Source file src/pkg/image/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 image composition functions. 6 // 7 // See "The Go image/draw package" for an introduction to this package: 8 // http://golang.org/doc/articles/image_draw.html 9 package draw 10 11 import ( 12 "image" 13 "image/color" 14 ) 15 16 // m is the maximum color value returned by image.Color.RGBA. 17 const m = 1<<16 - 1 18 19 // Op is a Porter-Duff compositing operator. 20 type Op int 21 22 const ( 23 // Over specifies ``(src in mask) over dst''. 24 Over Op = iota 25 // Src specifies ``src in mask''. 26 Src 27 ) 28 29 // A draw.Image is an image.Image with a Set method to change a single pixel. 30 type Image interface { 31 image.Image 32 Set(x, y int, c color.Color) 33 } 34 35 // Draw calls DrawMask with a nil mask. 36 func Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point, op Op) { 37 DrawMask(dst, r, src, sp, nil, image.ZP, op) 38 } 39 40 // clip clips r against each image's bounds (after translating into the 41 // destination image's co-ordinate space) and shifts the points sp and mp by 42 // the same amount as the change in r.Min. 43 func clip(dst Image, r *image.Rectangle, src image.Image, sp *image.Point, mask image.Image, mp *image.Point) { 44 orig := r.Min 45 *r = r.Intersect(dst.Bounds()) 46 *r = r.Intersect(src.Bounds().Add(orig.Sub(*sp))) 47 if mask != nil { 48 *r = r.Intersect(mask.Bounds().Add(orig.Sub(*mp))) 49 } 50 dx := r.Min.X - orig.X 51 dy := r.Min.Y - orig.Y 52 if dx == 0 && dy == 0 { 53 return 54 } 55 (*sp).X += dx 56 (*sp).Y += dy 57 (*mp).X += dx 58 (*mp).Y += dy 59 } 60 61 // DrawMask aligns r.Min in dst with sp in src and mp in mask and then replaces the rectangle r 62 // in dst with the result of a Porter-Duff composition. A nil mask is treated as opaque. 63 func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op) { 64 clip(dst, &r, src, &sp, mask, &mp) 65 if r.Empty() { 66 return 67 } 68 69 // Fast paths for special cases. If none of them apply, then we fall back to a general but slow implementation. 70 if dst0, ok := dst.(*image.RGBA); ok { 71 if op == Over { 72 if mask == nil { 73 switch src0 := src.(type) { 74 case *image.Uniform: 75 drawFillOver(dst0, r, src0) 76 return 77 case *image.RGBA: 78 drawCopyOver(dst0, r, src0, sp) 79 return 80 case *image.NRGBA: 81 drawNRGBAOver(dst0, r, src0, sp) 82 return 83 case *image.YCbCr: 84 drawYCbCr(dst0, r, src0, sp) 85 return 86 } 87 } else if mask0, ok := mask.(*image.Alpha); ok { 88 switch src0 := src.(type) { 89 case *image.Uniform: 90 drawGlyphOver(dst0, r, src0, mask0, mp) 91 return 92 } 93 } 94 } else { 95 if mask == nil { 96 switch src0 := src.(type) { 97 case *image.Uniform: 98 drawFillSrc(dst0, r, src0) 99 return 100 case *image.RGBA: 101 drawCopySrc(dst0, r, src0, sp) 102 return 103 case *image.NRGBA: 104 drawNRGBASrc(dst0, r, src0, sp) 105 return 106 case *image.YCbCr: 107 drawYCbCr(dst0, r, src0, sp) 108 return 109 } 110 } 111 } 112 drawRGBA(dst0, r, src, sp, mask, mp, op) 113 return 114 } 115 116 x0, x1, dx := r.Min.X, r.Max.X, 1 117 y0, y1, dy := r.Min.Y, r.Max.Y, 1 118 if image.Image(dst) == src && r.Overlaps(r.Add(sp.Sub(r.Min))) { 119 // Rectangles overlap: process backward? 