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/geometry/rect.h"
  10 #include "ui/gfx/geometry/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::ExpandRectIgnoringBordersToTileBounds(
 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(TileBounds(index_x, index_y));
 141   gfx::Rect rect_bottom_right(TileBounds(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() : index_x_(-1), index_y_(-1) {
 297 }
 298
 299 TilingData::Iterator::Iterator() {
 300   done();
 301 }
 302
 303 TilingData::Iterator::Iterator(const TilingData* tiling_data,
 304                                const gfx::Rect& consider_rect,
 305                                bool include_borders)
 306     : left_(-1), right_(-1), bottom_(-1) {
 307   if (tiling_data->num_tiles_x() <= 0 || tiling_data->num_tiles_y() <= 0) {
 308     done();
 309     return;
 310   }
 311
 312   gfx::Rect tiling_bounds_rect(tiling_data->tiling_size());
 313   gfx::Rect rect(consider_rect);
 314   rect.Intersect(tiling_bounds_rect);
 315
 316   gfx::Rect top_left_tile;
 317   if (include_borders) {
 318     index_x_ = tiling_data->FirstBorderTileXIndexFromSrcCoord(rect.x());
 319     index_y_ = tiling_data->FirstBorderTileYIndexFromSrcCoord(rect.y());
 320     right_ = tiling_data->LastBorderTileXIndexFromSrcCoord(rect.right() - 1);
 321     bottom_ = tiling_data->LastBorderTileYIndexFromSrcCoord(rect.bottom() - 1);
 322     top_left_tile = tiling_data->TileBoundsWithBorder(index_x_, index_y_);
 323   } else {
 324     index_x_ = tiling_data->TileXIndexFromSrcCoord(rect.x());
 325     index_y_ = tiling_data->TileYIndexFromSrcCoord(rect.y());
 326     right_ = tiling_data->TileXIndexFromSrcCoord(rect.right() - 1);
 327     bottom_ = tiling_data->TileYIndexFromSrcCoord(rect.bottom() - 1);
 328     top_left_tile = tiling_data->TileBounds(index_x_, index_y_);
 329   }
 330   left_ = index_x_;
 331
 332   // Index functions always return valid indices, so explicitly check
 333   // for non-intersecting rects.
 334   if (!top_left_tile.Intersects(rect))
 335     done();
 336 }
 337
 338 TilingData::Iterator& TilingData::Iterator::operator++() {
 339   if (!*this)
 340     return *this;
 341
 342   index_x_++;
 343   if (index_x_ > right_) {
 344     index_x_ = left_;
 345     index_y_++;
 346     if (index_y_ > bottom_)
 347       done();
 348   }
 349
 350   return *this;
 351 }
 352
 353 TilingData::BaseDifferenceIterator::BaseDifferenceIterator() {
 354   done();
 355 }
 356
 357 TilingData::BaseDifferenceIterator::BaseDifferenceIterator(
 358     const TilingData* tiling_data,
 359     const gfx::Rect& consider_rect,
 360     const gfx::Rect& ignore_rect)
 361     : consider_left_(-1),
 362       consider_top_(-1),
 363       consider_right_(-1),
 364       consider_bottom_(-1),
 365       ignore_left_(-1),
 366       ignore_top_(-1),
 367       ignore_right_(-1),
 368       ignore_bottom_(-1) {
 369   if (tiling_data->num_tiles_x() <= 0 || tiling_data->num_tiles_y() <= 0) {
 370     done();
 371     return;
 372   }
 373
 374   gfx::Rect tiling_bounds_rect(tiling_data->tiling_size());
 375   gfx::Rect consider(consider_rect);
 376   consider.Intersect(tiling_bounds_rect);
 377
 378   if (consider.IsEmpty()) {
 379     done();
 380     return;
 381   }
 382
 383   consider_left_ = tiling_data->TileXIndexFromSrcCoord(consider.x());
 384   consider_top_ = tiling_data->TileYIndexFromSrcCoord(consider.y());
 385   consider_right_ = tiling_data->TileXIndexFromSrcCoord(consider.right() - 1);
 386   consider_bottom_ = tiling_data->TileYIndexFromSrcCoord(consider.bottom() - 1);
 387
 388   gfx::Rect ignore(ignore_rect);
 389   ignore.Intersect(tiling_bounds_rect);
 390
 391   if (!ignore.IsEmpty()) {
 392     ignore_left_ = tiling_data->TileXIndexFromSrcCoord(ignore.x());
 393     ignore_top_ = tiling_data->TileYIndexFromSrcCoord(ignore.y());
 394     ignore_right_ = tiling_data->TileXIndexFromSrcCoord(ignore.right() - 1);
 395     ignore_bottom_ = tiling_data->TileYIndexFromSrcCoord(ignore.bottom() - 1);
 396
 397     // Clamp ignore indices to consider indices.
