Question

I have some troubles with rendering my canvas. Actually I’m trying to write game like space invaders, without using any OpenGL or DirectX. So at the background I have moving sky, and jet moving over it. But the jet is blinding, and sky moves not uniformly. Here’s my code

  sky := TBitmap.Create;
  sky.LoadFromFile('sky.bmp');
  jet := TBitmap.Create;
  jet.LoadFromFile('jet.bmp');
  jet.Transparent := True;

  while True do
  begin
       for k := 0 to sky.Height do
       begin
          for i := -1 to (pbMain.Height div sky.Height) do
          begin
                for j := 0 to (pbMain.Width div sky.Width) do
                begin
                    pbMain.Canvas.Draw(nx, ny, jet);
                    pbMain.Canvas.Draw(j*sky.Width, k + i*sky.Height, sky);
                end;
                Application.ProcessMessages;
          end;
          Sleep(1);
       end;
  end;

Thank you.

Answer 1

You can’t write a standard Windows app like that. You have to do your painting in response to WM_PAINT messages. In Delphi terms this equates to overriding the Paint method of a TWinControl descendent, or perhaps using a TPaintBox and providing an OnPaint event handler. I’m going to assume that you use a TPaintBox.

If you need to avoid flicker it is common practice to draw to an off-screen bitmap and then show this when you are asked to paint.

Your application should probably use a timer control to provide a regular pulse. Then, on each pulse, update your off-screen bitmap. Then call Invalidate on your paint box to force a paint cycle.

The code might look like this:

procedure TMainForm.RefreshTimerTimer(Sender: TObject);
begin
  RedrawOffscreenBitmap;
  PaintBox.Invalidate;
end;

procedure TMainForm.RedrawOffscreenBitmap;
begin
  //paint to FOffscreenBitmap
end;

procedure TMainForm.PaintBoxBox(Sender: TObject);
begin
  PaintBox.Canvas.Draw(0, 0, FOffscreenBitmap);
end;