120 if sp.Y < r.Min.Y || sp.Y == r.Min.Y && sp.X < r.Min.X { 121 x0, x1, dx = x1-1, x0-1, -1 122 y0, y1, dy = y1-1, y0-1, -1 123 } 124 } 125 126 var out *color.RGBA64 127 sy := sp.Y + y0 - r.Min.Y 128 my := mp.Y + y0 - r.Min.Y 129 for y := y0; y != y1; y, sy, my = y+dy, sy+dy, my+dy { 130 sx := sp.X + x0 - r.Min.X 131 mx := mp.X + x0 - r.Min.X 132 for x := x0; x != x1; x, sx, mx = x+dx, sx+dx, mx+dx { 133 ma := uint32(m) 134 if mask != nil { 135 _, _, _, ma = mask.At(mx, my).RGBA() 136 } 137 switch { 138 case ma == 0: 139 if op == Over { 140 // No-op. 141 } else { 142 dst.Set(x, y, color.Transparent) 143 } 144 case ma == m && op == Src: 145 dst.Set(x, y, src.At(sx, sy)) 146 default: 147 sr, sg, sb, sa := src.At(sx, sy).RGBA() 148 if out == nil { 149 out = new(color.RGBA64) 150 } 151 if op == Over { 152 dr, dg, db, da := dst.At(x, y).RGBA() 153 a := m - (sa * ma / m) 154 out.R = uint16((dr*a + sr*ma) / m) 155 out.G = uint16((dg*a + sg*ma) / m) 156 out.B = uint16((db*a + sb*ma) / m) 157 out.A = uint16((da*a + sa*ma) / m) 158 } else { 159 out.R = uint16(sr * ma / m) 160 out.G = uint16(sg * ma / m) 161 out.B = uint16(sb * ma / m) 162 out.A = uint16(sa * ma / m) 163 } 164 dst.Set(x, y, out) 165 } 166 } 167 } 168 } 169 170 func drawFillOver(dst *image.RGBA, r image.Rectangle, src *image.Uniform) { 171 sr, sg, sb, sa := src.RGBA() 172 // The 0x101 is here for the same reason as in drawRGBA. 173 a := (m - sa) * 0x101 174 i0 := dst.PixOffset(r.Min.X, r.Min.Y) 175 i1 := i0 + r.Dx()*4 176 for y := r.Min.Y; y != r.Max.Y; y++ { 177 for i := i0; i < i1; i += 4 { 178 dr := uint32(dst.Pix[i+0]) 179 dg := uint32(dst.Pix[i+1]) 180 db := uint32(dst.Pix[i+2]) 181 da := uint32(dst.Pix[i+3]) 182 183 dst.Pix[i+0] = uint8((dr*a/m + sr) >> 8) 184 dst.Pix[i+1] = uint8((dg*a/m + sg) >> 8) 185 dst.Pix[i+2] = uint8((db*a/m + sb) >> 8) 186 dst.Pix[i+3] = uint8((da*a/m + sa) >> 8) 187 } 188 i0 += dst.Stride 189 i1 += dst.Stride 190 } 191 } 192 193 func drawFillSrc(dst *image.RGBA, r image.Rectangle, src *image.Uniform) { 194 sr, sg, sb, sa := src.RGBA() 195 // The built-in copy function is faster than a straightforward for loop to fill the destination with 196 // the color, but copy requires a slice source. We therefore use a for loop to fill the first row, and 197 // then use the first row as the slice source for the remaining rows. 198 i0 := dst.PixOffset(r.Min.X, r.Min.Y) 199 i1 := i0 + r.Dx()*4 200 for i := i0; i < i1; i += 4 { 201 dst.Pix[i+0] = uint8(sr >> 8) 202 dst.Pix[i+1] = uint8(sg >> 8) 203 dst.Pix[i+2] = uint8(sb >> 8) 204 dst.Pix[i+3] = uint8(sa >> 8) 205 } 206 firstRow := dst.Pix[i0:i1] 207 for y := r.Min.Y + 1; y < r.Max.Y; y++ { 208 i0 += dst.Stride 209 i1 += dst.Stride 210 copy(dst.Pix[i0:i1], firstRow) 211 } 212 } 213 214 func drawCopyOver(dst *image.RGBA, r image.Rectangle, src *image.RGBA, sp