Bug 1207378 (Part 1) - Add support for a frame rect to Downscaler. r=tn

image/Downscaler.cpp

@@ -57,6 +57,7 @@ Downscaler::ReleaseWindow()
 
 nsresult
 Downscaler::BeginFrame(const nsIntSize& aOriginalSize,
+                       const Maybe<nsIntRect>& aFrameRect,
                        uint8_t* aOutputBuffer,
                        bool aHasAlpha,
                        bool aFlipVertically /* = false */)
@@ -71,6 +72,17 @@ Downscaler::BeginFrame(const nsIntSize& aOriginalSize,
   MOZ_ASSERT(aOriginalSize.width > 0 && aOriginalSize.height > 0,
              "Invalid original size");
 
+  mFrameRect = aFrameRect.valueOr(nsIntRect(nsIntPoint(), aOriginalSize));
+  MOZ_ASSERT(mFrameRect.x >= 0 && mFrameRect.y >= 0 &&
+             mFrameRect.width > 0 && mFrameRect.height > 0,
+             "Frame rect must have positive components");
+  MOZ_ASSERT(nsIntRect(0, 0, aOriginalSize.width, aOriginalSize.height)
+               .Contains(mFrameRect),
+             "Frame rect must fit inside image");
+  MOZ_ASSERT_IF(!nsIntRect(0, 0, aOriginalSize.width, aOriginalSize.height)
+                  .IsEqualEdges(mFrameRect),
+                aHasAlpha);
+
   mOriginalSize = aOriginalSize;
   mScale = gfxSize(double(mOriginalSize.width) / mTargetSize.width,
                    double(mOriginalSize.height) / mTargetSize.height);
@@ -78,7 +90,6 @@ Downscaler::BeginFrame(const nsIntSize& aOriginalSize,
   mHasAlpha = aHasAlpha;
   mFlipVertically = aFlipVertically;
 
-  ResetForNextProgressivePass();
   ReleaseWindow();
 
   auto resizeMethod = skia::ImageOperations::RESIZE_LANCZOS3;
@@ -124,9 +135,22 @@ Downscaler::BeginFrame(const nsIntSize& aOriginalSize,
     return NS_ERROR_OUT_OF_MEMORY;
   }
 
+  ResetForNextProgressivePass();
+
   return NS_OK;
 }
 
+void
+Downscaler::SkipToRow(int32_t aRow)
+{
+  if (mCurrentInLine < aRow) {
+    ClearRow();
+    do {
+      CommitRow();
+    } while (mCurrentInLine < aRow);
+  }
+}
+
 void
 Downscaler::ResetForNextProgressivePass()
 {
@@ -134,6 +158,9 @@ Downscaler::ResetForNextProgressivePass()
   mCurrentOutLine = 0;
   mCurrentInLine = 0;
   mLinesInBuffer = 0;
+
+  // If we have a vertical offset, commit rows to shift us past it.
+  SkipToRow(mFrameRect.y);
 }
 
 static void
@@ -193,6 +220,12 @@ Downscaler::CommitRow()
   }
 
   mCurrentInLine += 1;
+
+  // If we're at the end of the part of the original image that has data, commit
+  // rows to shift us to the end.
+  if (mCurrentInLine == (mFrameRect.y + mFrameRect.height)) {
+    SkipToRow(mOriginalSize.height - 1);
+  }
 }
 
 bool

image/Downscaler.h

@@ -12,10 +12,10 @@
 #ifndef mozilla_image_Downscaler_h
 #define mozilla_image_Downscaler_h
 
+#include "mozilla/Maybe.h"
 #include "mozilla/UniquePtr.h"
 #include "nsRect.h"
 
-
 namespace skia {
   class ConvolutionFilter1D;
 } // namespace skia
@@ -64,6 +64,9 @@ public:
    * Begins a new frame and reinitializes the Downscaler.
    *
    * @param aOriginalSize The original size of this frame, before scaling.
+   * @param aFrameRect The region of  the original image which has data.
+   *                   Every pixel outside @aFrameRect is considered blank and
+   *                   has zero alpha.
    * @param aOutputBuffer The buffer to which the Downscaler should write its
    *                      output; this is the same buffer where the Decoder
    *                      would write its output when not downscaling during
@@ -75,12 +78,16 @@ public:
    *                        the way they are stored in some image formats.
    */
   nsresult BeginFrame(const nsIntSize& aOriginalSize,
+                      const Maybe<nsIntRect>& aFrameRect,
                       uint8_t* aOutputBuffer,
                       bool aHasAlpha,
                       bool aFlipVertically = false);
 
