Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!udel!rochester!kodak!elmgate!jdg
From: jdg@elmgate.UUCP (Jeff Gortatowsky CUST)
Newsgroups: comp.sys.atari.st
Subject: Re: Fine scrollin'
Summary: What I have concluded?
Keywords: graphics atari helpx2
Message-ID: <1205@elmgate.UUCP>
Date: 16 Feb 90 01:04:29 GMT
References: <1199@elmgate.UUCP> <1990Feb13.162107.2537@gpu.utcs.utoronto.ca>
Reply-To: rg@aurora.UUCP
Organization: Eastman Kodak Company, Rochester NY
Lines: 36


Well, a few reponses are in. And, A few of my Own experiments.
I have tried the VDI raster form functions. And, the results were
poor (specially movin' the entire screen (over itself if you will, boy,
is it POKEY!). So, I decided to go straight to the BLIT Line-a function.
After some finaglin' I got it working, It too is unacceptable, and the
screen gets all funky unless one VSyncs(). So, I decided, to see what'd
happen if I just Blit one plane (What we are doing here, BTW, is taking
3 logical displays (making up a "playfield") if you will, in low-res,
that are to be horizontally scrolled either left or right, smoothly, and
at a decent rate of speed) and It too was unacceptable. All of "my"
tests of the scrolling have been all "on screen", which, If a blit has
any brains about should "make a difference" (as in my tests, the source
& dest rects overlap). And it's a REAL sad performer, matter o' fact,
I'd bet bottom dollar that it could be DRASTICALLY speeded up. This
eve I will try from my actual playfield. One reply I recieved (of all 2
so far) stated troubles with sprites. Using the BLIT I'd see no real
problems. The obvious way to implement color sprites (an virtually any
size (though collisions can be another matter)) is to take your image,
Shift it all the way left in your buffer (so your "lead pixel") aligns
on a word boundary (or long word) and start shiftin the image through
each and every permutation of the 16/32 bits, then all one need do
is bleam the proper permutation onto/into your screen/buffer et el.
All one need do is find the pixel index into the word/longword where
ones coordinates lay, use it as an index to your sprite permutations.
Zippity aye' it works too, I've done it. It's quite simple actually,
just a little memory hungry and that can be finagled if one wishes
to do an on the fly RLE or some such item. I have never pushed it
(never had the need) over the amount of 16 32 bit sprites, but, the
performance is more than adequete.

-- 
Jeff Gortatowsky-Eastman Kodak Company  .....sun!sunrock!elmgate!jdg
(716)-726-0084
Eastman Kodak makes film not comments.  Therefore these comments are mine
not theirs.