src/cc/base/tiling_data.cc

   1 // Copyright 2010 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "cc/base/tiling_data.h"
   6
   7 #include <algorithm>
   8
   9 #include "ui/gfx/rect.h"
  10 #include "ui/gfx/vector2d.h"
  11
  12 namespace cc {
  13
  14 static int ComputeNumTiles(int max_texture_size,
  15                            int total_size,
  16                            int border_texels) {
  17   if (max_texture_size - 2 * border_texels <= 0)
  18     return total_size > 0 && max_texture_size >= total_size ? 1 : 0;
  19
  20   int num_tiles = std::max(1,
  21                            1 + (total_size - 1 - 2 * border_texels) /
  22                            (max_texture_size - 2 * border_texels));
  23   return total_size > 0 ? num_tiles : 0;
  24 }
  25
  26 TilingData::TilingData()
  27     : border_texels_(0) {
  28   RecomputeNumTiles();
  29 }
  30
  31 TilingData::TilingData(const gfx::Size& max_texture_size,
  32                        const gfx::Size& tiling_size,
  33                        bool has_border_texels)
  34     : max_texture_size_(max_texture_size),
  35       tiling_size_(tiling_size),
  36       border_texels_(has_border_texels ? 1 : 0) {
  37   RecomputeNumTiles();
  38 }
  39
  40 TilingData::TilingData(const gfx::Size& max_texture_size,
  41                        const gfx::Size& tiling_size,
  42                        int border_texels)
  43     : max_texture_size_(max_texture_size),
  44       tiling_size_(tiling_size),
  45       border_texels_(border_texels) {
  46   RecomputeNumTiles();
  47 }
  48
  49 void TilingData::SetTilingSize(const gfx::Size& tiling_size) {
  50   tiling_size_ = tiling_size;
  51   RecomputeNumTiles();
  52 }
  53
  54 void TilingData::SetMaxTextureSize(const gfx::Size& max_texture_size) {
  55   max_texture_size_ = max_texture_size;
  56   RecomputeNumTiles();
  57 }
  58
  59 void TilingData::SetHasBorderTexels(bool has_border_texels) {
  60   border_texels_ = has_border_texels ? 1 : 0;
  61   RecomputeNumTiles();
  62 }
  63
  64 void TilingData::SetBorderTexels(int border_texels) {
  65   border_texels_ = border_texels;
  66   RecomputeNumTiles();
  67 }
  68
  69 int TilingData::TileXIndexFromSrcCoord(int src_position) const {
  70   if (num_tiles_x_ <= 1)
  71     return 0;
  72
  73   DCHECK_GT(max_texture_size_.width() - 2 * border_texels_, 0);
  74   int x = (src_position - border_texels_) /
  75       (max_texture_size_.width() - 2 * border_texels_);
  76   return std::min(std::max(x, 0), num_tiles_x_ - 1);
  77 }
  78
  79 int TilingData::TileYIndexFromSrcCoord(int src_position) const {
  80   if (num_tiles_y_ <= 1)
  81     return 0;
  82
  83   DCHECK_GT(max_texture_size_.height() - 2 * border_texels_, 0);
  84   int y = (src_position - border_texels_) /
  85       (max_texture_size_.height() - 2 * border_texels_);
  86   return std::min(std::max(y, 0), num_tiles_y_ - 1);
  87 }
  88
  89 int TilingData::FirstBorderTileXIndexFromSrcCoord(int src_position) const {
  90   if (num_tiles_x_ <= 1)
  91     return 0;
  92
  93   DCHECK_GT(max_texture_size_.width() - 2 * border_texels_, 0);
  94   int inner_tile_size = max_texture_size_.width() - 2 * border_texels_;
  95   int x = (src_position - 2 * border_texels_) / inner_tile_size;
  96   return std::min(std::max(x, 0), num_tiles_x_ - 1);
  97 }
  98
  99 int TilingData::FirstBorderTileYIndexFromSrcCoord(int src_position) const {
 100   if (num_tiles_y_ <= 1)
 101     return 0;
 102
 103   DCHECK_GT(max_texture_size_.height() - 2 * border_texels_, 0);
 104   int inner_tile_size = max_texture_size_.height() - 2 * border_texels_;
