Date   : Tue, 19 Jul 1994 08:49:36 +0100 (BST)
From   : amh15@... (Alan Hart)
Subject: Re: Teletext graphics question...

> > As I remember, 'hold' causes all colour-change characters to appear as the
> > previous graphics character [i.e. the one to the left] whilst still changing
> > the colour. The purpose of this is to give continuous blocks of graphics
> > which change colour, e.g. a narrow line changing colour along its
> > [horizontal] length with no breaks. There was a game that used this on the 
> > scores page!
> > 
> > Release reverts to normal mode.
> 
> Sounds like this shouldn't be too hard to implement.  Can you remember
> how the hold character and the character on it's left appear on the screen ?

I think you normally put it at the edge of the screen. I think it looks like 
a space, but I wouldn't swear to it.

> > > Also, there's a "conceal" display, which I assumes makes all characters
> > > from that position onwards appear blank, but how is it turned off ?
> > 
> > I think you press the 'reveal' button on your remote control [oh dear, I 
> > don't seem to have one] :)
> 
> It would appear that "conceal" is effectively useless in the context of
> the beeb display, then ?

Well, you could implement reveal in BBC programs by poking away the 'conceal'
bytes. Or maybe there's a tweak you can do with the 5050 to cause reveal to
occur. I wonder what the Acorn Teletext Adaptor did.

Alan

 Alan Hart  -  amh15@...  -  University of Cambridge, UK