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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package draw provides image composition functions.
//
// See "The Go image/draw package" for an introduction to this package:
// https://golang.org/doc/articles/image_draw.html
package draw
import (
"image"
"image/color"
"image/internal/imageutil"
)
// m is the maximum color value returned by image.Color.RGBA.
const m = 1<<16 - 1
// Image is an image.Image with a Set method to change a single pixel.
type Image interface {
image.Image
Set(x, y int, c color.Color)
}
// Quantizer produces a palette for an image.
type Quantizer interface {
// Quantize appends up to cap(p) - len(p) colors to p and returns the
// updated palette suitable for converting m to a paletted image.
Quantize(p color.Palette, m image.Image) color.Palette
}
// Op is a Porter-Duff compositing operator.
type Op int
const (
// Over specifies ``(src in mask) over dst''.
Over Op = iota
// Src specifies ``src in mask''.
Src
)
// Draw implements the Drawer interface by calling the Draw function with this
// Op.
func (op Op) Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point) {
DrawMask(dst, r, src, sp, nil, image.Point{}, op)
}
// Drawer contains the Draw method.
type Drawer interface {
// Draw aligns r.Min in dst with sp in src and then replaces the
// rectangle r in dst with the result of drawing src on dst.
Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point)
}
// FloydSteinberg is a Drawer that is the Src Op with Floyd-Steinberg error
// diffusion.
var FloydSteinberg Drawer = floydSteinberg{}
type floydSteinberg struct{}
func (floydSteinberg) Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point) {
clip(dst, &r, src, &sp, nil, nil)
if r.Empty() {
return
}
drawPaletted(dst, r, src, sp, true)
}
// clip clips r against each image's bounds (after translating into the
// destination image's coordinate space) and shifts the points sp and mp by
// the same amount as the change in r.Min.
func clip(dst Image, r *image.Rectangle, src image.Image, sp *image.Point, mask image.Image, mp *image.Point) {
orig := r.Min
*r = r.Intersect(dst.Bounds())
*r = r.Intersect(src.Bounds().Add(orig.Sub(*sp)))
if mask != nil {
*r = r.Intersect(mask.Bounds().Add(orig.Sub(*mp)))
}
dx := r.Min.X - orig.X
dy := r.Min.Y - orig.Y
if dx == 0 && dy == 0 {
return
}
sp.X += dx
sp.Y += dy
if mp != nil {
mp.X += dx
mp.Y += dy
}
}
func processBackward(dst Image, r image.Rectangle, src image.Image, sp image.Point) bool {
return image.Image(dst) == src &&
r.Overlaps(r.Add(sp.Sub(r.Min))) &&
(sp.Y < r.Min.Y || (sp.Y == r.Min.Y && sp.X < r.Min.X))
}
// Draw calls DrawMask with a nil mask.
func Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point, op Op) {
DrawMask(dst, r, src, sp, nil, image.Point{}, op)
}
// DrawMask aligns r.Min in dst with sp in src and mp in mask and then replaces the rectangle r
// in dst with the result of a Porter-Duff composition. A nil mask is treated as opaque.
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:
sr, sg, sb, sa := src0.RGBA()
if sa == 0xffff {
drawFillSrc(dst0, r, sr, sg, sb, sa)
} else {
drawFillOver(dst0, r, sr, sg, sb, sa)
}
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:
sr, sg, sb, sa := src0.RGBA()
drawFillSrc(dst0, r, sr, sg, sb, sa)
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)
}
}
}
}
func drawFillOver(dst *image.RGBA, r image.Rectangle, sr, sg, sb, sa uint32) {
// The 0x101 is here for the same reason as in drawRGBA.
