[Audacity-devel] wxGetClientDisplayRect

[Ed M. <edg...@ya...>]

Delving into the source code for wxRect wxGetClientDisplayRect() I learned some interesting things. Given that my concern was solely with width and height, that is where I focused my inspection. I found that to determine width and height 2 conditions for the Microsoft case exist; for other platforms things are a little confusing to me.
 
In file wx2.8.10\src\common\gdicmn.cpp (line 848):
wxRect wxGetClientDisplayRect()
{
    int x, y, width, height;
    wxClientDisplayRect(&x, &y, &width, &height);  // call plat-specific version
    return wxRect(x, y, width, height);
}
 
and in file wx2.8.10\src\msw\utilsgui.cpp (line 337; i.e. building for msw):
void wxClientDisplayRect(int *x, int *y, int *width, int *height)
{
#if defined(__WXMICROWIN__)
    *x = 0; *y = 0;
    wxDisplaySize(width, height);
#else
    // Determine the desktop dimensions minus the taskbar and any other
    // special decorations...
    RECT r;
    SystemParametersInfo(SPI_GETWORKAREA, 0, &r, 0);
    if (x)      *x = r.left;
    if (y)      *y = r.top;
    if (width)  *width = r.right - r.left;
    if (height) *height = r.bottom - r.top;
#endif
}
 
and in file wx2.8.10\src\unix\displayx11.cpp (line 327):
#if defined(__WXGTK__) || defined(__X__)
[... at line 348]:
// NB: this function is implemented using X11 and not GDK calls as it's shared
//     by wxGTK[12], wxX11 and wxMotif ports
void wxClientDisplayRect(int *x, int *y, int *width, int *height)
{
    Display * const dpy = (Display *)wxGetDisplay();
    wxCHECK_RET( dpy, _T("can't be called before initializing the GUI") );
    const Atom atomWorkArea = XInternAtom(dpy, "_NET_WORKAREA", True);
    if ( atomWorkArea )
    {
        [...]
        if ( XGetWindowProperty
             (
                 [...]
             ) == Success && workareas )
        {
            wxX11Ptr x11ptr(workareas); // ensure it will be freed
                 [...]
            if ( actualType != XA_CARDINAL ||
                    format != 32 ||
                        numItems != 4 )
            {
                wxLogDebug(_T("XGetWindowProperty(\"_NET_WORKAREA\") failed"));
                return;
            }
                 [...]
        }
    }
    // if we get here, _NET_WORKAREA is not supported so return the entire
    // screen size as fall back
                 [...]
    wxDisplaySize(width, height);
}
#else // !(wxGTK or X)
void wxClientDisplayRect(int *x, int *y, int *width, int *height)
{
                 [...]
    wxDisplaySize(width, height);
}
#endif // wxGTK or X
 
in file wx2.8.10\src\msw\utilsgui.cpp (line 278 -- note that as far as I can tell, this is the only definition and declaration of this function even though it's called in file wx2.8.10\src\unix\displayx11.cpp):
// Get size of display
void wxDisplaySize(int *width, int *height)
{
#ifdef __WXMICROWIN__
                 [...]
    if ( width )
        *width = rect.right - rect.left;
    if ( height )
        *height = rect.bottom - rect.top;
#else // !__WXMICROWIN__
                 [...]
    if ( width )
        *width = ::GetDeviceCaps(dc, HORZRES);
    if ( height )
        *height = ::GetDeviceCaps(dc, VERTRES);
#endif // __WXMICROWIN__/!__WXMICROWIN__
--------------------------------------------------------- 
Note that in file:
Audacity 1.3.9b\src\Project.cpp(527):
// BG: The default size and position of the first window
void GetDefaultWindowRect(wxRect *defRect)
{
[527]   *defRect = wxGetClientDisplayRect();
   defRect->width = 600;
   defRect->height = 400;
[...]
which assumes the platform is capable of supporting a specified resolution.
Please also note that in file wx2.8.10\src\unix\displayx11.cpp (line 389):
                wxLogDebug(_T("XGetWindowProperty(\"_NET_WORKAREA\") failed"));
                return;
the function returns without setting any values for x, y, width or height and might better return a bool that a void.

I suppose that needs to be taken up with the wxWidgets developers. Still, Audacity does rely on the x and y values being correctly filled out.
In fileAudacity 1.3.9b\src\Project.cpp(line 54 7):
  wxRect defWndRect;
  [...]
  GetDefaultWindowRect(&defWndRect);
relies on the default constructor:
wxRect()         : x(0), y(0), width(0), height(0)         { }
which at least seeds the values with a non-random number (0). As a sanity check Audacity might check the value of either width or height to ensure that it is not 0.

-Ed Musgrove