libgo/go/exp/draw/draw.go

   1 // Copyright 2009 The Go Authors.  All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Package draw provides basic graphics and drawing primitives,
   6 // in the style of the Plan 9 graphics library
   7 // (see http://plan9.bell-labs.com/magic/man2html/2/draw)
   8 // and the X Render extension.
   9 package draw
  10
  11 import "image"
  12
  13 // m is the maximum color value returned by image.Color.RGBA.
  14 const m = 1<<16 - 1
  15
  16 // A Porter-Duff compositing operator.
  17 type Op int
  18
  19 const (
  20         // Over specifies ``(src in mask) over dst''.
  21         Over Op = iota
  22         // Src specifies ``src in mask''.
  23         Src
  24 )
  25
  26 var zeroColor image.Color = image.AlphaColor{0}
  27
  28 // A draw.Image is an image.Image with a Set method to change a single pixel.
  29 type Image interface {
  30         image.Image
  31         Set(x, y int, c image.Color)
  32 }
  33
  34 // Draw calls DrawMask with a nil mask and an Over op.
  35 func Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point) {
  36         DrawMask(dst, r, src, sp, nil, image.ZP, Over)
  37 }
  38
  39 // DrawMask aligns r.Min in dst with sp in src and mp in mask and then replaces the rectangle r
  40 // in dst with the result of a Porter-Duff composition. A nil mask is treated as opaque.
  41 func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op) {
  42         sb := src.Bounds()
  43         dx, dy := sb.Max.X-sp.X, sb.Max.Y-sp.Y
  44         if mask != nil {
  45                 mb := mask.Bounds()
  46                 if dx > mb.Max.X-mp.X {
  47                         dx = mb.Max.X - mp.X
  48                 }
  49                 if dy > mb.Max.Y-mp.Y {
  50                         dy = mb.Max.Y - mp.Y
  51                 }
  52         }
  53         if r.Dx() > dx {
  54                 r.Max.X = r.Min.X + dx
  55         }
  56         if r.Dy() > dy {
  57                 r.Max.Y = r.Min.Y + dy
  58         }
  59         r = r.Intersect(dst.Bounds())
  60         if r.Empty() {
  61                 return
  62         }
  63
  64         // Fast paths for special cases. If none of them apply, then we fall back to a general but slow implementation.
  65         if dst0, ok := dst.(*image.RGBA); ok {
  66                 if op == Over {
  67                         if mask == nil {
  68                                 if src0, ok := src.(*image.ColorImage); ok {
  69                                         drawFillOver(dst0, r, src0)
  70                                         return
  71                                 }
  72                                 if src0, ok := src.(*image.RGBA); ok {
  73                                         drawCopyOver(dst0, r, src0, sp)
  74                                         return
  75                                 }
  76                         } else if mask0, ok := mask.(*image.Alpha); ok {
  77                                 if src0, ok := src.(*image.ColorImage); ok {
  78                                         drawGlyphOver(dst0, r, src0, mask0, mp)
  79                                         return
  80                                 }
  81                         }
  82                 } else {
  83                         if mask == nil {
  84                                 if src0, ok := src.(*image.ColorImage); ok {
  85                                         drawFillSrc(dst0, r, src0)
  86                                         return
  87                                 }
  88                                 if src0, ok := src.(*image.RGBA); ok {
  89                                         drawCopySrc(dst0, r, src0, sp)
  90                                         return
  91                                 }
  92                         }
  93                 }
  94                 drawRGBA(dst0, r, src, sp, mask, mp, op)
  95                 return
  96         }
  97
  98         x0, x1, dx := r.Min.X, r.Max.X, 1
  99         y0, y1, dy := r.Min.Y, r.Max.Y, 1
 100         if image.Image(dst) == src && r.Overlaps(r.Add(sp.Sub(r.Min))) {
 101                 // Rectangles overlap: process backward?
