gfx/src/TiledRegion.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "TiledRegion.h"

#include <algorithm>

#include "mozilla/fallible.h"

namespace mozilla {
namespace gfx {

static const int32_t kTileSize = 256;
static const size_t kMaxTiles = 1000;

/**
 * TiledRegionImpl stores an array of non-empty rectangles (pixman_box32_ts) to
 * represent the region. Each rectangle is contained in a single tile;
 * rectangles never cross tile boundaries. The rectangles are sorted by their
 * tile's origin in top-to-bottom, left-to-right order.
 * (Note that this can mean that a rectangle r1 can come before another
 * rectangle r2 even if r2.y1 < r1.y1, as long as the two rects are in the same
 * row of tiles and r1.x1 < r2.x1.)
 * Empty tiles take up no space in the array - there is no rectangle stored for
 * them. As a result, any algorithm that needs to deal with empty tiles will
 * iterate through the mRects array and compare the positions of two
 * consecutive rects to figure out whether there are any empty tiles between
 * them.
 */

static pixman_box32_t IntersectionOfNonEmptyBoxes(const pixman_box32_t& aBox1,
                                                  const pixman_box32_t& aBox2) {
  return pixman_box32_t{
      std::max(aBox1.x1, aBox2.x1), std::max(aBox1.y1, aBox2.y1),
      std::min(aBox1.x2, aBox2.x2), std::min(aBox1.y2, aBox2.y2)};
}

// A TileIterator points to a specific tile inside a certain tile range, or to
// the end of the tile range. Advancing a TileIterator will move to the next
// tile inside the range (or to the range end). The next tile is either the
// tile to the right of the current one, or the first tile of the next tile
// row if the current tile is already the last tile in the row.
class TileIterator {
 public:
  TileIterator(const pixman_box32_t& aTileBounds, const IntPoint& aPosition)
      : mTileBounds(aTileBounds), mPos(aPosition) {}

  bool operator!=(const TileIterator& aOther) { return mPos != aOther.mPos; }
  bool operator==(const TileIterator& aOther) { return mPos == aOther.mPos; }

  IntPoint operator*() const { return mPos; }

  const TileIterator& operator++() {
    mPos.x += kTileSize;
    if (mPos.x >= mTileBounds.x2) {
      mPos.x = mTileBounds.x1;
      mPos.y += kTileSize;
    }
    return *this;
  }

  TileIterator& operator=(const IntPoint& aPosition) {
    mPos = aPosition;
    return *this;
  }

  bool IsBeforeTileContainingPoint(const IntPoint& aPoint) const {
    return (mPos.y + kTileSize) <= aPoint.y ||
           (mPos.y <= aPoint.y && (mPos.x + kTileSize) <= aPoint.x);
  }

  bool IsAtTileContainingPoint(const IntPoint& aPoint) const {
    return mPos.y <= aPoint.y && aPoint.y < (mPos.y + kTileSize) &&
           mPos.x <= aPoint.x && aPoint.x < (mPos.x + kTileSize);
  }

  pixman_box32_t IntersectionWith(const pixman_box32_t& aRect) const {
    pixman_box32_t tile = {mPos.x, mPos.y, mPos.x + kTileSize,
                           mPos.y + kTileSize};
    return IntersectionOfNonEmptyBoxes(tile, aRect);
  }

 private:
  const pixman_box32_t& mTileBounds;
  IntPoint mPos;
};

// A TileRange describes a range of tiles contained inside a certain tile
// bounds (which is a rectangle that includes all tiles that you're
// interested in). The tile range can start and end at any point inside a
// tile row.
// The tile range end is described by the tile that starts at the bottom
// left corner of the tile bounds, i.e. the first tile under the tile
// bounds.
class TileRange {
 public:
  // aTileBounds, aStart and aEnd need to be aligned with the tile grid.
  TileRange(const pixman_box32_t& aTileBounds, const IntPoint& aStart,
            const IntPoint& aEnd)
      : mTileBounds(aTileBounds), mStart(aStart), mEnd(aEnd) {}
  // aTileBounds needs to be aligned with the tile grid.
  explicit TileRange(const pixman_box32_t& aTileBounds)
      : mTileBounds(aTileBounds),
        mStart(mTileBounds.x1, mTileBounds.y1),
        mEnd(mTileBounds.x1, mTileBounds.y2) {}

