CentrED/Imaging/ImagingBitmap.pas

{
  $Id: ImagingBitmap.pas 129 2008-08-06 20:01:30Z galfar $
  Vampyre Imaging Library
  by Marek Mauder 
  http://imaginglib.sourceforge.net

  The contents of this file are used with permission, subject to the Mozilla
  Public License Version 1.1 (the "License"); you may not use this file except
  in compliance with the License. You may obtain a copy of the License at
  http://www.mozilla.org/MPL/MPL-1.1.html

  Software distributed under the License is distributed on an "AS IS" basis,
  WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for
  the specific language governing rights and limitations under the License.

  Alternatively, the contents of this file may be used under the terms of the
  GNU Lesser General Public License (the  "LGPL License"), in which case the
  provisions of the LGPL License are applicable instead of those above.
  If you wish to allow use of your version of this file only under the terms
  of the LGPL License and not to allow others to use your version of this file
  under the MPL, indicate your decision by deleting  the provisions above and
  replace  them with the notice and other provisions required by the LGPL
  License.  If you do not delete the provisions above, a recipient may use
  your version of this file under either the MPL or the LGPL License.

  For more information about the LGPL: http://www.gnu.org/copyleft/lesser.html
}

{ This unit contains image format loader/saver for Windows Bitmap images.}
unit ImagingBitmap;

{$I ImagingOptions.inc}

interface

uses
  ImagingTypes, Imaging, ImagingUtility, ImagingFormats, ImagingIO;

type
  { Class for loading and saving Windows Bitmap images.
    It can load/save 8bit indexed, 16, 24, 32 bit RGB or ARGB
    images with or without RLE compression. It can also load 1/4 bit
    indexed images and OS2 bitmaps.}
  TBitmapFileFormat = class(TImageFileFormat)
  protected
    FUseRLE: LongBool;
    function LoadData(Handle: TImagingHandle; var Images: TDynImageDataArray;
      OnlyFirstLevel: Boolean): Boolean; override;
    function SaveData(Handle: TImagingHandle; const Images: TDynImageDataArray;
      Index: LongInt): Boolean; override;
    procedure ConvertToSupported(var Image: TImageData;
      const Info: TImageFormatInfo); override;
  public
    constructor Create; override;
    function TestFormat(Handle: TImagingHandle): Boolean; override;
  published  
    { Controls that RLE compression is used during saving. Accessible trough
      ImagingBitmapRLE option.}
    property UseRLE: LongBool read FUseRLE write FUseRLE;
  end;

implementation

const
  SBitmapFormatName = 'Windows Bitmap Image';
  SBitmapMasks =      '*.bmp,*.dib';
  BitmapSupportedFormats: TImageFormats = [ifIndex8, ifA1R5G5B5, ifA4R4G4B4,
    ifR5G6B5, ifR8G8B8, ifA8R8G8B8, ifX1R5G5B5, ifX4R4G4B4, ifX8R8G8B8];
  BitmapDefaultRLE = True;  

const
  { Bitmap file identifier 'BM'.}
  BMMagic: Word = 19778;

  { Constants for the TBitmapInfoHeader.Compression field.}
  BI_RGB = 0;
  BI_RLE8 = 1;
  BI_RLE4 = 2;
  BI_BITFIELDS = 3;

  V3InfoHeaderSize = 40;
  V4InfoHeaderSize = 108; 

type
  { File Header for Windows/OS2 bitmap file.}
  TBitmapFileHeader = packed record
    ID: Word;           // Is always 19778 : 'BM'
    Size: LongWord;     // Filesize
    Reserved1: Word;
    Reserved2: Word;
    Offset: LongWord;   // Offset from start pos to beginning of image bits
  end;

