Date   : Mon, 02 Jul 2018 15:59:48 +0100
From   : soruk@... (Michael McConnell)
Subject: Announce: Brandy Basic - with teletext?!

I guess, with the way the screen is currently done (including the other 
modes) that it would be computationally far to expensive to scan the 
screen for what should be flashing pixels. For Mode 7 at the very least 
to get a 100% true emulation it would need to maintain a 1000 byte 
screen memory buffer (somewhat akin to the BBC Micro screen memory at 
&7C00) and re-render the entire screen periodically - and for each 
character addition, to allow for the cascade of changes that can happen 
if there is liberal use of VDU141, and to flash characters on and off. 
Rewriting the entire SDL frame would be quite expensive computationally, 
and if this were to be extended to the 16-colour modes (e.g. MODE 2) a 
second copy of the entire screen memory would have to be maintained, and 
the checking done at a pixel level.

Unless there's a clever way in SDL to do it, perhaps with bank 
switching, where normal pixels are written to both banks, and teletext 
flash only in one bank, and the banks are toggled. But that's a 
challenge for another day...

On 02/07/18 14:43, nicola giacobbe wrote:
> Seems interesting. I for sure will give a look but is there anyone that
> could shed more details about the missing flashing colours in Brandy? I
> have never used it too much so I did not notices there were no flashing
> colours: is it too computationally intensive (like having to redraw the
> whole screen @ 2Hz) or is a compatibility issue?
> 
> 
> On 02/07/18 14:21, Michael McConnell wrote:
> ...
> 
>> It was interesting trying to get the Hold Graphics code to work
>> correctly, as two different BBC emulators (BeebEm and jsbeeb) gave me
>> different results, so I gave up on that and used RISC OS's emulation as
>> a guide to how things should render - and I now get the correct output
>> from the Ceefax engineering test page.
>>
>> I've put it up at http://brandy.matrixnetwork.co.uk/
> ...
> 
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