[hatari-devel] New support for STE's 224 bytes overscan

npomarede at corp.free.fr npomarede at corp.free.fr
Mon Dec 7 20:36:52 CET 2009


On Mon, 7 Dec 2009, Anders Eriksson wrote:

>> You mean on STE the screen is shifted to the left (not to the right) ?
>> Else I don't understand how the far right pixels would be more visible.
>
> Phu, how should I explain this..
>
> I mean that the STe 224 byte overscan is shifted to the right, look at
> this picture I threw together:
>
> http://ae.dhs.nu/pics/overscans.jpg
>
> The pictures are taken with a PAL capture machine from a real STe output.

Pictures are better than a thousand words :)
In fact, we're talking about the same result. I misexpressed myself, 
picture is shifted to the right, and the rightmost pixels are not masked 
by the stabiliser (which creates a black bar and alter some bitplanes), so 
they are "more" visible.

>
>
>> How do you count 416 pixels ? 224 bytes would give 448 pixels, and as the
>> first 16 are background ones, this would leave 432. Do you count only
>> usable pixels ? (I count 8 pixels per bytes, even if the hi/lo switch are
>> sometimes adding some black bars or things like that).
>
> Yes I count usable pixels, and as my understanding have always been that
> the traditional 230 byte overscan makes 416 usable pixels. Then when
> comparing to the 224 byte overscan, the same amount of usable pixels are
> available (look at the picture linked to above, you'll see that what the
> 224 byte overscan misses at the left, it gains at the right).
>
> There might be a misunderstanding though - that there in fact are not 416
> usable pixels on a 230 byte overscan line, then my calculations are not
> correct, but I also wonder why Hatari would then display graphics that are
> not displayed correct on a real ST/e.

Well, Hatari displays the "logical" representation of the video RAM, but 
it doesn't take into account the artefacts due to the hi/lo res switch. 
That's why I count a theorical value of 460 pixels, but some of them are 
altered by the hi res switch (so they're in a mixed state where you can 
use/change them, but the color is not correctly displayed).


>> But on real ST, you wouldn't change the color outside the visible area,
>> or you wouldn't see the colors there too. Do you mean something that would
>> use Hatari in a way a nomal ST can't be used ?
>
> Yes! As I said, for _coding_ fullscreens, plasmas etc, not watching them
> :)

OK, that's another matter, but I already thought about sthg like that that 
would display an additional area on the side with some pixels/colors 
indicating the state of the line (overscan, scroll, ...).
No time to code this now, but maybe later :)

Nicolas




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