  { Info Header for Windows bitmap file version 4.}
  TBitmapInfoHeader = packed record
    Size: LongWord;
    Width: LongInt;
    Height: LongInt;
    Planes: Word;
    BitCount: Word;
    Compression: LongWord;
    SizeImage: LongWord;
    XPelsPerMeter: LongInt;
    YPelsPerMeter: LongInt;
    ClrUsed: LongInt;
    ClrImportant: LongInt;
    RedMask: LongWord;
    GreenMask: LongWord;
    BlueMask: LongWord;
    AlphaMask: LongWord;
    CSType: LongWord;
    EndPoints: array[0..8] of LongWord;
    GammaRed: LongWord;
    GammaGreen: LongWord;
    GammaBlue: LongWord;
  end;

  { Info Header for OS2 bitmaps.}
  TBitmapCoreHeader = packed record
    Size: LongWord;
    Width: Word;
    Height: Word;
    Planes: Word;
    BitCount: Word;
  end;

  { Used in RLE encoding and decoding.} 
  TRLEOpcode = packed record
    Count: Byte;
    Command: Byte;
  end;
  PRLEOpcode = ^TRLEOpcode;

{ TBitmapFileFormat class implementation }

constructor TBitmapFileFormat.Create;
begin
  inherited Create;
  FName := SBitmapFormatName;
  FCanLoad := True;
  FCanSave := True;
  FIsMultiImageFormat := False;
  FSupportedFormats := BitmapSupportedFormats;

  FUseRLE := BitmapDefaultRLE;

  AddMasks(SBitmapMasks);
  RegisterOption(ImagingBitmapRLE, @FUseRLE);
end;

function TBitmapFileFormat.LoadData(Handle: TImagingHandle;
  var Images: TDynImageDataArray; OnlyFirstLevel: Boolean): Boolean;
var
  BF: TBitmapFileHeader;
  BI: TBitmapInfoHeader;
  BC: TBitmapCoreHeader;
  IsOS2: Boolean;
  PalRGB: PPalette24;
  I, FPalSize, AlignedSize, StartPos, HeaderSize, AlignedWidthBytes, WidthBytes: LongInt;
  Info: TImageFormatInfo;
  Data: Pointer;

  procedure LoadRGB;
  var
    I: LongInt;
    LineBuffer: PByte;
  begin
    with Images[0], GetIO do
    begin
      // If BI.Height is < 0 then image data are stored non-flipped
      // but default in windows is flipped so if Height is positive we must
      // flip it

      if BI.BitCount < 8 then
      begin
        // For 1 and 4 bit images load aligned data, they will be converted to
        // 8 bit and unaligned later
        GetMem(Data, AlignedSize);

        if BI.Height < 0 then
          Read(Handle, Data, AlignedSize)
        else
          for I := Height - 1 downto 0 do
            Read(Handle, @PByteArray(Data)[I * AlignedWidthBytes], AlignedWidthBytes);
      end
      else
      begin
        // Images with pixels of size >= 1 Byte are read line by line and
        // copied to image bits without padding bytes
        GetMem(LineBuffer, AlignedWidthBytes);
        try
          if BI.Height < 0 then
            for I := 0 to Height - 1 do
            begin
              Read(Handle, LineBuffer, AlignedWidthBytes);
              Move(LineBuffer^, PByteArray(Bits)[I * WidthBytes], WidthBytes);
            end
          else
            for I := Height - 1 downto 0 do
            begin
              Read(Handle, LineBuffer, AlignedWidthBytes);
              Move(LineBuffer^, PByteArray(Bits)[I * WidthBytes], WidthBytes);
            end;
        finally
          FreeMemNil(LineBuffer);
        end;
      end;
    end;
  end;

