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KevKelley

Over Cycling - When Is It Okay?

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I have read about maintaining scanlines  but I was curious if there were ever an occasion where the negative impact of having too many scanlines can be ignored or if there are underlying issues as to why this should be avoided? 

 

What leads me to this question was that I was programming the reset switch. When I made it the scan lines jump but since it resets everything anyway I asked myself "Does it really matter?" in this particular situation.

 

 

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Inconsistent scanlines can cause screen jumps or rolls. I think the reset switch is one example where that is less of a big deal.

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That was my thinking. When I tested it I didn't really experience much issue since as soon as I let go it jumped to the beginning. I didn't want to waste bytes for a repetition restrainer but was uncertain if there was anything in addition to rolling or flicker that I was unaware of.

 

Also made me wonder if anyone had purposely used it for an effect previously too...

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my game jumps a couple of scanlines on collision that I never fixed, but I like it as it kinda works as a screen shake 

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I have seen it cause a slow roll on a CRT which is pretty annoying if it happens at the wrong time in a game. Seems to really vary between CRTs. Doesn't happen on newer displays.

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That is really cool that some have used it for an effect.  

 

I had noticed recently that in Stella I would get a flicker of a high scan line count during gameplay.  When I tested it on hardware I got nothing.  I ran them both simultaneously and nothing.  But then again I wasn't using a CRT. Not a big deal with the reset switches but would hate for something like a random screen roll or flicker in the middle of playing.

I haven't seen anything, but is there possibility that depending on where it occurs it won't impact the screen at all? Or should I use a CRT for main testing?

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As long as you maintain a consistant scanline count and are doing VSYNC properly, you should be okay.

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I was going to play around with some code later to see if I can prevent any issues. I had noticed no issues with real hardware but have yet to try a CRT, which made me wonder if it is really an issue. I no longer worry about the reset switch over cycle, but I would hate to not experience any issues with my setup only for it to be unplayable for everyone else.

 

After reading I had found one site that said NTSC games have ranged from 246-282. I have had some games get some big screen rolls and flicker but is it safe to assume that the scanline probably jumped more than that range and if the scanline count is in that range, if there is any issue with syncing it may be much less noticeable? 

 

So let's say I have one frame where it goes to 263, that may not even present itself, versus if it jumped to 312?

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