Path: utzoo!mnetor!uunet!mcvax!ukc!its63b!hwcs!neil From: neil@cs.hw.ac.uk (Neil Forsyth) Newsgroups: comp.sys.atari.st Subject: Re: ST hardware scrolling Message-ID: <1794@brahma.cs.hw.ac.uk> Date: 22 Apr 88 09:07:58 GMT References: <544@csvax.liv.ac.uk> <4484@batcomputer.tn.cornell.edu> Reply-To: neil@cs.hw.ac.uk (Neil Forsyth) Organization: Computer Science, Heriot-Watt U., Scotland Lines: 34 In article <4484@batcomputer.tn.cornell.edu> braner@tcgould.tn.cornell.edu (braner) writes: >(1) The ST's video pointer must be on a 512-byte boundary, NOT 256. >Thus, incrementing it by $500 (1280) (to scroll by one text line) >is NOT feasible. (I tried it: the screen goes crazy!) One could >scroll TWO text lines at a time, though. No. It can go on a 256 byte boundary. I tried, and suceeded long ago for some smooth scrolling I did and it worked just fine for me. The screen just looks crazy because 256 bytes doesn't use an integer number of scanlines. (1.6 in colour modes) >(2) This solution only applies to scrolling the entire screen, >while Tempus, Laser C, etc fast-scroll arbitrary WINDOWS. Rather >impressive. Yup! I have not seen Tempus but my guess is they use "movem.l" all over the place and possibly force the windows to lie on 8 or 16 pixel boundaries so that there is no half characters to slow the thing down. It is often the case that a little machine (not OS) dependance goes a long way. ------------------------------------------------------------------------------- "I think all right thinking people in this country are sick and tired of being told that ordinary decent people are fed up in this country with being sick and tired. I'm certainly not and I'm sick and tired of being told that I am!" - Monty Python Neil Forsyth JANET: neil@uk.ac.hw.cs Dept. of Computer Science ARPA: neil@cs.hw.ac.uk Heriot-Watt University UUCP: ..!ukc!cs.hw.ac.uk!neil Edinburgh Scotland -------------------------------------------------------------------------------