  TileIterator Begin() const { return TileIterator(mTileBounds, mStart); }
  TileIterator End() const { return TileIterator(mTileBounds, mEnd); }

  // The number of tiles in this tile range.
  size_t Length() const {
    if (mEnd.y == mStart.y) {
      return (mEnd.x - mStart.x) / kTileSize;
    }
    int64_t numberOfFullRows =
        (((int64_t)mEnd.y - (int64_t)mStart.y) / kTileSize) - 1;
    int64_t tilesInFirstRow =
        ((int64_t)mTileBounds.x2 - (int64_t)mStart.x) / kTileSize;
    int64_t tilesInLastRow =
        ((int64_t)mEnd.x - (int64_t)mTileBounds.x1) / kTileSize;
    int64_t tilesInFullRow =
        ((int64_t)mTileBounds.x2 - (int64_t)mTileBounds.x1) / kTileSize;
    int64_t total =
        tilesInFirstRow + (tilesInFullRow * numberOfFullRows) + tilesInLastRow;
    MOZ_ASSERT(total > 0);
    // On 32bit systems the total may be larger than what fits in a size_t (4
    // bytes), so clamp it to size_t's max value in that case.
    return static_cast<uint64_t>(total) >=
                   static_cast<uint64_t>(std::numeric_limits<size_t>::max())
               ? std::numeric_limits<size_t>::max()
               : static_cast<size_t>(total);
  }

  // If aTileOrigin does not describe a tile inside our tile bounds, move it
  // to the next tile that you'd encounter by "advancing" a tile iterator
  // inside these tile bounds. If aTileOrigin is after the last tile inside
  // our tile bounds, move it to the range end tile.
  // The result of this method is a valid end tile for a tile range with our
  // tile bounds.
  IntPoint MoveIntoBounds(const IntPoint& aTileOrigin) const {
    IntPoint p = aTileOrigin;
    if (p.x < mTileBounds.x1) {
      p.x = mTileBounds.x1;
    } else if (p.x >= mTileBounds.x2) {
      p.x = mTileBounds.x1;
      p.y += kTileSize;
    }
    if (p.y < mTileBounds.y1) {
      p.y = mTileBounds.y1;
      p.x = mTileBounds.x1;
    } else if (p.y >= mTileBounds.y2) {
      // There's only one valid state after the end of the tile range, and
      // that's the bottom left point of the tile bounds.
      p.x = mTileBounds.x1;
      p.y = mTileBounds.y2;
    }
    return p;
  }

 private:
  const pixman_box32_t& mTileBounds;
  const IntPoint mStart;
  const IntPoint mEnd;
};

static IntPoint TileContainingPoint(const IntPoint& aPoint) {
  return IntPoint(RoundDownToMultiple(aPoint.x, kTileSize),
                  RoundDownToMultiple(aPoint.y, kTileSize));
}

enum class IterationAction : uint8_t { CONTINUE, STOP };

enum class IterationEndReason : uint8_t { NOT_STOPPED, STOPPED };

template <typename HandleEmptyTilesFunction,
          typename HandleNonEmptyTileFunction, typename RectArrayT>
IterationEndReason ProcessIntersectedTiles(
    const pixman_box32_t& aRect, RectArrayT& aRectArray,
    HandleEmptyTilesFunction aHandleEmptyTiles,
    HandleNonEmptyTileFunction aHandleNonEmptyTile) {
  pixman_box32_t tileBounds = {RoundDownToMultiple(aRect.x1, kTileSize),
                               RoundDownToMultiple(aRect.y1, kTileSize),
                               RoundUpToMultiple(aRect.x2, kTileSize),
                               RoundUpToMultiple(aRect.y2, kTileSize)};
  if (tileBounds.x2 < tileBounds.x1 || tileBounds.y2 < tileBounds.y1) {
    // RoundUpToMultiple probably overflowed. Bail out.
    return IterationEndReason::STOPPED;
  }