image.Point) { 215 dx, dy := r.Dx(), r.Dy() 216 d0 := dst.PixOffset(r.Min.X, r.Min.Y) 217 s0 := src.PixOffset(sp.X, sp.Y) 218 var ( 219 ddelta, sdelta int 220 i0, i1, idelta int 221 ) 222 if r.Min.Y < sp.Y || r.Min.Y == sp.Y && r.Min.X <= sp.X { 223 ddelta = dst.Stride 224 sdelta = src.Stride 225 i0, i1, idelta = 0, dx*4, +4 226 } else { 227 // If the source start point is higher than the destination start point, or equal height but to the left, 228 // then we compose the rows in right-to-left, bottom-up order instead of left-to-right, top-down. 229 d0 += (dy - 1) * dst.Stride 230 s0 += (dy - 1) * src.Stride 231 ddelta = -dst.Stride 232 sdelta = -src.Stride 233 i0, i1, idelta = (dx-1)*4, -4, -4 234 } 235 for ; dy > 0; dy-- { 236 dpix := dst.Pix[d0:] 237 spix := src.Pix[s0:] 238 for i := i0; i != i1; i += idelta { 239 sr := uint32(spix[i+0]) * 0x101 240 sg := uint32(spix[i+1]) * 0x101 241 sb := uint32(spix[i+2]) * 0x101 242 sa := uint32(spix[i+3]) * 0x101 243 244 dr := uint32(dpix[i+0]) 245 dg := uint32(dpix[i+1]) 246 db := uint32(dpix[i+2]) 247 da := uint32(dpix[i+3]) 248 249 // The 0x101 is here for the same reason as in drawRGBA. 250 a := (m - sa) * 0x101 251 252 dpix[i+0] = uint8((dr*a/m + sr) >> 8) 253 dpix[i+1] = uint8((dg*a/m + sg) >> 8) 254 dpix[i+2] = uint8((db*a/m + sb) >> 8) 255 dpix[i+3] = uint8((da*a/m + sa) >> 8) 256 } 257 d0 += ddelta 258 s0 += sdelta 259 } 260 } 261 262 func drawCopySrc(dst *image.RGBA, r image.Rectangle, src *image.RGBA, sp image.Point) { 263 n, dy := 4*r.Dx(), r.Dy() 264 d0 := dst.PixOffset(r.Min.X, r.Min.Y) 265 s0 := src.PixOffset(sp.X, sp.Y) 266 var ddelta, sdelta int 267 if r.Min.Y <= sp.Y { 268 ddelta = dst.Stride 269 sdelta = src.Stride 270 } else { 271 // If the source start point is higher than the destination start point, then we compose the rows 272 // in bottom-up order instead of top-down. Unlike the drawCopyOver function, we don't have to 273 // check the x co-ordinates because the built-in copy function can handle overlapping slices. 274 d0 += (dy - 1) * dst.Stride 275 s0 += (dy - 1) * src.Stride 276 ddelta = -dst.Stride 277 sdelta = -src.Stride 278 } 279 for ; dy > 0; dy-- { 280 copy(dst.Pix[d0:d0+n], src.Pix[s0:s0+n]) 281 d0 += ddelta 282 s0 += sdelta 283 } 284 } 285 286 func drawNRGBAOver(dst *image.RGBA, r image.Rectangle, src *image.NRGBA, sp image.Point) { 287 i0 := (r.Min.X - dst.Rect.Min.X) * 4 288 i1 := (r.Max.X - dst.Rect.Min.X) * 4 289 si0 := (sp.X - src.Rect.Min.X) * 4 290 yMax := r.Max.Y - dst.Rect.Min.Y 291 292 y := r.Min.Y - dst.Rect.Min.Y 293 sy := sp.Y - src.Rect.Min.Y 294 for ; y != yMax; y, sy = y+1, sy+1 { 295 dpix := dst.Pix[y*dst.Stride:] 296 spix := src.Pix[sy*src.Stride:] 297 298 for i, si := i0, si0; i < i1; i, si = i+4, si+4 { 299 // Convert from non-premultiplied color to pre-multiplied color. 300 sa := uint32(spix[si+3]) * 0x101 301 sr := uint32(spix[si+0]) * sa / 0xff 302 sg := uint32(spix[si+1]) * sa / 0xff 303 sb := uint32(spix[si+2]) * sa / 0xff 304 305 dr := uint32(dpix[i+0]) 306 dg := uint32(dpix[i+1]) 307 db := uint32(dpix[i+2]) 308 da := uint32(dpix[i+3]) 309 310 // The 0x101 is here for the same reason as in drawRGBA. 