Add image_diff from the chromium repo.

sky/tools/imagediff/image_diff_png.cc

Index: sky/tools/imagediff/image_diff_png.cc
diff --git a/ui/gfx/codec/png_codec.cc b/sky/tools/imagediff/image_diff_png.cc
similarity index 53%
copy from ui/gfx/codec/png_codec.cc
copy to sky/tools/imagediff/image_diff_png.cc
index 068a193b334cb7317a4a7eff673c7b4336bb0475..e9d98c8c907a421d4c1d1a884a428dbe1c4294a0 100644
--- a/ui/gfx/codec/png_codec.cc
+++ b/sky/tools/imagediff/image_diff_png.cc
@@ -1,23 +1,46 @@
-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Copyright 2013 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 "ui/gfx/codec/png_codec.h"
+#include "sky/tools/imagediff/image_diff_png.h"
+
+#include <stdlib.h>
+#include <string.h>
 
 #include "base/logging.h"
-#include "base/strings/string_util.h"
+#include "build/build_config.h"
 #include "third_party/libpng/png.h"
-#include "third_party/skia/include/core/SkBitmap.h"
-#include "third_party/skia/include/core/SkColorPriv.h"
-#include "third_party/skia/include/core/SkUnPreMultiply.h"
 #include "third_party/zlib/zlib.h"
-#include "ui/gfx/size.h"
-#include "ui/gfx/skia_util.h"
 
-namespace gfx {
+namespace image_diff_png {
 
+// This is a duplicate of ui/gfx/codec/png_codec.cc, after removing code related
+// to Skia, that we can use when running layout tests with minimal dependencies.
 namespace {
 
+enum ColorFormat {
+  // 3 bytes per pixel (packed), in RGB order regardless of endianness.
+  // This is the native JPEG format.
+  FORMAT_RGB,
+
+  // 4 bytes per pixel, in RGBA order in memory regardless of endianness.
+  FORMAT_RGBA,
+
+  // 4 bytes per pixel, in BGRA order in memory regardless of endianness.
+  // This is the default Windows DIB order.
+  FORMAT_BGRA,
+
+  // 4 bytes per pixel, in pre-multiplied kARGB_8888_Config format. For use
+  // with directly writing to a skia bitmap.
+  FORMAT_SkBitmap
+};
+
+// Represents a comment in the tEXt ancillary chunk of the png.
+struct Comment {
+  std::string key;
+  std::string text;
+};
+
 // Converts BGRA->RGBA and RGBA->BGRA.
 void ConvertBetweenBGRAandRGBA(const unsigned char* input, int pixel_width,
                                unsigned char* output, bool* is_opaque) {
@@ -33,35 +56,15 @@ void ConvertBetweenBGRAandRGBA(const unsigned char* input, int pixel_width,
 
 void ConvertRGBAtoRGB(const unsigned char* rgba, int pixel_width,
                       unsigned char* rgb, bool* is_opaque) {
-  for (int x = 0; x < pixel_width; x++)
-    memcpy(&rgb[x * 3], &rgba[x * 4], 3);
-}
-
-void ConvertSkiaToRGB(const unsigned char* skia, int pixel_width,
-                      unsigned char* rgb, bool* is_opaque) {
   for (int x = 0; x < pixel_width; x++) {
-    const uint32_t pixel_in = *reinterpret_cast<const uint32_t*>(&skia[x * 4]);
+    const unsigned char* pixel_in = &rgba[x * 4];
     unsigned char* pixel_out = &rgb[x * 3];
-
-    int alpha = SkGetPackedA32(pixel_in);
-    if (alpha != 0 && alpha != 255) {
-      SkColor unmultiplied = SkUnPreMultiply::PMColorToColor(pixel_in);
-      pixel_out[0] = SkColorGetR(unmultiplied);
-      pixel_out[1] = SkColorGetG(unmultiplied);
-      pixel_out[2] = SkColorGetB(unmultiplied);
-    } else {
-      pixel_out[0] = SkGetPackedR32(pixel_in);
-      pixel_out[1] = SkGetPackedG32(pixel_in);
-      pixel_out[2] = SkGetPackedB32(pixel_in);
-    }
+    pixel_out[0] = pixel_in[0];
+    pixel_out[1] = pixel_in[1];
+    pixel_out[2] = pixel_in[2];
   }
 }
 
