[vtkusers] Bug in vtkWin32OpenGLRenderWindow when using own Interactor and windowhandle

[Sander Niemeijer]

I was trying to get the wxVTKWindow by David Marshall and Brian Todd 
class to work under Windows but encountered some illegal memory access 
when destructing the wxVTKWindow. Something that didn't happen when 
running on a unix system. After some digging I found the root cause of 
this problem:

It seems that vtkWin32OpenGLRenderWindow in its destructor checks 
whether it owns the windowhandle. If it does it will clean up nicely. 
However with wxVTKWindow the windowhandle provided by wxWindows is used 
and thus when vtkWin32OpenGLRenderWindow gets destructed the cleanup 
part of the destructor is not called. This means that 
vtkWin32OpenGLRenderWindow::Clean()  will not be called and 
ren->SetRenderWindow(NULL) will also not be called. This means that 
after the destruction of the renderwindow the renderers (which haven't 
reached their referencecount=0, because they are still referenced by an 
InteractorStyle) have a reference to a non-existing renderwindow. In my 
code this caused a problem when trying to destruct the 
renderwindowinteractor, because at some point a 
vtkOpenGLPolyDataMapper::ReleaseGraphicsResources(vtkWindow *win) was 
called with this illegal windowreference and thus my program crashed at 
win->MakeCurrent().

The problem does not appear on unix because vtkXOpenGLRenderWindow 
doesn't check for ownership of the windowhandle.

I am not sure how to fix this bug properly, because I don't really know 
why the check for ownership is done inside the 
vtkWin32OpenGLRenderWindow destructor. My guess for the fix would be:
---
if (this->WindowId)
{
	this->Clean();
	if (this->OwnWindow)
	{
		ReleaseDC(this->WindowId, this->DeviceContext);
		// can't set WindowId=NULL, needed for DestroyWindow
		this->DeviceContext = NULL;

		// clear the extra data before calling destroy
		SetWindowLong(this->WindowId,4,(LONG)0);
		DestroyWindow(this->WindowId);
	}
}
---
but then again, I'm no windows programming expert, so I could be 
completely wrong.

P.S. The current hack I use in my program to eliminate the illegal 
memory access is to explicitly set the renderwindow of the render to 
NULL just before I delete the renderwindow and renderwindowinteractor 
(=wxVTKwindow).

Regards,
Sander Niemeijer