311 a := (m - sa) * 0x101 312 313 dpix[i+0] = uint8((dr*a/m + sr) >> 8) 314 dpix[i+1] = uint8((dg*a/m + sg) >> 8) 315 dpix[i+2] = uint8((db*a/m + sb) >> 8) 316 dpix[i+3] = uint8((da*a/m + sa) >> 8) 317 } 318 } 319 } 320 321 func drawNRGBASrc(dst *image.RGBA, r image.Rectangle, src *image.NRGBA, sp image.Point) { 322 i0 := (r.Min.X - dst.Rect.Min.X) * 4 323 i1 := (r.Max.X - dst.Rect.Min.X) * 4 324 si0 := (sp.X - src.Rect.Min.X) * 4 325 yMax := r.Max.Y - dst.Rect.Min.Y 326 327 y := r.Min.Y - dst.Rect.Min.Y 328 sy := sp.Y - src.Rect.Min.Y 329 for ; y != yMax; y, sy = y+1, sy+1 { 330 dpix := dst.Pix[y*dst.Stride:] 331 spix := src.Pix[sy*src.Stride:] 332 333 for i, si := i0, si0; i < i1; i, si = i+4, si+4 { 334 // Convert from non-premultiplied color to pre-multiplied color. 335 sa := uint32(spix[si+3]) * 0x101 336 sr := uint32(spix[si+0]) * sa / 0xff 337 sg := uint32(spix[si+1]) * sa / 0xff 338 sb := uint32(spix[si+2]) * sa / 0xff 339 340 dpix[i+0] = uint8(sr >> 8) 341 dpix[i+1] = uint8(sg >> 8) 342 dpix[i+2] = uint8(sb >> 8) 343 dpix[i+3] = uint8(sa >> 8) 344 } 345 } 346 } 347 348 func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Point) { 349 // An image.YCbCr is always fully opaque, and so if the mask is implicitly nil 350 // (i.e. fully opaque) then the op is effectively always Src. 351 x0 := (r.Min.X - dst.Rect.Min.X) * 4 352 x1 := (r.Max.X - dst.Rect.Min.X) * 4 353 y0 := r.Min.Y - dst.Rect.Min.Y 354 y1 := r.Max.Y - dst.Rect.Min.Y 355 switch src.SubsampleRatio { 356 case image.YCbCrSubsampleRatio422: 357 for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 { 358 dpix := dst.Pix[y*dst.Stride:] 359 yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X) 360 ciBase := (sy-src.Rect.Min.Y)*src.CStride - src.Rect.Min.X/2 361 for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 { 362 ci := ciBase + sx/2 363 rr, gg, bb := color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci]) 364 dpix[x+0] = rr 365 dpix[x+1] = gg 366 dpix[x+2] = bb 367 dpix[x+3] = 255 368 } 369 } 370 case image.YCbCrSubsampleRatio420: 371 for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 { 372 dpix := dst.Pix[y*dst.Stride:] 373 yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X) 374 ciBase := (sy/2-src.Rect.Min.Y/2)*src.CStride - src.Rect.Min.X/2 375 for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 { 376 ci := ciBase + sx/2 377 rr, gg, bb := color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci]) 378 dpix[x+0] = rr 379 dpix[x+1] = gg 380 dpix[x+2] = bb 381 dpix[x+3] = 255 382 } 383 } 384 default: 385 // Default to 4:4:4 subsampling. 