[wx2.8.0, wxGTK, gcc4.1.2] wxDC::Blit() and wxMask again

[Kövesdi György]

Hi,

I tried to put the SetMask() function call before the SelectObject() function, 
so the source is:

         wxMemoryDC mdc;
         wxBitmap bm(100, 100);
         bm.SetMask(new wxMask(bm, *wxBLUE));
         mdc.SelectObject(bm);
         mdc.SetBackground(*wxBLUE_BRUSH);
         mdc.SetPen(wxPen(wxColour(0, 0, 0), 8));
         mdc.Clear();
         mdc.DrawLine(5, 5, 20, 20);

         wxBitmap bm2(100, 100);
         wxMemoryDC dc2;
         dc2.SelectObject(bm2);
         dc2.SetBackground(*wxGREEN_BRUSH);
         dc2.Clear();
         dc2.Blit(0, 0, 100, 100, &mdc, 0, 0, wxCOPY, true);
         dc2.SelectObject(wxNullBitmap);
         mdc.SelectObject(wxNullBitmap);

         (void)new wxStaticBitmap(panel, wxID_ANY, bm2, wxPoint(300, 120));

This can be pasted into the file samples/controls/controls.cpp (at line 974 in 
2.8.0, or at line 981 in 2.6.3).

Funny thing happened: the result is sometimes good, and sometimes bad with the 
version 2.8.0. Starting the ./controls program the background is sometimes 
blue, sometimes green, and there is a noise in very few cases. I think there 
must be something uninitialized.
It does not work with the version 2.6.3 at all. (the background was always 
blue).

Is the behavior of the wxMask() changed in 2.8.0 ?

Regards:
Gyorgy Kovesdi

>1) in wxMSW CVS HEAD it asserts at bm.SetMask(new wxMask(bm, *wxBLUE)); 
saying
>that bm is already selected in another DC - and that's true. So I've moved 
this
>just after bm creation and before SelectObject() call.
>
>2) the MaskBlt() win32 API call seems to succeed and the mask passed to it
>seems valid to me so I'm not sure as why the code fails.
>I'd suggest you to rewrite it using directly win32 API and see if the problem
>persists... if you are not used to win32 API you can just copy & paste & 
adapt
>the win32 API calls done by wxWidgets functions (using a debugger to step 
into
>them).
>
>3) does it misbehave also on wxGTK?
>
>HTH,
>Francesco