-void ConvertSkiaToRGBA(const unsigned char* skia, int pixel_width,
-                       unsigned char* rgba, bool* is_opaque) {
-  gfx::ConvertSkiaToRGBA(skia, pixel_width, rgba);
-}
-
 }  // namespace
 
 // Decoder --------------------------------------------------------------------
@@ -79,77 +82,61 @@ const double kInverseGamma = 1.0 / kDefaultGamma;
 class PngDecoderState {
  public:
   // Output is a vector<unsigned char>.
-  PngDecoderState(PNGCodec::ColorFormat ofmt, std::vector<unsigned char>* o)
+  PngDecoderState(ColorFormat ofmt, std::vector<unsigned char>* o)
       : output_format(ofmt),
         output_channels(0),
-        bitmap(NULL),
         is_opaque(true),
         output(o),
+        row_converter(NULL),
         width(0),
         height(0),
         done(false) {
   }
 
-  // Output is an SkBitmap.
-  explicit PngDecoderState(SkBitmap* skbitmap)
-      : output_format(PNGCodec::FORMAT_SkBitmap),
-        output_channels(0),
-        bitmap(skbitmap),
-        is_opaque(true),
-        output(NULL),
-        width(0),
-        height(0),
-        done(false) {
-  }
-
-  PNGCodec::ColorFormat output_format;
+  ColorFormat output_format;
   int output_channels;
 
-  // An incoming SkBitmap to write to. If NULL, we write to output instead.
-  SkBitmap* bitmap;
-
   // Used during the reading of an SkBitmap. Defaults to true until we see a
   // pixel with anything other than an alpha of 255.
   bool is_opaque;
 
-  // The other way to decode output, where we write into an intermediary buffer
-  // instead of directly to an SkBitmap.
+  // An intermediary buffer for decode output.
   std::vector<unsigned char>* output;
 
+  // Called to convert a row from the library to the correct output format.
+  // When NULL, no conversion is necessary.
+  void (*row_converter)(const unsigned char* in, int w, unsigned char* out,
+                        bool* is_opaque);
+
   // Size of the image, set in the info callback.
   int width;
   int height;
 
   // Set to true when we've found the end of the data.
   bool done;
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(PngDecoderState);
 };
 
-// User transform (passed to libpng) which converts a row decoded by libpng to
-// Skia format. Expects the row to have 4 channels, otherwise there won't be
-// enough room in |data|.
-void ConvertRGBARowToSkia(png_structp png_ptr,
-                          png_row_infop row_info,
-                          png_bytep data) {
-  const int channels = row_info->channels;
-  DCHECK_EQ(channels, 4);
-
-  PngDecoderState* state =
-      static_cast<PngDecoderState*>(png_get_user_transform_ptr(png_ptr));
-  DCHECK(state) << "LibPNG user transform pointer is NULL";
-
-  unsigned char* const end = data + row_info->rowbytes;
-  for (unsigned char* p = data; p < end; p += channels) {
-    uint32_t* sk_pixel = reinterpret_cast<uint32_t*>(p);
-    const unsigned char alpha = p[channels - 1];
-    if (alpha != 255) {
-      state->is_opaque = false;
-      *sk_pixel = SkPreMultiplyARGB(alpha, p[0], p[1], p[2]);
-    } else {
-      *sk_pixel = SkPackARGB32(alpha, p[0], p[1], p[2]);
-    }
+void ConvertRGBtoRGBA(const unsigned char* rgb, int pixel_width,
+                      unsigned char* rgba, bool* is_opaque) {
+  for (int x = 0; x < pixel_width; x++) {
+    const unsigned char* pixel_in = &rgb[x * 3];
+    unsigned char* pixel_out = &rgba[x * 4];
+    pixel_out[0] = pixel_in[0];
+    pixel_out[1] = pixel_in[1];
+    pixel_out[2] = pixel_in[2];
+    pixel_out[3] = 0xff;
+  }
+}
+
+void ConvertRGBtoBGRA(const unsigned char* rgb, int pixel_width,
+                      unsigned char* bgra, bool* is_opaque) {
+  for (int x = 0; x < pixel_width; x++) {
+    const unsigned char* pixel_in = &rgb[x * 3];
+    unsigned char* pixel_out = &bgra[x * 4];
+    pixel_out[0] = pixel_in[2];
+    pixel_out[1] = pixel_in[1];
+    pixel_out[2] = pixel_in[0];
+    pixel_out[3] = 0xff;
   }
 }
 