  procedure LoadRLE4;
  var
    RLESrc: PByteArray;
    Row, Col, WriteRow, I: LongInt;
    SrcPos: LongWord;
    DeltaX, DeltaY, Low, High: Byte;
    Pixels: PByteArray;
    OpCode: TRLEOpcode;
    NegHeightBitmap: Boolean;
  begin
    GetMem(RLESrc, BI.SizeImage);
    GetIO.Read(Handle, RLESrc, BI.SizeImage);
    with Images[0] do
    try
      Low := 0;
      Pixels := Bits;
      SrcPos := 0;
      NegHeightBitmap := BI.Height < 0;
      Row := 0; // Current row in dest image
      Col := 0; // Current column in dest image
      // Row in dest image where actuall writting will be done
      WriteRow := Iff(NegHeightBitmap, Row, Height - 1 - Row);
      while (Row < Height) and (SrcPos < BI.SizeImage) do
      begin
        // Read RLE op-code
        OpCode := PRLEOpcode(@RLESrc[SrcPos])^;
        Inc(SrcPos, SizeOf(OpCode));
        if OpCode.Count = 0 then
        begin
          // A byte Count of zero means that this is a special
          // instruction.
          case OpCode.Command of
            0:
              begin
                // Move to next row
                Inc(Row);
                WriteRow := Iff(NegHeightBitmap, Row, Height - 1 - Row);
                Col := 0;
              end ;
            1: Break; // Image is finished
            2:
              begin
                // Move to a new relative position
                DeltaX := RLESrc[SrcPos];
                DeltaY := RLESrc[SrcPos + 1];
                Inc(SrcPos, 2);
                Inc(Col, DeltaX);
                Inc(Row, DeltaY);
              end
          else
            // Do not read data after EOF
            if SrcPos + OpCode.Command > BI.SizeImage then
              OpCode.Command := BI.SizeImage - SrcPos;
            // Take padding bytes and nibbles into account
            if Col + OpCode.Command > Width then
              OpCode.Command := Width - Col;
            // Store absolute data. Command code is the
            // number of absolute bytes to store
            for I := 0 to OpCode.Command - 1 do
            begin
              if (I and 1) = 0 then
              begin
                High := RLESrc[SrcPos] shr 4;
                Low := RLESrc[SrcPos] and $F;
                Pixels[WriteRow * Width + Col] := High;
                Inc(SrcPos);
              end
              else
                Pixels[WriteRow * Width + Col] := Low;
              Inc(Col);
            end;
            // Odd number of bytes is followed by a pad byte
            if (OpCode.Command mod 4) in [1, 2] then
              Inc(SrcPos);
          end;
        end
        else
        begin
          // Take padding bytes and nibbles into account
          if Col + OpCode.Count > Width then
            OpCode.Count := Width - Col;
          // Store a run of the same color value
          for I := 0 to OpCode.Count - 1 do
          begin
            if (I and 1) = 0 then
              Pixels[WriteRow * Width + Col] := OpCode.Command shr 4
            else
              Pixels[WriteRow * Width + Col] := OpCode.Command and $F;
            Inc(Col);
          end;
        end;
      end;
    finally
      FreeMem(RLESrc);
    end;
  end;

