Reland of r19131, this time with real Math:...

base/gfx/png_decoder.cc

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/gfx/png_decoder.h"
 
 #include "base/logging.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 
 extern "C" {
@@ skipping 243 matching lines @@
   }
  private:
   png_struct** ps_;
   png_info** pi_;
 };
 
 }  // namespace
 
 // static
 bool PNGDecoder::Decode(const unsigned char* input, size_t input_size,
-                      ColorFormat format, std::vector<unsigned char>* output,
-                      int* w, int* h) {
+                        ColorFormat format, std::vector<unsigned char>* output,
+                        int* w, int* h) {
   if (input_size < 8)
     return false;  // Input data too small to be a png
 
   // Have libpng check the signature, it likes the first 8 bytes.
   if (png_sig_cmp(const_cast<unsigned char*>(input), 0, 8) != 0)
     return false;
 
   png_struct* png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
                                                png_voidp_NULL,
                                                png_error_ptr_NULL,
@@ skipping 41 matching lines @@
                         SkBitmap* bitmap) {
   DCHECK(bitmap);
   if (!data || data->empty())
     return false;
   int width, height;
   std::vector<unsigned char> decoded_data;
   if (PNGDecoder::Decode(&data->front(), data->size(), PNGDecoder::FORMAT_BGRA,
                          &decoded_data, &width, &height)) {
     bitmap->setConfig(SkBitmap::kARGB_8888_Config, width, height);
     bitmap->allocPixels();
-    memcpy(bitmap->getPixels(), &decoded_data.front(), width * height * 4);
+    unsigned char* bitmap_data =
+        reinterpret_cast<unsigned char*>(bitmap->getAddr32(0, 0));
+    for (int i = width * height * 4 - 4; i >= 0; i -= 4) {
+      unsigned char alpha = decoded_data[i + 3];
+      if (alpha != 0 && alpha != 255) {
+        bitmap_data[i + 3] = alpha;
+        bitmap_data[i] = (decoded_data[i] * alpha) >> 8;
+        bitmap_data[i + 1] = (decoded_data[i + 1] * alpha) >> 8;
+        bitmap_data[i + 2] = (decoded_data[i + 2] * alpha) >> 8;
+      } else {
+        bitmap_data[i + 3] = alpha;
+        bitmap_data[i] = decoded_data[i];
+        bitmap_data[i + 1] = decoded_data[i + 1];
+        bitmap_data[i + 2] = decoded_data[i + 2];
+      }
+    }
     return true;
   }
   return false;
 }
 
 //static
 SkBitmap* PNGDecoder::CreateSkBitmapFromBGRAFormat(
     std::vector<unsigned char>& bgra, int width, int height) {
   SkBitmap* bitmap = new SkBitmap();
   bitmap->setConfig(SkBitmap::kARGB_8888_Config, width, height);
   bitmap->allocPixels();
 
   bool opaque = false;
   unsigned char* bitmap_data =
       reinterpret_cast<unsigned char*>(bitmap->getAddr32(0, 0));
   for (int i = width * height * 4 - 4; i >= 0; i -= 4) {
     unsigned char alpha = bgra[i + 3];
     if (!opaque && alpha != 255) {
       opaque = false;
     }
     bitmap_data[i + 3] = alpha;
     bitmap_data[i] = (bgra[i] * alpha) >> 8;
     bitmap_data[i + 1] = (bgra[i + 1] * alpha) >> 8;
     bitmap_data[i + 2] = (bgra[i + 2] * alpha) >> 8;
   }
 
   bitmap->setIsOpaque(opaque);
   return bitmap;
 }