@@ -160,7 +147,7 @@ void DecodeInfoCallback(png_struct* png_ptr, png_info* info_ptr) {
       png_get_progressive_ptr(png_ptr));
 
   int bit_depth, color_type, interlace_type, compression_type;
-  int filter_type;
+  int filter_type, channels;
   png_uint_32 w, h;
   png_get_IHDR(png_ptr, info_ptr, &w, &h, &bit_depth, &color_type,
                &interlace_type, &compression_type, &filter_type);
@@ -177,68 +164,19 @@ void DecodeInfoCallback(png_struct* png_ptr, png_info* info_ptr) {
   state->width = static_cast<int>(w);
   state->height = static_cast<int>(h);
 
-  // The following png_set_* calls have to be done in the order dictated by
-  // the libpng docs. Please take care if you have to move any of them. This
-  // is also why certain things are done outside of the switch, even though
-  // they look like they belong there.
-
   // Expand to ensure we use 24-bit for RGB and 32-bit for RGBA.
   if (color_type == PNG_COLOR_TYPE_PALETTE ||
       (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8))
     png_set_expand(png_ptr);
 
-  // The '!= 0' is for silencing a Windows compiler warning.
-  bool input_has_alpha = ((color_type & PNG_COLOR_MASK_ALPHA) != 0);
-
   // Transparency for paletted images.
-  if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) {
+  if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
     png_set_expand(png_ptr);
-    input_has_alpha = true;
-  }
 
   // Convert 16-bit to 8-bit.
   if (bit_depth == 16)
     png_set_strip_16(png_ptr);
 
-  // Pick our row format converter necessary for this data.
-  if (!input_has_alpha) {
-    switch (state->output_format) {
-      case PNGCodec::FORMAT_RGB:
-        state->output_channels = 3;
-        break;
-      case PNGCodec::FORMAT_RGBA:
-        state->output_channels = 4;
-        png_set_add_alpha(png_ptr, 0xFF, PNG_FILLER_AFTER);
-        break;
-      case PNGCodec::FORMAT_BGRA:
-        state->output_channels = 4;
-        png_set_bgr(png_ptr);
-        png_set_add_alpha(png_ptr, 0xFF, PNG_FILLER_AFTER);
-        break;
-      case PNGCodec::FORMAT_SkBitmap:
-        state->output_channels = 4;
-        png_set_add_alpha(png_ptr, 0xFF, PNG_FILLER_AFTER);
-        break;
-    }
-  } else {
-    switch (state->output_format) {
-      case PNGCodec::FORMAT_RGB:
-        state->output_channels = 3;
-        png_set_strip_alpha(png_ptr);
-        break;
-      case PNGCodec::FORMAT_RGBA:
-        state->output_channels = 4;
-        break;
-      case PNGCodec::FORMAT_BGRA:
-        state->output_channels = 4;
-        png_set_bgr(png_ptr);
-        break;
-      case PNGCodec::FORMAT_SkBitmap:
-        state->output_channels = 4;
-        break;
-    }
-  }
-
   // Expand grayscale to RGB.
   if (color_type == PNG_COLOR_TYPE_GRAY ||
       color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
@@ -256,49 +194,79 @@ void DecodeInfoCallback(png_struct* png_ptr, png_info* info_ptr) {
     png_set_gamma(png_ptr, kDefaultGamma, kInverseGamma);
   }
 