 105   int y = (src_position - 2 * border_texels_) / inner_tile_size;
 106   return std::min(std::max(y, 0), num_tiles_y_ - 1);
 107 }
 108
 109 int TilingData::LastBorderTileXIndexFromSrcCoord(int src_position) const {
 110   if (num_tiles_x_ <= 1)
 111     return 0;
 112
 113   DCHECK_GT(max_texture_size_.width() - 2 * border_texels_, 0);
 114   int inner_tile_size = max_texture_size_.width() - 2 * border_texels_;
 115   int x = src_position / inner_tile_size;
 116   return std::min(std::max(x, 0), num_tiles_x_ - 1);
 117 }
 118
 119 int TilingData::LastBorderTileYIndexFromSrcCoord(int src_position) const {
 120   if (num_tiles_y_ <= 1)
 121     return 0;
 122
 123   DCHECK_GT(max_texture_size_.height() - 2 * border_texels_, 0);
 124   int inner_tile_size = max_texture_size_.height() - 2 * border_texels_;
 125   int y = src_position / inner_tile_size;
 126   return std::min(std::max(y, 0), num_tiles_y_ - 1);
 127 }
 128
 129 gfx::Rect TilingData::ExpandRectIgnoringBordersToTileBoundsWithBorders(
 130     const gfx::Rect& rect) const {
 131   if (rect.IsEmpty() || has_empty_bounds())
 132     return gfx::Rect();
 133   if (rect.x() > tiling_size_.width() || rect.y() > tiling_size_.height())
 134     return gfx::Rect();
 135   int index_x = TileXIndexFromSrcCoord(rect.x());
 136   int index_y = TileYIndexFromSrcCoord(rect.y());
 137   int index_right = TileXIndexFromSrcCoord(rect.right() - 1);
 138   int index_bottom = TileYIndexFromSrcCoord(rect.bottom() - 1);
 139
 140   gfx::Rect rect_top_left(TileBoundsWithBorder(index_x, index_y));
 141   gfx::Rect rect_bottom_right(TileBoundsWithBorder(index_right, index_bottom));
 142
 143   return gfx::UnionRects(rect_top_left, rect_bottom_right);
 144 }
 145
 146 gfx::Rect TilingData::ExpandRectToTileBounds(const gfx::Rect& rect) const {
 147   if (rect.IsEmpty() || has_empty_bounds())
 148     return gfx::Rect();
 149   if (rect.x() > tiling_size_.width() || rect.y() > tiling_size_.height())
 150     return gfx::Rect();
 151   int index_x = FirstBorderTileXIndexFromSrcCoord(rect.x());
 152   int index_y = FirstBorderTileYIndexFromSrcCoord(rect.y());
 153   int index_right = LastBorderTileXIndexFromSrcCoord(rect.right() - 1);
 154   int index_bottom = LastBorderTileYIndexFromSrcCoord(rect.bottom() - 1);
 155
 156   gfx::Rect rect_top_left(TileBounds(index_x, index_y));
 157   gfx::Rect rect_bottom_right(TileBounds(index_right, index_bottom));
 158
 159   return gfx::UnionRects(rect_top_left, rect_bottom_right);
 160 }
 161
 162 gfx::Rect TilingData::TileBounds(int i, int j) const {
 163   AssertTile(i, j);
 164   int max_texture_size_x = max_texture_size_.width() - 2 * border_texels_;
 165   int max_texture_size_y = max_texture_size_.height() - 2 * border_texels_;
 166
 167   int lo_x = max_texture_size_x * i;
 168   if (i != 0)
 169     lo_x += border_texels_;
 170
 171   int lo_y = max_texture_size_y * j;
 172   if (j != 0)
 173     lo_y += border_texels_;
 174
 175   int hi_x = max_texture_size_x * (i + 1) + border_texels_;
 176   if (i + 1 == num_tiles_x_)
 177     hi_x += border_texels_;
 178
 179   int hi_y = max_texture_size_y * (j + 1) + border_texels_;
 180   if (j + 1 == num_tiles_y_)
 181     hi_y += border_texels_;
 182
 183   hi_x = std::min(hi_x, tiling_size_.width());
 184   hi_y = std::min(hi_y, tiling_size_.height());
 185
 186   int x = lo_x;
 187   int y = lo_y;
 188   int width = hi_x - lo_x;
 189   int height = hi_y - lo_y;
 190   DCHECK_GE(x, 0);
 191   DCHECK_GE(y, 0);
 192   DCHECK_GE(width, 0);
 193   DCHECK_GE(height, 0);
 194   DCHECK_LE(x, tiling_size_.width());
 195   DCHECK_LE(y, tiling_size_.height());
 196   return gfx::Rect(x, y, width, height);
 197 }
 198
 199 gfx::Rect TilingData::TileBoundsWithBorder(int i, int j) const {
 200   AssertTile(i, j);
 201   int max_texture_size_x = max_texture_size_.width() - 2 * border_texels_;
 202   int max_texture_size_y = max_texture_size_.height() - 2 * border_texels_;
 203
 204   int lo_x = max_texture_size_x * i;
 205   int lo_y = max_texture_size_y * j;
 206
 207   int hi_x = lo_x + max_texture_size_x + 2 * border_texels_;
 208   int hi_y = lo_y + max_texture_size_y + 2 * border_texels_;
 209
 210   hi_x = std::min(hi_x, tiling_size_.width());
 211   hi_y = std::min(hi_y, tiling_size_.height());
 212
 213   int x = lo_x;
 214   int y = lo_y;
 215   int width = hi_x - lo_x;
 216   int height = hi_y - lo_y;
 217   DCHECK_GE(x, 0);
 218   DCHECK_GE(y, 0);
 219   DCHECK_GE(width, 0);
 220   DCHECK_GE(height, 0);
 221   DCHECK_LE(x, tiling_size_.width());
 222   DCHECK_LE(y, tiling_size_.height());
 223   return gfx::Rect(x, y, width, height);
 224 }
 225
 226 int TilingData::TilePositionX(int x_index) const {
 227   DCHECK_GE(x_index, 0);
 228   DCHECK_LT(x_index, num_tiles_x_);
 229
 230   int pos = (max_texture_size_.width() - 2 * border_texels_) * x_index;
 231   if (x_index != 0)
 232     pos += border_texels_;
 233
 234   return pos;
 235 }
 236
 237 int TilingData::TilePositionY(int y_index) const {
 238   DCHECK_GE(y_index, 0);
 239   DCHECK_LT(y_index, num_tiles_y_);
 240
 241   int pos = (max_texture_size_.height() - 2 * border_texels_) * y_index;
 242   if (y_index != 0)
 243     pos += border_texels_;
 244
 245   return pos;
 246 }
 247
 248 int TilingData::TileSizeX(int x_index) const {
 249   DCHECK_GE(x_index, 0);
 250   DCHECK_LT(x_index, num_tiles_x_);
 251
 252   if (!x_index && num_tiles_x_ == 1)
 253     return tiling_size_.width();
 254   if (!x_index && num_tiles_x_ > 1)
 255     return max_texture_size_.width() - border_texels_;
 256   if (x_index < num_tiles_x_ - 1)
 257     return max_texture_size_.width() - 2 * border_texels_;
 258   if (x_index == num_tiles_x_ - 1)
 259     return tiling_size_.width() - TilePositionX(x_index);
 260
 261   NOTREACHED();
 262   return 0;
 263 }
 264
 265 int TilingData::TileSizeY(int y_index) const {
 266   DCHECK_GE(y_index, 0);
 267   DCHECK_LT(y_index, num_tiles_y_);
 268
 269   if (!y_index && num_tiles_y_ == 1)
 270     return tiling_size_.height();
 271   if (!y_index && num_tiles_y_ > 1)
 272     return max_texture_size_.height() - border_texels_;
 273   if (y_index < num_tiles_y_ - 1)
 274     return max_texture_size_.height() - 2 * border_texels_;
 275   if (y_index == num_tiles_y_ - 1)
 276     return tiling_size_.height() - TilePositionY(y_index);
 277
 278   NOTREACHED();
 279   return 0;
 280 }
 281
 282 gfx::Vector2d TilingData::TextureOffset(int x_index, int y_index) const {
 283   int left = (!x_index || num_tiles_x_ == 1) ? 0 : border_texels_;
 284   int top = (!y_index || num_tiles_y_ == 1) ? 0 : border_texels_;
 285
 286   return gfx::Vector2d(left, top);
 287 }
 288
 289 void TilingData::RecomputeNumTiles() {
 290   num_tiles_x_ = ComputeNumTiles(
 291       max_texture_size_.width(), tiling_size_.width(), border_texels_);
 292   num_tiles_y_ = ComputeNumTiles(
 293       max_texture_size_.height(), tiling_size_.height(), border_texels_);
 294 }
 295
 296 TilingData::BaseIterator::BaseIterator(const TilingData* tiling_data)
 297     : tiling_data_(tiling_data),
 298       index_x_(-1),
 299       index_y_(-1) {
 300 }
 301
 302 TilingData::Iterator::Iterator() : BaseIterator(NULL) { done(); }
 303
 304 TilingData::Iterator::Iterator(const TilingData* tiling_data,
 305                                const gfx::Rect& consider_rect,
 306                                bool include_borders)
 307     : BaseIterator(tiling_data), left_(-1), right_(-1), bottom_(-1) {
 308   if (tiling_data_->num_tiles_x() <= 0 || tiling_data_->num_tiles_y() <= 0) {
 309     done();
 310     return;
 311   }
 312
 313   gfx::Rect tiling_bounds_rect(tiling_data_->tiling_size());
 314   gfx::Rect rect(consider_rect);
 315   rect.Intersect(tiling_bounds_rect);
 316
 317   gfx::Rect top_left_tile;
 318   if (include_borders) {
 319     index_x_ = tiling_data_->FirstBorderTileXIndexFromSrcCoord(rect.x());
 320     index_y_ = tiling_data_->FirstBorderTileYIndexFromSrcCoord(rect.y());
 321     right_ = tiling_data_->LastBorderTileXIndexFromSrcCoord(rect.right() - 1);
 322     bottom_ = tiling_data_->LastBorderTileYIndexFromSrcCoord(rect.bottom() - 1);
 323     top_left_tile = tiling_data_->TileBoundsWithBorder(index_x_, index_y_);
 324   } else {
 325     index_x_ = tiling_data_->TileXIndexFromSrcCoord(rect.x());
 326     index_y_ = tiling_data_->TileYIndexFromSrcCoord(rect.y());
 327     right_ = tiling_data_->TileXIndexFromSrcCoord(rect.right() - 1);
 328     bottom_ = tiling_data_->TileYIndexFromSrcCoord(rect.bottom() - 1);
 329     top_left_tile = tiling_data_->TileBounds(index_x_, index_y_);
 330   }
 331   left_ = index_x_;
 332
 333   // Index functions always return valid indices, so explicitly check
 334   // for non-intersecting rects.
 335   if (!top_left_tile.Intersects(rect))
 336     done();
 337 }
 338
 339 TilingData::Iterator& TilingData::Iterator::operator++() {
 340   if (!*this)
 341     return *this;
 342
 343   index_x_++;
 344   if (index_x_ > right_) {
 345     index_x_ = left_;
 346     index_y_++;
 347     if (index_y_ > bottom_)
 348       done();
 349   }
 350
 351   return *this;
 352 }
 353
 354 TilingData::DifferenceIterator::DifferenceIterator(
 355     const TilingData* tiling_data,
 356     const gfx::Rect& consider_rect,
 357     const gfx::Rect& ignore_rect)
 358     : BaseIterator(tiling_data),
 359       consider_left_(-1),
 360       consider_top_(-1),
 361       consider_right_(-1),
 362       consider_bottom_(-1),
 363       ignore_left_(-1),
 364       ignore_top_(-1),
 365       ignore_right_(-1),
 366       ignore_bottom_(-1) {
 367   if (tiling_data_->num_tiles_x() <= 0 || tiling_data_->num_tiles_y() <= 0) {
 368     done();
 369     return;
 370   }
 371
 372   gfx::Rect tiling_bounds_rect(tiling_data_->tiling_size());
 373   gfx::Rect consider(consider_rect);
 374   gfx::Rect ignore(ignore_rect);
 375   consider.Intersect(tiling_bounds_rect);
 376   ignore.Intersect(tiling_bounds_rect);
 377   if (consider.IsEmpty()) {
 378     done();
 379     return;
 380   }
 381
 382   consider_left_ =
 383       tiling_data_->FirstBorderTileXIndexFromSrcCoord(consider.x());
 384   consider_top_ =
 385       tiling_data_->FirstBorderTileYIndexFromSrcCoord(consider.y());
 386   consider_right_ =
 387       tiling_data_->LastBorderTileXIndexFromSrcCoord(consider.right() - 1);
 388   consider_bottom_ =
 389       tiling_data_->LastBorderTileYIndexFromSrcCoord(consider.bottom() - 1);
 390
 391   if (!ignore.IsEmpty()) {
 392     ignore_left_ =
 393         tiling_data_->FirstBorderTileXIndexFromSrcCoord(ignore.x());
 394     ignore_top_ =
 395         tiling_data_->FirstBorderTileYIndexFromSrcCoord(ignore.y());
 396     ignore_right_ =
 397         tiling_data_->LastBorderTileXIndexFromSrcCoord(ignore.right() - 1);
 398     ignore_bottom_ =
 399         tiling_data_->LastBorderTileYIndexFromSrcCoord(ignore.bottom() - 1);
 400
 401     // Clamp ignore indices to consider indices.
 402     ignore_left_ = std::max(ignore_left_, consider_left_);
 403     ignore_top_ = std::max(ignore_top_, consider_top_);
 404     ignore_right_ = std::min(ignore_right_, consider_right_);
 405     ignore_bottom_ = std::min(ignore_bottom_, consider_bottom_);
 406   }
 407
 408   if (ignore_left_ == consider_left_ && ignore_right_ == consider_right_ &&
 409       ignore_top_ == consider_top_ && ignore_bottom_ == consider_bottom_) {
 410     done();
 411     return;
 412   }
 413
 414   index_x_ = consider_left_;
 415   index_y_ = consider_top_;
 416
 417   if (in_ignore_rect())
 418     ++(*this);
 419 }
 420
 421 TilingData::DifferenceIterator& TilingData::DifferenceIterator::operator++() {
 422   if (!*this)
 423     return *this;
 424
 425   index_x_++;
 426   if (in_ignore_rect())
 427     index_x_ = ignore_right_ + 1;
 428
 429   if (index_x_ > consider_right_) {
 430     index_x_ = consider_left_;
 431     index_y_++;
 432
 433     if (in_ignore_rect()) {
 434       index_x_ = ignore_right_ + 1;
 435       // If the ignore rect spans the whole consider rect horizontally, then
 436       // ignore_right + 1 will be out of bounds.
 437       if (in_ignore_rect() || index_x_ > consider_right_) {
 438         index_y_ = ignore_bottom_ + 1;
 439         index_x_ = consider_left_;
 440       }
 441     }
 442
 443     if (index_y_ > consider_bottom_)
 444       done();
 445   }
 446
 447   return *this;
 448 }
 449
 450 TilingData::SpiralDifferenceIterator::SpiralDifferenceIterator()
 451     : BaseIterator(NULL) {
 452   done();
 453 }
 454
 455 TilingData::SpiralDifferenceIterator::SpiralDifferenceIterator(
 456     const TilingData* tiling_data,
 457     const gfx::Rect& consider_rect,
 458     const gfx::Rect& ignore_rect,
 459     const gfx::Rect& center_rect)
 460     : BaseIterator(tiling_data),
 461       consider_left_(-1),
 462       consider_top_(-1),
 463       consider_right_(-1),
 464       consider_bottom_(-1),
 465       ignore_left_(-1),
 466       ignore_top_(-1),
 467       ignore_right_(-1),
 468       ignore_bottom_(-1),
 469       direction_(RIGHT),
 470       delta_x_(1),
 471       delta_y_(0),
 472       current_step_(0),
 473       horizontal_step_count_(0),
 474       vertical_step_count_(0) {
 475   if (tiling_data_->num_tiles_x() <= 0 || tiling_data_->num_tiles_y() <= 0) {
 476     done();
 477     return;
 478   }
 479
 480   gfx::Rect tiling_bounds_rect(tiling_data_->tiling_size());
 481   gfx::Rect consider(consider_rect);
 482   gfx::Rect ignore(ignore_rect);
 483   gfx::Rect center(center_rect);
 484   consider.Intersect(tiling_bounds_rect);
 485   ignore.Intersect(tiling_bounds_rect);
 486   if (consider.IsEmpty()) {
 487     done();
 488     return;
 489   }
 490
 491   consider_left_ =
 492       tiling_data_->FirstBorderTileXIndexFromSrcCoord(consider.x());
 493   consider_top_ = tiling_data_->FirstBorderTileYIndexFromSrcCoord(consider.y());
 494   consider_right_ =
 495       tiling_data_->LastBorderTileXIndexFromSrcCoord(consider.right() - 1);
 496   consider_bottom_ =
 497       tiling_data_->LastBorderTileYIndexFromSrcCoord(consider.bottom() - 1);
 498
 499   if (!ignore.IsEmpty()) {
 500     ignore_left_ = tiling_data_->FirstBorderTileXIndexFromSrcCoord(ignore.x());
 501     ignore_top_ = tiling_data_->FirstBorderTileYIndexFromSrcCoord(ignore.y());
 502     ignore_right_ =
 503         tiling_data_->LastBorderTileXIndexFromSrcCoord(ignore.right() - 1);
 504     ignore_bottom_ =
 505         tiling_data_->LastBorderTileYIndexFromSrcCoord(ignore.bottom() - 1);
 506
 507     // Clamp ignore indices to consider indices.
 508     ignore_left_ = std::max(ignore_left_, consider_left_);
 509     ignore_top_ = std::max(ignore_top_, consider_top_);
 510     ignore_right_ = std::min(ignore_right_, consider_right_);
 511     ignore_bottom_ = std::min(ignore_bottom_, consider_bottom_);
 512   }
 513
 514   if (ignore_left_ == consider_left_ && ignore_right_ == consider_right_ &&
 515       ignore_top_ == consider_top_ && ignore_bottom_ == consider_bottom_) {
 516     done();
 517     return;
 518   }
 519
 520   // Determine around left, such that it is between -1 and num_tiles_x.
 521   int around_left = 0;
 522   if (center.x() < 0 || center.IsEmpty())
 523     around_left = -1;
 524   else if (center.x() > tiling_data->tiling_size().width())
 525     around_left = tiling_data->num_tiles_x();
 526   else
 527     around_left = tiling_data->FirstBorderTileXIndexFromSrcCoord(center.x());
 528
 529   // Determine around top, such that it is between -1 and num_tiles_y.
 530   int around_top = 0;
 531   if (center.y() < 0 || center.IsEmpty())
 532     around_top = -1;
 533   else if (center.y() > tiling_data->tiling_size().height())
 534     around_top = tiling_data->num_tiles_y();
 535   else
 536     around_top = tiling_data->FirstBorderTileYIndexFromSrcCoord(center.y());
 537
 538   // Determine around right, such that it is between -1 and num_tiles_x.
 539   int right_src_coord = center.right() - 1;
 540   int around_right = 0;
 541   if (right_src_coord < 0 || center.IsEmpty()) {
 542     around_right = -1;
 543   } else if (right_src_coord > tiling_data->tiling_size().width()) {
 544     around_right = tiling_data->num_tiles_x();
 545   } else {
 546     around_right =
 547         tiling_data->LastBorderTileXIndexFromSrcCoord(right_src_coord);
 548   }
 549
 550   // Determine around bottom, such that it is between -1 and num_tiles_y.
 551   int bottom_src_coord = center.bottom() - 1;
 552   int around_bottom = 0;
 553   if (bottom_src_coord < 0 || center.IsEmpty()) {
 554     around_bottom = -1;
 555   } else if (bottom_src_coord > tiling_data->tiling_size().height()) {
 556     around_bottom = tiling_data->num_tiles_y();
 557   } else {
 558     around_bottom =
 559         tiling_data->LastBorderTileYIndexFromSrcCoord(bottom_src_coord);
 560   }
 561
 562   vertical_step_count_ = around_bottom - around_top + 1;
 563   horizontal_step_count_ = around_right - around_left + 1;
 564   current_step_ = horizontal_step_count_ - 1;
 565
 566   index_x_ = around_right;
 567   index_y_ = around_bottom;
 568
 569   // The current index is the bottom right of the around rect, which is also
 570   // ignored. So we have to advance.