   /// Retrieves the buffer into which the Decoder should write each row.
-  uint8_t* RowBuffer() { return mRowBuffer.get(); }
+  uint8_t* RowBuffer()
+  {
+    return mRowBuffer.get() + mFrameRect.x * sizeof(uint32_t);
+  }
 
   /// Clears the current row buffer (optionally starting at @aStartingAtCol).
   void ClearRow(uint32_t aStartingAtCol = 0);
@@ -104,9 +111,11 @@ public:
 private:
   void DownscaleInputLine();
   void ReleaseWindow();
+  void SkipToRow(int32_t aRow);
 
   nsIntSize mOriginalSize;
   nsIntSize mTargetSize;
+  nsIntRect mFrameRect;
   gfxSize mScale;
 
   uint8_t* mOutputBuffer;

image/decoders/nsBMPDecoder.cpp

@@ -461,7 +461,8 @@ nsBMPDecoder::WriteInternal(const char* aBuffer, uint32_t aCount)
       if (mDownscaler) {
         // BMPs store their rows in reverse order, so the downscaler needs to
         // reverse them again when writing its output.
-        rv = mDownscaler->BeginFrame(GetSize(), mImageData, hasTransparency,
+        rv = mDownscaler->BeginFrame(GetSize(), Nothing(),
+                                     mImageData, hasTransparency,
                                      /* aFlipVertically = */ true);
         if (NS_FAILED(rv)) {
           return;

image/decoders/nsGIFDecoder2.cpp

@@ -279,7 +279,7 @@ nsGIFDecoder2::BeginImageFrame(uint16_t aDepth)
   }
 
   if (mDownscaler) {
-    rv = mDownscaler->BeginFrame(frameRect.Size(), mImageData,
+    rv = mDownscaler->BeginFrame(frameRect.Size(), Nothing(), mImageData,
                                  mGIFStruct.is_transparent);
   }
 

image/decoders/nsICODecoder.cpp

@@ -553,7 +553,7 @@ nsICODecoder::PrepareForMask()
                  mDownscaler->TargetSize().height *
                  sizeof(uint32_t));
     mMaskBuffer = MakeUnique<uint8_t[]>(bmpDecoder->GetImageDataLength());
-    nsresult rv = mDownscaler->BeginFrame(GetRealSize(),
+    nsresult rv = mDownscaler->BeginFrame(GetRealSize(), Nothing(),
                                           mMaskBuffer.get(),
                                           /* aHasAlpha = */ true,
                                           /* aFlipVertically = */ true);

image/decoders/nsIconDecoder.cpp

@@ -93,7 +93,7 @@ nsIconDecoder::WriteInternal(const char* aBuffer, uint32_t aCount)
         MOZ_ASSERT(mImageData, "Should have a buffer now");
 
         if (mDownscaler) {
-          nsresult rv = mDownscaler->BeginFrame(GetSize(),
+          nsresult rv = mDownscaler->BeginFrame(GetSize(), Nothing(),
                                                 mImageData,
                                                 /* aHasAlpha = */ true);
           if (NS_FAILED(rv)) {

image/decoders/nsJPEGDecoder.cpp

@@ -398,7 +398,7 @@ nsJPEGDecoder::WriteInternal(const char* aBuffer, uint32_t aCount)
     MOZ_ASSERT(mImageData, "Should have a buffer now");
 
     if (mDownscaler) {
-      nsresult rv = mDownscaler->BeginFrame(GetSize(),
+      nsresult rv = mDownscaler->BeginFrame(GetSize(), Nothing(),
                                             mImageData,
                                             /* aHasAlpha = */ false);
       if (NS_FAILED(rv)) {

image/decoders/nsPNGDecoder.cpp

@@ -209,7 +209,8 @@ nsPNGDecoder::CreateFrame(png_uint_32 aXOffset, png_uint_32 aYOffset,
 
   if (mDownscaler) {
     bool hasAlpha = aFormat != SurfaceFormat::B8G8R8X8;
-    rv = mDownscaler->BeginFrame(frameRect.Size(), mImageData, hasAlpha);
+    rv = mDownscaler->BeginFrame(frameRect.Size(), Nothing(),
+                                 mImageData, hasAlpha);
     if (NS_FAILED(rv)) {
       return rv;
     }