| // 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: |
| // http://golang.org/doc/articles/image_draw.html |
| package draw |
| |
| import ( |
| "image" |
| "image/color" |
| ) |
| |
| // 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 co-ordinate 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 |
| (*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: |
| 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: |
| if drawYCbCr(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 drawYCbCr(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) |
| } |
| } |
| |
| 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, src *image.Uniform) { |
| sr, sg, sb, sa := src.RGBA() |
| // 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 := uint32(dst.Pix[i+0]) |
| dg := uint32(dst.Pix[i+1]) |
| db := uint32(dst.Pix[i+2]) |
| da := uint32(dst.Pix[i+3]) |
| |
| dst.Pix[i+0] = uint8((dr*a/m + sr) >> 8) |
| dst.Pix[i+1] = uint8((dg*a/m + sg) >> 8) |
| dst.Pix[i+2] = uint8((db*a/m + sb) >> 8) |
| dst.Pix[i+3] = uint8((da*a/m + sa) >> 8) |
| } |
| i0 += dst.Stride |
| i1 += dst.Stride |
| } |
| } |
| |
| func drawFillSrc(dst *image.RGBA, r image.Rectangle, src *image.Uniform) { |
| sr, sg, sb, sa := src.RGBA() |
| // 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] = uint8(sr >> 8) |
| dst.Pix[i+1] = uint8(sg >> 8) |
| dst.Pix[i+2] = uint8(sb >> 8) |
| dst.Pix[i+3] = uint8(sa >> 8) |
| } |
| 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 { |
| sr := uint32(spix[i+0]) * 0x101 |
| sg := uint32(spix[i+1]) * 0x101 |
| sb := uint32(spix[i+2]) * 0x101 |
| sa := uint32(spix[i+3]) * 0x101 |
| |
| dr := uint32(dpix[i+0]) |
| dg := uint32(dpix[i+1]) |
| db := uint32(dpix[i+2]) |
| da := uint32(dpix[i+3]) |
| |
| // The 0x101 is here for the same reason as in drawRGBA. |
| a := (m - sa) * 0x101 |
| |
| dpix[i+0] = uint8((dr*a/m + sr) >> 8) |
| dpix[i+1] = uint8((dg*a/m + sg) >> 8) |
| dpix[i+2] = uint8((db*a/m + sb) >> 8) |
| dpix[i+3] = uint8((da*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 co-ordinates 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. |
| sa := uint32(spix[si+3]) * 0x101 |
| sr := uint32(spix[si+0]) * sa / 0xff |
| sg := uint32(spix[si+1]) * sa / 0xff |
| sb := uint32(spix[si+2]) * sa / 0xff |
| |
| dr := uint32(dpix[i+0]) |
| dg := uint32(dpix[i+1]) |
| db := uint32(dpix[i+2]) |
| da := uint32(dpix[i+3]) |
| |
| // The 0x101 is here for the same reason as in drawRGBA. |
| a := (m - sa) * 0x101 |
| |
| dpix[i+0] = uint8((dr*a/m + sr) >> 8) |
| dpix[i+1] = uint8((dg*a/m + sg) >> 8) |
| dpix[i+2] = uint8((db*a/m + sb) >> 8) |
| dpix[i+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. |
| sa := uint32(spix[si+3]) * 0x101 |
| sr := uint32(spix[si+0]) * sa / 0xff |
| sg := uint32(spix[si+1]) * sa / 0xff |
| sb := uint32(spix[si+2]) * sa / 0xff |
| |
| dpix[i+0] = uint8(sr >> 8) |
| dpix[i+1] = uint8(sg >> 8) |
| dpix[i+2] = uint8(sb >> 8) |
| dpix[i+3] = uint8(sa >> 8) |
| } |
| } |
| } |
| |
| func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Point) (ok bool) { |
| // An image.YCbCr is always fully opaque, and so if the mask is implicitly nil |
| // (i.e. fully opaque) then the op is effectively always Src. |
| x0 := (r.Min.X - dst.Rect.Min.X) * 4 |
| x1 := (r.Max.X - dst.Rect.Min.X) * 4 |
| y0 := r.Min.Y - dst.Rect.Min.Y |
| y1 := r.Max.Y - dst.Rect.Min.Y |
| switch src.SubsampleRatio { |
| case image.YCbCrSubsampleRatio444: |
| for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 { |
| dpix := dst.Pix[y*dst.Stride:] |
| yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X) |
| ci := (sy-src.Rect.Min.Y)*src.CStride + (sp.X - src.Rect.Min.X) |
| for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 { |
| rr, gg, bb := color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci]) |
| dpix[x+0] = rr |
| dpix[x+1] = gg |
| dpix[x+2] = bb |
| dpix[x+3] = 255 |
| } |
| } |
| case image.YCbCrSubsampleRatio422: |
| for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 { |
| dpix := dst.Pix[y*dst.Stride:] |
| yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X) |
| ciBase := (sy-src.Rect.Min.Y)*src.CStride - src.Rect.Min.X/2 |
| for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 { |
| ci := ciBase + sx/2 |
| rr, gg, bb := color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci]) |
| dpix[x+0] = rr |
| dpix[x+1] = gg |
| dpix[x+2] = bb |
| dpix[x+3] = 255 |
| } |
| } |
| case image.YCbCrSubsampleRatio420: |
| for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 { |
| dpix := dst.Pix[y*dst.Stride:] |
| yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X) |
| ciBase := (sy/2-src.Rect.Min.Y/2)*src.CStride - src.Rect.Min.X/2 |
| for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 { |
| ci := ciBase + sx/2 |
| rr, gg, bb := color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci]) |
| dpix[x+0] = rr |
| dpix[x+1] = gg |
| dpix[x+2] = bb |
| dpix[x+3] = 255 |
| } |
| } |
| case image.YCbCrSubsampleRatio440: |
| for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 { |
| dpix := dst.Pix[y*dst.Stride:] |
| yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X) |
| ci := (sy/2-src.Rect.Min.Y/2)*src.CStride + (sp.X - src.Rect.Min.X) |
| for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 { |
| rr, gg, bb := color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci]) |
| dpix[x+0] = rr |
| dpix[x+1] = gg |
| dpix[x+2] = bb |
| dpix[x+3] = 255 |
| } |
| } |
| default: |
| return false |
| } |
| return true |
| } |
| |
| 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 |
| |
| dr := uint32(dst.Pix[i+0]) |
| dg := uint32(dst.Pix[i+1]) |
| db := uint32(dst.Pix[i+2]) |
| da := uint32(dst.Pix[i+3]) |
| |
| // The 0x101 is here for the same reason as in drawRGBA. |
| a := (m - (sa * ma / m)) * 0x101 |
| |
| dst.Pix[i+0] = uint8((dr*a + sr*ma) / m >> 8) |
| dst.Pix[i+1] = uint8((dg*a + sg*ma) / m >> 8) |
| dst.Pix[i+2] = uint8((db*a + sb*ma) / m >> 8) |
| dst.Pix[i+3] = uint8((da*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() |
| if op == Over { |
| dr := uint32(dst.Pix[i+0]) |
| dg := uint32(dst.Pix[i+1]) |
| db := uint32(dst.Pix[i+2]) |
| da := uint32(dst.Pix[i+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 |
| |
| dst.Pix[i+0] = uint8((dr*a + sr*ma) / m >> 8) |
| dst.Pix[i+1] = uint8((dg*a + sg*ma) / m >> 8) |
| dst.Pix[i+2] = uint8((db*a + sb*ma) / m >> 8) |
| dst.Pix[i+3] = uint8((da*a + sa*ma) / m >> 8) |
| |
| } else { |
| dst.Pix[i+0] = uint8(sr * ma / m >> 8) |
| dst.Pix[i+1] = uint8(sg * ma / m >> 8) |
| dst.Pix[i+2] = uint8(sb * ma / m >> 8) |
| dst.Pix[i+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 |
| } |
| |
| 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 := [][3]int32(nil), []byte(nil), 0 |
| if p, ok := dst.(*image.Paletted); ok { |
| palette = make([][3]int32, len(p.Palette)) |
| for i, col := range p.Palette { |
| r, g, b, _ := col.RGBA() |
| palette[i][0] = int32(r) |
| palette[i][1] = int32(g) |
| palette[i][2] = int32(b) |
| } |
| 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 [][3]int32 |
| if floydSteinberg { |
| quantErrorCurr = make([][3]int32, r.Dx()+2) |
| quantErrorNext = make([][3]int32, r.Dx()+2) |
| } |
| |
| // 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, _ := src.At(sp.X+x, sp.Y+y).RGBA() |
| er, eg, eb := int32(sr), int32(sg), int32(sb) |
| 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) |
| } |
| |
| if palette != nil { |
| // Find the closest palette color in Euclidean R,G,B space: the |
| // one that minimizes sum-squared-difference. We shift by 1 bit |
| // to avoid potential uint32 overflow in sum-squared-difference. |
| // TODO(nigeltao): consider smarter algorithms. |
| bestIndex, bestSSD := 0, uint32(1<<32-1) |
| for index, p := range palette { |
| delta := (er - p[0]) >> 1 |
| ssd := uint32(delta * delta) |
| delta = (eg - p[1]) >> 1 |
| ssd += uint32(delta * delta) |
| delta = (eb - p[2]) >> 1 |
| ssd += uint32(delta * delta) |
| if ssd < bestSSD { |
| bestIndex, bestSSD = index, ssd |
| if ssd == 0 { |
| break |
| } |
| } |
| } |
| pix[y*stride+x] = byte(bestIndex) |
| |
| if !floydSteinberg { |
| continue |
| } |
| er -= int32(palette[bestIndex][0]) |
| eg -= int32(palette[bestIndex][1]) |
| eb -= int32(palette[bestIndex][2]) |
| |
| } else { |
| out.R = uint16(er) |
| out.G = uint16(eg) |
| out.B = uint16(eb) |
| // 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, _ = dst.At(r.Min.X+x, r.Min.Y+y).RGBA() |
| er -= int32(sr) |
| eg -= int32(sg) |
| eb -= int32(sb) |
| } |
| |
| // 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+1][0] += er * 5 |
| quantErrorNext[x+1][1] += eg * 5 |
| quantErrorNext[x+1][2] += eb * 5 |
| quantErrorNext[x+2][0] += er * 1 |
| quantErrorNext[x+2][1] += eg * 1 |
| quantErrorNext[x+2][2] += eb * 1 |
| quantErrorCurr[x+2][0] += er * 7 |
| quantErrorCurr[x+2][1] += eg * 7 |
| quantErrorCurr[x+2][2] += eb * 7 |
| } |
| |
| // Recycle the quantization error buffers. |
| if floydSteinberg { |
| quantErrorCurr, quantErrorNext = quantErrorNext, quantErrorCurr |
| for i := range quantErrorNext { |
| quantErrorNext[i] = [3]int32{} |
| } |
| } |
| } |
| } |
