import from UXP: BMPs from the clipboard may include extra padding. (4f5c2d5a)

image/decoders/nsBMPDecoder.cpp

@@ -66,6 +66,17 @@
 //   compression, then instead of treating the pixel data as 0RGB it is treated
 //   as ARGB, but only if one or more of the A values are non-zero.
 //
+// Clipboard variants.
+// - It's the BMP format used for BMP images captured from the clipboard.
+// - It is missing the file header, containing the BM signature and the data
+//   offset. Instead the data begins after the header.
+// - If it uses BITFIELDS compression, then there is always an additional 12
+//   bytes of data after the header that must be read. In WinBMPv4+, the masks
+//   are supposed to be included in the header size, which are the values we use
+//   for decoding purposes, but there is additional three masks following the
+//   header which must be skipped to get to the pixel data.
+//
+//
 // OS/2 VERSIONS OF THE BMP FORMAT
 // -------------------------------
 // OS2-BMPv1.
@@ -168,10 +179,12 @@ static mozilla::LazyLogModule sBMPLog("BMPDecoder");
 // The length of the mBIHSize field in the info header.
 static const uint32_t BIHSIZE_FIELD_LENGTH = 4;
 
-nsBMPDecoder::nsBMPDecoder(RasterImage* aImage, State aState, size_t aLength)
+nsBMPDecoder::nsBMPDecoder(RasterImage* aImage, State aState, size_t aLength,
+                           bool aForClipboard)
   : Decoder(aImage)
   , mLexer(Transition::To(aState, aLength), Transition::TerminateSuccess())
   , mIsWithinICO(false)
+  , mIsForClipboard(aForClipboard)
   , mMayHaveTransparency(false)
   , mDoesHaveTransparency(false)
   , mNumColors(0)
@@ -188,14 +201,16 @@ nsBMPDecoder::nsBMPDecoder(RasterImage* aImage, State aState, size_t aLength)
 // Constructor for normal BMP files or from the clipboard.
 nsBMPDecoder::nsBMPDecoder(RasterImage* aImage, bool aForClipboard)
   : nsBMPDecoder(aImage,
-                 aForClipboard ? State::CLIPBOARD_HEADER : State::FILE_HEADER,
-                 aForClipboard ? BIHSIZE_FIELD_LENGTH : FILE_HEADER_LENGTH)
+                 aForClipboard ? State::INFO_HEADER_SIZE : State::FILE_HEADER,
+                 aForClipboard ? BIHSIZE_FIELD_LENGTH : FILE_HEADER_LENGTH,
+                 aForClipboard)
 {
 }
 
 // Constructor used for WinBMPv3-ICO files, which lack a file header.
 nsBMPDecoder::nsBMPDecoder(RasterImage* aImage, uint32_t aDataOffset)
-  : nsBMPDecoder(aImage, State::INFO_HEADER_SIZE, BIHSIZE_FIELD_LENGTH)
+  : nsBMPDecoder(aImage, State::INFO_HEADER_SIZE, BIHSIZE_FIELD_LENGTH,
+                 /* aForClipboard */ false)
 {
   SetIsWithinICO();
 
@@ -457,7 +472,6 @@ nsBMPDecoder::DoDecode(SourceBufferIterator& aIterator, IResumable* aOnResume)
                     [=](State aState, const char* aData, size_t aLength) {
     switch (aState) {
       case State::FILE_HEADER:      return ReadFileHeader(aData, aLength);
-      case State::CLIPBOARD_HEADER: return ReadClipboardHeader(aData, aLength);
       case State::INFO_HEADER_SIZE: return ReadInfoHeaderSize(aData, aLength);
       case State::INFO_HEADER_REST: return ReadInfoHeaderRest(aData, aLength);
       case State::BITFIELDS:        return ReadBitfields(aData, aLength);
@@ -491,14 +505,6 @@ nsBMPDecoder::ReadFileHeader(const char* aData, size_t aLength)
   return Transition::To(State::INFO_HEADER_SIZE, BIHSIZE_FIELD_LENGTH);
 }
 
-LexerTransition<nsBMPDecoder::State>
-nsBMPDecoder::ReadClipboardHeader(const char* aData, size_t aLength)
-{
-  // With the clipboard, the data offset is the header length.
-  mH.mDataOffset = LittleEndian::readUint32(aData);
-  return ReadInfoHeaderSize(aData, aLength);
-}
-
 // We read the info header in two steps: (a) read the mBIHSize field to
 // determine how long the header is; (b) read the rest of the header.
 LexerTransition<nsBMPDecoder::State>
@@ -609,6 +615,13 @@ nsBMPDecoder::ReadInfoHeaderRest(const char* aData, size_t aLength)
       // Bitfields are present in the info header, so we can read them
       // immediately.
       mBitFields.ReadFromHeader(aData + 36, /* aReadAlpha = */ true);
+
+      // If this came from the clipboard, then we know that even if the header
+      // explicitly includes the bitfield masks, we need to add an additional
+      // offset for the start of the RGB data.
+      if (mIsForClipboard) {
+        mH.mDataOffset += BitFields::LENGTH;
+      }
     } else {
       // Bitfields are present after the info header, so we will read them in
       // ReadBitfields().
@@ -723,6 +736,12 @@ nsBMPDecoder::ReadColorTable(const char* aData, size_t aLength)
     aData += mBytesPerColor;
   }
 
+  // If we are decoding a BMP from the clipboard, we did not know the data
+  // offset in advance. It is defined as just after the header and color table.
+  if (mIsForClipboard) {
+    mH.mDataOffset += mPreGapLength;
+  }
+
   // We know how many bytes we've read so far (mPreGapLength) and we know the
   // offset of the pixel data (mH.mDataOffset), so we can determine the length
   // of the gap (possibly zero) between the color table and the pixel data.

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