-  // Setting the user transforms here (as opposed to inside the switch above)
-  // because all png_set_* calls need to be done in the specific order
-  // mandated by libpng.
-  if (state->output_format == PNGCodec::FORMAT_SkBitmap) {
-    png_set_read_user_transform_fn(png_ptr, ConvertRGBARowToSkia);
-    png_set_user_transform_info(png_ptr, state, 0, 0);
-  }
-
   // Tell libpng to send us rows for interlaced pngs.
   if (interlace_type == PNG_INTERLACE_ADAM7)
     png_set_interlace_handling(png_ptr);
 
+  // Update our info now
   png_read_update_info(png_ptr, info_ptr);
+  channels = png_get_channels(png_ptr, info_ptr);
 
-  if (state->bitmap) {
-    state->bitmap->allocN32Pixels(state->width, state->height);
-  } else if (state->output) {
-    state->output->resize(
-        state->width * state->output_channels * state->height);
+  // Pick our row format converter necessary for this data.
+  if (channels == 3) {
+    switch (state->output_format) {
+      case FORMAT_RGB:
+        state->row_converter = NULL;  // no conversion necessary
+        state->output_channels = 3;
+        break;
+      case FORMAT_RGBA:
+        state->row_converter = &ConvertRGBtoRGBA;
+        state->output_channels = 4;
+        break;
+      case FORMAT_BGRA:
+        state->row_converter = &ConvertRGBtoBGRA;
+        state->output_channels = 4;
+        break;
+      default:
+        NOTREACHED() << "Unknown output format";
+        break;
+    }
+  } else if (channels == 4) {
+    switch (state->output_format) {
+      case FORMAT_RGB:
+        state->row_converter = &ConvertRGBAtoRGB;
+        state->output_channels = 3;
+        break;
+      case FORMAT_RGBA:
+        state->row_converter = NULL;  // no conversion necessary
+        state->output_channels = 4;
+        break;
+      case FORMAT_BGRA:
+        state->row_converter = &ConvertBetweenBGRAandRGBA;
+        state->output_channels = 4;
+        break;
+      default:
+        NOTREACHED() << "Unknown output format";
+        break;
+    }
+  } else {
+    NOTREACHED() << "Unknown input channels";
+    longjmp(png_jmpbuf(png_ptr), 1);
   }
+
+  state->output->resize(
+      state->width * state->output_channels * state->height);
 }
 
 void DecodeRowCallback(png_struct* png_ptr, png_byte* new_row,
                        png_uint_32 row_num, int pass) {
-  if (!new_row)
-    return;  // Interlaced image; row didn't change this pass.
-
   PngDecoderState* state = static_cast<PngDecoderState*>(
       png_get_progressive_ptr(png_ptr));
 
+  DCHECK(pass == 0);
   if (static_cast<int>(row_num) > state->height) {
     NOTREACHED() << "Invalid row";
     return;
   }
 
   unsigned char* base = NULL;
-  if (state->bitmap)
-    base = reinterpret_cast<unsigned char*>(state->bitmap->getAddr32(0, 0));
-  else if (state->output)
-    base = &state->output->front();
+  base = &state->output->front();
 
   unsigned char* dest = &base[state->width * state->output_channels * row_num];
-  png_progressive_combine_row(png_ptr, dest, new_row);
+  if (state->row_converter)
+    state->row_converter(new_row, state->width, dest, &state->is_opaque);
+  else
+    memcpy(dest, new_row, state->width * state->output_channels);
 }
 
