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

[Steve Lhomme]

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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