  TileRange tileRange(tileBounds);
  TileIterator rangeEnd = tileRange.End();

  // tileIterator points to the next tile in tileRange, or to rangeEnd if we're
  // done.
  TileIterator tileIterator = tileRange.Begin();

  // We iterate over the rectangle array. Depending on the position of the
  // rectangle we encounter, we may need to advance tileIterator by zero, one,
  // or more tiles:
  //  - Zero if the rectangle we encountered is outside the tiles that
  //    intersect aRect.
  //  - One if the rectangle is in the exact tile that we're interested in next
  //    (i.e. the tile that tileIterator points at).
  //  - More than one if the encountered rectangle is in a tile that's further
  //    to the right or to the bottom than tileIterator. In that case there is
  //    at least one empty tile between the last rectangle we encountered and
  //    the current one.
  for (size_t i = 0; i < aRectArray.Length() && tileIterator != rangeEnd; i++) {
    MOZ_ASSERT(aRectArray[i].x1 < aRectArray[i].x2 &&
                   aRectArray[i].y1 < aRectArray[i].y2,
               "empty rect");
    IntPoint rectOrigin(aRectArray[i].x1, aRectArray[i].y1);
    if (tileIterator.IsBeforeTileContainingPoint(rectOrigin)) {
      IntPoint tileOrigin = TileContainingPoint(rectOrigin);
      IntPoint afterEmptyTiles = tileRange.MoveIntoBounds(tileOrigin);
      TileRange emptyTiles(tileBounds, *tileIterator, afterEmptyTiles);
      if (aHandleEmptyTiles(aRectArray, i, emptyTiles) ==
          IterationAction::STOP) {
        return IterationEndReason::STOPPED;
      }
      tileIterator = afterEmptyTiles;
      if (tileIterator == rangeEnd) {
        return IterationEndReason::NOT_STOPPED;
      }
    }
    if (tileIterator.IsAtTileContainingPoint(rectOrigin)) {
      pixman_box32_t rectIntersection = tileIterator.IntersectionWith(aRect);
      if (aHandleNonEmptyTile(aRectArray, i, rectIntersection) ==
          IterationAction::STOP) {
        return IterationEndReason::STOPPED;
      }
      ++tileIterator;
    }
  }

  if (tileIterator != rangeEnd) {
    // We've looked at all of our existing rectangles but haven't covered all
    // of the tiles that we're interested in yet. So we need to deal with the
    // remaining tiles now.
    size_t endIndex = aRectArray.Length();
    TileRange emptyTiles(tileBounds, *tileIterator, *rangeEnd);
    if (aHandleEmptyTiles(aRectArray, endIndex, emptyTiles) ==
        IterationAction::STOP) {
      return IterationEndReason::STOPPED;
    }
  }
  return IterationEndReason::NOT_STOPPED;
}

static pixman_box32_t UnionBoundsOfNonEmptyBoxes(const pixman_box32_t& aBox1,
                                                 const pixman_box32_t& aBox2) {
  return {std::min(aBox1.x1, aBox2.x1), std::min(aBox1.y1, aBox2.y1),
          std::max(aBox1.x2, aBox2.x2), std::max(aBox1.y2, aBox2.y2)};
}

