Christopher Tumber wrote:
>But once I started fooling around with RESP0/RESP1 I got
>hooked on creating the ultimate 2600 version of that classic
>11x5 game...
I had the very same idea a few months ago.
>1) (Most importantly) As mentioned the last time this came up,
if you align the sprites closest together with RESP0/RESP1 then
when you remove a sprite, the previous sprite is shifted out of
alignment to the left. It is possible to eliminate this
shifting by spacing the spites a little further apart as I have
done, however if you do that then a row of 11 sprites is
extremely wide and there's no room for the Invaders to move
left and right (A full row could move like 2 or 3 pixels back
and forth).
Yes, that was a problem for me too. I managed to get a few more
pixels, but still maybe not enough. At least it where as many
steps as Inv21 does.
>2) With this wider configuration there aren't very many cycles
per scanline to process other things (specifically the player's
shot) - 4 cycles per sprite, plus any loop overhead and pushing
values into GRP0 and GRP1 doesn't leave a lot left over. I'm
not saying it'd be impossible but even with mine trimmed down 9
sprites it's an incredibly tight squeze.
It is possible using selfmodifying code in RAM.
>Heh, heh, only later did I realise that that couldn't be since
Invaders21 is available from Hozer and I'd read a couple
reference to how it and Inv30 run &etc. I went "Oooooooh!
Dhuh!" and had to check the docs to find out which key mapped
to the reset switch.... At which point I was able to check out
the source for Inv30 and realise that it was possible to
eliminate a sprite just by skipping the relevant RESP0 or
RESP1....
Inv30? Haven't found that in the archives.
>Anyway, this is geting rather lengthy as it is, so I'll wrap
it up now. Attached is the most recent bin, should run fine on
any emulator that supports the RESP0/RESP1 trick and real
hardware (At least it runs fine on my Supercharger, haven't
tried it on a real cart ROM but no reason why it shouldn't...)
Looking really good.
And as allways: If you need help in optimizing your code, just
ask. :-)
Have fun!
Thomas
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