  procedure LoadRLE8;
  var
    RLESrc: PByteArray;
    SrcCount, Row, Col, WriteRow: LongInt;
    SrcPos: LongWord;
    DeltaX, DeltaY: Byte;
    Pixels: PByteArray;
    OpCode: TRLEOpcode;
    NegHeightBitmap: Boolean;
  begin
    GetMem(RLESrc, BI.SizeImage);
    GetIO.Read(Handle, RLESrc, BI.SizeImage);
    with Images[0] do
    try
      Pixels := Bits;
      SrcPos := 0;
      NegHeightBitmap := BI.Height < 0;
      Row := 0; // Current row in dest image
      Col := 0; // Current column in dest image
      // Row in dest image where actuall writting will be done
      WriteRow := Iff(NegHeightBitmap, Row, Height - 1 - Row);
      while (Row < Height) and (SrcPos < BI.SizeImage) do
      begin
        // Read RLE op-code
        OpCode := PRLEOpcode(@RLESrc[SrcPos])^;
        Inc(SrcPos, SizeOf(OpCode));
        if OpCode.Count = 0 then
        begin
          // A byte Count of zero means that this is a special
          // instruction.
          case OpCode.Command of
            0:
              begin
                // Move to next row
                Inc(Row);
                WriteRow := Iff(NegHeightBitmap, Row, Height - 1 - Row);
                Col := 0;
              end ;
            1: Break; // Image is finished
            2:
              begin
                // Move to a new relative position
                DeltaX := RLESrc[SrcPos];
                DeltaY := RLESrc[SrcPos + 1];
                Inc(SrcPos, 2);
                Inc(Col, DeltaX);
                Inc(Row, DeltaY);
              end
          else
            SrcCount := OpCode.Command;
            // Do not read data after EOF
            if SrcPos + OpCode.Command > BI.SizeImage then
              OpCode.Command := BI.SizeImage - SrcPos;
            // Take padding bytes into account
            if Col + OpCode.Command > Width then
              OpCode.Command := Width - Col;
            // Store absolute data. Command code is the
            // number of absolute bytes to store
            Move(RLESrc[SrcPos], Pixels[WriteRow * Width + Col], OpCode.Command);
            Inc(SrcPos, SrcCount);
            Inc(Col, OpCode.Command);
            // Odd number of bytes is followed by a pad byte
            if (SrcCount mod 2) = 1 then
              Inc(SrcPos);
          end;
        end
        else
        begin
          // Take padding bytes into account
          if Col + OpCode.Count > Width then
            OpCode.Count := Width - Col;
          // Store a run of the same color value. Count is number of bytes to store
          FillChar(Pixels [WriteRow * Width + Col], OpCode.Count, OpCode.Command);
          Inc(Col, OpCode.Count);
        end;
      end;
    finally
      FreeMem(RLESrc);
    end;
  end;

begin
  Data := nil;
  SetLength(Images, 1);
  with GetIO, Images[0] do
  try
    FillChar(BI, SizeOf(BI), 0);
    StartPos := Tell(Handle);
    Read(Handle, @BF, SizeOf(BF));
    Read(Handle, @BI.Size, SizeOf(BI.Size));
    IsOS2 := BI.Size = SizeOf(TBitmapCoreHeader);

    // Bitmap Info reading
    if IsOS2 then
    begin
      // OS/2 type bitmap, reads info header without 4 already read bytes
      Read(Handle, @PByteArray(@BC)[SizeOf(BI.Size)],
        SizeOf(TBitmapCoreHeader) - SizeOf(BI.Size));
      with BI do
      begin
        ClrUsed := 0;
        Compression := BI_RGB;
        BitCount := BC.BitCount;
        Height := BC.Height;
        Width := BC.Width;
      end;
    end
    else
    begin
      // Windows type bitmap
      HeaderSize := Min(BI.Size - SizeOf(BI.Size), SizeOf(BI) - SizeOf(BI.Size)); // do not read more than size of BI!
      Read(Handle, @PByteArray(@BI)[SizeOf(BI.Size)], HeaderSize);
      // SizeImage can be 0 for BI_RGB images, but it is here because of:
      // I saved 8bit bitmap in Paint Shop Pro 8 as OS2 RLE compressed.
      // It wrote strange 64 Byte Info header with SizeImage set to 0
      // Some progs were able to open it, some were not.
      if BI.SizeImage = 0 then
        BI.SizeImage := BF.Size - BF.Offset;
    end;
    // Bit mask reading. Only read it if there is V3 header, V4 header has
    // masks laoded already (only masks for RGB in V3).
    if (BI.Compression = BI_BITFIELDS) and (BI.Size = V3InfoHeaderSize) then
      Read(Handle, @BI.RedMask, SizeOf(BI.RedMask) * 3);