a := (m - sa) * 0x101
i0 := dst.PixOffset(r.Min.X, r.Min.Y)
i1 := i0 + r.Dx()*4
for y := r.Min.Y; y != r.Max.Y; y++ {
for i := i0; i < i1; i += 4 {
dr := &dst.Pix[i+0]
dg := &dst.Pix[i+1]
db := &dst.Pix[i+2]
da := &dst.Pix[i+3]
*dr = uint8((uint32(*dr)*a/m + sr) >> 8)
*dg = uint8((uint32(*dg)*a/m + sg) >> 8)
*db = uint8((uint32(*db)*a/m + sb) >> 8)
*da = uint8((uint32(*da)*a/m + sa) >> 8)
}
i0 += dst.Stride
i1 += dst.Stride
}
}
func drawFillSrc(dst *image.RGBA, r image.Rectangle, sr, sg, sb, sa uint32) {
sr8 := uint8(sr >> 8)
sg8 := uint8(sg >> 8)
sb8 := uint8(sb >> 8)
sa8 := uint8(sa >> 8)
// The built-in copy function is faster than a straightforward for loop to fill the destination with
// the color, but copy requires a slice source. We therefore use a for loop to fill the first row, and
// then use the first row as the slice source for the remaining rows.
i0 := dst.PixOffset(r.Min.X, r.Min.Y)
i1 := i0 + r.Dx()*4
for i := i0; i < i1; i += 4 {
dst.Pix[i+0] = sr8
dst.Pix[i+1] = sg8
dst.Pix[i+2] = sb8
dst.Pix[i+3] = sa8
}
firstRow := dst.Pix[i0:i1]
for y := r.Min.Y + 1; y < r.Max.Y; y++ {
i0 += dst.Stride
i1 += dst.Stride
copy(dst.Pix[i0:i1], firstRow)
}
}
func drawCopyOver(dst *image.RGBA, r image.Rectangle, src *image.RGBA, sp image.Point) {
dx, dy := r.Dx(), r.Dy()
d0 := dst.PixOffset(r.Min.X, r.Min.Y)
s0 := src.PixOffset(sp.X, sp.Y)
var (
ddelta, sdelta int
i0, i1, idelta int
)
if r.Min.Y < sp.Y || r.Min.Y == sp.Y && r.Min.X <= sp.X {
ddelta = dst.Stride
sdelta = src.Stride
i0, i1, idelta = 0, dx*4, +4
} else {
// If the source start point is higher than the destination start point, or equal height but to the left,
// then we compose the rows in right-to-left, bottom-up order instead of left-to-right, top-down.
d0 += (dy - 1) * dst.Stride
s0 += (dy - 1) * src.Stride
ddelta = -dst.Stride
sdelta = -src.Stride
i0, i1, idelta = (dx-1)*4, -4, -4
}
for ; dy > 0; dy-- {
dpix := dst.Pix[d0:]
spix := src.Pix[s0:]
for i := i0; i != i1; i += idelta {
s := spix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
sr := uint32(s[0]) * 0x101
sg := uint32(s[1]) * 0x101
sb := uint32(s[2]) * 0x101
sa := uint32(s[3]) * 0x101
// The 0x101 is here for the same reason as in drawRGBA.
a := (m - sa) * 0x101
d := dpix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
d[0] = uint8((uint32(d[0])*a/m + sr) >> 8)
d[1] = uint8((uint32(d[1])*a/m + sg) >> 8)
d[2] = uint8((uint32(d[2])*a/m + sb) >> 8)
d[3] = uint8((uint32(d[3])*a/m + sa) >> 8)
}
d0 += ddelta
s0 += sdelta
}
}
func drawCopySrc(dst *image.RGBA, r image.Rectangle, src *image.RGBA, sp image.Point) {
n, dy := 4*r.Dx(), r.Dy()
d0 := dst.PixOffset(r.Min.X, r.Min.Y)
s0 := src.PixOffset(sp.X, sp.Y)
var ddelta, sdelta int
if r.Min.Y <= sp.Y {
ddelta = dst.Stride
sdelta = src.Stride
} else {
// If the source start point is higher than the destination start
// point, then we compose the rows in bottom-up order instead of
// top-down. Unlike the drawCopyOver function, we don't have to check
// the x coordinates because the built-in copy function can handle
// overlapping slices.