 void DecodeEndCallback(png_struct* png_ptr, png_info* info) {
@@ -322,25 +290,6 @@ class PngReadStructDestroyer {
  private:
   png_struct** ps_;
   png_info** pi_;
-  DISALLOW_COPY_AND_ASSIGN(PngReadStructDestroyer);
-};
-
-// Automatically destroys the given write structs on destruction to make
-// cleanup and error handling code cleaner.
-class PngWriteStructDestroyer {
- public:
-  explicit PngWriteStructDestroyer(png_struct** ps) : ps_(ps), pi_(0) {
-  }
-  ~PngWriteStructDestroyer() {
-    png_destroy_write_struct(ps_, pi_);
-  }
-  void SetInfoStruct(png_info** pi) {
-    pi_ = pi;
-  }
- private:
-  png_struct** ps_;
-  png_info** pi_;
-  DISALLOW_COPY_AND_ASSIGN(PngWriteStructDestroyer);
 };
 
 bool BuildPNGStruct(const unsigned char* input, size_t input_size,
@@ -365,31 +314,10 @@ bool BuildPNGStruct(const unsigned char* input, size_t input_size,
   return true;
 }
 
-// Libpng user error and warning functions which allows us to print libpng
-// errors and warnings using Chrome's logging facilities instead of stderr.
-
-void LogLibPNGDecodeError(png_structp png_ptr, png_const_charp error_msg) {
-  DLOG(ERROR) << "libpng decode error: " << error_msg;
-  longjmp(png_jmpbuf(png_ptr), 1);
-}
-
-void LogLibPNGDecodeWarning(png_structp png_ptr, png_const_charp warning_msg) {
-  DLOG(ERROR) << "libpng decode warning: " << warning_msg;
-}
-
-void LogLibPNGEncodeError(png_structp png_ptr, png_const_charp error_msg) {
-  DLOG(ERROR) << "libpng encode error: " << error_msg;
-  longjmp(png_jmpbuf(png_ptr), 1);
-}
-
-void LogLibPNGEncodeWarning(png_structp png_ptr, png_const_charp warning_msg) {
-  DLOG(ERROR) << "libpng encode warning: " << warning_msg;
-}
-
 }  // namespace
 
 // static
-bool PNGCodec::Decode(const unsigned char* input, size_t input_size,
+bool Decode(const unsigned char* input, size_t input_size,
                       ColorFormat format, std::vector<unsigned char>* output,
                       int* w, int* h) {
   png_struct* png_ptr = NULL;
@@ -407,7 +335,6 @@ bool PNGCodec::Decode(const unsigned char* input, size_t input_size,
 
   PngDecoderState state(format, output);
 
-  png_set_error_fn(png_ptr, NULL, LogLibPNGDecodeError, LogLibPNGDecodeWarning);
   png_set_progressive_read_fn(png_ptr, &state, &DecodeInfoCallback,
                               &DecodeRowCallback, &DecodeEndCallback);
   png_process_data(png_ptr,
@@ -427,43 +354,6 @@ bool PNGCodec::Decode(const unsigned char* input, size_t input_size,
   return true;
 }
 
-// static
-bool PNGCodec::Decode(const unsigned char* input, size_t input_size,
-                      SkBitmap* bitmap) {
-  DCHECK(bitmap);
-  png_struct* png_ptr = NULL;
-  png_info* info_ptr = NULL;
-  if (!BuildPNGStruct(input, input_size, &png_ptr, &info_ptr))
-    return false;
-
-  PngReadStructDestroyer destroyer(&png_ptr, &info_ptr);
-  if (setjmp(png_jmpbuf(png_ptr))) {
-    // The destroyer will ensure that the structures are cleaned up in this
-    // case, even though we may get here as a jump from random parts of the
-    // PNG library called below.
-    return false;
-  }
-
-  PngDecoderState state(bitmap);
-
-  png_set_progressive_read_fn(png_ptr, &state, &DecodeInfoCallback,
-                              &DecodeRowCallback, &DecodeEndCallback);
-  png_process_data(png_ptr,
-                   info_ptr,
-                   const_cast<unsigned char*>(input),
-                   input_size);
-
-  if (!state.done) {
-    return false;
-  }
-
-  // Set the bitmap's opaqueness based on what we saw.
-  bitmap->setAlphaType(state.is_opaque ?
-                       kOpaque_SkAlphaType : kPremul_SkAlphaType);
-
-  return true;
-}
-
 // Encoder --------------------------------------------------------------------
 //
 // This section of the code is based on nsPNGEncoder.cpp in Mozilla
@@ -505,9 +395,18 @@ void ConvertBGRAtoRGB(const unsigned char* bgra, int pixel_width,
 }
 
