Path: utzoo!mnetor!uunet!husc6!uwvax!rutgers!iuvax!bsu-cs!cfchiesa From: cfchiesa@bsu-cs.UUCP (Christopher Chiesa) Newsgroups: comp.sys.atari.8bit Subject: Re: 3D on the 8 bits Message-ID: <2841@bsu-cs.UUCP> Date: 3 May 88 15:32:52 GMT References: <8805020833.aa01825@ARDEC-3.ARDEC.ARPA> Organization: CS Dept, Ball St U, Muncie, Indiana Lines: 40 Summary: Display List flipping (Parent-article information lost due to hitting 'R' rather than 'f' first time through... sigh...) > ...use the jump at VBI at the end of a display list to > jump to an alternate display list. ... > I tried it on a 400 and found that the address in the jump instruction is > ignored, the computer continues to use the original display list and the > display doesn't change. > Perhaps as wallman-george@yale... points out, something has to be done to > 'shut-off' shadowing of memory locations pointing to the display list. Well, you've got the basic idea: that the OS VBI routine is restoring the hardware Display-List pointer from shadow locations 560,561 (dec), AFTER the Antic JMP instruction tries to go somewhere else. You need to either SHUT OFF shadowing of 560,561 into hardware, OR update THOSE locations so that THEY ALSO point at the new Display List. Shutting off shadowing may be as easy as setting the CRITIC flag, suppressing part of the VBI processing -- but I'm not absolutely sure that the shadowing you want to suppress, is part of the code getting suppressed, so that may not work. To be absolutely sure, you'd want to write your OWN VBI routine that took care of whatever OS operations you wanted still to happen, but DIDN'T shadow the Display List locations. Updating the shadow locations on the fly could be done most easily in a short DLI (Display List Interrupt) routine; in the middle of display "A", the DLI kicks in and changes the shadow registers to point to display list "B". And vice versa. Note that the DLI needs to know which display list it is currently in; you need to maintain a flag, or switch, in memory. The advantage to THIS method is that the code is relatively short, you don't have to take up the bur- den of anything the OS normally handles for you, and you can turn the page- flipping DLI on and off by playing ONLY with the Display List. Of course, in NEITHER application are you limited to TWO display lists, al- though if you're after STEREO that's all you really need. -- UUCP: !{iuvax,pur-ee,uunet}!bsu-cs!cfchiesa cfchiesa@bsu-cs.UUCP