 102                 if sp.Y < r.Min.Y || sp.Y == r.Min.Y && sp.X < r.Min.X {
 103                         x0, x1, dx = x1-1, x0-1, -1
 104                         y0, y1, dy = y1-1, y0-1, -1
 105                 }
 106         }
 107
 108         var out *image.RGBA64Color
 109         sy := sp.Y + y0 - r.Min.Y
 110         my := mp.Y + y0 - r.Min.Y
 111         for y := y0; y != y1; y, sy, my = y+dy, sy+dy, my+dy {
 112                 sx := sp.X + x0 - r.Min.X
 113                 mx := mp.X + x0 - r.Min.X
 114                 for x := x0; x != x1; x, sx, mx = x+dx, sx+dx, mx+dx {
 115                         ma := uint32(m)
 116                         if mask != nil {
 117                                 _, _, _, ma = mask.At(mx, my).RGBA()
 118                         }
 119                         switch {
 120                         case ma == 0:
 121                                 if op == Over {
 122                                         // No-op.
 123                                 } else {
 124                                         dst.Set(x, y, zeroColor)
 125                                 }
 126                         case ma == m && op == Src:
 127                                 dst.Set(x, y, src.At(sx, sy))
 128                         default:
 129                                 sr, sg, sb, sa := src.At(sx, sy).RGBA()
 130                                 if out == nil {
 131                                         out = new(image.RGBA64Color)
 132                                 }
 133                                 if op == Over {
 134                                         dr, dg, db, da := dst.At(x, y).RGBA()
 135                                         a := m - (sa * ma / m)
 136                                         out.R = uint16((dr*a + sr*ma) / m)
 137                                         out.G = uint16((dg*a + sg*ma) / m)
 138                                         out.B = uint16((db*a + sb*ma) / m)
 139                                         out.A = uint16((da*a + sa*ma) / m)
 140                                 } else {
 141                                         out.R = uint16(sr * ma / m)
 142                                         out.G = uint16(sg * ma / m)
 143                                         out.B = uint16(sb * ma / m)
 144                                         out.A = uint16(sa * ma / m)
 145                                 }
 146                                 dst.Set(x, y, out)
 147                         }
 148                 }
 149         }
 150 }
 151
 152 func drawFillOver(dst *image.RGBA, r image.Rectangle, src *image.ColorImage) {
 153         cr, cg, cb, ca := src.RGBA()
 154         // The 0x101 is here for the same reason as in drawRGBA.
 155         a := (m - ca) * 0x101
 156         x0, x1 := r.Min.X, r.Max.X
 157         y0, y1 := r.Min.Y, r.Max.Y
 158         for y := y0; y != y1; y++ {
 159                 dbase := y * dst.Stride
 160                 dpix := dst.Pix[dbase+x0 : dbase+x1]
 161                 for i, rgba := range dpix {
 162                         dr := (uint32(rgba.R)*a)/m + cr
 163                         dg := (uint32(rgba.G)*a)/m + cg
 164                         db := (uint32(rgba.B)*a)/m + cb
 165                         da := (uint32(rgba.A)*a)/m + ca
 166                         dpix[i] = image.RGBAColor{uint8(dr >> 8), uint8(dg >> 8), uint8(db >> 8), uint8(da >> 8)}
 167                 }
 168         }
 169 }
 170
 171 func drawCopyOver(dst *image.RGBA, r image.Rectangle, src *image.RGBA, sp image.Point) {
 172         dx0, dx1 := r.Min.X, r.Max.X
 173         dy0, dy1 := r.Min.Y, r.Max.Y
 174         nrows := dy1 - dy0
 175         sx0, sx1 := sp.X, sp.X+dx1-dx0
 176         d0 := dy0*dst.Stride + dx0
 177         d1 := dy0*dst.Stride + dx1
 178         s0 := sp.Y*src.Stride + sx0
 179         s1 := sp.Y*src.Stride + sx1
 180         var (
 181                 ddelta, sdelta int
 182                 i0, i1, idelta int
 183         )
 184         if r.Min.Y < sp.Y || r.Min.Y == sp.Y && r.Min.X <= sp.X {
 185                 ddelta = dst.Stride
 186                 sdelta = src.Stride
 187                 i0, i1, idelta = 0, d1-d0, +1
 188         } else {
 189                 // If the source start point is higher than the destination start point, or equal height but to the left,
 190                 // then we compose the rows in right-to-left, bottom-up order instead of left-to-right, top-down.