 #ifdef PNG_TEXT_SUPPORTED
+
+inline char* strdup(const char* str) {
+#if defined(OS_WIN)
+  return _strdup(str);
+#else
+  return ::strdup(str);
+#endif
+}
+
 class CommentWriter {
  public:
-  explicit CommentWriter(const std::vector<PNGCodec::Comment>& comments)
+  explicit CommentWriter(const std::vector<Comment>& comments)
       : comments_(comments),
         png_text_(new png_text[comments.size()]) {
     for (size_t i = 0; i < comments.size(); ++i)
@@ -535,12 +434,12 @@ class CommentWriter {
   }
 
  private:
-  void AddComment(size_t pos, const PNGCodec::Comment& comment) {
+  void AddComment(size_t pos, const Comment& comment) {
     png_text_[pos].compression = PNG_TEXT_COMPRESSION_NONE;
     // A PNG comment's key can only be 79 characters long.
     DCHECK(comment.key.length() < 79);
-    png_text_[pos].key = base::strdup(comment.key.substr(0, 78).c_str());
-    png_text_[pos].text = base::strdup(comment.text.c_str());
+    png_text_[pos].key = strdup(comment.key.substr(0, 78).c_str());
+    png_text_[pos].text = strdup(comment.text.c_str());
     png_text_[pos].text_length = comment.text.length();
 #ifdef PNG_iTXt_SUPPORTED
     png_text_[pos].itxt_length = 0;
@@ -549,9 +448,7 @@ class CommentWriter {
 #endif
   }
 
-  DISALLOW_COPY_AND_ASSIGN(CommentWriter);
-
-  const std::vector<PNGCodec::Comment> comments_;
+  const std::vector<Comment> comments_;
   png_text* png_text_;
 };
 #endif  // PNG_TEXT_SUPPORTED
@@ -570,7 +467,7 @@ bool DoLibpngWrite(png_struct* png_ptr, png_info* info_ptr,
                    const unsigned char* input, int compression_level,
                    int png_output_color_type, int output_color_components,
                    FormatConverter converter,
-                   const std::vector<PNGCodec::Comment>& comments) {
+                   const std::vector<Comment>& comments) {
 #ifdef PNG_TEXT_SUPPORTED
   CommentWriter comment_writer(comments);
 #endif
@@ -588,7 +485,6 @@ bool DoLibpngWrite(png_struct* png_ptr, png_info* info_ptr,
 
   // Set our callback for libpng to give us the data.
   png_set_write_fn(png_ptr, state, EncoderWriteCallback, FakeFlushCallback);
-  png_set_error_fn(png_ptr, NULL, LogLibPNGEncodeError, LogLibPNGEncodeWarning);
 
   png_set_IHDR(png_ptr, info_ptr, width, height, 8, png_output_color_type,
                PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,
@@ -623,12 +519,14 @@ bool DoLibpngWrite(png_struct* png_ptr, png_info* info_ptr,
   return true;
 }
 
