third_party/libwebp/dec/io.c

   1 // Copyright 2011 Google Inc. All Rights Reserved.
   2 //
   3 // Use of this source code is governed by a BSD-style license
   4 // that can be found in the COPYING file in the root of the source
   5 // tree. An additional intellectual property rights grant can be found
   6 // in the file PATENTS. All contributing project authors may
   7 // be found in the AUTHORS file in the root of the source tree.
   8 // -----------------------------------------------------------------------------
   9 //
  10 // functions for sample output.
  11 //
  12 // Author: Skal (pascal.massimino@gmail.com)
  13
  14 #include <assert.h>
  15 #include <stdlib.h>
  16 #include "../dec/vp8i.h"
  17 #include "./webpi.h"
  18 #include "../dsp/dsp.h"
  19 #include "../dsp/yuv.h"
  20 #include "../utils/utils.h"
  21
  22 //------------------------------------------------------------------------------
  23 // Main YUV<->RGB conversion functions
  24
  25 static int EmitYUV(const VP8Io* const io, WebPDecParams* const p) {
  26   WebPDecBuffer* output = p->output;
  27   const WebPYUVABuffer* const buf = &output->u.YUVA;
  28   uint8_t* const y_dst = buf->y + io->mb_y * buf->y_stride;
  29   uint8_t* const u_dst = buf->u + (io->mb_y >> 1) * buf->u_stride;
  30   uint8_t* const v_dst = buf->v + (io->mb_y >> 1) * buf->v_stride;
  31   const int mb_w = io->mb_w;
  32   const int mb_h = io->mb_h;
  33   const int uv_w = (mb_w + 1) / 2;
  34   const int uv_h = (mb_h + 1) / 2;
  35   int j;
  36   for (j = 0; j < mb_h; ++j) {
  37     memcpy(y_dst + j * buf->y_stride, io->y + j * io->y_stride, mb_w);
  38   }
  39   for (j = 0; j < uv_h; ++j) {
  40     memcpy(u_dst + j * buf->u_stride, io->u + j * io->uv_stride, uv_w);
  41     memcpy(v_dst + j * buf->v_stride, io->v + j * io->uv_stride, uv_w);
  42   }
  43   return io->mb_h;
  44 }
  45
  46 // Point-sampling U/V sampler.
  47 static int EmitSampledRGB(const VP8Io* const io, WebPDecParams* const p) {
  48   WebPDecBuffer* const output = p->output;
  49   WebPRGBABuffer* const buf = &output->u.RGBA;
  50   uint8_t* const dst = buf->rgba + io->mb_y * buf->stride;
  51   WebPSamplerProcessPlane(io->y, io->y_stride,
  52                           io->u, io->v, io->uv_stride,
  53                           dst, buf->stride, io->mb_w, io->mb_h,
  54                           WebPSamplers[output->colorspace]);
  55   return io->mb_h;
  56 }
  57
  58 //------------------------------------------------------------------------------
  59 // YUV444 -> RGB conversion
  60
  61 #if 0   // TODO(skal): this is for future rescaling.
