DX6 more compatibility.

[Michael Karcher]

Am Freitag, den 27.06.2008, 07:46 -0400 schrieb Christopher J. Ahrendt:
> > If I get it right, the correct fix is to add a thunk vtable for
> > IDirectDraw4 that uses relaxed parameter checks on AddAttachedSurface.
> > 
> > Regards,
> >   Michael Karcher
> Are we sure its 6.0 and not 6.1? from what I remember and can find 6.0 
> was mainly for the dreamcast and possibly CE.
I don't know. Probably it is 6.1. The Interface is called IDirectDraw6.
It does not matter in this case.

> I don't have my manual 
> handy (stuck in a bloody airport all night due to weather) but I think 
> it should work with a 6.1 implementation which wouldn't need to be 
> thunk'ed just the relaxed parm check.
The problem is that currently, if the application requests a
IDirectDrawSurface4 what it gets is a IDirectDrawSurface7. Which is (on
the first look) not a issue, as the vtables are compatible (same
functions with same signature at same offsets, except for
IDirectDrawSurface7 having added some functions at the end), but on the
second look, the IDirectDrawSurface7 vtable contains the pointer to the
strict AddAttachedSurface, whereas the vtable for IDirectDraw4 must
contain a pointer to a relaxed AddAttachedSurface. This we need two
different vtables (You can query an IDirectDraw7 and an IDirectDraw4
surface on the same object, so a flag in the object does not do,
probably[1]) to get the different behaviours. Two different vtables for
the same object inherently is thunking.

Regards,
  Michael Karcher

[1] In fact, an API test is required. Strict or relaxed semantics might
also depend on how the surface was created (from IDirectDraw4 or
IDirectDraw7) instead of the interfaced used to add an attached surface.
This would be strange IMO, as the idea about COM is that the interface
describes semantics that work regardless how the object was created, but
let's test that, nevertheless.