d0 += (dy - 1) * dst.Stride
s0 += (dy - 1) * src.Stride
ddelta = -dst.Stride
sdelta = -src.Stride
}
for ; dy > 0; dy-- {
copy(dst.Pix[d0:d0+n], src.Pix[s0:s0+n])
d0 += ddelta
s0 += sdelta
}
}
func drawNRGBAOver(dst *image.RGBA, r image.Rectangle, src *image.NRGBA, sp image.Point) {
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 {
// Convert from non-premultiplied color to pre-multiplied color.
s := spix[si : si+4 : si+4] // Small cap improves performance, see https://golang.org/issue/27857
sa := uint32(s[3]) * 0x101
sr := uint32(s[0]) * sa / 0xff
sg := uint32(s[1]) * sa / 0xff
sb := uint32(s[2]) * sa / 0xff
d := dpix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
dr := uint32(d[0])
dg := uint32(d[1])
db := uint32(d[2])
da := uint32(d[3])
// The 0x101 is here for the same reason as in drawRGBA.
a := (m - sa) * 0x101
d[0] = uint8((dr*a/m + sr) >> 8)
d[1] = uint8((dg*a/m + sg) >> 8)
d[2] = uint8((db*a/m + sb) >> 8)
d[3] = uint8((da*a/m + sa) >> 8)
}
}
}
func drawNRGBASrc(dst *image.RGBA, r image.Rectangle, src *image.NRGBA, sp image.Point) {
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 {
// Convert from non-premultiplied color to pre-multiplied color.
s := spix[si : si+4 : si+4] // Small cap improves performance, see https://golang.org/issue/27857
sa := uint32(s[3]) * 0x101
sr := uint32(s[0]) * sa / 0xff
sg := uint32(s[1]) * sa / 0xff
sb := uint32(s[2]) * sa / 0xff
d := dpix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
d[0] = uint8(sr >> 8)
d[1] = uint8(sg >> 8)
d[2] = uint8(sb >> 8)
d[3] = uint8(sa >> 8)
}
}
}
func drawGray(dst *image.RGBA, r image.Rectangle, src *image.Gray, sp image.Point) {
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) * 1
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+1 {
p := spix[si]
d := dpix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
d[0] = p
d[1] = p
d[2] = p
d[3] = 255
}
}
}
func drawCMYK(dst *image.RGBA, r image.Rectangle, src *image.CMYK, sp image.Point) {
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 {
s := spix[si : si+4 : si+4] // Small cap improves performance, see https://golang.org/issue/27857
d := dpix[i : i+4 : i+4]
d[0], d[1], d[2] = color.CMYKToRGB(s[0], s[1], s[2], s[3])
d[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
mi0 := mask.PixOffset(mp.X, mp.Y)
sr, sg, sb, sa := src.RGBA()
for y, my := r.Min.Y, mp.Y; y != r.Max.Y; y, my = y+1, my+1 {
for i, mi := i0, mi0; i < i1; i, mi = i+4, mi+1 {
ma := uint32(mask.Pix[mi])
if ma == 0 {
continue
}
ma |= ma << 8
// The 0x101 is here for the same reason as in drawRGBA.