  62 static int EmitRGB(const VP8Io* const io, WebPDecParams* const p) {
  63   WebPDecBuffer* output = p->output;
  64   const WebPRGBABuffer* const buf = &output->u.RGBA;
  65   uint8_t* dst = buf->rgba + io->mb_y * buf->stride;
  66   const uint8_t* y_src = io->y;
  67   const uint8_t* u_src = io->u;
  68   const uint8_t* v_src = io->v;
  69   const WebPYUV444Converter convert = WebPYUV444Converters[output->colorspace];
  70   const int mb_w = io->mb_w;
  71   const int last = io->mb_h;
  72   int j;
  73   for (j = 0; j < last; ++j) {
  74     convert(y_src, u_src, v_src, dst, mb_w);
  75     y_src += io->y_stride;
  76     u_src += io->uv_stride;
  77     v_src += io->uv_stride;
  78     dst += buf->stride;
  79   }
  80   return io->mb_h;
  81 }
  82 #endif
  83
  84 //------------------------------------------------------------------------------
  85 // Fancy upsampling
  86
  87 #ifdef FANCY_UPSAMPLING
  88 static int EmitFancyRGB(const VP8Io* const io, WebPDecParams* const p) {
  89   int num_lines_out = io->mb_h;   // a priori guess
  90   const WebPRGBABuffer* const buf = &p->output->u.RGBA;
  91   uint8_t* dst = buf->rgba + io->mb_y * buf->stride;
  92   WebPUpsampleLinePairFunc upsample = WebPUpsamplers[p->output->colorspace];
  93   const uint8_t* cur_y = io->y;
  94   const uint8_t* cur_u = io->u;
  95   const uint8_t* cur_v = io->v;
  96   const uint8_t* top_u = p->tmp_u;
  97   const uint8_t* top_v = p->tmp_v;
  98   int y = io->mb_y;
  99   const int y_end = io->mb_y + io->mb_h;
 100   const int mb_w = io->mb_w;
 101   const int uv_w = (mb_w + 1) / 2;
 102
 103   if (y == 0) {
 104     // First line is special cased. We mirror the u/v samples at boundary.
 105     upsample(cur_y, NULL, cur_u, cur_v, cur_u, cur_v, dst, NULL, mb_w);
 106   } else {
 107     // We can finish the left-over line from previous call.
 108     upsample(p->tmp_y, cur_y, top_u, top_v, cur_u, cur_v,
 109              dst - buf->stride, dst, mb_w);
 110     ++num_lines_out;
 111   }
 112   // Loop over each output pairs of row.
 113   for (; y + 2 < y_end; y += 2) {
 114     top_u = cur_u;
 115     top_v = cur_v;
 116     cur_u += io->uv_stride;
 117     cur_v += io->uv_stride;
 118     dst += 2 * buf->stride;
 119     cur_y += 2 * io->y_stride;
 120     upsample(cur_y - io->y_stride, cur_y,
 121              top_u, top_v, cur_u, cur_v,
 122              dst - buf->stride, dst, mb_w);
 123   }
 124   // move to last row
 125   cur_y += io->y_stride;
 126   if (io->crop_top + y_end < io->crop_bottom) {
 127     // Save the unfinished samples for next call (as we're not done yet).
 128     memcpy(p->tmp_y, cur_y, mb_w * sizeof(*p->tmp_y));
 129     memcpy(p->tmp_u, cur_u, uv_w * sizeof(*p->tmp_u));
 130     memcpy(p->tmp_v, cur_v, uv_w * sizeof(*p->tmp_v));
 131     // The fancy upsampler leaves a row unfinished behind
 132     // (except for the very last row)
 133     num_lines_out--;
 134   } else {
 135     // Process the very last row of even-sized picture
 136     if (!(y_end & 1)) {
 137       upsample(cur_y, NULL, cur_u, cur_v, cur_u, cur_v,
 138                dst + buf->stride, NULL, mb_w);
 139     }
 140   }
 141   return num_lines_out;
 142 }
 143
 144 #endif    /* FANCY_UPSAMPLING */
 145
 146 //------------------------------------------------------------------------------
 147
 148 static int EmitAlphaYUV(const VP8Io* const io, WebPDecParams* const p) {
 149   const uint8_t* alpha = io->a;
 150   const WebPYUVABuffer* const buf = &p->output->u.YUVA;
 151   const int mb_w = io->mb_w;
 152   const int mb_h = io->mb_h;
 153   uint8_t* dst = buf->a + io->mb_y * buf->a_stride;
 154   int j;
 155
 156   if (alpha != NULL) {
 157     for (j = 0; j < mb_h; ++j) {
 158       memcpy(dst, alpha, mb_w * sizeof(*dst));
 159       alpha += io->width;
 160       dst += buf->a_stride;
 161     }
 162   } else if (buf->a != NULL) {
 163     // the user requested alpha, but there is none, set it to opaque.
 164     for (j = 0; j < mb_h; ++j) {
 165       memset(dst, 0xff, mb_w * sizeof(*dst));
 166       dst += buf->a_stride;
 167     }
 168   }
 169   return 0;
 170 }
 171
 172 static int GetAlphaSourceRow(const VP8Io* const io,
 173                              const uint8_t** alpha, int* const num_rows) {
 174   int start_y = io->mb_y;
 175   *num_rows = io->mb_h;
 176
 177   // Compensate for the 1-line delay of the fancy upscaler.
 178   // This is similar to EmitFancyRGB().
 179   if (io->fancy_upsampling) {
 180     if (start_y == 0) {
 181       // We don't process the last row yet. It'll be done during the next call.
 182       --*num_rows;
 183     } else {
 184       --start_y;
 185       // Fortunately, *alpha data is persistent, so we can go back
 186       // one row and finish alpha blending, now that the fancy upscaler
 187       // completed the YUV->RGB interpolation.
 188       *alpha -= io->width;
 189     }
 190     if (io->crop_top + io->mb_y + io->mb_h == io->crop_bottom) {
 191       // If it's the very last call, we process all the remaining rows!
 192       *num_rows = io->crop_bottom - io->crop_top - start_y;
 193     }
 194   }
 195   return start_y;
 196 }
 197
 198 static int EmitAlphaRGB(const VP8Io* const io, WebPDecParams* const p) {
 199   const uint8_t* alpha = io->a;
 200   if (alpha != NULL) {
 201     const int mb_w = io->mb_w;
 202     const WEBP_CSP_MODE colorspace = p->output->colorspace;
 203     const int alpha_first =
 204         (colorspace == MODE_ARGB || colorspace == MODE_Argb);
 205     const WebPRGBABuffer* const buf = &p->output->u.RGBA;
 206     int num_rows;
 207     const int start_y = GetAlphaSourceRow(io, &alpha, &num_rows);
 208     uint8_t* const base_rgba = buf->rgba + start_y * buf->stride;
 209     uint8_t* dst = base_rgba + (alpha_first ? 0 : 3);
 210     uint32_t alpha_mask = 0xff;
 211     int i, j;
 212
 213     for (j = 0; j < num_rows; ++j) {
 214       for (i = 0; i < mb_w; ++i) {
 215         const uint32_t alpha_value = alpha[i];
 216         dst[4 * i] = alpha_value;
 217         alpha_mask &= alpha_value;
 218       }
 219       alpha += io->width;
 220       dst += buf->stride;
 221     }
 222     // alpha_mask is < 0xff if there's non-trivial alpha to premultiply with.
 223     if (alpha_mask != 0xff && WebPIsPremultipliedMode(colorspace)) {
 224       WebPApplyAlphaMultiply(base_rgba, alpha_first,
 225                              mb_w, num_rows, buf->stride);
 226     }
 227   }
 228   return 0;
 229 }
 230
 231 static int EmitAlphaRGBA4444(const VP8Io* const io, WebPDecParams* const p) {
 232   const uint8_t* alpha = io->a;
 233   if (alpha != NULL) {
 234     const int mb_w = io->mb_w;
 235     const WEBP_CSP_MODE colorspace = p->output->colorspace;
 236     const WebPRGBABuffer* const buf = &p->output->u.RGBA;
 237     int num_rows;
 238     const int start_y = GetAlphaSourceRow(io, &alpha, &num_rows);
 239     uint8_t* const base_rgba = buf->rgba + start_y * buf->stride;
 240 #ifdef WEBP_SWAP_16BIT_CSP
 241     uint8_t* alpha_dst = base_rgba;
 242 #else
 243     uint8_t* alpha_dst = base_rgba + 1;
 244 #endif
 245     uint32_t alpha_mask = 0x0f;
 246     int i, j;
 247
 248     for (j = 0; j < num_rows; ++j) {
 249       for (i = 0; i < mb_w; ++i) {
 250         // Fill in the alpha value (converted to 4 bits).
 251         const uint32_t alpha_value = alpha[i] >> 4;
 252         alpha_dst[2 * i] = (alpha_dst[2 * i] & 0xf0) | alpha_value;
 253         alpha_mask &= alpha_value;
 254       }
 255       alpha += io->width;
 256       alpha_dst += buf->stride;
 257     }
 258     if (alpha_mask != 0x0f && WebPIsPremultipliedMode(colorspace)) {
 259       WebPApplyAlphaMultiply4444(base_rgba, mb_w, num_rows, buf->stride);
 260     }
 261   }
 262   return 0;
 263 }
 264
 265 //------------------------------------------------------------------------------
 266 // YUV rescaling (no final RGB conversion needed)
 267
 268 static int Rescale(const uint8_t* src, int src_stride,
 269                    int new_lines, WebPRescaler* const wrk) {
 270   int num_lines_out = 0;
 271   while (new_lines > 0) {    // import new contributions of source rows.
 272     const int lines_in = WebPRescalerImport(wrk, new_lines, src, src_stride);
 273     src += lines_in * src_stride;
 274     new_lines -= lines_in;
 275     num_lines_out += WebPRescalerExport(wrk);    // emit output row(s)
 276   }
 277   return num_lines_out;
 278 }
 279
 280 static int EmitRescaledYUV(const VP8Io* const io, WebPDecParams* const p) {
 281   const int mb_h = io->mb_h;
 282   const int uv_mb_h = (mb_h + 1) >> 1;
 283   WebPRescaler* const scaler = &p->scaler_y;
 284   int num_lines_out = 0;
 285   if (WebPIsAlphaMode(p->output->colorspace) && io->a != NULL) {
 286     // Before rescaling, we premultiply the luma directly into the io->y
 287     // internal buffer. This is OK since these samples are not used for
 288     // intra-prediction (the top samples are saved in cache_y_/u_/v_).
 289     // But we need to cast the const away, though.
 290     WebPMultRows((uint8_t*)io->y, io->y_stride,
 291                  io->a, io->width, io->mb_w, mb_h, 0);
 292   }
 293   num_lines_out = Rescale(io->y, io->y_stride, mb_h, scaler);
 294   Rescale(io->u, io->uv_stride, uv_mb_h, &p->scaler_u);
 295   Rescale(io->v, io->uv_stride, uv_mb_h, &p->scaler_v);
 296   return num_lines_out;
 297 }
 298
 299 static int EmitRescaledAlphaYUV(const VP8Io* const io, WebPDecParams* const p) {
 300   if (io->a != NULL) {
 301     const WebPYUVABuffer* const buf = &p->output->u.YUVA;
 302     uint8_t* dst_y = buf->y + p->last_y * buf->y_stride;
 303     const uint8_t* src_a = buf->a + p->last_y * buf->a_stride;
 304     const int num_lines_out = Rescale(io->a, io->width, io->mb_h, &p->scaler_a);
 305     if (num_lines_out > 0) {   // unmultiply the Y
 306       WebPMultRows(dst_y, buf->y_stride, src_a, buf->a_stride,
 307                    p->scaler_a.dst_width, num_lines_out, 1);
 308     }
 309   }
 310   return 0;
 311 }
 312
 313 static int InitYUVRescaler(const VP8Io* const io, WebPDecParams* const p) {
