Re: [stella] TIA writes to overscan

Subject: Re: [stella] TIA writes to overscan
From: Greg Troutman <mor@xxxxxxx>
Date: Tue, 16 Sep 1997 07:53:21 -0700
Glenn Saunders wrote:
> On Mon, 15 Sep 1997, Robin Harbron wrote:
> > 2) Why is overscan differentiated from the main 192 line
> > display?  Can you not display graphics there?  Should
> > you blank the screen for that area?  Is there anything
> > special you should do in that area?

When your game gets big, you may need the processor time during overscan
to do off-screen calculations.  In Rescue, there is not enough time
during VBLANK to perform everything and I'm doing quite a lot in
overscan now.  Anyway, you don't need to do anything special, other than
count the scanlines to make sure you VSYNC at the right time. 
> As far as I know, this is just a LCD convention to insure that a game will
> be fully visible on all TVs.  It should be possible to extend your display
> a few pixels below and above the conventional 2600 display.  IMHO, most
> TVs have more visible bandwidth available than they did 20 years ago.

Yes, if you continue to write graphics during overscan, most of the
extra lines will display on all the televisions I've used for testing. 
In fact, the main set I use will display 222 lines, if I include all of
overscan in the display kernel.  Possibly even more, if I shorten
VBLANK, but I haven't tried that.
> The whole debate over 2600s generating closed captioning has to do with
> writing to the overscan area, for instance.

I didn't quite follow this thread.  Does anyone know of a web resource
for specs or overview on closed-captioning?


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