a := (m - (sa * ma / m)) * 0x101
d := dst.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
d[0] = uint8((uint32(d[0])*a + sr*ma) / m >> 8)
d[1] = uint8((uint32(d[1])*a + sg*ma) / m >> 8)
d[2] = uint8((uint32(d[2])*a + sb*ma) / m >> 8)
d[3] = uint8((uint32(d[3])*a + sa*ma) / m >> 8)
}
i0 += dst.Stride
i1 += dst.Stride
mi0 += mask.Stride
}
}
func drawRGBA(dst *image.RGBA, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op) {
x0, x1, dx := r.Min.X, r.Max.X, 1
y0, y1, dy := r.Min.Y, r.Max.Y, 1
if image.Image(dst) == src && r.Overlaps(r.Add(sp.Sub(r.Min))) {
if sp.Y < r.Min.Y || sp.Y == r.Min.Y && sp.X < r.Min.X {
x0, x1, dx = x1-1, x0-1, -1
y0, y1, dy = y1-1, y0-1, -1
}
}
sy := sp.Y + y0 - r.Min.Y
my := mp.Y + y0 - r.Min.Y
sx0 := sp.X + x0 - r.Min.X
mx0 := mp.X + x0 - r.Min.X
sx1 := sx0 + (x1 - x0)
i0 := dst.PixOffset(x0, y0)
di := dx * 4
for y := y0; y != y1; y, sy, my = y+dy, sy+dy, my+dy {
for i, sx, mx := i0, sx0, mx0; sx != sx1; i, sx, mx = i+di, sx+dx, mx+dx {
ma := uint32(m)
if mask != nil {
_, _, _, ma = mask.At(mx, my).RGBA()
}
sr, sg, sb, sa := src.At(sx, sy).RGBA()
d := dst.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
if op == Over {
dr := uint32(d[0])
dg := uint32(d[1])
db := uint32(d[2])
da := uint32(d[3])
// dr, dg, db and da are all 8-bit color at the moment, ranging in [0,255].
// We work in 16-bit color, and so would normally do:
// dr |= dr << 8
// and similarly for dg, db and da, but instead we multiply a
// (which is a 16-bit color, ranging in [0,65535]) by 0x101.
// This yields the same result, but is fewer arithmetic operations.
a := (m - (sa * ma / m)) * 0x101
d[0] = uint8((dr*a + sr*ma) / m >> 8)
d[1] = uint8((dg*a + sg*ma) / m >> 8)
d[2] = uint8((db*a + sb*ma) / m >> 8)
d[3] = uint8((da*a + sa*ma) / m >> 8)
} else {
d[0] = uint8(sr * ma / m >> 8)
d[1] = uint8(sg * ma / m >> 8)
d[2] = uint8(sb * ma / m >> 8)
d[3] = uint8(sa * ma / m >> 8)
}
}
i0 += dy * dst.Stride
}
}
// clamp clamps i to the interval [0, 0xffff].
func clamp(i int32) int32 {
if i < 0 {
return 0
}
if i > 0xffff {
return 0xffff
}
return i
}
// sqDiff returns the squared-difference of x and y, shifted by 2 so that
// adding four of those won't overflow a uint32.
//
// x and y are both assumed to be in the range [0, 0xffff].
func sqDiff(x, y int32) uint32 {
// This is an optimized code relying on the overflow/wrap around
// properties of unsigned integers operations guaranteed by the language
// spec. See sqDiff from the image/color package for more details.
d := uint32(x - y)
return (d * d) >> 2
}
func drawPaletted(dst Image, r image.Rectangle, src image.Image, sp image.Point, floydSteinberg bool) {
// TODO(nigeltao): handle the case where the dst and src overlap.
// Does it even make sense to try and do Floyd-Steinberg whilst
// walking the image backward (right-to-left bottom-to-top)?
// If dst is an *image.Paletted, we have a fast path for dst.Set and
// dst.At. The dst.Set equivalent is a batch version of the algorithm
// used by color.Palette's Index method in image/color/color.go, plus
// optional Floyd-Steinberg error diffusion.
palette, pix, stride := [][4]int32(nil), []byte(nil), 0
if p, ok := dst.(*image.Paletted); ok {
palette = make([][4]int32, len(p.Palette))
for i, col := range p.Palette {
r, g, b, a := col.RGBA()
palette[i][0] = int32(r)
palette[i][1] = int32(g)
palette[i][2] = int32(b)
palette[i][3] = int32(a)
}
pix, stride = p.Pix[p.PixOffset(r.Min.X, r.Min.Y):], p.Stride
}
// quantErrorCurr and quantErrorNext are the Floyd-Steinberg quantization
// errors that have been propagated to the pixels in the current and next
// rows. The +2 simplifies calculation near the edges.
