sBadBlock		= 'Unknown GIF block type';
  sUnsupportedClass	= 'Object type not supported for operation';
  sInvalidData		= 'Invalid GIF data';
  sBadHeight		= 'Image height too small for contained frames';
  sBadWidth		= 'Image width too small for contained frames';
{$IFNDEF REGISTER_TGIFIMAGE}
  sGIFToClipboard	= 'Clipboard operations not supported for GIF objects';
{$ELSE}
  sFailedPaste		= 'Failed to store GIF on clipboard';
{$IFDEF VER9x}
  sUnknownClipboardFormat= 'Unsupported clipboard format';
{$ENDIF}
{$ENDIF}
  sScreenSizeExceeded	= 'Image exceeds Logical Screen size';
  sNoColorTable		= 'No global or local color table defined';
  sBadPixelCoordinates	= 'Invalid pixel coordinates';
  sUnsupportedBitmap	= 'Unsupported bitmap format';
  sInvalidPixelFormat	= 'Unsupported PixelFormat';
  sBadDimension		= 'Invalid image dimensions';
  sNoDIB		= 'Image has no DIB';
  sInvalidStream	= 'Invalid stream operation';
  sInvalidColor		= 'Color not in color table';
  sInvalidBitSize	= 'Invalid Bits Per Pixel value';
  sEmptyColorMap	= 'Color table is empty';
  sEmptyImage		= 'Image is empty';
  sInvalidBitmapList	= 'Invalid bitmap list';
  sInvalidReduction	= 'Invalid reduction method';
{$IFDEF VER9x}
  // From Delphi 3 consts.pas
  SOutOfResources	= 'Out of system resources';
  SInvalidBitmap	= 'Bitmap image is not valid';
  SScanLine		= 'Scan line index out of range';
{$ENDIF}

////////////////////////////////////////////////////////////////////////////////
//
//                      Misc texts
//
////////////////////////////////////////////////////////////////////////////////
  // File filter name
  sGIFImageFile		= 'GIF Image';

  // Progress messages
  sProgressLoading	= 'Loading...';
  sProgressSaving	= 'Saving...';
  sProgressConverting	= 'Converting...';
  sProgressRendering	= 'Rendering...';
  sProgressCopying	= 'Copying...';
  sProgressOptimizing	= 'Optimizing...';


////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
//
//			Implementation
//
////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
implementation

{ This makes me long for the C preprocessor... }
{$ifdef DEBUG}
  {$ifdef DEBUG_COMPRESSPERFORMANCE}
    {$define DEBUG_PERFORMANCE}
  {$else}
    {$ifdef DEBUG_DECOMPRESSPERFORMANCE}
      {$define DEBUG_PERFORMANCE}
    {$else}
      {$ifdef DEBUG_DITHERPERFORMANCE}
        {$define DEBUG_PERFORMANCE}
      {$else}
        {$ifdef DEBUG_DITHERPERFORMANCE}
          {$define DEBUG_PERFORMANCE}
        {$else}
          {$ifdef DEBUG_DRAWPERFORMANCE}
            {$define DEBUG_PERFORMANCE}
          {$else}
            {$ifdef DEBUG_RENDERPERFORMANCE}
              {$define DEBUG_PERFORMANCE}
            {$endif}
          {$endif}
        {$endif}
      {$endif}
    {$endif}
  {$endif}
{$endif}

uses
{$ifdef DEBUG}
  dialogs,
{$endif}
  mmsystem, // timeGetTime()
  messages,
  Consts;


////////////////////////////////////////////////////////////////////////////////
//
//			Misc consts
//
////////////////////////////////////////////////////////////////////////////////
const
  { Extension/block label values }
  bsPlainTextExtension		= $01;
  bsGraphicControlExtension	= $F9;
  bsCommentExtension		= $FE;
  bsApplicationExtension	= $FF;

  bsImageDescriptor		= Ord(',');
  bsExtensionIntroducer		= Ord('!');
  bsTrailer			= ord(';');

  // Thread messages - Used by TThread.Synchronize()
  CM_DESTROYWINDOW	= $8FFE; // Defined in classes.pas
  CM_EXECPROC 		= $8FFF; // Defined in classes.pas


////////////////////////////////////////////////////////////////////////////////
//
//                      Design Time support
//
////////////////////////////////////////////////////////////////////////////////
//: Dummy component registration to add design-time support of GIFs to TImage.
// Since TGIFImage isn't a component there's nothing to register here, but
// since Register is only called at design time we can set the design time
// GIF paint options here (modify as you please):
procedure Register;
begin
  // Don't loop animations at design-time. Animated GIFs will animate once and
  // then stop thus not using CPU resources and distracting the developer.
  Exclude(GIFImageDefaultDrawOptions, goLoop);
end;

