Why did the C64/128 have "the boarder"?
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From: Lars Haugseth on 7 Jan 2010 10:27 * Brandon Staggs <nospam(a)a.b.c> wrote: > > "Rudolf Harras" wrote on Thu, 07 Jan 2010 13:36:58 +0100: > >> I wonder for what reason Commodore used a boarder in all their Computers >> like the VC20, C64/128? >> >> I don't know any other computers having this and it also wasn't so usual >> that time, was it? >> >> It makes the picture smaller and it seems to be difficult to have some >> sprites there since I don't know any game where the boarder is useful. >> >> On the other hand I'm really so used to it that an OS without "Boarder" >> does not seem to be complete for me. :) > > Google "Overscan." It varies widely between old CRT sets. That's > just one reason -- there are probably additional technical reasons, > though it is possible to code around the border thing and put sprites > and other things in the borders. Interestingly, C64 and border removal using coding tricks are mentioned in the Wikipedia article: http://en.wikipedia.org/wiki/Overscan -- Lars Haugseth
From: Rudolf Harras on 7 Jan 2010 13:41 Brandon Staggs schrieb: >though it is possible to code around the border thing and put sprites >and other things in the borders. Do you know any game that actually did that? Was it easy?
From: Brandon Staggs on 7 Jan 2010 17:20 "Rudolf Harras" wrote on Thu, 07 Jan 2010 19:41:05 +0100: > Brandon Staggs schrieb: > >>though it is possible to code around the border thing and put sprites >>and other things in the borders. > > Do you know any game that actually did that? I've seen demos/intros that did; not that I can recall any names. I don't recall any games. > Was it easy? No idea. But the overscan issue is overriding -- You would never want anything important outside of the safe-title area of the frame because some TV sets would crop it. Having stuff scroll in is one thing, but putting targets/static text/etc outside the border wouldn't be a good idea. -- -Brandon http://www.brandonstaggs.com/c64.html
From: Martijn van Buul on 8 Jan 2010 04:21 * Rudolf Harras: > Brandon Staggs schrieb: > >>though it is possible to code around the border thing and put sprites >>and other things in the borders. > > Do you know any game that actually did that? I seem to recall a game that put a score counter in the lower border, but I may be wrong. > Was it easy? The theory was relatively straightforward. In order to support soft-scrolling, the VIC-II had a 24- line mode and a 38- column mode. In 24-line mode, the border would end 4 lines later, and start 4 lines earlier, the 38-column mode had a similar influence on the vertical borders. In order to turn off the borders, "all you have to do" is switching from 25 line mode to 24 line mode (or from 40 character mode to 38 character mode) while the VIC was processing the part of the border that is present in 24 line (38 character) mode, but not in 25 line (40 character) mode. It would then get confused, and 'forget' to switch on the border. The catch is that you will have to do this *every time*. For the lower- and upper border this is relatively easy. There's a large window of 4 raster lines to toggle the video size, and the VIC has an option to generate an interrupt when it starts processing a certain line. Also, you only had to twiddle with the video size once per video frame. Even a novice programmer like me can pull it off :) Getting the left- and right border to open is a lot harder, as the window is only a single clockcycle, so you will need to do cycle-exact programming, which is an art in itself. In addition to that, you will have to trick the VIC on *every* raster line. See http://www.antimon.org/dl/c64/code/opening.txt for a nice detailed explanation. -- Martijn van Buul - pino(a)dohd.org
From: Lars Haugseth on 8 Jan 2010 04:47
* Rudolf Harras <rudi007(a)temporaryforwarding.com> wrote: > > Brandon Staggs schrieb: > >>though it is possible to code around the border thing and put sprites >>and other things in the borders. > > Do you know any game that actually did that? Several games used sprites in the upper and lower borders. One early example is Delta: http://www.mobygames.com/game/c64/delta/screenshots > Was it easy? Upper/lower borders yes, sideborders not so much. Which is why I don't think any games used the sideborders, at least not outside intro screens and such. -- Lars Haugseth |