// Returns true when adding the rectangle was successful, and false if
// allocation failed.
// When this returns false, our internal state might not be consistent and we
// need to be cleared.
bool TiledRegionImpl::AddRect(const pixman_box32_t& aRect) {
  // We are adding a rectangle that can span multiple tiles.
  // For each empty tile that aRect intersects, we need to add the intersection
  // of aRect with that tile to mRects, respecting the order of mRects.
  // For each tile that already has a rectangle, we need to enlarge that
  // existing rectangle to include the intersection of aRect with the tile.
  return ProcessIntersectedTiles(
             aRect, mRects,
             [&aRect](nsTArray<pixman_box32_t>& rects, size_t& rectIndex,
                      TileRange emptyTiles) {
               CheckedInt<size_t> newLength(rects.Length());
               newLength += emptyTiles.Length();
               if (!newLength.isValid() || newLength.value() >= kMaxTiles ||
                   !rects.InsertElementsAt(rectIndex, emptyTiles.Length(),
                                           fallible)) {
                 return IterationAction::STOP;
               }
               for (TileIterator tileIt = emptyTiles.Begin();
                    tileIt != emptyTiles.End(); ++tileIt, ++rectIndex) {
                 rects[rectIndex] = tileIt.IntersectionWith(aRect);
               }
               return IterationAction::CONTINUE;
             },
             [](nsTArray<pixman_box32_t>& rects, size_t rectIndex,
                const pixman_box32_t& rectIntersectionWithTile) {
               rects[rectIndex] = UnionBoundsOfNonEmptyBoxes(
                   rects[rectIndex], rectIntersectionWithTile);
               return IterationAction::CONTINUE;
             }) == IterationEndReason::NOT_STOPPED;
}

static bool NonEmptyBoxesIntersect(const pixman_box32_t& aBox1,
                                   const pixman_box32_t& aBox2) {
  return aBox1.x1 < aBox2.x2 && aBox2.x1 < aBox1.x2 && aBox1.y1 < aBox2.y2 &&
         aBox2.y1 < aBox1.y2;
}

bool TiledRegionImpl::Intersects(const pixman_box32_t& aRect) const {
  // aRect intersects this region if it intersects any of our rectangles.
  return ProcessIntersectedTiles(
             aRect, mRects,
             [](const nsTArray<pixman_box32_t>& rects, size_t& rectIndex,
                TileRange emptyTiles) {
               // Ignore empty tiles and keep on iterating.
               return IterationAction::CONTINUE;
             },
             [](const nsTArray<pixman_box32_t>& rects, size_t rectIndex,
                const pixman_box32_t& rectIntersectionWithTile) {
               if (NonEmptyBoxesIntersect(rects[rectIndex],
                                          rectIntersectionWithTile)) {
                 // Found an intersecting rectangle, so aRect intersects this
                 // region.
                 return IterationAction::STOP;
               }
               return IterationAction::CONTINUE;
             }) == IterationEndReason::STOPPED;
}

static bool NonEmptyBoxContainsNonEmptyBox(const pixman_box32_t& aBox1,
                                           const pixman_box32_t& aBox2) {
  return aBox1.x1 <= aBox2.x1 && aBox2.x2 <= aBox1.x2 && aBox1.y1 <= aBox2.y1 &&
         aBox2.y2 <= aBox1.y2;
}

bool TiledRegionImpl::Contains(const pixman_box32_t& aRect) const {
  // aRect is contained in this region if aRect does not intersect any empty
  // tiles and, for each non-empty tile, if the intersection of aRect with that
  // tile is contained in the existing rectangle we have in that tile.
  return ProcessIntersectedTiles(
             aRect, mRects,
             [](const nsTArray<pixman_box32_t>& rects, size_t& rectIndex,
                TileRange emptyTiles) {
               // Found an empty tile that intersects aRect, so aRect is not
               // contained in this region.
               return IterationAction::STOP;
             },
             [](const nsTArray<pixman_box32_t>& rects, size_t rectIndex,
                const pixman_box32_t& rectIntersectionWithTile) {
               if (!NonEmptyBoxContainsNonEmptyBox(rects[rectIndex],
                                                   rectIntersectionWithTile)) {
                 // Our existing rectangle in this tile does not cover the part
                 // of aRect that intersects this tile, so aRect is not
                 // contained in this region.
                 return IterationAction::STOP;
               }
               return IterationAction::CONTINUE;
             }) == IterationEndReason::NOT_STOPPED;
}

}  // namespace gfx
}  // namespace mozilla