-bool EncodeWithCompressionLevel(const unsigned char* input,
-                                PNGCodec::ColorFormat format,
-                                const Size& size,
+}  // namespace
+
+// static
+bool EncodeWithCompressionLevel(const unsigned char* input, ColorFormat format,
+                                const int width, const int height,
                                 int row_byte_width,
                                 bool discard_transparency,
-                                const std::vector<PNGCodec::Comment>& comments,
+                                const std::vector<Comment>& comments,
                                 int compression_level,
                                 std::vector<unsigned char>* output) {
   // Run to convert an input row into the output row format, NULL means no
@@ -638,13 +536,14 @@ bool EncodeWithCompressionLevel(const unsigned char* input,
   int input_color_components, output_color_components;
   int png_output_color_type;
   switch (format) {
-    case PNGCodec::FORMAT_RGB:
+    case FORMAT_RGB:
       input_color_components = 3;
       output_color_components = 3;
       png_output_color_type = PNG_COLOR_TYPE_RGB;
+      discard_transparency = false;
       break;
 
-    case PNGCodec::FORMAT_RGBA:
+    case FORMAT_RGBA:
       input_color_components = 4;
       if (discard_transparency) {
         output_color_components = 3;
@@ -657,7 +556,7 @@ bool EncodeWithCompressionLevel(const unsigned char* input,
       }
       break;
 
-    case PNGCodec::FORMAT_BGRA:
+    case FORMAT_BGRA:
       input_color_components = 4;
       if (discard_transparency) {
         output_color_components = 3;
@@ -670,141 +569,75 @@ bool EncodeWithCompressionLevel(const unsigned char* input,
       }
       break;
 
-    case PNGCodec::FORMAT_SkBitmap:
-      // Compare row_byte_width and size.width() to detect the format of
-      // SkBitmap. kA8_Config (1bpp) and kARGB_8888_Config (4bpp) are the two
-      // supported formats.
-      if (row_byte_width < 4 * size.width()) {
-        // Not 4bpp, so must be 1bpp.
-        // Ignore discard_transparency - it doesn't make sense in this context,
-        // since alpha is the only thing we have and it needs to be used for
-        // color intensity.
-        input_color_components = 1;
-        output_color_components = 1;
-        png_output_color_type = PNG_COLOR_TYPE_GRAY;
-        // |converter| is left as null
-      } else {
-        input_color_components = 4;
-        if (discard_transparency) {
-          output_color_components = 3;
-          png_output_color_type = PNG_COLOR_TYPE_RGB;
-          converter = ConvertSkiaToRGB;
-        } else {
-          output_color_components = 4;
-          png_output_color_type = PNG_COLOR_TYPE_RGB_ALPHA;
-          converter = ConvertSkiaToRGBA;
-        }
-      }
-      break;
-
     default:
       NOTREACHED() << "Unknown pixel format";
       return false;
   }
 
   // Row stride should be at least as long as the length of the data.
-  DCHECK(input_color_components * size.width() <= row_byte_width);
+  DCHECK(input_color_components * width <= row_byte_width);
 
   png_struct* png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,
                                                 NULL, NULL, NULL);
   if (!png_ptr)
     return false;
-  PngWriteStructDestroyer destroyer(&png_ptr);
   png_info* info_ptr = png_create_info_struct(png_ptr);
-  if (!info_ptr)
+  if (!info_ptr) {
+    png_destroy_write_struct(&png_ptr, NULL);
     return false;
-  destroyer.SetInfoStruct(&info_ptr);
-
-  output->clear();
+  }
 
   PngEncoderState state(output);
   bool success = DoLibpngWrite(png_ptr, info_ptr, &state,
-                               size.width(), size.height(), row_byte_width,
+                               width, height, row_byte_width,
                                input, compression_level, png_output_color_type,
                                output_color_components, converter, comments);
+  png_destroy_write_struct(&png_ptr, &info_ptr);
 