 398     ignore_left_ = std::max(ignore_left_, consider_left_);
 399     ignore_top_ = std::max(ignore_top_, consider_top_);
 400     ignore_right_ = std::min(ignore_right_, consider_right_);
 401     ignore_bottom_ = std::min(ignore_bottom_, consider_bottom_);
 402
 403     if (ignore_left_ == consider_left_ && ignore_right_ == consider_right_ &&
 404         ignore_top_ == consider_top_ && ignore_bottom_ == consider_bottom_) {
 405       consider_left_ = consider_top_ = consider_right_ = consider_bottom_ = -1;
 406       done();
 407       return;
 408     }
 409   }
 410 }
 411
 412 bool TilingData::BaseDifferenceIterator::HasConsiderRect() const {
 413   // Consider indices are either all valid or all equal to -1.
 414   DCHECK((0 <= consider_left_ && consider_left_ <= consider_right_ &&
 415           0 <= consider_top_ && consider_top_ <= consider_bottom_) ||
 416          (consider_left_ == -1 && consider_top_ == -1 &&
 417           consider_right_ == -1 && consider_bottom_ == -1));
 418   return consider_left_ != -1;
 419 }
 420
 421 TilingData::DifferenceIterator::DifferenceIterator() {
 422 }
 423
 424 TilingData::DifferenceIterator::DifferenceIterator(
 425     const TilingData* tiling_data,
 426     const gfx::Rect& consider_rect,
 427     const gfx::Rect& ignore_rect)
 428     : BaseDifferenceIterator(tiling_data, consider_rect, ignore_rect) {
 429   if (!HasConsiderRect()) {
 430     done();
 431     return;
 432   }
 433
 434   index_x_ = consider_left_;
 435   index_y_ = consider_top_;
 436
 437   if (in_ignore_rect())
 438     ++(*this);
 439 }
 440
 441 TilingData::DifferenceIterator& TilingData::DifferenceIterator::operator++() {
 442   if (!*this)
 443     return *this;
 444
 445   index_x_++;
 446   if (in_ignore_rect())
 447     index_x_ = ignore_right_ + 1;
 448
 449   if (index_x_ > consider_right_) {
 450     index_x_ = consider_left_;
 451     index_y_++;
 452
 453     if (in_ignore_rect()) {
 454       index_x_ = ignore_right_ + 1;
 455       // If the ignore rect spans the whole consider rect horizontally, then
 456       // ignore_right + 1 will be out of bounds.
 457       if (in_ignore_rect() || index_x_ > consider_right_) {
 458         index_y_ = ignore_bottom_ + 1;
 459         index_x_ = consider_left_;
 460       }
 461     }
 462
 463     if (index_y_ > consider_bottom_)
 464       done();
 465   }
 466
 467   return *this;
 468 }
 469
 470 TilingData::SpiralDifferenceIterator::SpiralDifferenceIterator() {
 471   done();
 472 }
 473
 474 TilingData::SpiralDifferenceIterator::SpiralDifferenceIterator(
 475     const TilingData* tiling_data,
 476     const gfx::Rect& consider_rect,
 477     const gfx::Rect& ignore_rect,
 478     const gfx::Rect& center_rect)
 479     : BaseDifferenceIterator(tiling_data, consider_rect, ignore_rect),
 480       direction_(RIGHT),
 481       delta_x_(1),
 482       delta_y_(0),
 483       current_step_(0),
 484       horizontal_step_count_(0),
 485       vertical_step_count_(0) {
 486   if (!HasConsiderRect()) {
 487     done();
 488     return;
 489   }
 490
 491   // Determine around left, such that it is between -1 and num_tiles_x.
 492   int around_left = 0;
 493   if (center_rect.x() < 0 || center_rect.IsEmpty())
 494     around_left = -1;
 495   else if (center_rect.x() >= tiling_data->tiling_size().width())
 496     around_left = tiling_data->num_tiles_x();
 497   else
 498     around_left = tiling_data->TileXIndexFromSrcCoord(center_rect.x());
 499
 500   // Determine around top, such that it is between -1 and num_tiles_y.
 501   int around_top = 0;
 502   if (center_rect.y() < 0 || center_rect.IsEmpty())
 503     around_top = -1;
 504   else if (center_rect.y() >= tiling_data->tiling_size().height())
 505     around_top = tiling_data->num_tiles_y();
 506   else
 507     around_top = tiling_data->TileYIndexFromSrcCoord(center_rect.y());
 508
 509   // Determine around right, such that it is between -1 and num_tiles_x.
 510   int right_src_coord = center_rect.right() - 1;
 511   int around_right = 0;
 512   if (right_src_coord < 0 || center_rect.IsEmpty()) {
 513     around_right = -1;
 514   } else if (right_src_coord >= tiling_data->tiling_size().width()) {
 515     around_right = tiling_data->num_tiles_x();
 516   } else {
 517     around_right = tiling_data->TileXIndexFromSrcCoord(right_src_coord);
 518   }
 519
 520   // Determine around bottom, such that it is between -1 and num_tiles_y.
 521   int bottom_src_coord = center_rect.bottom() - 1;
 522   int around_bottom = 0;
 523   if (bottom_src_coord < 0 || center_rect.IsEmpty()) {
 524     around_bottom = -1;
 525   } else if (bottom_src_coord >= tiling_data->tiling_size().height()) {
 526     around_bottom = tiling_data->num_tiles_y();
 527   } else {
 528     around_bottom = tiling_data->TileYIndexFromSrcCoord(bottom_src_coord);
 529   }
 530
 531   vertical_step_count_ = around_bottom - around_top + 1;
 532   horizontal_step_count_ = around_right - around_left + 1;
 533   current_step_ = horizontal_step_count_ - 1;
 534
 535   index_x_ = around_right;
 536   index_y_ = around_bottom;
 537
 538   // The current index is the bottom right of the around rect, which is also
 539   // ignored. So we have to advance.
 540   ++(*this);
 541 }
 542
 543 TilingData::SpiralDifferenceIterator& TilingData::SpiralDifferenceIterator::
 544 operator++() {
 545   int cannot_hit_consider_count = 0;
 546   while (cannot_hit_consider_count < 4) {
 547     if (needs_direction_switch())
 548       switch_direction();
 549
 550     index_x_ += delta_x_;
 551     index_y_ += delta_y_;
 552     ++current_step_;
 553
 554     if (in_consider_rect()) {
 555       cannot_hit_consider_count = 0;
 556
 557       if (!in_ignore_rect())
 558         break;
 559
 560       // Steps needed to reach the very edge of the ignore rect, while remaining
 561       // inside (so that the continue would take us outside).
 562       int steps_to_edge = 0;
 563       switch (direction_) {
 564         case UP:
 565           steps_to_edge = index_y_ - ignore_top_;
 566           break;
 567         case LEFT:
 568           steps_to_edge = index_x_ - ignore_left_;
 569           break;
 570         case DOWN:
 571           steps_to_edge = ignore_bottom_ - index_y_;
 572           break;
 573         case RIGHT:
 574           steps_to_edge = ignore_right_ - index_x_;
 575           break;
 576       }
 577
 578       // We need to switch directions in |max_steps|.
