MiSTer FPGA Forum

This seems like such a fundamental feature that I am surprised that so many cores are missing it. Are core authors just not aware that there are many people using old CRTs or is it down to something else? E.g. limited memory, etc?

Its not easy to do on analogue video output. There was plenty of over/under scan back in the day we couldnt adjust on TVs

Arcade cores are the worst but arcade cab monitors were adjusted with every board swap for position and over/under scan

its one of those things if you want more control use the HDMI output and scaler

It seems that most of the arcade cores actually have these options, it's all the other cores (console, computer) that don't.

It's a bigger problem for arcade cores because the scan frequency can be way out of spec for TVs and RGB monitors. The console and computer cores really shouldn't have as many issues.

wmd wrote: ↑Sat Jul 22, 2023 4:58 pm

It seems that most of the arcade cores actually have these options, it's all the other cores (console, computer) that don't.

Even with the adjustment in arcade cores it doesn't help much. You can shift the image around but that's about it. It doesn't really solve the over scan

On my analogue setup at least, x, y positioning is a more significant issue than overscan. That is, for those cores that currently allow for x, y repositioning, once correctly positioned, overscan is rarely an issue. That said, full repositioning and image stretching would be the ideal situation. Two cores that come to mind that do have overscan issues are Rastan and Tatsujin Ou. In fact, the overscan is so bad on those games that even with my CRT's vertical size set to min, all the graphics are still not fully visible.

The Amiga core could really use this, IMO. Its positioned so far out compared to other cores!

But it does work perfectly on the Commodore 1942 and 1084 CRT monitors, FWIW. Of course, it would be great with more flexibility here, agreed. :)

You cannot fix the overscan, it is what it is. The only thing we can do on the analogue output is move the synchronization pulses around a bit. That has the effect of moving the relative image position within the screen. I also included an option to stretch the image horizontally a bit, but it can only help so much.

In the end, we cannot emulate the analogue dial on the back of a CRT tube because that was moving the angle of the electron beam, whereas in the core we need to work with the lines in the video signal.

Overscan being difficult / impossible to implement is understandable, but it would be nice to see hori / vert adjustment settings in all cores. It would also be nice to see the max values of adjustment levels being increased too, as -7 to +7 isn't always enough to get the position right.

Back in the day, when you switched devices, you would often need to adjust your TV set for the new device. People didn't switch between devices so often because most people didn't have multiple devices (and certainly didn't play arcade boards on their home TV). Analog TVs/monitors all have adjustements such as horizontal hold and vertical hold (and some have more adjustments as well). Back in the days of analog, these needed to be adjusted from time to time. You might consider this "part of the nostalgic journey"...

The original goal of MiSTer was to emulate the original hardware - and if the original hardware was a bit offset, that's the "gold standard" for the base core.

-> Fundamentally, horizontal and vertical position settings is not a function which is "missing", but rather a feature which has not been added.

In order to adjust vertical/horizontal offset, another layer of the system needs to capture the sync pulses (and remove them), understand the timing, and implement a delay to either the sync pulse of the signal data, before recombining into a new signal. That's non-trivial even for an "easy" core, so it's no surprise that it's something to be added later as an upgrade. Also, many of the developers don't have such monitors, so they are unable to test such modifications (so there is no incentive for them to build it).

When one starts talking about arcade cores, they often had very non-standard timing, custom setup and tuning, and often unique hardware in order to display the picture. In many cases, these signals cannot be output to a normal NTSC monitor. In any case, the special timings create another layer of complexity in making any sort of adjustment.

If centering the picture without adjusting the monitor is important, HDMI is probably a better choice. And HDMI will be required for some cores because of the weird timings of some arcade systems.

I've done a lot of comparisons of MiSTer's analogue output vs real hardware on CRTs and in most cases it's 1:1. Meaning that if you get your set adjusted once for general 240p, it should display MiSTer's content fine out of the box, without the need for additional tweaking.

Amiga with its horizontal shift is an outlier, but this problem is the same on OG hardware so MiSTer simply replicates it (similar to its multum of different in-game resolutions/positions). In this case I'd also appreciate if there was an OSD-based adjustment option.

Arcades are a resolution wild west and a major rabbit hole regarding this subject. It's a well known fact, even in the world of dedicated solutions such as groovymame, and so at some point I gave up chasing "perfect" output and just went with an approximate "best". Honestly recomend it this mindset service menu change, gives you much more time to simply play games ;)

For those on a mission there are also hardware solutions - some cheap Extrons let you manipulate H+, and there is also this RGBS adjuster (seems to work, though I haven't tried it with MiSTer myself so proceed with caution).

akeley wrote: ↑Tue Jul 25, 2023 3:40 pm

For those on a mission there are also hardware solutions - some cheap Extrons let you manipulate H+, and there is also this RGBS adjuster (seems to work, though I haven't tried it with MiSTer myself so proceed with caution).

I've seen people on reddit mention that those aliexpress devices result in reduced video quality. Would definitely be interested in a similar device that was better made though.

Lots of cheap Extron equipment available on ebay now that was used in professional CRT applications. You should be able to find something that can do some position adjustment there and deliver fairly good quality.

Any idea exactly what Extron units I would be looking for that supports h / v position and h / v size? Presumably I need something that keeps all signals in the analogue domain or there is going to be lag introduced due to digital processing.

I've never been able to find anything that does size properly, but the RGB 203rxi does h and v position well. Provided you aren't using an interlaced signal.

FoxbatStargazer wrote: ↑Mon Jul 24, 2023 12:57 pm

The Amiga core could really use this, IMO. Its positioned so far out compared to other cores!

Here's a particularly egregious example (VideoKid):

Notice that it is significantly shifted downwards, whereas normally on the Amiga you get a slight shift to the right: