Re: Scanlines??

[toddpw@cco.caltech.edu (Todd P. Whitesel)]

philip@labtam.labtam.oz.au (Philip Stephens) writes:

>  Lode Runner GS does an amazing trick when you pause the game--it scrolls a
>message in large characters in the BORDER below the super hires screen, so
>evidently a stock standard 2.8 Mhz GS can toggle colours every couple of
>pixels (but I haven't worked out the maths yet).

That sort of thing is _only_ possible in the border area, or in text modes if
you have a real thing for pain. The resolution you can toggle at is limited
very strictly: the finest position you can get is a one-microsecond sweep of
the video beam (in 320 mode that counts for 8 pixels) and the fastest you can
change the color that's being drawn is every three microseconds (if you fire
those demos up again you will see that this is indeed the case with their stuff
as well). Most of this has to do with the fact that you are changing the value
of the border color register in real-time and must have the processor at 1 mhz
in order to guarantee that you won't lose synchronization with the video beam
once you've got it.

I've actually written one of these as a heartbeat task; it's not fun. It makes
for great demos that are supposed to suck up the machine, but I wouldn't get
all enamored with the idea for any kind of general use.

Todd Whitesel
toddpw @ cco.caltech.edu