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 Post subject: Scanlines filter and Interlaced screenmodes
PostPosted: Sat Oct 27, 2012 5:41 pm 
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Someone's expressed a wish for change to the Chameleon Minimig core, which would make the scanline mode independently settable for normal and interlaced modes. It's a simple enough change that I could backport to the "real" Minimig very easily - except that I don't currently have any way of building the menu code for the Minimig. WIthout menu support the scanlines would simply be disabled in interlaced modes.

So time for a quick show of hands:
Would anyone miss the scanline effect in interlaced modes if I made that change?

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 Post subject: Re: Scanlines filter and Interlaced screenmodes
PostPosted: Sat Oct 27, 2012 6:07 pm 
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I find this question a bit confusing: are you referring to scanlines in chipset modes? Since these where originally interlaced modes, you could be referring to those..
Or do you mean scanlines in the 15Hz modes that the Minimig physically generates when it's using VGA->SCART cable and the right jumper setting?

If it's the first, then please keep them...games and demos using chipset modes over VGA look SO sweet with scanlines on my LCD!
If it's the second, then I don't know what to say.


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 Post subject: Re: Scanlines filter and Interlaced screenmodes
PostPosted: Sat Oct 27, 2012 6:31 pm 
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Edit:
Quote:
I find this question a bit confusing: are you referring to scanlines in chipset modes? Since these where originally interlaced modes, you could be referring to those..


Yeah, sorry - my post could have been worded more clearly!
The point is that chipset modes - most of the time at least - *weren't* interlaced. Interlaced video has odd and even fields, and they're identified by a different sync pattern, which tells the monitor whether or not to offset the vertical position. Since most of the time the Amiga outputs only "even" fields (or maybe it's only "odd" fields, I don't know!), you can see the scanlines, because the gaps between them are never filled in by the alternative fields.

That's the effect scanline emulation attempts to simulate, but it attempts to simulate it even when the Minimig chipset *is* outputting an interlaced frame. It could be argued that this is the correct thing to do - and it does altnerate which scanlines are dimmed - but on a TFT the framerate generally doesn't match up well enough for this to look good.

gaula92 wrote:
If it's the first, then please keep them...games and demos using chipset modes over VGA look SO sweet with scanlines on my LCD!


It won't affect the vast majority of games and demos - only interlaced screenmodes.

The feature that was requested was to duplicate the scanlines option in the OSD menu, so instead of looking like:

Lores filter : Off/H/V/H+V
Hires filter : Off/H/V/H+V
Scanlines : Off / Dim / Black

it looks like:

Lores filter : Off/H/V/H+V
Hires filter : Off/H/V/H+V
Scanlines
Normal modes : Off / Dim / Black
Interlaced modes : Off / Dim / Black

Which I've done, and it works nicely. But since I can't currently build the menu code for the real Minimig, if I make this core change to the "real" Minimig as well, scanlines won't work for interlaced modes until or unless the menu's updated.

I presume the reason for the request is that however nice they look in normal modes, scanlines look pretty awful in interlaced modes - but that's my opinion, and I wanted to know whether anyone disagrees. :)
(Just change a Workbench screenmode to Hi-res Laced, enable scanlines and let me know whether you think it looks OK or not. It might look half decent on a CRT I suppose.)

(The reason I'd like to include this change in the "real" Minimig codebase is simply that I've now worked on *four* different Minimig variants, and my long-term goal is to get them all working and building from a single source tree, or at least a single coherent set of repositories, and avoid having four distinct sets of duplicated but subtly different code.)

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 Post subject: Re: Scanlines filter and Interlaced screenmodes
PostPosted: Sat Oct 27, 2012 7:08 pm 
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To me the scanline emulation has positive effect to the interlace mode too.
Without scanline emulation the VGA interlace screen flicker a lot more intensive.
With active scanline emulation the interlace appear less flickering and more smooth to my eyes.

Also the graphics looks too sharp without scanlines. On real Amiga game/demo graphics was created mostly on 1084 monitor or TV set, so the graphics "depend" on scanlines. else it looks totally different. Thats why I included this effect in the Minimig core once (when it was selectable via spare-io jumper ;)).

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 Post subject: Re: Scanlines filter and Interlaced screenmodes
PostPosted: Sat Oct 27, 2012 7:19 pm 
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boing4000 wrote:
To me the scanline emulation has positive effect to the interlace mode too.


OK - thanks for that - I'll leave it be then, and parameterize the codebase to handle such differences. :)

Just out of interest, do you use a CRT or TFT with the Minimig?

Edit: Having tested further, I have to agree that you're right - even though on my TFT there are interference patterns caused by framerate mismatch, the actual detail of UI elements on interlaced screens is more visible with the scanline filter enabled.

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 Post subject: Re: Scanlines filter and Interlaced screenmodes
PostPosted: Sun Oct 28, 2012 8:35 pm 
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I actually only use CRT with the Minimig, because of true smooth scrolling :)

TFT/LCD/Plasma screen also don't like interlace flickering!
My Samsung 940BF VGA screen show the flickering even at down draged screen when there only is the neat grey from the workbench background for a while until the matrix has "recovered" itself.
Thats why LCD TV has interna flickerfixer and can not show the normal TV signal interlace any more.

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 Post subject: Re: Scanlines filter and Interlaced screenmodes
PostPosted: Sun Oct 28, 2012 8:46 pm 
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boing4000 wrote:
I actually only use CRT with the Minimig, because of true smooth scrolling :)


Ah yes :)

Quote:
My Samsung 940BF VGA screen show the flickering even at down draged screen when there only is the neat grey from the workbench background for a while until the matrix has "recovered" itself.


Yeah some of them do some very strange things (in order to try and maximise response time, I think) - so I guess it's no surprise than an interlaced signal confuses them. Actually since my Dell U2311 supports 576i video I must see what difference, if any, disabling the scandoubler makes to its handling of interlaced modes.

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 Post subject: Re: Scanlines filter and Interlaced screenmodes
PostPosted: Sun Oct 28, 2012 9:30 pm 
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I have both CRT and LCD screens and all of them are connected to Minimig one way or another: DE1, Chameleon 64, Minimig 1.1 board...
Chameleon 64 port seems to have a much better resolution, resulting in better syncing from the LCD screen.
Anyway, I have true smooth scroll on some of the LCD screens: and when I say smooth I mean it, I'm equally obsessive with scroll smoothness as I am with sound output.

So, what do you guys mean by "true smooth scroll"? If an LCD is really 50Hz-capable, then smooth scroll is a reality.


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 Post subject: Re: Scanlines filter and Interlaced screenmodes
PostPosted: Mon Oct 29, 2012 9:56 am 
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Until now I only saw ugly scrolling on any tested LCD screen.
Some show even more ugly due to "ghosting image" and you can not even read any text scrolling over the screen.
Better model have better scrolling but still it is not that smooth and week as on a normal CRT (no matter if 15KHz or 31KHz).

In my opinion the LCD firmware and screen matrix can not handle the retro style very well.
Graphics are based on big pixel (compared to the matrix) and has big differences in brightness and color. On TV or modern PC/Mac screen there mostly is no such big differences on the screen. And if so (like window border etc.), this will not scroll/move over the screen all the time ;)

At least to me a CRT still is the best screen for C64, Amiga and so on computer :)

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