Image can show preview-image in dwg file (autocad file name)

Problem/Question/Abstract:

I have writen a component from image which can show the preview-image in dwg file

Answer:

unit DWGView;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  ExtCtrls;

type
  BITMAPINFO256 = record
    bmiHeader: BITMAPINFOHEADER;
    bmiColors: array[0..255] of RGBQUAD;
  end;

type
  TNoPreviewEvent = procedure(Sender: TOBject) of object;
  TFileErrorEvent = procedure(Sender: TOBject; DWGName: string) of object;

  TDWGView = class(TImage)
  private
    FDWGVersion: string;
    FDWGFile: string;
    FNoPreviewEvent: TNoPreviewEvent;
    FOnFileError: TFileErrorEvent;
    FImage: TImage;
    procedure SetDWGFile(const Value: string);
    procedure SetFImage(const Value: TImage);
    { Private declarations }
  protected
    procedure ReadDWG;
    constructor TDWGView;
    { Protected declarations }
  public
    { Public declarations }
  published
    { Published declarations }
    property Image: TImage read FImage write SetFImage;

    property DWGFile: string read FDWGFile write SetDWGFile;
    property DWGVersion: string read FDWGVersion;
    property OnNoPreview: TNoPreviewEvent read FNoPreviewEvent write FNoPreviewEvent;
    property OnFileError: TFileErrorEvent read FOnFileError write FOnFileError;
  end;

procedure Register;

implementation

procedure Register;
begin
  RegisterComponents('Voice', [TDWGView]);
end;

procedure TDWGView.ReadDWG;
var
  DWGF: TFileStream; // ?�???ġ?
  MemF: TMemoryStream; // ??µ????�?�
  BMPF: TMemoryStream; // ?»?�?ġ?
  SentinelF: TMemoryStream; //?�����¶?  16�ֽ?

  bif: BITMAPINFO256; // ?»?�?ġ??�?�
  bfh: BITMAPFILEHEADER; // ?»?�?ġ??ġ??· 14�ֽ?

  PosSentinel: LongInt; // ?�����¶??»�?

  LenPreview: Integer; // �??�����¶?�®??�?¬�?�???��¬??µ?µij�¶?
  RasterPreview: ShortInt; // ?µ?�?�???��¬????µ�?»¬�µ?�ֽ?�???
  // 0  �»±�???�???��¬ 1  ±�??BMP?��¬
    // 2  ±�??WMF?��¬    3  ?¬?±±�??BMP??WMF?��¬
  PosBMP: Integer; // ?��¬µ�տ?µ?»�?�¬�»?»¶«???»?�
  LenBMP: Integer; // ?��¬��¶?�¬�»?¬BITMAPFILEHEADER??µ?�¬�»?»¶«???»?�
  IndexPreview: Integer;
  TypePreview: Shortint; // ?��¬????
begin
  if Assigned(FOnFileError) then
    FOnFileError(Self, FDWGFile);
  DWGF := TFileStream.Create(FDWGFile, fmOpenRead);
  BMPF := TMemoryStream.Create;
  MemF := TMemoryStream.Create;
  SentinelF := TMemoryStream.Create;
  try
    SetLength(FDWGVersion, 6);
    DWGF.ReadBuffer(FDWGVersion[1], 6);
    DWGF.Position := 13; // ?ġ?�??�13�¦�¬???�����¶?
    DWGF.Read(PosSentinel, 4);
    DWGF.Position := PosSentinel;
    SentinelF.CopyFrom(DWGF, 16); // ¶????�����¶?
    DWGF.Read(LenPreview, 4); // ¶???
    DWGF.Read(RasterPreview, 1); // ¶????��¬????
    for IndexPreview := RasterPreview - 1 downto 0 do
    begin
      MemF.Position := 0;
      MemF.CopyFrom(DWGF, 9); // ?��¬???�?� 9�ֽ?
      MemF.Position := 0;
      MemF.Read(TypePreview, 1); // TypePreview ?��¬????
      case TypePreview of
        1: ; // ?�??µ�???��???
        2:
          begin
            // BMP?��¬,??DWG?ġ?�?±���µ�BMP?��¬?�????????�?BMP±�·¶µ�
            // ?�?�?ġ???µ?�¬µ«??�»±���BITMAPFILEHEADER??µ?
            MemF.Position := 1;
            MemF.Read(PosBMP, 4); // 2,5
            MemF.Read(LenBMP, 4); // 6,9
            DWGF.Position := PosBMP;
            DWGF.ReadBuffer(bif, sizeof(bif));

            with bif do
            begin
              bmiColors[0].rgbBlue := 0;
              bmiColors[0].rgbGreen := 0;
              bmiColors[0].rgbRed := 0;

              bmiColors[225].rgbBlue := 255;
              bmiColors[225].rgbGreen := 255;
              bmiColors[225].rgbRed := 255;
            end;

            bfh.bfType := $4D42;
            bfh.bfSize := LenBMP + sizeof(bfh); //
            bfh.bfReserved1 := 0;
            bfh.bfReserved2 := 0;
            bfh.bfOffBits := 14 + $28 + 1024;

            BMPF.Position := 0;
            BMPF.Write(bfh, sizeof(bfh));
            BMPF.WriteBuffer(bif, sizeof(bif));
            BMPF.CopyFrom(DWGF, LenBMP - 1064);
            BMPF.Position := 0;
            Picture.Bitmap.LoadFromStream(BMPF);
          end;
        3: ; // WMF?ġ?�¬?��?22�ֽ?��µ�Aldus?ġ??·
      end;

    end;
  finally
    SentinelF.Free;
    MemF.Free;
    DWGF.Free;
    BMPF.Free;
  end;

end;

procedure TDWGView.SetDWGFile(const Value: string);
begin
  FDWGFile := Value;
  ReadDWG;
end;

procedure TDWGView.SetFImage(const Value: TImage);
begin
  FImage := Value;
end;

constructor TDWGView.TDWGView;
begin
  //TODO: Add your source code here
  FDWGFile := '';
  FDWGVersion := '';
end;

end.