 579       int max_steps = current_step_count() - current_step_;
 580
 581       int steps_to_take = std::min(steps_to_edge, max_steps);
 582       DCHECK_GE(steps_to_take, 0);
 583
 584       index_x_ += steps_to_take * delta_x_;
 585       index_y_ += steps_to_take * delta_y_;
 586       current_step_ += steps_to_take;
 587     } else {
 588       int max_steps = current_step_count() - current_step_;
 589       int steps_to_take = max_steps;
 590       bool can_hit_consider_rect = false;
 591       switch (direction_) {
 592         case UP:
 593           if (valid_column() && consider_bottom_ < index_y_)
 594             steps_to_take = index_y_ - consider_bottom_ - 1;
 595           can_hit_consider_rect |= consider_right_ >= index_x_;
 596           break;
 597         case LEFT:
 598           if (valid_row() && consider_right_ < index_x_)
 599             steps_to_take = index_x_ - consider_right_ - 1;
 600           can_hit_consider_rect |= consider_top_ <= index_y_;
 601           break;
 602         case DOWN:
 603           if (valid_column() && consider_top_ > index_y_)
 604             steps_to_take = consider_top_ - index_y_ - 1;
 605           can_hit_consider_rect |= consider_left_ <= index_x_;
 606           break;
 607         case RIGHT:
 608           if (valid_row() && consider_left_ > index_x_)
 609             steps_to_take = consider_left_ - index_x_ - 1;
 610           can_hit_consider_rect |= consider_bottom_ >= index_y_;
 611           break;
 612       }
 613       steps_to_take = std::min(steps_to_take, max_steps);
 614       DCHECK_GE(steps_to_take, 0);
 615
 616       index_x_ += steps_to_take * delta_x_;
 617       index_y_ += steps_to_take * delta_y_;
 618       current_step_ += steps_to_take;
 619
 620       if (can_hit_consider_rect)
 621         cannot_hit_consider_count = 0;
 622       else
 623         ++cannot_hit_consider_count;
 624     }
 625   }
 626
 627   if (cannot_hit_consider_count >= 4)
 628     done();
 629   return *this;
 630 }
 631
 632 bool TilingData::SpiralDifferenceIterator::needs_direction_switch() const {
 633   return current_step_ >= current_step_count();
 634 }
 635
 636 void TilingData::SpiralDifferenceIterator::switch_direction() {
 637   // Note that delta_x_ and delta_y_ always remain between -1 and 1.
 638   int new_delta_x_ = delta_y_;
 639   delta_y_ = -delta_x_;
 640   delta_x_ = new_delta_x_;
 641
 642   current_step_ = 0;
 643   direction_ = static_cast<Direction>((direction_ + 1) % 4);
 644
 645   if (direction_ == RIGHT || direction_ == LEFT) {
 646     ++vertical_step_count_;
 647     ++horizontal_step_count_;
 648   }
 649 }
 650
 651 TilingData::ReverseSpiralDifferenceIterator::ReverseSpiralDifferenceIterator() {
 652   done();
 653 }
 654
 655 TilingData::ReverseSpiralDifferenceIterator::ReverseSpiralDifferenceIterator(
 656     const TilingData* tiling_data,
 657     const gfx::Rect& consider_rect,
 658     const gfx::Rect& ignore_rect,
 659     const gfx::Rect& center_rect)
 660     : BaseDifferenceIterator(tiling_data, consider_rect, ignore_rect),
 661       around_left_(-1),
 662       around_top_(-1),
 663       around_right_(-1),
 664       around_bottom_(-1),
 665       direction_(LEFT),
 666       delta_x_(-1),
 667       delta_y_(0),
 668       current_step_(0),
 669       horizontal_step_count_(0),
 670       vertical_step_count_(0) {
 671   if (!HasConsiderRect()) {
 672     done();
 673     return;
 674   }
 675
 676   // Determine around left, such that it is between -1 and num_tiles_x.
