Bug 1145560 - During downscale-during-decode, compute the original size invalid rect based on the target size invalid rect. r=tn

image/decoders/nsJPEGDecoder.cpp

@@ -719,16 +719,16 @@ nsJPEGDecoder::OutputScanlines(bool* suspend)
       }
   }
 
-  if (top != mInfo.output_scanline) {
+  if (mDownscaler && mDownscaler->HasInvalidation()) {
+    DownscalerInvalidRect invalidRect = mDownscaler->TakeInvalidRect();
+    PostInvalidation(invalidRect.mOriginalSizeRect,
+                     Some(invalidRect.mTargetSizeRect));
+    MOZ_ASSERT(!mDownscaler->HasInvalidation());
+  } else if (!mDownscaler && top != mInfo.output_scanline) {
     PostInvalidation(nsIntRect(0, top,
                                mInfo.output_width,
-                               mInfo.output_scanline - top),
-                     mDownscaler ? Some(mDownscaler->TakeInvalidRect())
-                                 : Nothing());
+                               mInfo.output_scanline - top));
   }
-
-  MOZ_ASSERT(!mDownscaler || !mDownscaler->HasInvalidation(),
-             "Didn't send downscaler's invalidation");
 }
 
 // Override the standard error method in the IJG JPEG decoder code.

image/src/Downscaler.cpp

@@ -69,6 +69,8 @@ Downscaler::BeginFrame(const nsIntSize& aOriginalSize,
              "Invalid original size");
 
   mOriginalSize = aOriginalSize;
+  mScale = gfxSize(double(mOriginalSize.width) / mTargetSize.width,
+                   double(mOriginalSize.height) / mTargetSize.height);
   mOutputBuffer = aOutputBuffer;
   mHasAlpha = aHasAlpha;
 
@@ -183,17 +185,25 @@ Downscaler::HasInvalidation() const
   return mCurrentOutLine > mPrevInvalidatedLine;
 }
 
-nsIntRect
+DownscalerInvalidRect
 Downscaler::TakeInvalidRect()
 {
   if (MOZ_UNLIKELY(!HasInvalidation())) {
-    return nsIntRect();
+    return DownscalerInvalidRect();
   }
 
-  nsIntRect invalidRect(0, mPrevInvalidatedLine,
-                        mTargetSize.width,
-                        mCurrentOutLine - mPrevInvalidatedLine);
+  DownscalerInvalidRect invalidRect;
+
+  // Compute the target size invalid rect.
+  invalidRect.mTargetSizeRect =
+    nsIntRect(0, mPrevInvalidatedLine,
+              mTargetSize.width, mCurrentOutLine - mPrevInvalidatedLine);
   mPrevInvalidatedLine = mCurrentOutLine;
+
+  // Compute the original size invalid rect.
+  invalidRect.mOriginalSizeRect = invalidRect.mTargetSizeRect;
+  invalidRect.mOriginalSizeRect.ScaleRoundOut(mScale.width, mScale.height);
+
   return invalidRect;
 }
 

image/src/Downscaler.h

@@ -24,6 +24,16 @@ namespace skia {
 namespace mozilla {
 namespace image {
 
+/**
+ * DownscalerInvalidRect wraps two invalidation rects: one in terms of the
+ * original image size, and one in terms of the target size.
+ */
+struct DownscalerInvalidRect
+{
+  nsIntRect mOriginalSizeRect;
+  nsIntRect mTargetSizeRect;
+};
+
 /**
  * Downscaler is a high-quality, streaming image downscaler based upon Skia's
  * scaling implementation.
@@ -47,6 +57,7 @@ public:
 
   const nsIntSize& OriginalSize() const { return mOriginalSize; }
   const nsIntSize& TargetSize() const { return mTargetSize; }
+  const gfxSize& Scale() const { return mScale; }
 
   /**
    * Begins a new frame and reinitializes the Downscaler.
@@ -73,7 +84,7 @@ public:
   bool HasInvalidation() const;
 
   /// Takes the Downscaler's current invalid rect and resets it.
-  nsIntRect TakeInvalidRect();
+  DownscalerInvalidRect TakeInvalidRect();
 
   /**
    * Resets the Downscaler's position in the image, for a new progressive pass
@@ -88,6 +99,7 @@ private:
 
   nsIntSize mOriginalSize;
   nsIntSize mTargetSize;
+  gfxSize mScale;
 
   uint8_t* mOutputBuffer;