A vrend_context structure contains a current vrend_sub_context, which
in turn keeps references on various resources like textures, VBOs,
index buffers, etc. which are used for actual drawing operations.
Certain actions can change the current sub-context in use.
There is a split of what resources are cleaned up directly as part of
a context destruction and which are handled by the sub-context
destruction. VBOs, while referenced by sub-contexts, are cleaned up by
the context. To do that, it uses the at the time of destruction
current sub-context to access these. As a result, only the VBOs in the
active sub-context are cleaned up; every other sub-context referenced
by the context will keep references to the VBOs used.
The responsibility of VBO dereferencing is moved to the destruction of
the sub-context, so all VBOs, not just the one from the current
sub-context, are dereferenced during the destruction of a context.
Closes#198
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>
Robert Wetzel
53774760dd