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Old 28 January 2016, 19:33   #11
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Join Date: Sep 2011
Location: Cardiff, UK
Posts: 889
This is really fascinating, a bit switch that can change the behaviour of the actual video output! I had this happen to me as well, back when I had real hardware in the 1990s:

I had a demo called "Boundless Void" by Nemol ( which at one point, at around 3:14 (see video) displays two "plasma" effects on the screen, one multicolour and then one blue - on my Amiga 500, these parts and the whole demo ran fine, as it was designed for OCS/ECS.

HOWEVER, and this is the interesting part, the demo behaved differently when I ran it on my new Amiga 1200: I was using a CRT TV at the time, and this part of the demo actually caused the picture to roll, like you see with a badly-tuned channel or a faulty TV. But when it went onto the next part of the demo, the picture immediately stabilised!

I know that Standard NTSC/PAL video is KEY to the Amiga's graphical operations, but I wonder what could've caused a bit to be set that would actually alter the fundamental video signal sent out to the TV, just like that? I'm thinking it was somehow similar to the Microcosm trick, but more "down to the metal", so to speak.

Of course, this sort of thing is impossible to see in emulation (haven't actually tried Boundless Void on an A1200 config yet, mind) and of course, CRT TVs are hardly around these days, so it's probably tough to find proof of what I'm saying, but I swear this happened.

Of course, as far as I know, plasma effects simply alter the colour registers, but I'm guessing there was a difference between OCS/ECS and AGA colour registers that involved video hardware.

What do you think?
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