 191                 d0 += (nrows - 1) * dst.Stride
 192                 d1 += (nrows - 1) * dst.Stride
 193                 s0 += (nrows - 1) * src.Stride
 194                 s1 += (nrows - 1) * src.Stride
 195                 ddelta = -dst.Stride
 196                 sdelta = -src.Stride
 197                 i0, i1, idelta = d1-d0-1, -1, -1
 198         }
 199         for ; nrows > 0; nrows-- {
 200                 dpix := dst.Pix[d0:d1]
 201                 spix := src.Pix[s0:s1]
 202                 for i := i0; i != i1; i += idelta {
 203                         // For unknown reasons, even though both dpix[i] and spix[i] are
 204                         // image.RGBAColors, on an x86 CPU it seems fastest to call RGBA
 205                         // for the source but to do it manually for the destination.
 206                         sr, sg, sb, sa := spix[i].RGBA()
 207                         rgba := dpix[i]
 208                         dr := uint32(rgba.R)
 209                         dg := uint32(rgba.G)
 210                         db := uint32(rgba.B)
 211                         da := uint32(rgba.A)
 212                         // The 0x101 is here for the same reason as in drawRGBA.
 213                         a := (m - sa) * 0x101
 214                         dr = (dr*a)/m + sr
 215                         dg = (dg*a)/m + sg
 216                         db = (db*a)/m + sb
 217                         da = (da*a)/m + sa
 218                         dpix[i] = image.RGBAColor{uint8(dr >> 8), uint8(dg >> 8), uint8(db >> 8), uint8(da >> 8)}
 219                 }
 220                 d0 += ddelta
 221                 d1 += ddelta
 222                 s0 += sdelta
 223                 s1 += sdelta
 224         }
 225 }
 226
 227 func drawGlyphOver(dst *image.RGBA, r image.Rectangle, src *image.ColorImage, mask *image.Alpha, mp image.Point) {
 228         x0, x1 := r.Min.X, r.Max.X
 229         y0, y1 := r.Min.Y, r.Max.Y
 230         cr, cg, cb, ca := src.RGBA()
 231         for y, my := y0, mp.Y; y != y1; y, my = y+1, my+1 {
 232                 dbase := y * dst.Stride
 233                 dpix := dst.Pix[dbase+x0 : dbase+x1]
 234                 mbase := my * mask.Stride
 235                 mpix := mask.Pix[mbase+mp.X:]
 236                 for i, rgba := range dpix {
 237                         ma := uint32(mpix[i].A)
 238                         if ma == 0 {
 239                                 continue
 240                         }
 241                         ma |= ma << 8
 242                         dr := uint32(rgba.R)
 243                         dg := uint32(rgba.G)
 244                         db := uint32(rgba.B)
 245                         da := uint32(rgba.A)
 246                         // The 0x101 is here for the same reason as in drawRGBA.
