Bug 1083079 - Prevent the size of TiledDrawTarget from being zero due to its tiles having negative offsets. r=mattwoodrow

gfx/2d/DrawTargetTiled.h

@@ -40,7 +40,10 @@ public:
   virtual DrawTargetType GetType() const MOZ_OVERRIDE { return mTiles[0].mDrawTarget->GetType(); }
   virtual BackendType GetBackendType() const { return mTiles[0].mDrawTarget->GetBackendType(); }
   virtual TemporaryRef<SourceSurface> Snapshot();
-  virtual IntSize GetSize() { return IntSize(mRect.XMost(), mRect.YMost()); }
+  virtual IntSize GetSize() {
+    MOZ_ASSERT(mRect.width > 0 && mRect.height > 0);
+    return IntSize(mRect.XMost(), mRect.YMost());
+  }
 
   virtual void Flush();
   virtual void DrawSurface(SourceSurface *aSurface,
@@ -162,7 +165,10 @@ public:
   }
 
   virtual SurfaceType GetType() const { return SurfaceType::TILED; }
-  virtual IntSize GetSize() const { return IntSize(mRect.XMost(), mRect.YMost()); }
+  virtual IntSize GetSize() const {
+    MOZ_ASSERT(mRect.width > 0 && mRect.height > 0);
+    return IntSize(mRect.XMost(), mRect.YMost());
+  }
   virtual SurfaceFormat GetFormat() const { return mSnapshots[0]->GetFormat(); }
 
   virtual TemporaryRef<DataSourceSurface> GetDataSurface()

gfx/layers/client/TiledContentClient.cpp

@@ -1056,6 +1056,9 @@ ClientTiledLayerBuffer::PostValidate(const nsIntRegion& aPaintRegion)
 {
   if (gfxPrefs::TiledDrawTargetEnabled() && mMoz2DTiles.size() > 0) {
     gfx::TileSet tileset;
+    for (size_t i = 0; i < mMoz2DTiles.size(); ++i) {
+      mMoz2DTiles[i].mTileOrigin -= mTilingOrigin;
+    }
     tileset.mTiles = &mMoz2DTiles[0];
     tileset.mTileCount = mMoz2DTiles.size();
     RefPtr<DrawTarget> drawTarget = gfx::Factory::CreateTiledDrawTarget(tileset);
@@ -1063,10 +1066,13 @@ ClientTiledLayerBuffer::PostValidate(const nsIntRegion& aPaintRegion)
 
     RefPtr<gfxContext> ctx = new gfxContext(drawTarget);
     ctx->SetMatrix(
-      ctx->CurrentMatrix().Scale(mResolution, mResolution));
+      ctx->CurrentMatrix().Scale(mResolution, mResolution).Translate(ThebesPoint(-mTilingOrigin)));
 
     mCallback(mPaintedLayer, ctx, aPaintRegion, DrawRegionClip::DRAW, nsIntRegion(), mCallbackData);
     mMoz2DTiles.clear();
+    // Reset:
+    mTilingOrigin = IntPoint(std::numeric_limits<int32_t>::max(),
+                             std::numeric_limits<int32_t>::max());
   }
 }
 
@@ -1188,6 +1194,8 @@ ClientTiledLayerBuffer::ValidateTile(TileClient aTile,
     }
 
     mMoz2DTiles.push_back(moz2DTile);
+    mTilingOrigin.x = std::min(mTilingOrigin.x, moz2DTile.mTileOrigin.x);
+    mTilingOrigin.y = std::min(mTilingOrigin.y, moz2DTile.mTileOrigin.y);
 
     nsIntRegionRectIterator it(aDirtyRegion);
     for (const nsIntRect* dirtyRect = it.Next(); dirtyRect != nullptr; dirtyRect = it.Next()) {

gfx/layers/client/TiledContentClient.h

@@ -9,6 +9,7 @@
 #include <stddef.h>                     // for size_t
 #include <stdint.h>                     // for uint16_t
 #include <algorithm>                    // for swap
+#include <limits>
 #include "Layers.h"                     // for LayerManager, etc
 #include "TiledLayerBuffer.h"           // for TiledLayerBuffer
 #include "Units.h"                      // for CSSPoint
@@ -399,6 +400,8 @@ public:
     , mLastPaintContentType(gfxContentType::COLOR)
     , mLastPaintSurfaceMode(SurfaceMode::SURFACE_OPAQUE)
     , mSharedFrameMetricsHelper(nullptr)
+    , mTilingOrigin(std::numeric_limits<int32_t>::max(),
+                    std::numeric_limits<int32_t>::max())
   {}
 
   void PaintThebes(const nsIntRegion& aNewValidRegion,
@@ -475,6 +478,16 @@ private:
   SharedFrameMetricsHelper*  mSharedFrameMetricsHelper;
   // When using Moz2D's CreateTiledDrawTarget we maintain a list of gfx::Tiles
   std::vector<gfx::Tile> mMoz2DTiles;
+  /**
+   * While we're adding tiles, this is used to keep track of the position of
+   * the top-left of the top-left-most tile.  When we come to wrap the tiles in
+   * TiledDrawTarget we subtract the value of this member from each tile's
+   * offset so that all the tiles have a positive offset, then add a
+   * translation to the TiledDrawTarget to compensate.  This is important so
+   * that the mRect of the TiledDrawTarget is always at a positive x/y
+   * position, otherwise its GetSize() methods will be broken.
+   */
+  gfx::IntPoint mTilingOrigin;
   /**
    * Calculates the region to update in a single progressive update transaction.
    * This employs some heuristics to update the most 'sensible' region to