[PATCH] user32: Allow WM_CAPTURECHANGE indicating SetCapture() parameter.

[Christopher Thielen]

Thank you Alexandre, you're absolutely right.

Below is a further analysis on toolbar, trackbar, and button:

Toolbar: Assumes a WM_CAPTURECHANGED messages implies a toolbar button 
is no longer pressed. The proposed patch would therefore break existing 
behavior if and only if the toolbar code also calls SetCapture() on 
itself while it already has capture. Toolbar currently only calls 
SetCapture() in the case of a LButtonDown on itself. Notably, another 
piece of code could in theory call SetCapture() on the toolbar's hWnd as 
well.

Trackbar: Assumes a WM_CAPTURECHANGED message implies a TB_ENDTRACK, 
again, only breaking current behavior if trackbar calls SetCapture() 
while it already has mouse capture. Like Toolbar above, Trackbar only 
calls SetCapture() if it receives a LButtonDown. Again, another piece of 
code could in theory call SetCapture() and pass the trackbar's hWnd even 
when it already has mouse focus.

dlls/user32/button.c: Causes a button with mouse focus and 
BUTTON_BTNPRESSED to lose its highlighted state as documented at 
https://msdn.microsoft.com/en-us/library/aa931528.aspx. Like the two 
cases above, button would need to call SetCapture() on itself for this 
patch's behavioral changes to be relevant. Button calls SetCapture() on 
KEYDOWN, LBUTTONDBCLK, and LBUTTONDOWN.

I would be grateful if a seasoned Wine developer could chime in as to 
whether or not the above scenarios are possible, or what further 
research they would recommend. Otherwise, one safe course of action 
could be to emulate the existing Wine behavior of requiring the newly 
mouse-focused hWnds to be different from the existing hWnd in order for 
these three code paths to run (thus maintaining the current behavior for 
these specific cases). That would correct the SetCapture() behavior, fix 
the documented bug, and prevent any side effects in this code, though 
I'd prefer to better understand the above three code paths than rely on 
that idea.

Thank you again to anyone who can offer any guidance.

On 01/14/2016 03:02 AM, Alexandre Julliard wrote:
> Christopher Thielen <cthielen at gmail.com> writes:
>
>> dlls/comctl32/toolbar.c:	case WM_CAPTURECHANGED:
>>
>> Probably fine? Appears to be a ToolbarProc translating window messages into toolbar-based equivalents.
>
> That's too superficial, you need to look into what it's doing with the
> message. In this case it's clearly assuming that capture is lost, which
> wouldn't be the case with your change. The same thing probably applies
> to other message handlers.
>