 314   const int has_alpha = WebPIsAlphaMode(p->output->colorspace);
 315   const WebPYUVABuffer* const buf = &p->output->u.YUVA;
 316   const int out_width  = io->scaled_width;
 317   const int out_height = io->scaled_height;
 318   const int uv_out_width  = (out_width + 1) >> 1;
 319   const int uv_out_height = (out_height + 1) >> 1;
 320   const int uv_in_width  = (io->mb_w + 1) >> 1;
 321   const int uv_in_height = (io->mb_h + 1) >> 1;
 322   const size_t work_size = 2 * out_width;   // scratch memory for luma rescaler
 323   const size_t uv_work_size = 2 * uv_out_width;  // and for each u/v ones
 324   size_t tmp_size;
 325   int32_t* work;
 326
 327   tmp_size = (work_size + 2 * uv_work_size) * sizeof(*work);
 328   if (has_alpha) {
 329     tmp_size += work_size * sizeof(*work);
 330   }
 331   p->memory = WebPSafeCalloc(1ULL, tmp_size);
 332   if (p->memory == NULL) {
 333     return 0;   // memory error
 334   }
 335   work = (int32_t*)p->memory;
 336   WebPRescalerInit(&p->scaler_y, io->mb_w, io->mb_h,
 337                    buf->y, out_width, out_height, buf->y_stride, 1,
 338                    io->mb_w, out_width, io->mb_h, out_height,
 339                    work);
 340   WebPRescalerInit(&p->scaler_u, uv_in_width, uv_in_height,
 341                    buf->u, uv_out_width, uv_out_height, buf->u_stride, 1,
 342                    uv_in_width, uv_out_width,
 343                    uv_in_height, uv_out_height,
 344                    work + work_size);
 345   WebPRescalerInit(&p->scaler_v, uv_in_width, uv_in_height,
 346                    buf->v, uv_out_width, uv_out_height, buf->v_stride, 1,
 347                    uv_in_width, uv_out_width,
 348                    uv_in_height, uv_out_height,
 349                    work + work_size + uv_work_size);
 350   p->emit = EmitRescaledYUV;
 351
 352   if (has_alpha) {
 353     WebPRescalerInit(&p->scaler_a, io->mb_w, io->mb_h,
 354                      buf->a, out_width, out_height, buf->a_stride, 1,
 355                      io->mb_w, out_width, io->mb_h, out_height,
 356                      work + work_size + 2 * uv_work_size);
 357     p->emit_alpha = EmitRescaledAlphaYUV;
 358     WebPInitAlphaProcessing();
 359   }
 360   return 1;
 361 }
 362
 363 //------------------------------------------------------------------------------
 364 // RGBA rescaling
 365
 366 static int ExportRGB(WebPDecParams* const p, int y_pos) {
 367   const WebPYUV444Converter convert =
 368       WebPYUV444Converters[p->output->colorspace];
 369   const WebPRGBABuffer* const buf = &p->output->u.RGBA;
 370   uint8_t* dst = buf->rgba + (p->last_y + y_pos) * buf->stride;
 371   int num_lines_out = 0;
 372   // For RGB rescaling, because of the YUV420, current scan position
 373   // U/V can be +1/-1 line from the Y one.  Hence the double test.
