Question

Based on this article:

I use this code to make some animation on a given Window Handle while doing some job on my database:

while not Terminated do 
begin
// some code....

// draw onto the Window DC
DC := GetDC(FWnd); // FWnd is the Window Handle
// DC := GetDCEx(FWnd, 0, DCX_VALIDATE or DCX_LOCKWINDOWUPDATE);
if DC <> 0 then
  try
    BitBlt(DC,
      FPaintRect.Left,
      FPaintRect.Top,
      ImageRect.Right,
      ImageRect.Bottom,
      Bitmap.Canvas.handle,
      0, 0,
      SRCCOPY);
  finally
    ReleaseDC(FWnd, DC);
  end;

  // more code....

end; // end while

Is it thread safe, or should I somehow Lock the DC?

Also, Can I use the GetDCEx?
Thanks.

Answer 1

No, your code is not threadsafe assuming that the window handle (FWnd) is created in main (GUI) thread. A standard VCL approach is to call all GDI functions in GUI thread, via Synchronize or Queue methods of TThread class.