gecko/image/decoders/nsBMPDecoder.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_image_decoders_nsBMPDecoder_h
#define mozilla_image_decoders_nsBMPDecoder_h

#include "BMPHeaders.h"
#include "Decoder.h"
#include "gfxColor.h"
#include "StreamingLexer.h"
#include "mozilla/UniquePtr.h"

namespace mozilla {
namespace image {

namespace bmp {

/// This struct contains the fields from the file header and info header that
/// we use during decoding. (Excluding bitfields fields, which are kept in
/// BitFields.)
struct Header {
  uint32_t mDataOffset;     // Offset to raster data.
  uint32_t mBIHSize;        // Header size.
  int32_t  mWidth;          // Image width.
  int32_t  mHeight;         // Image height.
  uint16_t mBpp;            // Bits per pixel.
  uint32_t mCompression;    // See struct Compression for valid values.
  uint32_t mImageSize;      // (compressed) image size. Can be 0 if
                            // mCompression==0.
  uint32_t mNumColors;      // Used colors.

  Header()
   : mDataOffset(0)
   , mBIHSize(0)
   , mWidth(0)
   , mHeight(0)
   , mBpp(0)
   , mCompression(0)
   , mImageSize(0)
   , mNumColors(0)
  {}
};

/// An entry in the color table.
struct ColorTableEntry {
  uint8_t mRed;
  uint8_t mGreen;
  uint8_t mBlue;
};

/// All the color-related bitfields for 16bpp and 32bpp images. We use this
/// even for older format BMPs that don't have explicit bitfields.
class BitFields {
  class Value {
    friend class BitFields;

    uint32_t mMask;       // The mask for the value.
    uint8_t mRightShift;  // The amount to right-shift after masking.
    uint8_t mBitWidth;    // The width (in bits) of the value.

    /// Sets the mask (and thus the right-shift and bit-width as well).
    void Set(uint32_t aMask);

  public:
    Value()
    {
      mMask = 0;
      mRightShift = 0;
      mBitWidth = 0;
    }

    /// Returns true if this channel is used. Only used for alpha.
    bool IsPresent() const { return mMask != 0x0; }

    /// Extracts the single color value from the multi-color value.
    uint8_t Get(uint32_t aVal) const;

    /// Like Get(), but specially for alpha.
    uint8_t GetAlpha(uint32_t aVal, bool& aHasAlphaOut) const;

    /// Specialized versions of Get() for when the bit-width is 5 or 8.
    /// (They will assert if called and the bit-width is not 5 or 8.)
    uint8_t Get5(uint32_t aVal) const;
    uint8_t Get8(uint32_t aVal) const;
  };

public:
  /// The individual color channels.
  Value mRed;
  Value mGreen;
  Value mBlue;
  Value mAlpha;

  /// Set bitfields to the standard 5-5-5 16bpp values.
  void SetR5G5B5();

  /// Set bitfields to the standard 8-8-8 32bpp values.
  void SetR8G8B8();

  /// Test if bitfields have the standard 5-5-5 16bpp values.
  bool IsR5G5B5() const;

  /// Test if bitfields have the standard 8-8-8 32bpp values.
  bool IsR8G8B8() const;

  /// Read the bitfields from a header. The reading of the alpha mask is
  /// optional.
  void ReadFromHeader(const char* aData, bool aReadAlpha);

  /// Length of the bitfields structure in the BMP file.
  static const size_t LENGTH = 12;
};

} // namespace bmp

class RasterImage;

/// Decoder for BMP-Files, as used by Windows and OS/2.

class nsBMPDecoder : public Decoder
{
public:
  ~nsBMPDecoder();

  /// Obtains the internal output image buffer.
  uint32_t* GetImageData() { return reinterpret_cast<uint32_t*>(mImageData); }

  /// Obtains the length of the internal output image buffer.
  size_t GetImageDataLength() const { return mImageDataLength; }

  /// Obtains the size of the compressed image resource.
  int32_t GetCompressedImageSize() const;

  /// Mark this BMP as being within an ICO file. Only used for testing purposes
  /// because the ICO-specific constructor does this marking automatically.
  void SetIsWithinICO() { mIsWithinICO = true; }

  /// Did the BMP file have alpha data of any kind? (Only use this after the
  /// bitmap has been fully decoded.)
  bool HasTransparency() const { return mDoesHaveTransparency; }

  /// Force transparency from outside. (Used by the ICO decoder.)
  void SetHasTransparency()
  {
    mMayHaveTransparency = true;
    mDoesHaveTransparency = true;
  }

  virtual void WriteInternal(const char* aBuffer,
                             uint32_t aCount) override;
  virtual void FinishInternal() override;

private:
  friend class DecoderFactory;
  friend class nsICODecoder;

  enum class State {
    FILE_HEADER,
    INFO_HEADER_SIZE,
    INFO_HEADER_REST,
    BITFIELDS,
    COLOR_TABLE,
    GAP,
    PIXEL_ROW,
    RLE_SEGMENT,
    RLE_DELTA,
    RLE_ABSOLUTE
  };

  // This is the constructor used by DecoderFactory.
  explicit nsBMPDecoder(RasterImage* aImage);

  // This is the constructor used by nsICODecoder.
  // XXX(seth): nsICODecoder is temporarily an exception to the rule that
  //            decoders should only be instantiated via DecoderFactory.
  nsBMPDecoder(RasterImage* aImage, uint32_t aDataOffset);

  // Helper constructor called by the other two.
  nsBMPDecoder(RasterImage* aImage, State aState, size_t aLength);

  int32_t AbsoluteHeight() const { return abs(mH.mHeight); }

  uint32_t* RowBuffer();

  void FinishRow();

  LexerTransition<State> ReadFileHeader(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);
  LexerTransition<State> ReadColorTable(const char* aData, size_t aLength);
  LexerTransition<State> SkipGap();
  LexerTransition<State> ReadPixelRow(const char* aData);
  LexerTransition<State> ReadRLESegment(const char* aData);
  LexerTransition<State> ReadRLEDelta(const char* aData);
  LexerTransition<State> ReadRLEAbsolute(const char* aData, size_t aLength);

  StreamingLexer<State> mLexer;

  bmp::Header mH;

  // If the BMP is within an ICO file our treatment of it differs slightly.
  bool mIsWithinICO;

  bmp::BitFields mBitFields;

  // Might the image have transparency? Determined from the headers during
  // metadata decode. (Does not guarantee the image actually has transparency.)
  bool mMayHaveTransparency;

  // Does the image have transparency? Determined during full decoding, so only
  // use this after that has been completed.
  bool mDoesHaveTransparency;

  uint32_t mNumColors;      // The number of used colors, i.e. the number of
                            // entries in mColors, if it's present.
  UniquePtr<bmp::ColorTableEntry[]> mColors; // The color table, if it's present.
  uint32_t mBytesPerColor;  // 3 or 4, depending on the format

  // The number of bytes prior to the optional gap that have been read. This
  // is used to find the start of the pixel data.
  uint32_t mPreGapLength;

  uint32_t mPixelRowSize;   // The number of bytes per pixel row.

  int32_t mCurrentRow;      // Index of the row of the image that's currently
                            // being decoded: [height,1].
  int32_t mCurrentPos;      // Index into the current line. Used when
                            // doing RLE decoding and when filling in pixels
                            // for truncated files.

  // Only used in RLE_ABSOLUTE state: the number of pixels to read.
  uint32_t mAbsoluteModeNumPixels;
};

} // namespace image
} // namespace mozilla

#endif // mozilla_image_decoders_nsBMPDecoder_h