BMPs from the clipboard may include extra padding.

In the original Windows clipboard BMP decoder implementation in
nsImageFromClipboard::ConvertColorBitMap, if the bitmap used bitfields
compression, it always adjusted the offset to the RGB data by 12 bytes.
It did this even for newer BMP header formats which explicitly include
space for the bitfields in their header sizes. This patch updates our
BMP decoder to do the same for clipboard BMPs, since we have observed
pasted BMPs using bitfield compression appearing incorrectly. To the
user this appears as if we read a color mask; completely red, blue,
green pixels at the start of the last row, causing all of the other rows
to start with the last three pixels of the previous row.

1 files changed, 4 insertions, 3 deletions

diff --git a/image/decoders/nsBMPDecoder.h b/image/decoders/nsBMPDecoder.h
index 258381649..4b9568487 100644
--- a/image/decoders/nsBMPDecoder.h
+++ b/image/decoders/nsBMPDecoder.h
@@ -152,7 +152,6 @@ private:
 
   enum class State {
     FILE_HEADER,
-    CLIPBOARD_HEADER,
     INFO_HEADER_SIZE,
     INFO_HEADER_REST,
     BITFIELDS,
@@ -172,7 +171,7 @@ private:
   nsBMPDecoder(RasterImage* aImage, uint32_t aDataOffset);
 
   // Helper constructor called by the other two.
-  nsBMPDecoder(RasterImage* aImage, State aState, size_t aLength);
+  nsBMPDecoder(RasterImage* aImage, State aState, size_t aLength, bool aForClipboard);
 
   int32_t AbsoluteHeight() const { return abs(mH.mHeight); }
 
@@ -181,7 +180,6 @@ private:
   void FinishRow();
 
   LexerTransition<State> ReadFileHeader(const char* aData, size_t aLength);
-  LexerTransition<State> ReadClipboardHeader(const char* aData, size_t aLength);
   LexerTransition<State> ReadInfoHeaderSize(const char* aData, size_t aLength);
   LexerTransition<State> ReadInfoHeaderRest(const char* aData, size_t aLength);
   LexerTransition<State> ReadBitfields(const char* aData, size_t aLength);
@@ -200,6 +198,9 @@ private:
   // If the BMP is within an ICO file our treatment of it differs slightly.
   bool mIsWithinICO;
 
+  // If the BMP is decoded from the clipboard, we start with a data offset.
+  bool mIsForClipboard;
+
   bmp::BitFields mBitFields;
 
   // Might the image have transparency? Determined from the headers during