1 files changed, 9 insertions, 5 deletions
diff --git a/dom/canvas/CanvasRenderingContext2D.cpp b/dom/canvas/CanvasRenderingContext2D.cpp
index 1b44c8289..8c202f26b 100644
--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -1435,8 +1435,6 @@ CanvasRenderingContext2D::GetHeight() const
 NS_IMETHODIMP
 CanvasRenderingContext2D::SetDimensions(int32_t width, int32_t height)
 {
-  ClearTarget();
-
   // Zero sized surfaces can cause problems.
   mZero = false;
   if (height == 0) {
@@ -1447,14 +1445,14 @@ CanvasRenderingContext2D::SetDimensions(int32_t width, int32_t height)
     width = 1;
     mZero = true;
   }
-  mWidth = width;
-  mHeight = height;
 
+  ClearTarget(width, height);
+  
   return NS_OK;
 }
 
 void
-CanvasRenderingContext2D::ClearTarget()
+CanvasRenderingContext2D::ClearTarget(int32_t aWidth, int32_t aHeight)
 {
   Reset();
 
@@ -1473,6 +1471,12 @@ CanvasRenderingContext2D::ClearTarget()
   state->colorStyles[Style::STROKE] = NS_RGB(0,0,0);
   state->shadowColor = NS_RGBA(0,0,0,0);
 
+  // Update dimensions only if new (strictly positive) values were passed.
+  if (aWidth > 0 && aHeight > 0) {
+    mWidth = aWidth;
+    mHeight = aHeight;
+  }  
+  
   // For vertical writing-mode, unless text-orientation is sideways,
   // we'll modify the initial value of textBaseline to 'middle'.
   nsRefPtr<nsStyleContext> canvasStyle;