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I'm thinking of writing a version of Rally-X for the BBC
http://www.retrosoftware.co.uk/forum/viewtopic.php?f=19&t=903		 Page 2 of 2
Author:  tricky [ Sat May 17, 2014 9:27 am ]
Post subject:  Re: I'm thinking of writing a version of Rally-X for the BBC
Just thought I would give it one more try and dug out a couple of CRTs, they work exactly as B-Em does, but with a slight curving to the top of the 1UP 2UP radar (the top row also has a curve, but that is blanked to hide the vertical rupture).

So, all back on again. I will move the adjustment to a "calibration mode" for modern displays and minimising the dashboard curve.

Sorry I ever doubted you B-Em and RichTW.

I'll start a new thread when I get back to working on it.
Author:  TomW [ Sat May 17, 2014 10:56 am ]
Post subject:  Re: I'm thinking of writing a version of Rally-X for the BBC
The curving is a result of the CRT's horizontal PLL adjusting to the new sync position; it's somewhat described here : http://www.reenigne.org/blog/crtc-emulation-for-mess/. I didn't implement it in B-em due to laziness. You could eliminate it by having a gap between the playfield and the dashboard I suppose.
Author:  tricky [ Sat May 17, 2014 3:16 pm ]
Post subject:  Re: I'm thinking of writing a version of Rally-X for the BBC
Thanks Tom for the link and the excellent B-Em.

I was hoping to minimise the curving by leaving a couple of scan lines blank, over compensating the sync pulse width and possibly animating the top line or two to minimise any remaining wobble.
Author:  RobC [ Sun May 25, 2014 7:06 pm ]
Post subject:  Re: I'm thinking of writing a version of Rally-X for the BBC
Just tested it on a Master 512 with a CM8833 CRT monitor and it works perfectly - no curving of the dashboard and the scrolling is fine (there's a little flicker at the horizontal edges).

Same result with an Eizo Flexiscan 9060 multisync CRT.

1942 on a Beeb would be ace mind :D
Author:  tricky [ Mon May 26, 2014 8:43 am ]
Post subject:  Re: I'm thinking of writing a version of Rally-X for the BBC
Does it look like extra offsets might make things better or worse?
I was thinking that I could blank one or three pixels if I couldn't get the adjustment correct
1942seems doable, but not with the full gfx
I might have got distracted with another game ;)
There is a beeb version that is OK, but it really needs a very close convertion to do it justice.
Author:  RobC [ Mon May 26, 2014 8:48 am ]
Post subject:  Re: I'm thinking of writing a version of Rally-X for the BBC
Things are right without changing the offsets. In fact, pressing 'Z', 'X' or 'C' collapses the display alarmingly on the multisync monitor! 'V' recovers the display.

I've always wondered about re-writing Paperboy as the Beeb version is pretty poor. There's a thread on YouTube where the author says the Beeb couldn't handle the scrolling in hardware, hence the issues converting it.

Had he known about vertical rupture then it could have been much better.

EDIT: Just tried FireTrack on the multisync monitor as it happened to still be connected and I fancied a game. It really doesn't work very well as it causes random vertical juddering. I'm guessing that the timing is a bit too critical to work reliably.

Tried RallyX immediately afterwards and the scrolling was fine. So it works better than Firetrack on my CRTs.
Author:  tricky [ Mon May 26, 2014 4:55 pm ]
Post subject:  Re: I'm thinking of writing a version of Rally-X for the BBC
Wow, Firetrack was the reason Gil and I spent quite a lot of time messing with the video registers. When I found out about virticall rupture, I assumed Firetrack must have used it - I guess it doesn't then!

EDIT: Just had a look at paperboy, and you should be able to either draw the whole frame if it was uncompressed, or only draw the bits that change and make it smooth.
Author:  RichTW [ Mon May 26, 2014 8:26 pm ]
Post subject:  Re: I'm thinking of writing a version of Rally-X for the BBC
No, Firetrack doesn't use vertical rupture - instead it makes life harder for itself by using a technique which requires far more careful timing - essentially it moves the top border by writing to R5, and maintaining a stationary edge with an interrupt timed off VSync (so far, the same), but it then makes up the requisite 312 PAL lines by changing R9 (scanlines per row) for one offscreen row before resetting it back to the default again. Seems to me that the vertical rupture method is easier, plus provides a stationary panel at the bottom in which you can display useful info.
Author:  tricky [ Tue May 27, 2014 12:18 pm ]
Post subject:  Re: I'm thinking of writing a version of Rally-X for the BBC
Thanks Rich, that was what I remembered from the 80s - I think Gil and I may have missed the extra deep row and that was why it always bounced all over the place :idea:
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