 677   if (center_rect.x() < 0 || center_rect.IsEmpty())
 678     around_left_ = -1;
 679   else if (center_rect.x() >= tiling_data->tiling_size().width())
 680     around_left_ = tiling_data->num_tiles_x();
 681   else
 682     around_left_ = tiling_data->TileXIndexFromSrcCoord(center_rect.x());
 683
 684   // Determine around top, such that it is between -1 and num_tiles_y.
 685   if (center_rect.y() < 0 || center_rect.IsEmpty())
 686     around_top_ = -1;
 687   else if (center_rect.y() >= tiling_data->tiling_size().height())
 688     around_top_ = tiling_data->num_tiles_y();
 689   else
 690     around_top_ = tiling_data->TileYIndexFromSrcCoord(center_rect.y());
 691
 692   // Determine around right, such that it is between -1 and num_tiles_x.
 693   int right_src_coord = center_rect.right() - 1;
 694   if (right_src_coord < 0 || center_rect.IsEmpty()) {
 695     around_right_ = -1;
 696   } else if (right_src_coord >= tiling_data->tiling_size().width()) {
 697     around_right_ = tiling_data->num_tiles_x();
 698   } else {
 699     around_right_ = tiling_data->TileXIndexFromSrcCoord(right_src_coord);
 700   }
 701
 702   // Determine around bottom, such that it is between -1 and num_tiles_y.
 703   int bottom_src_coord = center_rect.bottom() - 1;
 704   if (bottom_src_coord < 0 || center_rect.IsEmpty()) {
 705     around_bottom_ = -1;
 706   } else if (bottom_src_coord >= tiling_data->tiling_size().height()) {
 707     around_bottom_ = tiling_data->num_tiles_y();
 708   } else {
 709     around_bottom_ = tiling_data->TileYIndexFromSrcCoord(bottom_src_coord);
 710   }
 711
 712   // Figure out the maximum distance from the around edge to consider edge.
 713   int max_distance = 0;
 714   max_distance = std::max(max_distance, around_top_ - consider_top_);
 715   max_distance = std::max(max_distance, around_left_ - consider_left_);
 716   max_distance = std::max(max_distance, consider_bottom_ - around_bottom_);
 717   max_distance = std::max(max_distance, consider_right_ - around_right_);
 718
 719   // The step count is the length of the edge (around_right_ - around_left_ + 1)
 720   // plus twice the max distance to pad (to the right and to the left). This way
 721   // the initial rect is the size proportional to the center, but big enough
 722   // to cover the consider rect.
 723   //
 724   // C = consider rect
 725   // A = around rect
 726   // . = area of the padded around rect
 727   // md = max distance (note in the picture below, there's md written vertically
 728   //      as well).
 729   // I = initial starting position
 730   //
 731   //       |md|  |md|
 732   //
 733   //     - ..........
 734   //     m ..........
 735   //     d ..........
 736   //     - CCCCCCC...
 737   //       CCCCAAC...
 738   //       CCCCAAC...
 739   //     - ..........
 740   //     m ..........
 741   //     d ..........
 742   //     - ..........I
 743   vertical_step_count_ = around_bottom_ - around_top_ + 1 + 2 * max_distance;
 744   horizontal_step_count_ = around_right_ - around_left_ + 1 + 2 * max_distance;
 745
 746   // Start with one to the right of the padded around rect.
 747   index_x_ = around_right_ + max_distance + 1;
 748   index_y_ = around_bottom_ + max_distance;
 749
 750   // The current index is outside a valid tile, so advance immediately.
