Re: [Gzz] Background

[Tuomas Lukka]

On Thu, Sep 05, 2002 at 12:52:36PM +0200, Benja Fallenstein wrote:
> Tuomas Lukka wrote:
> 
> >I'm saying that the ordering of drawing different things is different
> >between OpenGL and AWT for two important reasons:
> >
> >     - AWT doesn't have a depth buffer, have to draw back to front
> >     - OpenGL has all kinds of funny modes and it's a LOT faster
> >       to draw the same kinds of things at the same time; and also
> >       it's good to allow the user to set and reset modes at whim.
> >
> 
> Ah, moment, maybe there was a misunderstanding. I'm not saying that 
> OpenGL should draw vobs in any particular order: I'm saying that the end 
> result on the screen should look like in AWT. I.e., let's say you have 
> overlapping cells two cells, A and B:
> 
> +-------+
> |   A   +-----+
> +-------+ B   |
>       +-------+
> 
> 
> In these cells, you should see the content of A over the background of A 
> over the content of B over the background of B. You do not, for example, 
> want to see the content of B shown over the background of A. This is 
> what I care about, not warping OpenGL to draw things with the algorithm 
> AWT uses ;-)

Yes, I know. The problem is related to what you said earlier about 
the background being in coordsys 0. The problem is that the background
vob *doesn't* obey the Z buffer (it clears it) so there the difference
between the two drawing mechanisms is apparent. In AWT, when you draw
something, it's drawn immediately so you have to depth-sort things.
In OpenGL you have the Z buffer so for most things you don't have
to worry about the order.

With the exception of setting modes, and (the current subject) the
background vob. If you draw the background vob at any other time than
right at the beginning, you'll wipe out everything you had drawn
until that. That's the same as in AWT, but here the ordering
is important on the OpenGL side.

        Tuomas