 374   while (WebPRescalerHasPendingOutput(&p->scaler_y) &&
 375          WebPRescalerHasPendingOutput(&p->scaler_u)) {
 376     assert(p->last_y + y_pos + num_lines_out < p->output->height);
 377     assert(p->scaler_u.y_accum == p->scaler_v.y_accum);
 378     WebPRescalerExportRow(&p->scaler_y, 0);
 379     WebPRescalerExportRow(&p->scaler_u, 0);
 380     WebPRescalerExportRow(&p->scaler_v, 0);
 381     convert(p->scaler_y.dst, p->scaler_u.dst, p->scaler_v.dst,
 382             dst, p->scaler_y.dst_width);
 383     dst += buf->stride;
 384     ++num_lines_out;
 385   }
 386   return num_lines_out;
 387 }
 388
 389 static int EmitRescaledRGB(const VP8Io* const io, WebPDecParams* const p) {
 390   const int mb_h = io->mb_h;
 391   const int uv_mb_h = (mb_h + 1) >> 1;
 392   int j = 0, uv_j = 0;
 393   int num_lines_out = 0;
 394   while (j < mb_h) {
 395     const int y_lines_in =
 396         WebPRescalerImport(&p->scaler_y, mb_h - j,
 397                            io->y + j * io->y_stride, io->y_stride);
 398     const int u_lines_in =
 399         WebPRescalerImport(&p->scaler_u, uv_mb_h - uv_j,
 400                            io->u + uv_j * io->uv_stride, io->uv_stride);
 401     const int v_lines_in =
 402         WebPRescalerImport(&p->scaler_v, uv_mb_h - uv_j,
 403                            io->v + uv_j * io->uv_stride, io->uv_stride);
 404     (void)v_lines_in;   // remove a gcc warning
 405     assert(u_lines_in == v_lines_in);
 406     j += y_lines_in;
 407     uv_j += u_lines_in;
 408     num_lines_out += ExportRGB(p, num_lines_out);
 409   }
 410   return num_lines_out;
 411 }
 412
 413 static int ExportAlpha(WebPDecParams* const p, int y_pos) {
 414   const WebPRGBABuffer* const buf = &p->output->u.RGBA;
 415   uint8_t* const base_rgba = buf->rgba + (p->last_y + y_pos) * buf->stride;
 416   const WEBP_CSP_MODE colorspace = p->output->colorspace;
 417   const int alpha_first =
 418       (colorspace == MODE_ARGB || colorspace == MODE_Argb);
 419   uint8_t* dst = base_rgba + (alpha_first ? 0 : 3);
 420   int num_lines_out = 0;
 421   const int is_premult_alpha = WebPIsPremultipliedMode(colorspace);
 422   uint32_t alpha_mask = 0xff;
 423   const int width = p->scaler_a.dst_width;
 424
 425   while (WebPRescalerHasPendingOutput(&p->scaler_a)) {
 426     int i;
 427     assert(p->last_y + y_pos + num_lines_out < p->output->height);
 428     WebPRescalerExportRow(&p->scaler_a, 0);
 429     for (i = 0; i < width; ++i) {
 430       const uint32_t alpha_value = p->scaler_a.dst[i];
 431       dst[4 * i] = alpha_value;
 432       alpha_mask &= alpha_value;
 433     }
 434     dst += buf->stride;
 435     ++num_lines_out;
 436   }
 437   if (is_premult_alpha && alpha_mask != 0xff) {
 438     WebPApplyAlphaMultiply(base_rgba, alpha_first,
 439                            width, num_lines_out, buf->stride);
 440   }
 441   return num_lines_out;
 442 }
 443
 444 static int ExportAlphaRGBA4444(WebPDecParams* const p, int y_pos) {
 445   const WebPRGBABuffer* const buf = &p->output->u.RGBA;
 446   uint8_t* const base_rgba = buf->rgba + (p->last_y + y_pos) * buf->stride;
 447 #ifdef WEBP_SWAP_16BIT_CSP
 448   uint8_t* alpha_dst = base_rgba;
 449 #else
 450   uint8_t* alpha_dst = base_rgba + 1;
 451 #endif
 452   int num_lines_out = 0;
 453   const WEBP_CSP_MODE colorspace = p->output->colorspace;
 454   const int width = p->scaler_a.dst_width;
 455   const int is_premult_alpha = WebPIsPremultipliedMode(colorspace);
 456   uint32_t alpha_mask = 0x0f;
 457
 458   while (WebPRescalerHasPendingOutput(&p->scaler_a)) {
 459     int i;
 460     assert(p->last_y + y_pos + num_lines_out < p->output->height);
 461     WebPRescalerExportRow(&p->scaler_a, 0);
 462     for (i = 0; i < width; ++i) {
 463       // Fill in the alpha value (converted to 4 bits).