    case BI.BitCount of
      1, 4, 8: Format := ifIndex8;
      16:
        if BI.RedMask = $0F00 then
          // Set XRGB4 or ARGB4 according to value of alpha mask
          Format := IffFormat(BI.AlphaMask = 0, ifX4R4G4B4, ifA4R4G4B4)
        else if BI.RedMask = $F800 then
          Format := ifR5G6B5
        else
          // R5G5B5 is default 16bit format (with Compression = BI_RGB or masks).
          // We set it to A1.. and later there is a check if there are any alpha values
          // and if not it is changed to X1R5G5B5
          Format := ifA1R5G5B5;
      24: Format := ifR8G8B8;
      32: Format := ifA8R8G8B8; // As with R5G5B5 there is alpha check later 
    end;

    NewImage(BI.Width, Abs(BI.Height), Format, Images[0]);
    Info := GetFormatInfo(Format);
    WidthBytes := Width * Info.BytesPerPixel;
    AlignedWidthBytes := (((Width * BI.BitCount) + 31) shr 5) * 4;
    AlignedSize := Height * LongInt(AlignedWidthBytes);

    // Palette settings and reading
    if BI.BitCount <= 8 then
    begin
      // Seek to the begining of palette
      Seek(Handle, StartPos + SizeOf(TBitmapFileHeader) + LongInt(BI.Size),
        smFromBeginning);
      if IsOS2 then
      begin
        // OS/2 type
        FPalSize := 1 shl BI.BitCount;
        GetMem(PalRGB, FPalSize * SizeOf(TColor24Rec));
        try
          Read(Handle, PalRGB, FPalSize * SizeOf(TColor24Rec));
          for I := 0 to FPalSize - 1 do
          with PalRGB[I] do
          begin
            Palette[I].R := R;
            Palette[I].G := G;
            Palette[I].B := B;
          end;
        finally
          FreeMemNil(PalRGB);
        end;
      end
      else
      begin
        // Windows type
        FPalSize := BI.ClrUsed;
        if FPalSize = 0 then
          FPalSize := 1 shl BI.BitCount;
        Read(Handle, Palette, FPalSize * SizeOf(TColor32Rec));
      end;
      for I := 0 to Info.PaletteEntries - 1 do
        Palette[I].A := $FF;
    end;

    // Seek to the beginning of image bits
    Seek(Handle, StartPos + LongInt(BF.Offset), smFromBeginning);

    case BI.Compression of
      BI_RGB: LoadRGB;
      BI_RLE4: LoadRLE4;
      BI_RLE8: LoadRLE8;
      BI_BITFIELDS: LoadRGB;
    end;

    if BI.AlphaMask = 0 then
    begin
      // Alpha mask is not stored in file (V3) or not defined.
      // Check alpha channels of loaded images if they might contain them.
      if Format = ifA1R5G5B5 then
      begin
        // Check if there is alpha channel present in A1R5GB5 images, if it is not
        // change format to X1R5G5B5
        if not Has16BitImageAlpha(Width * Height, Bits) then
          Format := ifX1R5G5B5;
      end
      else if Format = ifA8R8G8B8 then
      begin
        // Check if there is alpha channel present in A8R8G8B8 images, if it is not
        // change format to X8R8G8B8
        if not Has32BitImageAlpha(Width * Height, Bits) then
          Format := ifX8R8G8B8;
      end;
    end;

    if BI.BitCount < 8 then
    begin
      // 1 and 4 bpp images are supported only for loading which is now
      // so we now convert them to 8bpp (and unalign scanlines).
      case BI.BitCount of
        1: Convert1To8(Data, Bits, Width, Height, AlignedWidthBytes);
        4:
          begin
            // RLE4 bitmaps are translated to 8bit during RLE decoding
            if BI.Compression <> BI_RLE4 then
               Convert4To8(Data, Bits, Width, Height, AlignedWidthBytes);
          end;
      end;
      // Enlarge palette
      ReallocMem(Palette, Info.PaletteEntries * SizeOf(TColor32Rec));
    end;

