[wxPython] Problems with wxDragImage on Windows in latest binary release

wxPython Users
1

Hello, I'm new to the list. I've been doing some wxPython development under
Windows 98 using an older binary release (the release from June of last
year). I just upgraded to the latest binary release. The new features are
great (particularly the new popup windows), but I'm having some problems
with wxDragImage.

With the earlier release I was having the problem that sometimes when memory
was low the bitmap wasn't being created when using wxDragImage in fullscreen
mode, and it wasn't throwing an exception at that point, just silently
failing. But other than that, it worked perfectly. With the latest release
the same code exhibits serious problems. All is well as long as the pointer
is over the window that has captured the mouse for the wxDragImage
operation, but when the pointer leaves the capturing window two things
happen- the capturing window starts continually redrawing itself, and the
dragged image starts jumping around relative to the pointer. This doesn't
happen if you very slowly pull the pointer out of the capturing window.

My code is based on the demo for wxDragImage, which also exhibits this
behaviour. So it seems to me as if either the demo is doing something
incorrectly, or there is a bug in the underlying libraries. Since it worked
properly with an earlier release, and it can be avoided if you slowly mouse
out of the capturing window, my guess is the latter. I searched the list
archive, but I couldn't find anything about it.

Anyway, on a hunch I defined a handler for the capturing window's
EVT_LEAVE_WINDOW event, and defined it as just pass. This stopped the
problem, but it makes me a little nervous- I don't know wx well enough yet
to know if this might break something else; also it doesn't seem to be
documented anywhere, and it doesn't seem to me that you should have to do
this. Of course I may just be misunderstanding something :).

If this is ground that has already been covered, I apologize for bringing it
up again, but I couldn't find anything about it in the docs or in the list
archive.

Thanks
Tagore Smith

2

Anyway, on a hunch I defined a handler for the capturing window's
EVT_LEAVE_WINDOW event, and defined it as just pass. This stopped the
problem, but it makes me a little nervous- I don't know wx well enough yet
to know if this might break something else; also it doesn't seem to be
documented anywhere, and it doesn't seem to me that you should have to do
this. Of course I may just be misunderstanding something :).

On MSW EVT_LEAVE_WINDOW events are generated by wx because the system
doesn't send an equivallent message. Something has probably changed in the
default handler for it, or perhaps where it is generated.

I looked at the C++ sample for wxDragImage and it catches all mouse events
with EVT_MOUSE_EVENTS instead of just the ones that are needed like is done
in the Python sample. That probably prevents the generation of
EVT_LEAVE_WINDOW so it is essentially the same as what you've done.

ยทยทยท

--
Robin Dunn
Software Craftsman
robin@AllDunn.com Java give you jitters?
http://wxPython.org Relax with wxPython!

3

Robin Dunn wrote:

On MSW EVT_LEAVE_WINDOW events are generated by wx because the system
doesn't send an equivallent message. Something has probably changed in

the

default handler for it, or perhaps where it is generated.

I looked at the C++ sample for wxDragImage and it catches all mouse events
with EVT_MOUSE_EVENTS instead of just the ones that are needed like is

done

in the Python sample. That probably prevents the generation of
EVT_LEAVE_WINDOW so it is essentially the same as what you've done.

OK then I'll assume it is both safe and necessary :). Thanks for the reply.
As soon as I have a chance I'll take a look at the sources and see if I can
figure out what changed.

Thanks
Tagore Smith