 247                         a := (m - (ca * ma / m)) * 0x101
 248                         dr = (dr*a + cr*ma) / m
 249                         dg = (dg*a + cg*ma) / m
 250                         db = (db*a + cb*ma) / m
 251                         da = (da*a + ca*ma) / m
 252                         dpix[i] = image.RGBAColor{uint8(dr >> 8), uint8(dg >> 8), uint8(db >> 8), uint8(da >> 8)}
 253                 }
 254         }
 255 }
 256
 257 func drawFillSrc(dst *image.RGBA, r image.Rectangle, src *image.ColorImage) {
 258         if r.Dy() < 1 {
 259                 return
 260         }
 261         cr, cg, cb, ca := src.RGBA()
 262         color := image.RGBAColor{uint8(cr >> 8), uint8(cg >> 8), uint8(cb >> 8), uint8(ca >> 8)}
 263         // The built-in copy function is faster than a straightforward for loop to fill the destination with
 264         // the color, but copy requires a slice source. We therefore use a for loop to fill the first row, and
 265         // then use the first row as the slice source for the remaining rows.
 266         dx0, dx1 := r.Min.X, r.Max.X
 267         dy0, dy1 := r.Min.Y, r.Max.Y
 268         dbase := dy0 * dst.Stride
 269         i0, i1 := dbase+dx0, dbase+dx1
 270         firstRow := dst.Pix[i0:i1]
 271         for i, _ := range firstRow {
 272                 firstRow[i] = color
 273         }
 274         for y := dy0 + 1; y < dy1; y++ {
 275                 i0 += dst.Stride
 276                 i1 += dst.Stride
 277                 copy(dst.Pix[i0:i1], firstRow)
 278         }
 279 }
 280
 281 func drawCopySrc(dst *image.RGBA, r image.Rectangle, src *image.RGBA, sp image.Point) {
 282         dx0, dx1 := r.Min.X, r.Max.X
 283         dy0, dy1 := r.Min.Y, r.Max.Y
 284         nrows := dy1 - dy0
 285         sx0, sx1 := sp.X, sp.X+dx1-dx0
 286         d0 := dy0*dst.Stride + dx0
 287         d1 := dy0*dst.Stride + dx1
 288         s0 := sp.Y*src.Stride + sx0
 289         s1 := sp.Y*src.Stride + sx1
 290         var ddelta, sdelta int
 291         if r.Min.Y <= sp.Y {
 292                 ddelta = dst.Stride
 293                 sdelta = src.Stride
 294         } else {
 295                 // If the source start point is higher than the destination start point, then we compose the rows
 296                 // in bottom-up order instead of top-down. Unlike the drawCopyOver function, we don't have to
 297                 // check the x co-ordinates because the built-in copy function can handle overlapping slices.
 298                 d0 += (nrows - 1) * dst.Stride
 299                 d1 += (nrows - 1) * dst.Stride
 300                 s0 += (nrows - 1) * src.Stride
 301                 s1 += (nrows - 1) * src.Stride
 302                 ddelta = -dst.Stride
 303                 sdelta = -src.Stride
 304         }
 305         for ; nrows > 0; nrows-- {
 306                 copy(dst.Pix[d0:d1], src.Pix[s0:s1])
 307                 d0 += ddelta
 308                 d1 += ddelta
 309                 s0 += sdelta
 310                 s1 += sdelta
 311         }
 312 }
 313
 314 func drawRGBA(dst *image.RGBA, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op) {
 315         x0, x1, dx := r.Min.X, r.Max.X, 1
 316         y0, y1, dy := r.Min.Y, r.Max.Y, 1
 317         if image.Image(dst) == src && r.Overlaps(r.Add(sp.Sub(r.Min))) {
 318                 if sp.Y < r.Min.Y || sp.Y == r.Min.Y && sp.X < r.Min.X {
 319                         x0, x1, dx = x1-1, x0-1, -1
 320                         y0, y1, dy = y1-1, y0-1, -1
 321                 }
 322         }
 323
 324         sy := sp.Y + y0 - r.Min.Y
 325         my := mp.Y + y0 - r.Min.Y
 326         for y := y0; y != y1; y, sy, my = y+dy, sy+dy, my+dy {
 327                 sx := sp.X + x0 - r.Min.X
 328                 mx := mp.X + x0 - r.Min.X
 329                 dpix := dst.Pix[y*dst.Stride : (y+1)*dst.Stride]
 330                 for x := x0; x != x1; x, sx, mx = x+dx, sx+dx, mx+dx {
 331                         ma := uint32(m)
 332                         if mask != nil {
 333                                 _, _, _, ma = mask.At(mx, my).RGBA()
 334                         }
 335                         sr, sg, sb, sa := src.At(sx, sy).RGBA()
 336                         var dr, dg, db, da uint32
 337                         if op == Over {
 338                                 rgba := dpix[x]
 339                                 dr = uint32(rgba.R)
 340                                 dg = uint32(rgba.G)
 341                                 db = uint32(rgba.B)
 342                                 da = uint32(rgba.A)
 343                                 // dr, dg, db and da are all 8-bit color at the moment, ranging in [0,255].
