ui/gfx/codec/png_codec.h

// Copyright (c) 2011 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.

#ifndef UI_GFX_CODEC_PNG_CODEC_H_
#define UI_GFX_CODEC_PNG_CODEC_H_

#include <stddef.h>

#include <string>
#include <vector>

#include "base/macros.h"
#include "ui/gfx/codec/codec_export.h"

class SkBitmap;

namespace gfx {

class Size;

// Interface for encoding and decoding PNG data. This is a wrapper around
// libpng, which has an inconvenient interface for callers. This is currently
// designed for use in tests only (where we control the files), so the handling
// isn't as robust as would be required for a browser (see Decode() for more).
// WebKit has its own more complicated PNG decoder which handles, among other
// things, partially downloaded data.
class CODEC_EXPORT PNGCodec {
 public:
  static constexpr int DEFAULT_ZLIB_COMPRESSION = 6;

  enum ColorFormat {
    // 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,

    // SkBitmap format. For Encode() kN32_SkColorType (4 bytes per pixel) and
    // kAlpha_8_SkColorType (1 byte per pixel) formats are supported.
    // kAlpha_8_SkColorType gets encoded into a grayscale PNG treating alpha as
    // the color intensity. For Decode() kN32_SkColorType is always used.
    FORMAT_SkBitmap
  };

  // Represents a comment in the tEXt ancillary chunk of the png.
  struct CODEC_EXPORT Comment {
    Comment(const std::string& k, const std::string& t);
    ~Comment();

    std::string key;
    std::string text;
  };

  // Encodes the given raw 'input' data, with each pixel being represented as
  // given in 'format'. The encoded PNG data will be written into the supplied
  // vector and true will be returned on success. On failure (false), the
  // contents of the output buffer are undefined.
  //
  // When writing alpha values, the input colors are assumed to be post
  // multiplied.
  //
  // size: dimensions of the image
  // row_byte_width: the width in bytes of each row. This may be greater than
  //   w * bytes_per_pixel if there is extra padding at the end of each row
  //   (often, each row is padded to the next machine word).
  // discard_transparency: when true, and when the input data format includes
  //   alpha values, these alpha values will be discarded and only RGB will be
  //   written to the resulting file. Otherwise, alpha values in the input
  //   will be preserved.
  // comments: comments to be written in the png's metadata.
  static bool 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);

  // Call PNGCodec::Encode on the supplied SkBitmap |input|, which is assumed to
  // be kN32_SkColorType, 32 bits per pixel. The params |discard_transparency|
  // and |output| are passed directly to Encode; refer to Encode for more
  // information.
  static bool EncodeBGRASkBitmap(const SkBitmap& input,
                                 bool discard_transparency,
                                 std::vector<unsigned char>* output);

  // Call PNGCodec::Encode on the supplied SkBitmap |input|. The difference
  // between this and the previous method is that this restricts compression to
  // zlib q1, which is just rle encoding.
  static bool FastEncodeBGRASkBitmap(const SkBitmap& input,
                                     bool discard_transparency,
                                     std::vector<unsigned char>* output);

  // Call PNGCodec::Encode on the supplied SkBitmap |input|, which is assumed to
  // be kAlpha_8_SkColorType, 8 bits per pixel. The bitmap is encoded as a
  // grayscale PNG with alpha used for color intensity. The |output| param is
  // passed directly to Encode; refer to Encode for more information.
  static bool EncodeA8SkBitmap(const SkBitmap& input,
                               std::vector<unsigned char>* output);

  // Decodes the PNG data contained in input of length input_size. The
  // decoded data will be placed in *output with the dimensions in *w and *h
  // on success (returns true). This data will be written in the 'format'
  // format. On failure, the values of these output variables are undefined.
  //
  // This function may not support all PNG types, and it hasn't been tested
  // with a large number of images, so assume a new format may not work. It's
  // really designed to be able to read in something written by Encode() above.
  static bool Decode(const unsigned char* input, size_t input_size,
                     ColorFormat format, std::vector<unsigned char>* output,
                     int* w, int* h);

  // Decodes the PNG data directly into the passed in SkBitmap. This is
  // significantly faster than the vector<unsigned char> version of Decode()
  // above when dealing with PNG files that are >500K, which a lot of theme
  // images are. (There are a lot of themes that have a NTP image of about ~1
  // megabyte, and those require a 7-10 megabyte side buffer.)
  //
  // Returns true if data is non-null and can be decoded as a png, false
  // otherwise.
  static bool Decode(const unsigned char* input, size_t input_size,
                     SkBitmap* bitmap);

 private:
  DISALLOW_COPY_AND_ASSIGN(PNGCodec);
};

}  // namespace gfx

#endif  // UI_GFX_CODEC_PNG_CODEC_H_