Path: utzoo!attcan!uunet!mcvax!kth!draken!umecs!zeus!christer From: christer@zeus.cs.umu.se (Christer Ericson) Newsgroups: comp.sys.apple Subject: Re: Page flipping Message-ID: <823@umecs.cs.umu.se> Date: 20 Mar 89 17:36:43 GMT References: <8903161724.aa22311@SMOKE.BRL.MIL> Sender: news@umecs.cs.umu.se Reply-To: christer@zeus.UUCP (Christer Ericson) Organization: Dep. of Inform.Proc.,University of Umea,Sweden Lines: 66 In article <8903161724.aa22311@SMOKE.BRL.MIL> PGOETZ@LOYVAX.BITNET writes: > > The method Bob Bishop published in Softalk involved finding when >the vertical blank was and then counting cycles until the next one. Thus, >it could only be used with static images, and NOT with animation (unless >you want to time your entire program loop!) For an example of a similar >technique, see the boot display for Nasir Gebelli's _Gorgon_. > The article named 'Hi-Lo Split', as someone already mentioned, appeared in the August (possibly the September) '82 issue. I have it somewhere deep down in one of the piles in the Apple bookshelf at home if someone would want a hardcopy of the article. I'd guess it is some 6-7 pages long. Now to the real reason to my reply. Phillie, where did you get the impression that 'scan-line interrupts' couldn't be used together with animation. Just take a look at the games on the 64 (sorry if I offended someone by mentioning that particular number) - they do it all the time! Sure, the VIC chip can automatically tell you which raster line you're at and on the Apple we have to rely on tagging the off-screen screen-memory. But after having detected the raster line we're interested in we have some 7200 cycles (that's PAL, NOT NTSC, you have fewer) during which we can do anything, like animation, before we return to the same raster line. With a little imagination awsome effects can be made! Virtually all cracked programs in circulation have some sort of flashy graphical 'pirate page' and some pirate groups have exploited the 'scan-line interrupt' feature to make quite astonishing intros. Next time you stumble on the inevitable cracked copy of 'Mutant Appleeaters from Space' - check the intro out, it's sometimes better than the game itself. I don't approve of pirating software despite what I just said above so just DON'T copy the game, ok. You might also want to try this small routine out. This should work for an NTSC machine giving a *vertical* split instead of the common horizontal split. Note: I hand-coded this w/o having a 6502 assembly manual at hand so I can only hope it is correct. No flames, please. 0300:AD 50 C0 LDA $C050 AD 52 C0 LDA $C052 AD 56 C0 X:LDA $C056 4 20 58 FF JSR $FF58 12 20 58 FF JSR $FF58 12 EA NOP 2 EA NOP 2 20 57 C0 LDA $C057 4 20 58 FF JSR $FF58 12 20 58 FF JSR $FF58 12 EA NOP 2 4C 06 03 JMP X(306) 3 ------------------------------- 65 CYCLES BTW, Bob Bishop also wrote a game for Datamost called Money Munchers where he superimposed text and lores by rapidly switching between those two modes. However the total effect were lost since it flickered too much... > >Phil Goetz /Christer Christer Ericson Inst. for Information Processing University of Umea S-90187 Sweden Internet: christer@cs.umu.se a.k.a. christer@[130.239.1.101]