var quantErrorCurr, quantErrorNext [][4]int32
if floydSteinberg {
quantErrorCurr = make([][4]int32, r.Dx()+2)
quantErrorNext = make([][4]int32, r.Dx()+2)
}
pxRGBA := func(x, y int) (r, g, b, a uint32) { return src.At(x, y).RGBA() }
// Fast paths for special cases to avoid excessive use of the color.Color
// interface which escapes to the heap but need to be discovered for
// each pixel on r. See also https://golang.org/issues/15759.
switch src0 := src.(type) {
case *image.RGBA:
pxRGBA = func(x, y int) (r, g, b, a uint32) { return src0.RGBAAt(x, y).RGBA() }
case *image.NRGBA:
pxRGBA = func(x, y int) (r, g, b, a uint32) { return src0.NRGBAAt(x, y).RGBA() }
case *image.YCbCr:
pxRGBA = func(x, y int) (r, g, b, a uint32) { return src0.YCbCrAt(x, y).RGBA() }
}
// Loop over each source pixel.
out := color.RGBA64{A: 0xffff}
for y := 0; y != r.Dy(); y++ {
for x := 0; x != r.Dx(); x++ {
// er, eg and eb are the pixel's R,G,B values plus the
// optional Floyd-Steinberg error.
sr, sg, sb, sa := pxRGBA(sp.X+x, sp.Y+y)
er, eg, eb, ea := int32(sr), int32(sg), int32(sb), int32(sa)
if floydSteinberg {
er = clamp(er + quantErrorCurr[x+1][0]/16)
eg = clamp(eg + quantErrorCurr[x+1][1]/16)
eb = clamp(eb + quantErrorCurr[x+1][2]/16)
ea = clamp(ea + quantErrorCurr[x+1][3]/16)
}
if palette != nil {
// Find the closest palette color in Euclidean R,G,B,A space:
// the one that minimizes sum-squared-difference.
// TODO(nigeltao): consider smarter algorithms.
bestIndex, bestSum := 0, uint32(1<<32-1)
for index, p := range palette {
sum := sqDiff(er, p[0]) + sqDiff(eg, p[1]) + sqDiff(eb, p[2]) + sqDiff(ea, p[3])
if sum < bestSum {
bestIndex, bestSum = index, sum
if sum == 0 {
break
}
}
}
pix[y*stride+x] = byte(bestIndex)
if !floydSteinberg {
continue
}
er -= palette[bestIndex][0]
eg -= palette[bestIndex][1]
eb -= palette[bestIndex][2]
ea -= palette[bestIndex][3]
} else {
out.R = uint16(er)
out.G = uint16(eg)
out.B = uint16(eb)
out.A = uint16(ea)
// 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(r.Min.X+x, r.Min.Y+y, &out)
if !floydSteinberg {
continue
}
sr, sg, sb, sa = dst.At(r.Min.X+x, r.Min.Y+y).RGBA()
er -= int32(sr)
eg -= int32(sg)
eb -= int32(sb)
ea -= int32(sa)
}
// Propagate the Floyd-Steinberg quantization error.
quantErrorNext[x+0][0] += er * 3
quantErrorNext[x+0][1] += eg * 3
quantErrorNext[x+0][2] += eb * 3
quantErrorNext[x+0][3] += ea * 3
quantErrorNext[x+1][0] += er * 5
quantErrorNext[x+1][1] += eg * 5
quantErrorNext[x+1][2] += eb * 5
quantErrorNext[x+1][3] += ea * 5
quantErrorNext[x+2][0] += er * 1
quantErrorNext[x+2][1] += eg * 1
quantErrorNext[x+2][2] += eb * 1
quantErrorNext[x+2][3] += ea * 1
quantErrorCurr[x+2][0] += er * 7
quantErrorCurr[x+2][1] += eg * 7
quantErrorCurr[x+2][2] += eb * 7
quantErrorCurr[x+2][3] += ea * 7
}
// Recycle the quantization error buffers.
if floydSteinberg {
quantErrorCurr, quantErrorNext = quantErrorNext, quantErrorCurr
for i := range quantErrorNext {
quantErrorNext[i] = [4]int32{}
}
}
}
}