    Result := True;
  finally
    FreeMemNil(Data);
  end;
end;

function TBitmapFileFormat.SaveData(Handle: TImagingHandle;
  const Images: TDynImageDataArray; Index: LongInt): Boolean;
var
  StartPos, EndPos, I, Pad, PadSize, WidthBytes: LongInt;
  BF: TBitmapFileHeader;
  BI: TBitmapInfoHeader;
  Info: TImageFormatInfo;
  ImageToSave: TImageData;
  MustBeFreed: Boolean;

  procedure SaveRLE8;
  const
    BufferSize = 8 * 1024;
  var
    X, Y, I, SrcPos: LongInt;
    DiffCount, SameCount: Byte;
    Pixels: PByteArray;
    Buffer: array[0..BufferSize - 1] of Byte;
    BufferPos: LongInt;

    procedure WriteByte(ByteToWrite: Byte);
    begin
      if BufferPos = BufferSize then
      begin
        // Flush buffer if necessary
        GetIO.Write(Handle, @Buffer, BufferPos);
        BufferPos := 0;
      end;
      Buffer[BufferPos] := ByteToWrite;
      Inc(BufferPos);
    end;

  begin
    BufferPos := 0;
    with GetIO, ImageToSave do
    begin
      for Y := Height - 1 downto 0 do
      begin
        X := 0;
        SrcPos := 0;
        Pixels := @PByteArray(Bits)[Y * Width];

        while X < Width do
        begin
          SameCount := 1;
          DiffCount := 0;
          // Determine run length
          while X + SameCount < Width do
          begin
            // If we reach max run length or byte with different value
            // we end this run
            if (SameCount = 255) or (Pixels[SrcPos + SameCount] <> Pixels[SrcPos]) then
              Break;
            Inc(SameCount);
          end;

          if SameCount = 1 then
          begin
            // If there are not some bytes with the same value we
            // compute how many different bytes are there
            while X + DiffCount < Width do
            begin
              // Stop diff byte counting if there two bytes with the same value
              // or DiffCount is too big
              if (DiffCount = 255) or (Pixels[SrcPos + DiffCount + 1] =
                Pixels[SrcPos + DiffCount]) then
                Break;
              Inc(DiffCount);
            end;
          end;

          // Now store absolute data (direct copy image->file) or
          // store RLE code only (number of repeats + byte to be repeated)
          if DiffCount > 2 then
          begin
            // Save 'Absolute Data' (0 + number of bytes) but only
            // if number is >2 because (0+1) and (0+2) are other special commands
            WriteByte(0);
            WriteByte(DiffCount);
            // Write absolute data to buffer
            for I := 0 to DiffCount - 1 do
              WriteByte(Pixels[SrcPos + I]);
            Inc(X, DiffCount);
            Inc(SrcPos, DiffCount);
            // Odd number of bytes must be padded
            if (DiffCount mod 2) = 1 then
              WriteByte(0);
          end
          else
          begin
            // Save number of repeats and byte that should be repeated
            WriteByte(SameCount);
            WriteByte(Pixels[SrcPos]);
            Inc(X, SameCount);
            Inc(SrcPos, SameCount);
          end;
        end;
        // Save 'End Of Line' command
        WriteByte(0);
        WriteByte(0);
      end;
      // Save 'End Of Bitmap' command
      WriteByte(0);
      WriteByte(1);
      // Flush buffer
      GetIO.Write(Handle, @Buffer, BufferPos);
    end;
  end;