////////////////////////////////////////////////////////////////////////////////
//
//			Utilities
//
////////////////////////////////////////////////////////////////////////////////
//: Creates a 216 color uniform non-dithering Netscape palette.
function WebPalette: HPalette;
type
  TLogWebPalette	= packed record
    palVersion		: word;
    palNumEntries	: word;
    PalEntries		: array[0..5,0..5,0..5] of TPaletteEntry;
  end;
var
  r, g, b		: byte;
  LogWebPalette		: TLogWebPalette;
  LogPalette		: TLogpalette absolute LogWebPalette; // Stupid typecast
begin
  with LogWebPalette do
  begin
    palVersion:= $0300;
    palNumEntries:= 216;
    for r:=0 to 5 do
      for g:=0 to 5 do
        for b:=0 to 5 do
        begin
          with PalEntries[r,g,b] do
          begin
            peRed := 51 * r;
            peGreen := 51 * g;
            peBlue := 51 * b;
            peFlags := 0;
          end;
        end;
  end;
  Result := CreatePalette(Logpalette);
end;

(*
**  GDI Error handling
**  Adapted from graphics.pas
*)
{$IFOPT R+}
  {$DEFINE R_PLUS}
  {$RANGECHECKS OFF}
{$ENDIF}
{$ifdef D3_BCB3}
function GDICheck(Value: Integer): Integer;
{$else}
function GDICheck(Value: Cardinal): Cardinal;
{$endif}
var
  ErrorCode		: integer;
  Buf			: array [byte] of char;

  function ReturnAddr: Pointer;
  // From classes.pas
  asm
    MOV		EAX,[EBP+4] // sysutils.pas says [EBP-4], but this works !
  end;

begin
  if (Value = 0) then
  begin
    ErrorCode := GetLastError;
    if (ErrorCode <> 0) and (FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, nil,
      ErrorCode, LOCALE_USER_DEFAULT, Buf, sizeof(Buf), nil) <> 0) then
      raise EOutOfResources.Create(Buf) at ReturnAddr
    else
      raise EOutOfResources.Create(SOutOfResources) at ReturnAddr;
  end;
  Result := Value;
end;
{$IFDEF R_PLUS}
  {$RANGECHECKS ON}
  {$UNDEF R_PLUS}
{$ENDIF}

(*
**  Raise error condition
*)
procedure Error(msg: string);
  function ReturnAddr: Pointer;
  // From classes.pas
  asm
    MOV		EAX,[EBP+4] // sysutils.pas says [EBP-4] !
  end;
begin
  raise GIFException.Create(msg) at ReturnAddr;
end;

(*
**  Return number bytes required to
**  hold a given number of bits.
*)
function ByteAlignBit(Bits: Cardinal): Cardinal;
begin
  Result := (Bits+7) SHR 3;
end;
// Rounded up to nearest 2
function WordAlignBit(Bits: Cardinal): Cardinal;
begin
  Result := ((Bits+15) SHR 4) SHL 1;
end;
// Rounded up to nearest 4
function DWordAlignBit(Bits: Cardinal): Cardinal;
begin
  Result := ((Bits+31) SHR 5) SHL 2;
end;
// Round to arbitrary number of bits
function AlignBit(Bits, BitsPerPixel, Alignment: Cardinal): Cardinal;
begin
  Dec(Alignment);
  Result := ((Bits * BitsPerPixel) + Alignment) and not Alignment;
  Result := Result SHR 3;
end;

(*
**  Compute Bits per Pixel from Number of Colors
**  (Return the ceiling log of n)
*)
function Colors2bpp(Colors: integer): integer;
var
  MaxColor		: integer;
begin
  (*
  ** This might be faster computed by multiple if then else statements
  *)

  if (Colors = 0) then
    Result := 0
  else
  begin
    Result := 1;
    MaxColor := 2;
    while (Colors > MaxColor) do
    begin
      inc(Result);
      MaxColor := MaxColor SHL 1;
    end;
  end;
end;

(*
**  Write an ordinal byte value to a stream
*)
procedure WriteByte(Stream: TStream; b: BYTE);
begin
  Stream.Write(b, 1);
end;

(*
**  Read an ordinal byte value from a stream
*)
function ReadByte(Stream: TStream): BYTE;
begin
  Stream.Read(Result, 1);
end;

(*
**  Read data from stream and raise exception of EOF
*)
procedure ReadCheck(Stream: TStream; var Buffer; Size: LongInt);
var
  ReadSize		: integer;
begin
  ReadSize := Stream.Read(Buffer, Size);
  if (ReadSize <> Size) then
    Error(sOutOfData);
end;

(*
**  Write a string list to a stream as multiple blocks
**  of max 255 characters in each.
*)
procedure WriteStrings(Stream: TStream; Text: TStrings);
var
  i			: integer;
  b			: BYTE;
  size			: integer;
  s			: string;
begin
  for i := 0 to Text.Count-1 do
  begin
    s := Text[i];
    size := length(s);
    if (size > 255) then
      b := 255
    else
      b := size;
    while (size > 0) do
    begin
      dec(size, b);
      WriteByte(Stream, b);
      Stream.Write(PChar(s)^, b);
      delete(s, 1, b);