   return success;
 }
 
-bool InternalEncodeSkBitmap(const SkBitmap& input,
-                            bool discard_transparency,
-                            int compression_level,
-                            std::vector<unsigned char>* output) {
-  if (input.empty() || input.isNull())
-    return false;
-  int bpp = input.bytesPerPixel();
-  DCHECK(bpp == 1 || bpp == 4);  // We support kA8_Config and kARGB_8888_Config.
-
-  SkAutoLockPixels lock_input(input);
-  unsigned char* inputAddr = bpp == 1 ?
-      reinterpret_cast<unsigned char*>(input.getAddr8(0, 0)) :
-      reinterpret_cast<unsigned char*>(input.getAddr32(0, 0));    // bpp = 4
-  return EncodeWithCompressionLevel(
-      inputAddr,
-      PNGCodec::FORMAT_SkBitmap,
-      Size(input.width(), input.height()),
-      static_cast<int>(input.rowBytes()),
-      discard_transparency,
-      std::vector<PNGCodec::Comment>(),
-      compression_level,
-      output);
-}
-
-
-}  // namespace
-
 // static
-bool PNGCodec::Encode(const unsigned char* input,
-                      ColorFormat format,
-                      const Size& size,
-                      int row_byte_width,
-                      bool discard_transparency,
-                      const std::vector<Comment>& comments,
-                      std::vector<unsigned char>* output) {
-  return EncodeWithCompressionLevel(input,
-                                    format,
-                                    size,
+bool Encode(const unsigned char* input, ColorFormat format,
+            const int width, const int height, int row_byte_width,
+            bool discard_transparency,
+            const std::vector<Comment>& comments,
+            std::vector<unsigned char>* output) {
+  return EncodeWithCompressionLevel(input, format, width, height,
                                     row_byte_width,
                                     discard_transparency,
-                                    comments,
-                                    Z_DEFAULT_COMPRESSION,
+                                    comments, Z_DEFAULT_COMPRESSION,
                                     output);
 }
 
-// static
-bool PNGCodec::EncodeBGRASkBitmap(const SkBitmap& input,
-                                  bool discard_transparency,
-                                  std::vector<unsigned char>* output) {
-  return InternalEncodeSkBitmap(input,
-                                discard_transparency,
-                                Z_DEFAULT_COMPRESSION,
-                                output);
-}
-
-// static
-bool PNGCodec::EncodeA8SkBitmap(const SkBitmap& input,
-                                std::vector<unsigned char>* output) {
-  return InternalEncodeSkBitmap(input,
-                                false,
-                                Z_DEFAULT_COMPRESSION,
-                                output);
-}
-
-// static
-bool PNGCodec::FastEncodeBGRASkBitmap(const SkBitmap& input,
-                                      bool discard_transparency,
-                                      std::vector<unsigned char>* output) {
-  return InternalEncodeSkBitmap(input,
-                                discard_transparency,
-                                Z_BEST_SPEED,
-                                output);
+// Decode a PNG into an RGBA pixel array.
+bool DecodePNG(const unsigned char* input, size_t input_size,
+               std::vector<unsigned char>* output,
+               int* width, int* height) {
+  return Decode(input, input_size, FORMAT_RGBA, output, width, height);
 }
 
-PNGCodec::Comment::Comment(const std::string& k, const std::string& t)
-    : key(k), text(t) {
+// Encode an RGBA pixel array into a PNG.
+bool EncodeRGBAPNG(const unsigned char* input,
+                   int width,
+                   int height,
+                   int row_byte_width,
+                   std::vector<unsigned char>* output) {
+  return Encode(input, FORMAT_RGBA,
+      width, height, row_byte_width, false,
+      std::vector<Comment>(), output);
 }
 
-PNGCodec::Comment::~Comment() {
+// Encode an BGRA pixel array into a PNG.
+bool EncodeBGRAPNG(const unsigned char* input,
+                   int width,
+                   int height,
+                   int row_byte_width,
+                   bool discard_transparency,
+                   std::vector<unsigned char>* output) {
+  return Encode(input, FORMAT_BGRA,
+      width, height, row_byte_width, discard_transparency,
+      std::vector<Comment>(), output);
 }
 
-}  // namespace gfx
+}  // image_diff_png