[vlc-devel] [PATCH] win32/drawable: process the WM_SIZE asynchronously

[Alexandre Janniaux]

Hi,

After some thoughts on it, isn't Thomas's suggestion more
adequate than Steve's one? Though less elegant, it actually
does not break the synchronicity of the resize, right?

Regards,
--
Alexandre Janniaux
Videolabs

On Mon, Mar 01, 2021 at 11:57:16AM +0100, Thomas Guillem wrote:
> I tested it, no more deadlock and better than my proposal.
>
> LGTM.
>
> On Mon, Feb 22, 2021, at 15:29, Steve Lhomme wrote:
> > On 2021-02-22 14:20, Alexandre Janniaux wrote:
> > > Hi,
> > >
> > > How does resizing work with asynchronous posting? I had the
> > > feeling that win32 API needed synchronous resizing to be able
> > > to achieve smooth resizing, is it wrong or unrelated here?
> >
> > Technically our underlying HWND is still there but possibly not matching
> > the parent. If it's too small the area may not be looking too good. If
> > it's too big it's clipped in the parent so no artefacts, just not
> > displayed at the right size. There is nothing in Windows that says our
> > HWND needs to fit exactly in its parent, so a lag here won't cause
> > troubles, just possibly some visual oddness.
> >
> > In practice I have not seen such things. But on my system I can hardly
> > get the original reentrant issue anyway, so the resizing is applied
> > quickly.
> > > Regards,
> > > --
> > > Alexandre Janniaux
> > > Videolabs
> > >
> > > On Mon, Feb 22, 2021 at 08:25:30AM +0100, Steve Lhomme wrote:
> > >> The vout_window_ReportSize call may make changes in underlying HWND's which in
> > >> turn might make reentrant calls to WinVoutEventProc, which might in turn call
> > >> WM_SIZE in the same stack (when resizing quickly).
> > >>
> > >> vout_window_ReportSize() is not reentrant so we should avoid calling it in
> > >> calls that might be reentrant (WM_SIZE in this case).
> > >>
> > >> We keep the latest WM_SIZE so when the asynchronous call is done, we already
> > >> have the most up to date value.
> > >> ---
> > >>   modules/video_output/win32/drawable.c | 10 +++++++++-
> > >>   1 file changed, 9 insertions(+), 1 deletion(-)
> > >>
> > >> diff --git a/modules/video_output/win32/drawable.c b/modules/video_output/win32/drawable.c
> > >> index 90106558848..c6f2f573a2f 100644
> > >> --- a/modules/video_output/win32/drawable.c
> > >> +++ b/modules/video_output/win32/drawable.c
> > >> @@ -77,6 +77,8 @@ struct drawable_sys
> > >>       HWND hWnd;
> > >>       HWND embed_hwnd;
> > >>       RECT rect_parent;
> > >> +
> > >> +    unsigned int width, height;
> > >>   };
> > >>
> > >>   static LRESULT CALLBACK WinVoutEventProc(HWND hwnd, UINT message,
> > >> @@ -131,7 +133,13 @@ static LRESULT CALLBACK WinVoutEventProc(HWND hwnd, UINT message,
> > >>           return 0;
> > >>
> > >>       case WM_SIZE:
> > >> -        vout_window_ReportSize(wnd, LOWORD(lParam), HIWORD(lParam));
> > >> +        sys->width  = LOWORD(lParam);
> > >> +        sys->height = HIWORD(lParam);
> > >> +        PostMessage(hwnd, WM_USER, 0, lParam);
> > >> +        return 0;
> > >> +
> > >> +    case WM_USER:
> > >> +        vout_window_ReportSize(wnd, sys->width, sys->height);
> > >>           return 0;
> > >>
> > >>       default:
> > >> --
> > >> 2.29.2
> > >>
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