386 for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 { 387 dpix := dst.Pix[y*dst.Stride:] 388 yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X) 389 ci := (sy-src.Rect.Min.Y)*src.CStride + (sp.X - src.Rect.Min.X) 390 for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 { 391 rr, gg, bb := color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci]) 392 dpix[x+0] = rr 393 dpix[x+1] = gg 394 dpix[x+2] = bb 395 dpix[x+3] = 255 396 } 397 } 398 } 399 } 400 401 func drawGlyphOver(dst *image.RGBA, r image.Rectangle, src *image.Uniform, mask *image.Alpha, mp image.Point) { 402 i0 := dst.PixOffset(r.Min.X, r.Min.Y) 403 i1 := i0 + r.Dx()*4 404 mi0 := mask.PixOffset(mp.X, mp.Y) 405 sr, sg, sb, sa := src.RGBA() 406 for y, my := r.Min.Y, mp.Y; y != r.Max.Y; y, my = y+1, my+1 { 407 for i, mi := i0, mi0; i < i1; i, mi = i+4, mi+1 { 408 ma := uint32(mask.Pix[mi]) 409 if ma == 0 { 410 continue 411 } 412 ma |= ma << 8 413 414 dr := uint32(dst.Pix[i+0]) 415 dg := uint32(dst.Pix[i+1]) 416 db := uint32(dst.Pix[i+2]) 417 da := uint32(dst.Pix[i+3]) 418 419 // The 0x101 is here for the same reason as in drawRGBA. 420 a := (m - (sa * ma / m)) * 0x101 421 422 dst.Pix[i+0] = uint8((dr*a + sr*ma) / m >> 8) 423 dst.Pix[i+1] = uint8((dg*a + sg*ma) / m >> 8) 424 dst.Pix[i+2] = uint8((db*a + sb*ma) / m >> 8) 425 dst.Pix[i+3] = uint8((da*a + sa*ma) / m >> 8) 426 } 427 i0 += dst.Stride 428 i1 += dst.Stride 429 mi0 += mask.Stride 430 } 431 } 432 433 func drawRGBA(dst *image.RGBA, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op) { 434 x0, x1, dx := r.Min.X, r.Max.X, 1 435 y0, y1, dy := r.Min.Y, r.Max.Y, 1 436 if image.Image(dst) == src && r.Overlaps(r.Add(sp.Sub(r.Min))) { 437 if sp.Y < r.Min.Y || sp.Y == r.Min.Y && sp.X < r.Min.X { 438 x0, x1, dx = x1-1, x0-1, -1 439 y0, y1, dy = y1-1, y0-1, -1 440 } 441 } 442 443 sy := sp.Y + y0 - r.Min.Y 444 my := mp.Y + y0 - r.Min.Y 445 sx0 := sp.X + x0 - r.Min.X 446 mx0 := mp.X + x0 - r.Min.X 447 sx1 := sx0 + (x1 - x0) 448 i0 := dst.PixOffset(x0, y0) 449 di := dx * 4 450 for y := y0; y != y1; y, sy, my = y+dy, sy+dy, my+dy { 451 for i, sx, mx := i0, sx0, mx0; sx != sx1; i, sx, mx = i+di, sx+dx, mx+dx { 452 ma := uint32(m) 453 if mask != nil { 454 _, _, _, ma = mask.At(mx, my).RGBA() 455 } 456 sr, sg, sb, sa := src.At(sx, sy).RGBA() 457 if op == Over { 458 dr := uint32(dst.Pix[i+0]) 459 dg := uint32(dst.Pix[i+1]) 460 db := uint32(dst.Pix[i+2]) 461 da := uint32(dst.Pix[i+3]) 462 463 // dr, dg, db and da are all 8-bit color at the moment, ranging in [0,255]. 464 // We work in 16-bit color, and so would normally do: 465 // dr |= dr << 8 466 // and similarly for dg, db and da, but instead we multiply a 467 // (which is a 16-bit color, ranging in [0,65535]) by 0x101. 468 // This yields the same result, but is fewer arithmetic operations. 469 a := (m - (sa * ma / m)) * 0x101 470 471 dst.Pix[i+0] = uint8((dr*a + sr*ma) / m >> 8) 472 dst.Pix[i+1] = uint8((dg*a + sg*ma) / m >> 8) 473 dst.Pix[i+2] = uint8((db*a + sb*ma) / m >> 8) 474 dst.Pix[i+3] = uint8((da*a + sa*ma) / m >> 8) 475 476 } else { 477 dst.Pix[i+0] = uint8(sr * ma / m >> 8) 478 dst.Pix[i+1] = uint8(sg * ma / m >> 8) 479 dst.Pix[i+2] = uint8(sb * ma / m >> 8) 480 dst.Pix[i+3] = uint8(sa * ma / m >> 8) 481 } 482 } 483 i0 += dy * dst.Stride 484 } 485 }