Separate zeroing pixel data from setting alpha

third_party/WebKit/Source/platform/image-decoders/bmp/BMPImageReader.cpp

 /*
  * Copyright (c) 2008, 2009, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 106 matching lines @@
   // Initialize the framebuffer if needed.
   DCHECK(m_buffer);  // Parent should set this before asking us to decode!
   if (m_buffer->getStatus() == ImageFrame::FrameEmpty) {
     if (!m_buffer->allocatePixelData(m_parent->size().width(),
                                      m_parent->size().height(),
                                      m_parent->colorSpaceForSkImages())) {
       return m_parent->setFailed();  // Unable to allocate.
     }
     m_buffer->zeroFillPixelData();
     m_buffer->setStatus(ImageFrame::FramePartial);
-    // setSize() calls eraseARGB(), which resets the alpha flag, so we force
-    // it back to false here.  We'll set it true below in all cases where
-    // these 0s could actually show through.
-    m_buffer->setHasAlpha(false);
 
     // For BMPs, the frame always fills the entire image.
     m_buffer->setOriginalFrameRect(IntRect(IntPoint(), m_parent->size()));
 
     if (!m_isTopDown)
       m_coord.setY(m_parent->size().height() - 1);
   }
 
   // Decode the data.
   if (!m_decodingAndMask && !pastEndOfImage(0) &&
@@ skipping 676 matching lines @@
         // images where all alpha values are 255; opaque images are
         // faster to draw.
         int alpha = getAlpha(pixel);
         if (!m_seenNonZeroAlphaPixel && !alpha) {
           m_seenZeroAlphaPixel = true;
           alpha = 255;
         } else {
           m_seenNonZeroAlphaPixel = true;
           if (m_seenZeroAlphaPixel) {
             m_buffer->zeroFillPixelData();
+            m_buffer->setHasAlpha(true);
             m_seenZeroAlphaPixel = false;
           } else if (alpha != 255)
             m_buffer->setHasAlpha(true);
         }
 
         setRGBA(getComponent(pixel, 0), getComponent(pixel, 1),
                 getComponent(pixel, 2), alpha);
       }
     }
 
     // Success, keep going.
     m_decodedOffset += paddedNumBytes;
     if (inRLE)
       return Success;
     moveBufferToNextRow();
   }
 
   // Finished decoding whole image.
   return Success;
 }
 
 void BMPImageReader::moveBufferToNextRow() {
   m_coord.move(-m_coord.x(), m_isTopDown ? 1 : -1);
 }
 
 }  // namespace blink