Delphi Magazine Collection 2001/Delphi Magazine Collection 20001 (2001).iso/DISKS/ISSUE03/CLINIC/LISTING3.PAS

Pascal/Delphi Source File | 1995-07-28 | 906 b | 26 lines

  procedure TForm1.Button1Click(Sender: TObject);
  var
    LoopX, LoopY: Word;
  begin
    { save typing this all the time }
    with Image1.Picture do
      { Canvas property is only in bitmaps }
      if Graphic is TBitmap then
        with Graphic as TBitmap do
          { invert all pixels a column at a time }
          for LoopX := 0 to Pred(Width) do
          begin
            for LoopY := 0 to Pred(Height) do
            begin
              Canvas.Pixels[LoopX, LoopY] := clWhite - Canvas.Pixels[LoopX, LoopY];
            end;
            { standard technique to stop flickering on VGA }
            while Port[$3DA] and 8 = 0 do;
            { be multi-user friendly - yield after each column }
            Application.ProcessMessages;
            { also let user terminate app }
            if Application.Terminated then
              Break;
          end;
  end;