//  Robert Poyntz, rpoyntz@vaneyk.com.au
//
//  Assumes TGIFImage is installed:  http://www.melander.dk/delphi/gifimage
//
//  September 2000

unit GraphicUtils;

interface

uses
  SysUtils, Windows, Graphics, Classes;

Procedure SpecialGIF(ABitmap: TBitmap; Const ARes: Integer; Const AFileName: String);

implementation

Uses
  GIFImage;  // Assumes TGIFImage is installed:


Procedure SpecialGIF(ABitmap: TBitmap; Const ARes: Integer; Const AFileName: String);
Const
  HeaderOffset = $36;
  PixelFormats : Array[1..6] of Integer = (1, 4, 8, 15, 16, 24);
Var
  FileHeader: TBitmapFileHeader;
  InfoHeader: TBitmapInfo;
  ImageSize: Integer;
  BMP: TBitmap;
  GIF: TGIFImage;
  SourceStream: TMemoryStream;
  DestStream: TMemoryStream;
  AlignBytes: Integer;
Begin

  If not(ABitmap.PixelFormat in [pf1bit, pf4bit, pf8bit, pf15bit, pf16bit, pf24bit]) then
    Raise Exception.Create('Cannot process this bitmap type');

  // Bitmap rows need to be word aligned, hence the need for the AlignBytes variable
  AlignBytes := ABitmap.Width mod 2;

  // Calculate the size of the bitmap image data
  ImageSize := (ABitmap.Height * ABitmap.Width) + (ABitmap.Height * AlignBytes);

  // Set up the bitmap file header
  FileHeader.bfType := $4d42;
  FileHeader.bfSize := SizeOf(TBitmapInfoHeader) + SizeOf(TBitmapInfo) + ImageSize;
  FileHeader.bfReserved1 := 0;
  FileHeader.bfReserved2 := 0;
  FileHeader.bfOffBits := SizeOf(TBitmapFileHeader) + SizeOf(TBitmapInfo);

  // Now set up the bitmap info header
  InfoHeader.bmiHeader.biSize := SizeOf(TBitmapInfoHeader);
  InfoHeader.bmiHeader.biWidth := ABitmap.Width;
  InfoHeader.bmiHeader.biHeight := ABitmap.Height;
  InfoHeader.bmiHeader.biPlanes := 1;
  InfoHeader.bmiHeader.biBitCount := PixelFormats[Ord(ABitmap.PixelFormat)];
  InfoHeader.bmiHeader.biCompression := BI_RGB;
  InfoHeader.bmiHeader.biSizeImage := 0;
  InfoHeader.bmiHeader.biXPelsPerMeter := ARes;
  InfoHeader.bmiHeader.biYPelsPerMeter := ARes;
  InfoHeader.bmiHeader.biClrUsed := 0;
  InfoHeader.bmiHeader.biClrImportant := 0;

  SourceStream := TMemoryStream.Create;
  Try
    ABitmap.SaveToStream(SourceStream);
    DestStream := TMemoryStream.Create;
    Try
      DestStream.Write(FileHeader, SizeOf(FileHeader));
      DestStream.Write(InfoHeader.bmiHeader, SizeOf(InfoHeader.bmiHeader));

      SourceStream.Position := HeaderOffset;
      DestStream.CopyFrom(SourceStream, SourceStream.Size - HeaderOffset);

      BMP := TBitmap.Create;
      Try
        DestStream.Position := 0;
        BMP.LoadFromStream(DestStream);

        GIF := TGIFImage.Create;
        Try
          GIF.Assign(BMP);
          GIF.OptimizeColorMap;
          GIF.SaveToFile(AFileName);
        Finally
          GIF.Free;
        End;
      Finally
        BMP.Free;
      End;
    Finally
      DestStream.Free;
    End;
  Finally
    SourceStream.Free;
  End;
End;


end.