When using pbuffer or back buffer offscreen rendering the content of
the drawable will have been overwritten. Thus the texture has to be
written into the drawable. An exception is the (pretty common) case
that the whole render target is cleared before rendering to it.
Previously the surfaces stored a flag if the system memory copy was
ahead of the gl copy(SFLAG_DIRTY) or the gl copy is
ahead(SFLAG_GLDIRTY). The pbuffer copy was 'managed' differently using
SFLAG_INPBUFFER and SFLAG_INTEXTURE.
This patch replaces them with 3 flags, INSYSMEM, INPBUFFER and
INTEXTURE which specify which copy contains the most up to date
copy. It is perfectly valid to have more than one of those flags
set. One must be set at least (except at init, when no content is in
the surface yet). When one copy is modified, the flags for the others
are removed.
The method is removed because it does not really help with
anything. It should not be exported from wined3d, there is no need for
the other libs to call it. It does not help abstraction and code
simplification in any way because it is very specific and the code
calling it has to know what is happening in the surface to use this
method.
OpenGL AUX buffers provide a way for offscreen rendering which is very
similar to our back buffer "offscreen" rendering emulation. Not all
card support aux buffers, but if they are available they are a nice
present which is easy to use.
