if op == Over {
dr, dg, db, da := dst.At(x, y).RGBA()
a := m - (sa * ma / m)
out.R = uint16((dr*a + sr*ma) / m)
out.G = uint16((dg*a + sg*ma) / m)
out.B = uint16((db*a + sb*ma) / m)
out.A = uint16((da*a + sa*ma) / m)
} else {
out.R = uint16(sr * ma / m)
out.G = uint16(sg * ma / m)
out.B = uint16(sb * ma / m)
out.A = uint16(sa * ma / m)
}
// The third argument is &out instead of out (and out is
// declared outside of the inner loop) to avoid the implicit
// conversion to color.Color here allocating memory in the
// inner loop if sizeof(color.RGBA64) > sizeof(uintptr).
dst.Set(x, y, &out)
}
}
}
}
// applyBlack combines d.img3 and d.blackPix into a CMYK image. The formula
// used depends on whether the JPEG image is stored as CMYK or YCbCrK,
// indicated by the APP14 (Adobe) metadata.
//
// Adobe CMYK JPEG images are inverted, where 255 means no ink instead of full
// ink, so we apply "v = 255 - v" at various points. Note that a double
// inversion is a no-op, so inversions might be implicit in the code below.
func (d *decoder) applyBlack() (image.Image, error) {
if !d.adobeTransformValid {
return nil, UnsupportedError("unknown color model: 4-component JPEG doesn't have Adobe APP14 metadata")
}
// If the 4-component JPEG image isn't explicitly marked as "Unknown (RGB
// or CMYK)" as per
// http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html#Adobe
// we assume that it is YCbCrK. This matches libjpeg's jdapimin.c.
if d.adobeTransform != adobeTransformUnknown {
// Convert the YCbCr part of the YCbCrK to RGB, invert the RGB to get
// CMY, and patch in the original K. The RGB to CMY inversion cancels
// out the 'Adobe inversion' described in the applyBlack doc comment
// above, so in practice, only the fourth channel (black) is inverted.
bounds := d.img3.Bounds()
img := image.NewRGBA(bounds)
imageutil.DrawYCbCr(img, bounds, d.img3, bounds.Min)
for iBase, y := 0, bounds.Min.Y; y < bounds.Max.Y; iBase, y = iBase+img.Stride, y+1 {
for i, x := iBase+3, bounds.Min.X; x < bounds.Max.X; i, x = i+4, x+1 {
img.Pix[i] = 255 - d.blackPix[(y-bounds.Min.Y)*d.blackStride+(x-bounds.Min.X)]
}
}
return &image.CMYK{
Pix: img.Pix,
Stride: img.Stride,
Rect: img.Rect,
}, nil
}
// The first three channels (cyan, magenta, yellow) of the CMYK
// were decoded into d.img3, but each channel was decoded into a separate
// []byte slice, and some channels may be subsampled. We interleave the
// separate channels into an image.CMYK's single []byte slice containing 4
// contiguous bytes per pixel.
bounds := d.img3.Bounds()
img := image.NewCMYK(bounds)
translations := [4]struct {
src []byte
stride int
}{
{d.img3.Y, d.img3.YStride},
{d.img3.Cb, d.img3.CStride},
{d.img3.Cr, d.img3.CStride},
{d.blackPix, d.blackStride},
}
for t, translation := range translations {
subsample := d.comp[t].h != d.comp[0].h || d.comp[t].v != d.comp[0].v
for iBase, y := 0, bounds.Min.Y; y < bounds.Max.Y; iBase, y = iBase+img.Stride, y+1 {
sy := y - bounds.Min.Y
if subsample {
sy /= 2
}
for i, x := iBase+t, bounds.Min.X; x < bounds.Max.X; i, x = i+4, x+1 {
sx := x - bounds.Min.X
if subsample {
sx /= 2
}
img.Pix[i] = 255 - translation.src[sy*translation.stride+sx]
}
}
}
return img, nil
}