 571   ++(*this);
 572 }
 573
 574 TilingData::SpiralDifferenceIterator& TilingData::SpiralDifferenceIterator::
 575 operator++() {
 576   int cannot_hit_consider_count = 0;
 577   while (cannot_hit_consider_count < 4) {
 578     if (needs_direction_switch())
 579       switch_direction();
 580
 581     index_x_ += delta_x_;
 582     index_y_ += delta_y_;
 583     ++current_step_;
 584
 585     if (in_consider_rect()) {
 586       cannot_hit_consider_count = 0;
 587
 588       if (!in_ignore_rect())
 589         break;
 590
 591       // Steps needed to reach the very edge of the ignore rect, while remaining
 592       // inside (so that the continue would take us outside).
 593       int steps_to_edge = 0;
 594       switch (direction_) {
 595         case UP:
 596           steps_to_edge = index_y_ - ignore_top_;
 597           break;
 598         case LEFT:
 599           steps_to_edge = index_x_ - ignore_left_;
 600           break;
 601         case DOWN:
 602           steps_to_edge = ignore_bottom_ - index_y_;
 603           break;
 604         case RIGHT:
 605           steps_to_edge = ignore_right_ - index_x_;
 606           break;
 607       }
 608
 609       // We need to switch directions in |max_steps|.
 610       int max_steps = current_step_count() - current_step_;
 611
 612       int steps_to_take = std::min(steps_to_edge, max_steps);
 613       DCHECK_GE(steps_to_take, 0);
 614
 615       index_x_ += steps_to_take * delta_x_;
 616       index_y_ += steps_to_take * delta_y_;
 617       current_step_ += steps_to_take;
 618     } else {
 619       int max_steps = current_step_count() - current_step_;
 620       int steps_to_take = max_steps;
 621       bool can_hit_consider_rect = false;
 622       switch (direction_) {
 623         case UP:
 624           if (valid_column() && consider_bottom_ < index_y_)
 625             steps_to_take = index_y_ - consider_bottom_ - 1;
 626           can_hit_consider_rect |= consider_right_ >= index_x_;
 627           break;
 628         case LEFT:
 629           if (valid_row() && consider_right_ < index_x_)
 630             steps_to_take = index_x_ - consider_right_ - 1;
 631           can_hit_consider_rect |= consider_top_ <= index_y_;
 632           break;
 633         case DOWN:
 634           if (valid_column() && consider_top_ > index_y_)
 635             steps_to_take = consider_top_ - index_y_ - 1;
 636           can_hit_consider_rect |= consider_left_ <= index_x_;
 637           break;
 638         case RIGHT:
 639           if (valid_row() && consider_left_ > index_x_)
 640             steps_to_take = consider_left_ - index_x_ - 1;
 641           can_hit_consider_rect |= consider_bottom_ >= index_y_;
 642           break;
 643       }
 644       steps_to_take = std::min(steps_to_take, max_steps);
 645       DCHECK_GE(steps_to_take, 0);
 646
 647       index_x_ += steps_to_take * delta_x_;
 648       index_y_ += steps_to_take * delta_y_;
 649       current_step_ += steps_to_take;
 650
 651       if (can_hit_consider_rect)
 652         cannot_hit_consider_count = 0;
 653       else
 654         ++cannot_hit_consider_count;
 655     }
 656   }
 657
 658   if (cannot_hit_consider_count >= 4)
 659     done();
 660   return *this;
 661 }
 662
 663 bool TilingData::SpiralDifferenceIterator::needs_direction_switch() const {
 664   return current_step_ >= current_step_count();
 665 }
 666
 667 void TilingData::SpiralDifferenceIterator::switch_direction() {
 668   int new_delta_x_ = delta_y_;
 669   delta_y_ = -delta_x_;
 670   delta_x_ = new_delta_x_;
 671
 672   current_step_ = 0;
 673   direction_ = static_cast<Direction>((direction_ + 1) % 4);
 674
 675   if (direction_ == RIGHT || direction_ == LEFT) {
 676     ++vertical_step_count_;
 677     ++horizontal_step_count_;
 678   }
 679 }
 680
 681 }  // namespace cc