Bug 757329: Support changing transforms while emitting path instructions. r=roc

gfx/2d/Matrix.h

@@ -140,7 +140,7 @@ public:
   /* Returns true if the matrix is a rectilinear transformation (i.e.
    * grid-aligned rectangles are transformed to grid-aligned rectangles)
    */
-  bool IsRectilinear() {
+  bool IsRectilinear() const {
     if (FuzzyEqual(_12, 0) && FuzzyEqual(_21, 0)) {
       return true;
     } else if (FuzzyEqual(_22, 0) && FuzzyEqual(_11, 0)) {

gfx/thebes/gfxContext.cpp

@@ -210,6 +210,9 @@ gfxContext::Restore()
     mStateStack.RemoveElementAt(mStateStack.Length() - 1);
 
     if (mPathBuilder || mPath || mPathIsRect) {
+      // Support here isn't fully correct if the path is continued -after-
+      // the restore. We don't currently have users that do this and we should
+      // make sure there will not be any. Sadly we can't assert this easily.
       mTransformChanged = true;
       mPathTransform = mDT->GetTransform();
     }
@@ -551,11 +554,9 @@ gfxContext::Translate(const gfxPoint& pt)
   if (mCairo) {
     cairo_translate(mCairo, pt.x, pt.y);
   } else {
-    MOZ_ASSERT(!mPathBuilder);
-
     Matrix newMatrix = mDT->GetTransform();
-    TransformWillChange();
-    mDT->SetTransform(newMatrix.Translate(Float(pt.x), Float(pt.y)));
+
+    ChangeTransform(newMatrix.Translate(Float(pt.x), Float(pt.y)));
   }
 }
 
@@ -565,11 +566,9 @@ gfxContext::Scale(gfxFloat x, gfxFloat y)
   if (mCairo) {
     cairo_scale(mCairo, x, y);
   } else {
-    MOZ_ASSERT(!mPathBuilder);
-
     Matrix newMatrix = mDT->GetTransform();
-    TransformWillChange();
-    mDT->SetTransform(newMatrix.Scale(Float(x), Float(y)));
+
+    ChangeTransform(newMatrix.Scale(Float(x), Float(y)));
   }
 }
 
@@ -579,11 +578,8 @@ gfxContext::Rotate(gfxFloat angle)
   if (mCairo) {
     cairo_rotate(mCairo, angle);
   } else {
-    MOZ_ASSERT(!mPathBuilder);
-
-    TransformWillChange();
     Matrix rotation = Matrix::Rotation(Float(angle));
-    mDT->SetTransform(rotation * mDT->GetTransform());
+    ChangeTransform(rotation * mDT->GetTransform());
   }
 }
 
@@ -594,10 +590,7 @@ gfxContext::Multiply(const gfxMatrix& matrix)
     const cairo_matrix_t& mat = reinterpret_cast<const cairo_matrix_t&>(matrix);
     cairo_transform(mCairo, &mat);
   } else {
-    MOZ_ASSERT(!mPathBuilder);
-
-    TransformWillChange();
-    mDT->SetTransform(ToMatrix(matrix) * mDT->GetTransform());
+    ChangeTransform(ToMatrix(matrix) * mDT->GetTransform());
   }
 }
 
@@ -608,10 +601,7 @@ gfxContext::SetMatrix(const gfxMatrix& matrix)
     const cairo_matrix_t& mat = reinterpret_cast<const cairo_matrix_t&>(matrix);
     cairo_set_matrix(mCairo, &mat);
   } else {
-    MOZ_ASSERT(!mPathBuilder);
-
-    TransformWillChange();
-    mDT->SetTransform(ToMatrix(matrix));
+    ChangeTransform(ToMatrix(matrix));
   }
 }
 
@@ -621,10 +611,7 @@ gfxContext::IdentityMatrix()
   if (mCairo) {
     cairo_identity_matrix(mCairo);
   } else {
-    MOZ_ASSERT(!mPathBuilder);
-
-    TransformWillChange();
-    mDT->SetTransform(Matrix());
+    ChangeTransform(Matrix());
   }
 }
 
@@ -2075,7 +2062,7 @@ gfxContext::GetOp()
  * if the pattern is actually used.
  */
 void
-gfxContext::TransformWillChange()
+gfxContext::ChangeTransform(Matrix &aNewMatrix)
 {
   AzureState &state = CurrentState();
 
@@ -2084,4 +2071,32 @@ gfxContext::TransformWillChange()
     state.patternTransform = mDT->GetTransform();
     state.patternTransformChanged = true;
   }
+
+  if (mPathBuilder || mPathIsRect) {
+    Matrix invMatrix = aNewMatrix;
+    
+    invMatrix.Invert();
+
+    Matrix toNewUS = mDT->GetTransform() * invMatrix;
+
+    if (toNewUS.IsRectilinear() && mPathIsRect) {
+      mRect = toNewUS.TransformBounds(mRect);
+    } else if (mPathIsRect) {
+      mPathBuilder = mDT->CreatePathBuilder(CurrentState().fillRule);
+      
+      mPathBuilder->MoveTo(toNewUS * mRect.TopLeft());
+      mPathBuilder->LineTo(toNewUS * mRect.TopRight());
+      mPathBuilder->LineTo(toNewUS * mRect.BottomRight());
+      mPathBuilder->LineTo(toNewUS * mRect.BottomLeft());
+      mPathBuilder->Close();
+    } else {
+      RefPtr<Path> path = mPathBuilder->Finish();
+      // Create path in device space.
+      mPathBuilder = path->TransformedCopyToBuilder(toNewUS);
+    }
+    // No need to consider the transform changed now!
+    mTransformChanged = false;
+  }
+
+  mDT->SetTransform(aNewMatrix);
 }

gfx/thebes/gfxContext.h

@@ -741,7 +741,7 @@ private:
   void FillAzure(mozilla::gfx::Float aOpacity);
   void PushClipsToDT(mozilla::gfx::DrawTarget *aDT);
   CompositionOp GetOp();
-  void TransformWillChange();
+  void ChangeTransform(mozilla::gfx::Matrix &aNewMatrix);
 
   bool mPathIsRect;
   bool mTransformChanged;