How to flip a bitmap image

Windows with Delphi
Windows API (94)
Windows Filesystem (41)
Windows Forms (69)
Windows Graphics (38)

How to flip a bitmap image

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Question:
Is there a RTL or API function to flip a bitmap image?

Answer:

You can use the Windows function StrechBlt() to help you with this. Some older versions of Windows (Windows 3.1, Windows 95) had problems with the graphic card drivers for these functions.
I myself had a Diamond Stealth (or was it a Diamond Speedstar?) where this Windows function was not implemented properly in the Windows 95 driver. There is another Win API function for it.. for device independant bitmaps - it is called StretchDIBits(), but StretchBlt() is faster.

And nowadays (June 2004), all graphic cards should be supported properly.

type
  TMirror = (mtHorizontal, mtVertical, mtBoth );

procedure Mirror(Picture: TPicture; MirrorType: TMirror);
var
  MemBmp: Graphics.TBitmap;
  Dest: TRect;
begin { Mirror }
  if Assigned(Picture.Graphic) then
  begin
    MemBmp := Graphics.TBitmap.Create;
    try
      MemBmp.PixelFormat := pf24bit;
      MemBmp.HandleType := bmDIB;
      MemBmp.Width := Self.Picture.Graphic.Width;
      MemBmp.Height := Self.Picture.Height;
      MemBmp.Canvas.Draw(0, 0, Picture.Graphic);

      case MirrorType of
        mtHorizontal:
          begin
            //SpiegelnVertikal(MemBmp);
            //SpiegelnHorizontal(MemBmp);
            Dest.Left := MemBmp.Width;
            Dest.Top := 0;
            Dest.Right := -MemBmp.Width;
            Dest.Bottom := MemBmp.Height
          end;
        mtVertical:
          begin
            Dest.Left := 0;
            Dest.Top := MemBmp.Height;
            Dest.Right := MemBmp.Width;
            Dest.Bottom := -MemBmp.Height
          end;
        mtBoth:
          begin
            Dest.Left := MemBmp.Width;
            Dest.Top := MemBmp.Height;
            Dest.Right := -MemBmp.Width;
            Dest.Bottom := -MemBmp.Height
          end;
      end; { case MirrorType }
      StretchBlt(MemBmp.Canvas.Handle, Dest.Left, Dest.Top, Dest.Right, Dest.Bottom,
                 MemBmp.Canvas.Handle, 0, 0, MemBmp.Width, MemBmp.Height,
                 SRCCOPY);

      Picture.Graphic.Assign(MemBmp);
      Invalidate
    finally
      FreeAndNil(MemBmp)
    end; { try }
  end; { Assigned(Picture.Graphic) }
end; { Mirror }

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