 464       const uint32_t alpha_value = p->scaler_a.dst[i] >> 4;
 465       alpha_dst[2 * i] = (alpha_dst[2 * i] & 0xf0) | alpha_value;
 466       alpha_mask &= alpha_value;
 467     }
 468     alpha_dst += buf->stride;
 469     ++num_lines_out;
 470   }
 471   if (is_premult_alpha && alpha_mask != 0x0f) {
 472     WebPApplyAlphaMultiply4444(base_rgba, width, num_lines_out, buf->stride);
 473   }
 474   return num_lines_out;
 475 }
 476
 477 static int EmitRescaledAlphaRGB(const VP8Io* const io, WebPDecParams* const p) {
 478   if (io->a != NULL) {
 479     WebPRescaler* const scaler = &p->scaler_a;
 480     int j = 0;
 481     int pos = 0;
 482     while (j < io->mb_h) {
 483       j += WebPRescalerImport(scaler, io->mb_h - j,
 484                               io->a + j * io->width, io->width);
 485       pos += p->emit_alpha_row(p, pos);
 486     }
 487   }
 488   return 0;
 489 }
 490
 491 static int InitRGBRescaler(const VP8Io* const io, WebPDecParams* const p) {
 492   const int has_alpha = WebPIsAlphaMode(p->output->colorspace);
 493   const int out_width  = io->scaled_width;
 494   const int out_height = io->scaled_height;
 495   const int uv_in_width  = (io->mb_w + 1) >> 1;
 496   const int uv_in_height = (io->mb_h + 1) >> 1;
 497   const size_t work_size = 2 * out_width;   // scratch memory for one rescaler
 498   int32_t* work;  // rescalers work area
 499   uint8_t* tmp;   // tmp storage for scaled YUV444 samples before RGB conversion
 500   size_t tmp_size1, tmp_size2, total_size;
 501
 502   tmp_size1 = 3 * work_size;
 503   tmp_size2 = 3 * out_width;
 504   if (has_alpha) {
 505     tmp_size1 += work_size;
 506     tmp_size2 += out_width;
 507   }
 508   total_size = tmp_size1 * sizeof(*work) + tmp_size2 * sizeof(*tmp);
 509   p->memory = WebPSafeCalloc(1ULL, total_size);
 510   if (p->memory == NULL) {
 511     return 0;   // memory error
 512   }
 513   work = (int32_t*)p->memory;
 514   tmp = (uint8_t*)(work + tmp_size1);
 515   WebPRescalerInit(&p->scaler_y, io->mb_w, io->mb_h,
 516                    tmp + 0 * out_width, out_width, out_height, 0, 1,
 517                    io->mb_w, out_width, io->mb_h, out_height,
 518                    work + 0 * work_size);
 519   WebPRescalerInit(&p->scaler_u, uv_in_width, uv_in_height,
 520                    tmp + 1 * out_width, out_width, out_height, 0, 1,
 521                    io->mb_w, 2 * out_width, io->mb_h, 2 * out_height,
 522                    work + 1 * work_size);
 523   WebPRescalerInit(&p->scaler_v, uv_in_width, uv_in_height,
 524                    tmp + 2 * out_width, out_width, out_height, 0, 1,
 525                    io->mb_w, 2 * out_width, io->mb_h, 2 * out_height,
 526                    work + 2 * work_size);
 527   p->emit = EmitRescaledRGB;
 528
 529   if (has_alpha) {
 530     WebPRescalerInit(&p->scaler_a, io->mb_w, io->mb_h,
 531                      tmp + 3 * out_width, out_width, out_height, 0, 1,
 532                      io->mb_w, out_width, io->mb_h, out_height,
 533                      work + 3 * work_size);
 534     p->emit_alpha = EmitRescaledAlphaRGB;
 535     if (p->output->colorspace == MODE_RGBA_4444 ||
 536         p->output->colorspace == MODE_rgbA_4444) {
 537       p->emit_alpha_row = ExportAlphaRGBA4444;
 538     } else {
 539       p->emit_alpha_row = ExportAlpha;
 540     }
 541     WebPInitAlphaProcessing();
 542   }
