Shader artifacts on PAL refresh rates

I observed that when playing PAL games in a LCD display set to a 50Hz refresh rate some artifacts arise. This is true when using a shader (observed in crt-royale and crt-aperture) in any core (tested genesis plus gx and bsnes-balances-mercury) specially on screen tilts (camera up-down motion). It looks like blinking or a shadow blink.

If I disable the shader it looks fine (well, some corner case artifacts with flashing lights like this one on alien soldier). I’m guessing but I wonder if the shader system is tied to the refresh rate or some aspect of the custom modeline in some form.

Hmm, it shouldn’t, AFAIK, aside from whatever the driver is doing under the hood.

Do you have any other displays to see if the issue follows to it?

I have my monitor, the main game display is the 1080p HDTV so I configured the modelines for that display only, I just tried to set my monitor to 50Hz to test but it tops at a bitdepth of 16.

I will try to record some clips tomorrow if nobody can reproduce the issue, will test with more shaders. Aside Retroarch I tested other emulators (Dolphin, PCSX2) and so far I didn’t spot any issues, granted I don’t use scanlines there but I would have expected something similar to Alien Soldier, which should be a more profound problem (maybe linked to this too), or find some flashing lights to compare against. In case the artifacts look like a damaged GPU, I bought it just 8 months ago.

In my opinion these are two different issues but I think this one is easier to trace and also the more frequent I get. Guess an image/video will speak volumes.

The modeline is a standard 1920x1080 with 720 and 45 blanking lines at 148.50Mhz.

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I did some tests, for the Alien Soldier issue (no shaders here) I run it in stand alone blastem and it also presents the same artifacts at 50Hz, so I think this is a problem related to modelines, should be nice if someone with a CRT could test if it runs fine there.

For the shader artifacts I tested with most of them inside the crt folder. To some degree they all show the scanline flicker, if I play at 60Hz the scanlines blends in and everything is smooth. I tried recording a video with my smartphone but quality is crappy at only 720p, anyway here it is, (link) at second 29 it can be clearly seen on shade areas.

I tried recording with OBS and it recorded and played fine without the shader issues, so this also seems to be an issue with modelines and presentation. I guess I should run more tests with the shader test suite and see where and why it fails.

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hmm, yeah, i couldn’t tell much from the video, but yeah, if it’s recording fine in OBS, it seems likely that it’s something/somewhere between the GPU and the display. Dunno, though.