bug#55208: 29.0.50; MS-Windows GUI selection dialogs and double-buffering

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: 55208@debbugs.gnu.org
> Date: Mon, 02 May 2022 09:10:53 +0800
> 
> But try adding some code along the following lines under `WM_PAINT' in
> `w32_msg_pump':

w32_msg_pump doesn't handle WM_PAINT, so I'm not sure what you mean
here.  Also, AFAIK w32_msg_pump runs in a separate thread, so is it
safe to call BitBlt from that thread?

>   	if (popup is active)
> 	  {
> 	    enter_crit ();
> 	    if (FRAME_OUTPUT_DATA (f)->paint_dc)
> 	      {
> 		BeginPaint (hwnd, &paintStruct);
> 
> 		BitBlt (FRAME_OUTPUT_DATA (f)->paint_buffer_handle,
> 			0, 0, FRAME_PIXEL_WIDTH (f), FRAME_PIXEL_HEIGHT (f),
> 			FRAME_OUTPUT_DATA (f)->paint_dc, 0, 0, SRCCOPY);
> 
> 		EndPaint (hwnd, &paintStruct);
> 	      }
> 	    leave_crit ();
> 
> 	    return 0;
> 	  }
> 
> (I don't know how to implement the "popup is active" part,
> unfortunately.)

I do know, but the above issues bother me more, so I didn't yet try
this.

Thanks.