Re: [PATCH 3/4] ddraw: Don't read clipper methods from the vtable.

[Henri Verbeet]

On Wed, 13 Mar 2019 at 15:48, Stefan Dösinger  wrote:
> struct ddraw_clipper *unsafe_impl_from_IDirectDrawClipper(IDirectDrawClipper *iface)
>  {
> - struct ddraw_clipper *clipper;
> - if (!iface)
>        return NULL;
> -
>
> assert(iface->lpVtbl == &ddraw_clipper_vtbl);
> -
>
> return impl_from_IDirectDrawClipper(iface);
> - clipper = impl_from_IDirectDrawClipper(iface);
> -
> - if (!clipper || iface->lpVtbl != &ddraw_clipper_vtbl)
> -
>    WARN("The application passed us a bad clipper object.\n");
> -
> - return clipper;
>
> }

"if (!ddraw_clipper_is_valid(clipper)) return NULL;", right?
> +/* Invoke clipper methods directly instead of going through the vtable. Clipper methods have
> -
> - protections against invalid clipper objects, but that won't work if we crash when reading
> -
> - the vtable. */

Sure, but that protection involves pretty much just calling
ddraw_clipper_is_valid(). Just calling that function in the
appropriate place in e.g. ddraw_surface_blt_clipped() seems both nicer
and more robust.