Horizontal and Vertical Shift Options for Analog Output

Discussion about displays and related hardware including MiSTer filters and video settings.
SuperSpongo
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Horizontal and Vertical Shift Options for Analog Output

Unread post by SuperSpongo »

Hi guys!

The Jotego cores have an option to shift the image in both axes when outputting natively via the IO board. It seems that this is a per core feature. Is it possible to implement this in more cores? Would I have to nag each core developer to implement this? It's such a handy feature and solves the necessity to use RGB shifters.

TomCig
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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by TomCig »

Yes, this would be great if possible.
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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by jimmystones »

Unfortunately it is indeed something that has to be developed for each core, and it's not a trival process as you have to modify the original horizontal/vertical blank and sync generators. Lot's of trial error, and every core is a bit different!

Having said that I'm going to try and give it a go on some of the arcade cores at some point, as I'm primarily an arcade+crt user myself :)
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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by SuperSpongo »

Yeah, I was afraid of that. Thank you for looking into it!

By the way, how does an external RGB shifter shift the signal to the left anyway? I was under the impression that, in order to shift the picture to the right, you'd have to modify the front porch. So far so good, I can imagine some kind of circuitry for delaying a falling edge, but how does one let the edge fall sooner without a crystal ball to predict the future?
Or is my understanding of the signal totally wrong? :D
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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by thorr »

I also would greatly appreciate this. I have tried a bunch of cores and set the TV the best I can so as little as possible is cut off across all the cores, but each core is positioned differently. I am using the HDMI output and converting directly to component video without the I/O board using direct video. I think this probably provides a better picture with higher color bit depth than the I/O board (I have another thread about this).
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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by jimmystones »

Regarding an RGB shifter I'll be honest - no idea how they work! I'm sure someone around here would be able to tell us if they are listening though :)

I feel your pain - my CRT is a total pain to adjust as well! The thing about arcade cores is they were all designed to work on their own specific hardware, the engineers presumably just tweaked them after installation until they looked right.
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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by SuperSpongo »

https://nfggames.com/forum2/index.php?topic=3017.0

viletim had a go at it in 2007. I also know moosmann's RGB shifter, it seems to work well.
I'll have to take a look at the circuit and try to understand it.
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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by SuperSpongo »

Jotego seems to have also seen the need for this feature and has provided the means to implement his awesome feature into other cores.

https://mobile.twitter.com/topapate/sta ... 6515126273
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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by wmd »

About the values that core authors allow for vertical and horizontal offsets - can the max values be arbitrarily changed (in the source file) or is there a reason why those max values are set to those values? I notice that these max values are sometimes different between cores. I ask because on a few arcade cores, even when v/h offset is adjusted, ideal game screen position is still not always possible. Example - Rod Land -->

dUUFdsS.jpg
dUUFdsS.jpg (167.59 KiB) Viewed 455 times

I know someone will suggest "why don't you just adjust your monitor settings", however, for most arcade cores the permitted H/V offset range is sufficient, and adjusting for the few games that don't allow larger offsets breaks the alignment of all the rest.

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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by Flandango »

In this case, the Rodland core, the min/max values can't be changed arbitrarily without making big changes to Jotego's underlying module that handles the video shifting (using Rodland as an example).
In short, the module only accepts (and uses) 4 bits of data, hence the range.

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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by wmd »

Would that be the jtframe_resync.v module? How difficult is it to change from 4-bit to 8-bit values? Haven't some cores already done this? I'm sure I've seen some that allow for values > 7

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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by Flandango »

That would be the module. I can't speak for difficulty on modifying the module to allow for larger values, because I am no video signal expert. Even worse, I don't have a CRT to conduct tests/research on.
As for other cores that do video shifting and use a different range, they may be doing it a different way and maybe not even using a modified Jotego module.
One thing to note is that a wider option range doesn't necessarily equate to a wider shift in video position...could be just finer control. For example, each value in a -8 to 7 range could be 10 pixels in either direction or in another core's...say -32 to 31 could be 5 pixels.

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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by valerino »

sorry for necroposting, just wanted to suggest this: https://www.aliexpress.us/item/32568044 ... 4itemAdapt

very cheap (50€ shipped to italy), i just received it and it works flawlessy with my crt, you can tune both V and H offsets!

v.

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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by thorr »

Wish it worked with component video. If this exists, then maybe it can be implemented in the main part of the MiSTer in the video chain similar to the scaler. Then in each core save the offsets when saving the core settings.

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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by wmd »

I would need to see some lag test results before buying a device like that. Even the expensive Extron units introduce lag.

valerino
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Re: Horizontal and Vertical Shift Options for Analog Output

Unread post by valerino »

wmd wrote: Wed Mar 27, 2024 1:56 pm

I would need to see some lag test results before buying a device like that. Even the expensive Extron units introduce lag.

i have read this before buying that, it is a review of basically the same device. overall, i can say it works flawlessy: i'm using an old Mivar TV. i haven't done any lag test though, just played a bit with c64 and snes cores.

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