begin
  Result := False;
  if MakeCompatible(Images[Index], ImageToSave, MustBeFreed) then
  with GetIO, ImageToSave do
  try
    Info := GetFormatInfo(Format);
    StartPos := Tell(Handle);
    FillChar(BF, SizeOf(BF), 0);
    FillChar(BI, SizeOf(BI), 0);
    // Other fields will be filled later - we don't know all values now
    BF.ID := BMMagic;
    Write(Handle, @BF, SizeOf(BF));
    if Info.HasAlphaChannel and (Info.BytesPerPixel = 2){V4 temp hack} then
      // Save images with alpha in V4 format
      BI.Size := V4InfoHeaderSize
    else
      // Save images without alpha in V3 format - for better compatibility
      BI.Size := V3InfoHeaderSize;
    BI.Width := Width;
    BI.Height := Height;
    BI.Planes := 1;
    BI.BitCount := Info.BytesPerPixel * 8;
    BI.XPelsPerMeter := 2835; // 72 dpi
    BI.YPelsPerMeter := 2835; // 72 dpi
    // Set compression
    if (Info.BytesPerPixel = 1) and FUseRLE then
      BI.Compression := BI_RLE8
    else if (Info.HasAlphaChannel or
      ((BI.BitCount = 16) and (Format <> ifX1R5G5B5))) and (Info.BytesPerPixel = 2){V4 temp hack} then
      BI.Compression := BI_BITFIELDS
    else
      BI.Compression := BI_RGB;
    // Write header (first time)
    Write(Handle, @BI, BI.Size);

    // Write mask info
    if BI.Compression = BI_BITFIELDS then
    begin
      if BI.BitCount = 16 then
      with Info.PixelFormat^ do
      begin
        BI.RedMask   := RBitMask;
        BI.GreenMask := GBitMask;
        BI.BlueMask  := BBitMask;
        BI.AlphaMask := ABitMask;
      end
      else
      begin
        // Set masks for A8R8G8B8
        BI.RedMask   := $00FF0000;
        BI.GreenMask := $0000FF00;
        BI.BlueMask  := $000000FF;
        BI.AlphaMask := $FF000000;
      end;
      // If V3 header is used RGB masks must be written to file separately.
      // V4 header has embedded masks (V4 is default for formats with alpha).
      if BI.Size = V3InfoHeaderSize then
        Write(Handle, @BI.RedMask, SizeOf(BI.RedMask) * 3);
    end;
    // Write palette
    if Palette <> nil then
      Write(Handle, Palette, Info.PaletteEntries * SizeOf(TColor32Rec));

    BF.Offset := Tell(Handle) - StartPos;

    if BI.Compression <> BI_RLE8 then
    begin
      // Save uncompressed data, scanlines must be filled with pad bytes
      // to be multiples of 4, save as bottom-up (Windows native) bitmap
      Pad := 0;
      WidthBytes := Width * Info.BytesPerPixel;
      PadSize := ((Width * BI.BitCount + 31) div 32) * 4 - WidthBytes;

      for I := Height - 1 downto 0 do
      begin
        Write(Handle, @PByteArray(Bits)[I * WidthBytes], WidthBytes);
        if PadSize > 0 then
          Write(Handle, @Pad, PadSize);
      end;
    end
    else
    begin
      // Save data with RLE8 compression
      SaveRLE8;
    end;

    EndPos := Tell(Handle);
    Seek(Handle, StartPos, smFromBeginning);
    // Rewrite header with new values
    BF.Size := EndPos - StartPos;
    BI.SizeImage := BF.Size - BF.Offset;
    Write(Handle, @BF, SizeOf(BF));
    Write(Handle, @BI, BI.Size);
    Seek(Handle, EndPos, smFromBeginning);

