Video artifacts (black snow effect) if "curve" effect enabled.

[ale-79]

This is very likely an issue with my ancient hardware rather than with Gopher2600...

Anyway, a few days ago I started experiencing system freezing and crashes caused by my video card, so as a quick fix, I replaced it with another one I had in my stack of old PC parts.
The "new" card is a Radeon HD 4670, and in addition of fixing the crashes and still being adequate for the basic "office" tasks my PC is used for 99% of the times, I was extremely pleased to discover that Gopher2600 now runs most games at full-speed, with only occasional slight slowdown for ARM ones, while with my old card it struggled a lot!

On the flip side, I'm now experiencing a black "snow effect" artifact, only visible if I set the "curve" effect in the CRT tab (and so also if enable the bevel). The display was fine, albeit slow, with the "old" card.

Here is a video showing the issue.
https://youtu.be/rpwzDTJL5tY

The intensitiy of the snow effect isn't always the same. On occasion it's barely visible, but most of the time is quite heavy like in the video.

A few screenshots:

As I said, it's probably an issue with my system, but I decided to report it anyway, just in case.
I'm aware that the fix is likely to use hardware made at least in the last decade! 😄

[JetSetIlly]

Gosh. That is strange. I develop with an Nvidia card but I have access to a Radeon so I'll test it out.

The fact that the problem disappears completely when you disable the curve option narrows it down a bit.

What OS are you on? What version of the Radeon driver are you using?

What was the old card?

[JetSetIlly]

The other thing you could try is disabling the "RF Noise" option with the "curve" option enabled.

The black snow looks a bit like the RF noise generation after all. Not sure why it would only be an issue with the curve option though.

[ale-79]

What OS are you on?

Arch Linux

What version of the Radeon driver are you using?

I'm using the open source driver which, if I understand it correctly, is built in to the kernel. Kernel version is 7.0.10.

What was the old card?

Radeon HD 5450

The other thing you could try is disabling the "RF Noise" option with the "curve" option enabled.

I already tried every combination of options, but the only one that causes the snoweffect is "curve", no matter how the other options are set.

[JetSetIlly]

I tested this on my Radeon GPU and it works as expected. That and the fact your previous Radeon was okay suggests that it's an issue specific to your current GPU.

We'll keep the issue open though in case anybody knows different.

For reference, the curve is achieved through UV distortion. I also add a chromatic aberration and a vignette effect when curve is enabled. Both effects are more intense towards the outer edges of the screen.

[ale-79]

Many thanks for taking the time to look into this.

[JetSetIlly]

I've asked around and the best suggestion I've got so far is that it's an issue with the open source driver for that specific Radeon GPU. An actual hardware defect seems unlikely because it's a very specific error.

[ale-79]

Thanks again.
I've looked into installing the old "catalyst" proprietary driver, but it's unsupported and deprecated in Arch Linux, and reported to frequently break with kernel updates.

I'll just keep the "curve" effect turned off for now.