GdkWindow for wxWidgets

Question

For many years I have been using this code to get a GdkWindow, but now it doesn't seem to return a result that can be used in other gdk functions. Any suggestions?

  GdkWindow *Tvgintf_wx::getSurface (Point2D sizeParam) {
    dcbuffer = new wxBitmap(sizeParam.getX(), sizeParam.getY());
    wxMemoryDC memory (*dcbuffer);
    GdkWindow* result = (GdkWindow*)memory.GetHandle();
    memory.SelectObject( wxNullBitmap);
    return result;
  }

Answer 1

wxDC::GetHandle() not always makes sense, so not always returns a valid pointer.

For your case, wxMemoryDC::GetHandle() in GTK+ returns a GdkPixmap*. And according to GDK docs a GdkPixmap is a GdkDrawable, not a GdkWindow (which derives from GdkDrawable as GdkPixmap does).

So, the line

GdkWindow* result = (GdkWindow*)memory.GetHandle();

should be

GdkDrawable* result = (GdkDrawable*)memory.GetHandle();

I don't know why your (erroneous) code worked for you in past years. Likely, the common parts of GdkWindow and GdkDrawable structs were hidding the consequences of the unsafe casting, and now something in newer gdk/gtk or the functions you use rise the issue.