 751   ++(*this);
 752 }
 753
 754 TilingData::ReverseSpiralDifferenceIterator&
 755     TilingData::ReverseSpiralDifferenceIterator::
 756     operator++() {
 757   while (!in_around_rect()) {
 758     if (needs_direction_switch())
 759       switch_direction();
 760
 761     index_x_ += delta_x_;
 762     index_y_ += delta_y_;
 763     ++current_step_;
 764
 765     if (in_around_rect()) {
 766       break;
 767     } else if (in_consider_rect()) {
 768       // If the tile is in the consider rect but not in ignore rect, then it's a
 769       // valid tile to visit.
 770       if (!in_ignore_rect())
 771         break;
 772
 773       // Steps needed to reach the very edge of the ignore rect, while remaining
 774       // inside it (so that the continue would take us outside).
 775       int steps_to_edge = 0;
 776       switch (direction_) {
 777         case UP:
 778           steps_to_edge = index_y_ - ignore_top_;
 779           break;
 780         case LEFT:
 781           steps_to_edge = index_x_ - ignore_left_;
 782           break;
 783         case DOWN:
 784           steps_to_edge = ignore_bottom_ - index_y_;
 785           break;
 786         case RIGHT:
 787           steps_to_edge = ignore_right_ - index_x_;
 788           break;
 789       }
 790
 791       // We need to switch directions in |max_steps|.
 792       int max_steps = current_step_count() - current_step_;
 793
 794       int steps_to_take = std::min(steps_to_edge, max_steps);
 795       DCHECK_GE(steps_to_take, 0);
 796
 797       index_x_ += steps_to_take * delta_x_;
 798       index_y_ += steps_to_take * delta_y_;
 799       current_step_ += steps_to_take;
 800     } else {
 801       // We're not in the consider rect.
 802
 803       int max_steps = current_step_count() - current_step_;
 804       int steps_to_take = max_steps;
 805
 806       // We might hit the consider rect before needing to switch directions:
 807       // update steps to take.
 808       switch (direction_) {
 809         case UP:
 810           if (valid_column() && consider_bottom_ < index_y_)
 811             steps_to_take = index_y_ - consider_bottom_ - 1;
 812           break;
 813         case LEFT:
 814           if (valid_row() && consider_right_ < index_x_)
 815             steps_to_take = index_x_ - consider_right_ - 1;
 816           break;
 817         case DOWN:
 818           if (valid_column() && consider_top_ > index_y_)
 819             steps_to_take = consider_top_ - index_y_ - 1;
 820           break;
 821         case RIGHT:
 822           if (valid_row() && consider_left_ > index_x_)
 823             steps_to_take = consider_left_ - index_x_ - 1;
 824           break;
 825       }
 826       steps_to_take = std::min(steps_to_take, max_steps);
 827       DCHECK_GE(steps_to_take, 0);
 828
 829       index_x_ += steps_to_take * delta_x_;
 830       index_y_ += steps_to_take * delta_y_;
 831       current_step_ += steps_to_take;
 832     }
 833   }
 834
 835   // Once we enter the around rect, we're done.
 836   if (in_around_rect())
 837     done();
 838   return *this;
 839 }
 840
 841 bool TilingData::ReverseSpiralDifferenceIterator::needs_direction_switch()
 842     const {
 843   return current_step_ >= current_step_count();
 844 }
 845
 846 void TilingData::ReverseSpiralDifferenceIterator::switch_direction() {
 847   // Note that delta_x_ and delta_y_ always remain between -1 and 1.
 848   int new_delta_y_ = delta_x_;
 849   delta_x_ = -delta_y_;
 850   delta_y_ = new_delta_y_;
 851
 852   current_step_ = 0;
 853   direction_ = static_cast<Direction>((direction_ + 1) % 4);
 854
 855   if (direction_ == UP || direction_ == DOWN) {
 856     --vertical_step_count_;
 857     --horizontal_step_count_;
 858
 859     // We should always end up in an around rect at some point.
 860     // Since the direction is now vertical, we have to ensure that we will
 861     // advance.
 862     DCHECK_GE(horizontal_step_count_, 1);
 863     DCHECK_GE(vertical_step_count_, 1);
 864   }
 865 }
 866
 867 }  // namespace cc