From df71bb31056428a47d5e5d979fbb52f0cd56950d Mon Sep 17 00:00:00 2001
From: Matt Woodrow <mwoodrow@mozilla.com>
Date: Tue, 6 Nov 2018 00:39:59 +0000
Subject: [PATCH] Bug 1456555 - Fix bugs in DrawTargetOffset. r=mstange

MozReview-Commit-ID: I4XFoTp1szZ

Depends on D10033

Differential Revision: https://phabricator.services.mozilla.com/D10036

--HG--
extra : moz-landing-system : lando
---
 gfx/2d/DrawTargetOffset.cpp | 28 +++++++++++++++++++---------
 gfx/2d/DrawTargetOffset.h   |  2 +-
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/gfx/2d/DrawTargetOffset.cpp b/gfx/2d/DrawTargetOffset.cpp
index bffc3ec18d71..f901fe68fdb8 100644
--- a/gfx/2d/DrawTargetOffset.cpp
+++ b/gfx/2d/DrawTargetOffset.cpp
@@ -83,7 +83,9 @@ DrawTargetOffset::DrawFilter(FilterNode* aNode, const Rect& aSourceRect, const P
 {
   auto clone = mTransform;
   bool invertible = clone.Invert();
-  auto src = aSourceRect;
+  // aSourceRect is in filter space. The filter outputs from aSourceRect need
+  // to be drawn at aDestPoint in user space.
+  Rect userSpaceSource = Rect(aDestPoint, aSourceRect.Size());
   if (invertible) {
     // Try to reduce the source rect so that it's not much bigger
     // than the draw target. The result is not minimal. Examples
@@ -92,11 +94,16 @@ DrawTargetOffset::DrawFilter(FilterNode* aNode, const Rect& aSourceRect, const P
                          mOrigin.y,
                          mDrawTarget->GetSize().width,
                          mDrawTarget->GetSize().height);
-    auto dtBounds = clone.TransformBounds(destRect);
-    src = aSourceRect.Intersect(dtBounds);
+    Rect userSpaceBounds = clone.TransformBounds(destRect);
+    userSpaceSource = userSpaceSource.Intersect(userSpaceBounds);
   }
-  auto shift = src.TopLeft() - aSourceRect.TopLeft();
-  mDrawTarget->DrawFilter(aNode, src, aDestPoint + shift, aOptions);
+
+  // Compute how much we moved the top-left of the source rect by, and use that
+  // to compute the new dest point, and move our intersected source rect back
+  // into the (new) filter space.
+  Point shift = userSpaceSource.TopLeft() - aDestPoint;
+  Rect filterSpaceSource = Rect(aSourceRect.TopLeft() + shift, userSpaceSource.Size());
+  mDrawTarget->DrawFilter(aNode, filterSpaceSource, aDestPoint + shift, aOptions);
 }
 
 void
@@ -184,9 +191,10 @@ DrawTargetOffset::PushLayer(bool aOpaque, Float aOpacity, SourceSurface* aMask,
                            const Matrix& aMaskTransform, const IntRect& aBounds,
                            bool aCopyBackground)
 {
-  IntRect bounds = aBounds;
-  bounds.MoveBy(mOrigin);
+  IntRect bounds = aBounds - mOrigin;
+
   mDrawTarget->PushLayer(aOpaque, aOpacity, aMask, aMaskTransform, bounds, aCopyBackground);
+  SetPermitSubpixelAA(mDrawTarget->GetPermitSubpixelAA());
 }
 
 void
@@ -197,15 +205,17 @@ DrawTargetOffset::PushLayerWithBlend(bool aOpaque, Float aOpacity,
                                     bool aCopyBackground,
                                     CompositionOp aOp)
 {
-  IntRect bounds = aBounds;
-  bounds.MoveBy(mOrigin);
+  IntRect bounds = aBounds - mOrigin;
+
   mDrawTarget->PushLayerWithBlend(aOpaque, aOpacity, aMask, aMaskTransform, bounds, aCopyBackground, aOp);
+  SetPermitSubpixelAA(mDrawTarget->GetPermitSubpixelAA());
 }
 
 void
 DrawTargetOffset::PopLayer()
 {
   mDrawTarget->PopLayer();
+  SetPermitSubpixelAA(mDrawTarget->GetPermitSubpixelAA());
 }
 
 } // namespace gfx
diff --git a/gfx/2d/DrawTargetOffset.h b/gfx/2d/DrawTargetOffset.h
index 647018b0f04b..bab7a09a93e8 100644
--- a/gfx/2d/DrawTargetOffset.h
+++ b/gfx/2d/DrawTargetOffset.h
@@ -38,7 +38,7 @@ public:
     return mDrawTarget->GetSize();
   }
   virtual IntRect GetRect() const override {
-    return mDrawTarget->GetRect();
+    return IntRect(mOrigin, GetSize());
   }
 
   virtual void Flush() override;