 543   return 1;
 544 }
 545
 546 //------------------------------------------------------------------------------
 547 // Default custom functions
 548
 549 static int CustomSetup(VP8Io* io) {
 550   WebPDecParams* const p = (WebPDecParams*)io->opaque;
 551   const WEBP_CSP_MODE colorspace = p->output->colorspace;
 552   const int is_rgb = WebPIsRGBMode(colorspace);
 553   const int is_alpha = WebPIsAlphaMode(colorspace);
 554
 555   p->memory = NULL;
 556   p->emit = NULL;
 557   p->emit_alpha = NULL;
 558   p->emit_alpha_row = NULL;
 559   if (!WebPIoInitFromOptions(p->options, io, is_alpha ? MODE_YUV : MODE_YUVA)) {
 560     return 0;
 561   }
 562   if (is_alpha && WebPIsPremultipliedMode(colorspace)) {
 563     WebPInitUpsamplers();
 564   }
 565   if (io->use_scaling) {
 566     const int ok = is_rgb ? InitRGBRescaler(io, p) : InitYUVRescaler(io, p);
 567     if (!ok) {
 568       return 0;    // memory error
 569     }
 570   } else {
 571     if (is_rgb) {
 572       p->emit = EmitSampledRGB;   // default
 573       if (io->fancy_upsampling) {
 574 #ifdef FANCY_UPSAMPLING
 575         const int uv_width = (io->mb_w + 1) >> 1;
 576         p->memory = WebPSafeMalloc(1ULL, (size_t)(io->mb_w + 2 * uv_width));
 577         if (p->memory == NULL) {
 578           return 0;   // memory error.
 579         }
 580         p->tmp_y = (uint8_t*)p->memory;
 581         p->tmp_u = p->tmp_y + io->mb_w;
 582         p->tmp_v = p->tmp_u + uv_width;
 583         p->emit = EmitFancyRGB;
 584         WebPInitUpsamplers();
 585 #endif
 586       } else {
 587         WebPInitSamplers();
 588       }
 589     } else {
 590       p->emit = EmitYUV;
 591     }
 592     if (is_alpha) {  // need transparency output
 593       p->emit_alpha =
 594           (colorspace == MODE_RGBA_4444 || colorspace == MODE_rgbA_4444) ?
 595               EmitAlphaRGBA4444
 596           : is_rgb ? EmitAlphaRGB
 597           : EmitAlphaYUV;
 598       if (is_rgb) {
 599         WebPInitAlphaProcessing();
 600       }
 601     }
 602   }
 603
 604   if (is_rgb) {
 605     VP8YUVInit();
 606   }
 607   return 1;
 608 }
 609
 610 //------------------------------------------------------------------------------
 611
 612 static int CustomPut(const VP8Io* io) {
 613   WebPDecParams* const p = (WebPDecParams*)io->opaque;
 614   const int mb_w = io->mb_w;
 615   const int mb_h = io->mb_h;
 616   int num_lines_out;
 617   assert(!(io->mb_y & 1));
 618
 619   if (mb_w <= 0 || mb_h <= 0) {
 620     return 0;
 621   }
 622   num_lines_out = p->emit(io, p);
 623   if (p->emit_alpha != NULL) {
 624     p->emit_alpha(io, p);
 625   }
 626   p->last_y += num_lines_out;
 627   return 1;
 628 }
 629
 630 //------------------------------------------------------------------------------
 631
 632 static void CustomTeardown(const VP8Io* io) {
 633   WebPDecParams* const p = (WebPDecParams*)io->opaque;
 634   WebPSafeFree(p->memory);
 635   p->memory = NULL;
 636 }
 637
 638 //------------------------------------------------------------------------------
 639 // Main entry point
 640
 641 void WebPInitCustomIo(WebPDecParams* const params, VP8Io* const io) {
 642   io->put      = CustomPut;
 643   io->setup    = CustomSetup;
 644   io->teardown = CustomTeardown;
 645   io->opaque   = params;
 646 }
 647
 648 //------------------------------------------------------------------------------