 344                                 // We work in 16-bit color, and so would normally do:
 345                                 // dr |= dr << 8
 346                                 // and similarly for dg, db and da, but instead we multiply a
 347                                 // (which is a 16-bit color, ranging in [0,65535]) by 0x101.
 348                                 // This yields the same result, but is fewer arithmetic operations.
 349                                 a := (m - (sa * ma / m)) * 0x101
 350                                 dr = (dr*a + sr*ma) / m
 351                                 dg = (dg*a + sg*ma) / m
 352                                 db = (db*a + sb*ma) / m
 353                                 da = (da*a + sa*ma) / m
 354                         } else {
 355                                 dr = sr * ma / m
 356                                 dg = sg * ma / m
 357                                 db = sb * ma / m
 358                                 da = sa * ma / m
 359                         }
 360                         dpix[x] = image.RGBAColor{uint8(dr >> 8), uint8(dg >> 8), uint8(db >> 8), uint8(da >> 8)}
 361                 }
 362         }
 363 }
 364
 365 // Border aligns r.Min in dst with sp in src and then replaces pixels
 366 // in a w-pixel border around r in dst with the result of the Porter-Duff compositing
 367 // operation ``src over dst.''  If w is positive, the border extends w pixels inside r.
 368 // If w is negative, the border extends w pixels outside r.
 369 func Border(dst Image, r image.Rectangle, w int, src image.Image, sp image.Point) {
 370         i := w
 371         if i > 0 {
 372                 // inside r
 373                 Draw(dst, image.Rect(r.Min.X, r.Min.Y, r.Max.X, r.Min.Y+i), src, sp)                                // top
 374                 Draw(dst, image.Rect(r.Min.X, r.Min.Y+i, r.Min.X+i, r.Max.Y-i), src, sp.Add(image.Pt(0, i)))        // left
 375                 Draw(dst, image.Rect(r.Max.X-i, r.Min.Y+i, r.Max.X, r.Max.Y-i), src, sp.Add(image.Pt(r.Dx()-i, i))) // right
 376                 Draw(dst, image.Rect(r.Min.X, r.Max.Y-i, r.Max.X, r.Max.Y), src, sp.Add(image.Pt(0, r.Dy()-i)))     // bottom
 377                 return
 378         }
 379
 380         // outside r;
 381         i = -i
 382         Draw(dst, image.Rect(r.Min.X-i, r.Min.Y-i, r.Max.X+i, r.Min.Y), src, sp.Add(image.Pt(-i, -i))) // top
 383         Draw(dst, image.Rect(r.Min.X-i, r.Min.Y, r.Min.X, r.Max.Y), src, sp.Add(image.Pt(-i, 0)))      // left
 384         Draw(dst, image.Rect(r.Max.X, r.Min.Y, r.Max.X+i, r.Max.Y), src, sp.Add(image.Pt(r.Dx(), 0)))  // right
 385         Draw(dst, image.Rect(r.Min.X-i, r.Max.Y, r.Max.X+i, r.Max.Y+i), src, sp.Add(image.Pt(-i, 0)))  // bottom
 386 }