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Re: Scrolling HGR Screen Up 8 Lines
On Sat, 18 Mar 2000 01:02:47 +1300, dempson@actrix.gen.nz (David Empson) wrote:
>Christer Ericson <christer_ericson@playstation.sony.nospam.com> wrote:
>
>> You definitely do *not* want to do it this way!
>
>How do you know what I want? :-)
Fair enough, you might want to do it that way, but you should at least
consider doing it the faster way. ;)
>My purpose was not to write the fastest possible way of doing this, just
>a reasonable implementation that would do the task required, without
>being too huge.
My point was really that whenever you are doing a gargantuan blockmove
like that, you're likely to want it to be as fast as possible.
Especially in the case you are not page-flipping, in which case a slower
approach will give you motion sickness as the screen sort of buckles as
it scrolls up the screen.
>I initially thought of doing a faster move, but decided in favour of a
>prettier one, with no attempts at optimization. This is left as an
>exercise for the reader.
I guess I was that reader then ;)
>> Indirect-comma-Y addressing is the slowest addressing mode.
>
>No it isn't. Pre-indexed indirect (with X) is one cycle slower, except
>in the case where post-indexed indirect (with Y) crosses a page
>boundary, when they are equally bad.
True. I did mean that as in of the addressing modes you would
reasonably use to solve the problem, though.
I used to wish that indirect-comma-X had been post-indexed just
like indirect-comma-Y. IMO, it's such a useless addressing mode.
Did anyone ever find a really good use for it? (I mean other than
with X as constant.)
Christer Ericson
989 Studios/SCEA, Santa Monica