    Result := True;
  finally
    if MustBeFreed then
      FreeImage(ImageToSave);
  end;
end;

procedure TBitmapFileFormat.ConvertToSupported(var Image: TImageData;
  const Info: TImageFormatInfo);
var
  ConvFormat: TImageFormat;
begin
  if Info.IsFloatingPoint then
    // Convert FP image to RGB/ARGB according to presence of alpha channel
    ConvFormat := IffFormat(Info.HasAlphaChannel, ifA8R8G8B8, ifR8G8B8)
  else if Info.HasGrayChannel or Info.IsIndexed then
    // Convert all grayscale and indexed images to Index8 unless they have alpha
    // (preserve it)
    ConvFormat := IffFormat(Info.HasAlphaChannel, ifA8R8G8B8, ifIndex8)
  else if Info.HasAlphaChannel then
    // Convert images with alpha channel to A8R8G8B8
    ConvFormat := ifA8R8G8B8
  else if Info.UsePixelFormat then
    // Convert 16bit RGB images (no alpha) to X1R5G5B5
    ConvFormat := ifX1R5G5B5
  else
    // Convert all other formats to R8G8B8
    ConvFormat := ifR8G8B8;

  ConvertImage(Image, ConvFormat);
end;

function TBitmapFileFormat.TestFormat(Handle: TImagingHandle): Boolean;
var
  Hdr: TBitmapFileHeader;
  ReadCount: LongInt;
begin
  Result := False;
  if Handle <> nil then
  with GetIO do
  begin
    ReadCount := Read(Handle, @Hdr, SizeOf(Hdr));
    Seek(Handle, -ReadCount, smFromCurrent);
    Result := (Hdr.ID = BMMagic) and (ReadCount = SizeOf(Hdr));
  end;
end;

initialization
  RegisterImageFileFormat(TBitmapFileFormat);

{
  File Notes:

  -- TODOS ----------------------------------------------------
    - nothing now
    - Add option to choose to save V3 or V4 headers. 

  -- 0.25.0 Changes/Bug Fixes ---------------------------------
    - Fixed problem with indexed BMP loading - some pal entries
      could end up with alpha=0. 

  -- 0.23 Changes/Bug Fixes -----------------------------------
    - Now saves bitmaps as bottom-up for better compatibility
      (mainly Lazarus' TImage!).
    - Fixed crash when loading bitmaps with headers larger than V4.
    - Temp hacks to disable V4 headers for 32bit images (compatibility with
      other soft).

  -- 0.21 Changes/Bug Fixes -----------------------------------
    - Removed temporary data allocation for image with aligned scanlines.
      They are now directly written to output so memory requirements are
      much lower now.
    - Now uses and recognizes BITMAPINFOHEADERV4 when loading/saving.
      Mainly for formats with alpha channels.
    - Added ifR5G6B5 to supported formats, changed converting to supported
      formats little bit.
    - Rewritten SaveRLE8 nested procedure. Old code was long and
      mysterious - new is short and much more readable.
    - MakeCompatible method moved to base class, put ConvertToSupported here.
      GetSupportedFormats removed, it is now set in constructor.
    - Rewritten LoadRLE4 and LoadRLE8 nested procedures.
      Should be less buggy an more readable (load inspired by Colosseum Builders' code).
    - Made public properties for options registered to SetOption/GetOption
      functions. 
    - Addded alpha check to 32b bitmap loading too (teh same as in 16b
      bitmap loading).
    - Moved Convert1To8 and Convert4To8 to ImagingFormats
    - Changed extensions to filename masks.
    - Changed SaveData, LoadData, and MakeCompatible methods according
      to changes in base class in Imaging unit.

  -- 0.19 Changes/Bug Fixes -----------------------------------
    - fixed wrong const that caused A4R4G4B4 BMPs to load as A1R5G5B5
    - fixed the bug that caused 8bit RLE compressed bitmaps to load as
      whole black

  -- 0.17 Changes/Bug Fixes -----------------------------------
    - 16 bit images are usually without alpha but some has alpha
      channel and there is no indication of it - so I have added
      a check: if all pixels of image are with alpha = 0 image is treated
      as X1R5G5B5 otherwise as A1R5G5B5

  -- 0.13 Changes/Bug Fixes -----------------------------------
    - when loading 1/4 bit images with dword aligned dimensions
      there was ugly memory rewritting bug causing image corruption

}

end.