Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!garfield!roger From: roger@garfield.cs.mun.ca (Roger White) Newsgroups: comp.sys.cbm Subject: Re: C128 Housekeeping Message-ID: <1991Feb4.171456.8038@garfield.cs.mun.ca> Date: 4 Feb 91 17:14:56 GMT References: Organization: CS Dept, Memorial University of Newfoundland Lines: 34 The interlace display is not a hardware effect but a software effect. It is true that the screen is only being moved a pixel at a time, back and forth (using the VIC's horizontal and vertical movement address) thus every second row is on top of the other. It causes the image to blur thus making it look better and give the illusion of interlace. The bitmap has every second pixel row cut out (starting at the top row and/or at the side) for one part and every second pixel (starting at one down from the top row and/or one from the side) for the other. Each bitmap is flashed on the screen during its specified interval (when the screen is moved one pixel the second bitmap is flashed, when the screen is normal the other bitmap is flashed) giving it the jitters and the illusion of an interlace screen. You are actually seeing a 640x400 display, but it is just two bitmaps flashed on top of the other. It does give a nice effect though, if only the jittering could be calmed down a little. The reason why Snapshot only shows a half bitmap is because when you press the button it only freezes one of the screens and you get a half bitmap. You could end up with the second half if you freeze it later on. (by half bitmap I mean every second pixel removed) This may not be the way it is done, but is the only way I can see it working for a C64. As mentioned they may only be using one screen and moving it to make it look like interlace thus only really showing a 320x100/160x200/160x100 screen and lying about the resolution. I have only seen the demo, I haven't looked into the code. R.White -- Boot it up? I did A LOT of that!| Roger White (Sam-Cheers) | Memorial University of Newfoundland --------------------------------| St. John's, Newfoundland, Canada ..uunet!odie.cs.mun.ca!roger, roger@odie.mun.edu, roger@odie.cs.mun.ca