Scalability of shaders


I love the crt_lottes_multipass filter, and use it for all my old emulated consoles. However, I recently started using Flycast for Naomi/Atomiswave arcade games, and the filter doesn’t look quite right. The grid aperture simulation looks somewhat stretched, and the overall effect just feels a bit off.

I have these games set up for 480p in the core options. When I reduce it to 224p, the shader looks right again, but the emulated image suffers from some visual glitches at this resolution, with our without shaders. Besides, games in that platform had a mix of 224p and 480p images, so I would not want to run it that low anyway.

It seems the shader in question is specifically tuned for the 320x224 resolution of old consoles, which makes sense and does the job admirably. The question is whether there is a way make the image look correct at twice the resolution. There is a scale parameter in the shader (from the Retroarch menu), but it doesn’t seem to make any difference when I change it.

Any ideas?

You’re on the right track. Unless the shader is designed to handle higher resolutions (and few are), you’ll need to run a first pass that scales the image down to 240p if you want the shader to look right.

Thanks for the tip, sir. I’ll monkey around with the shader settings to see if can achieve this.

There are some examples in the ‘presets’ directory of the slang shaders (check the “stock” variants of some of the CRT shaders), as well as some posts about it here on the forum. Search for the keyword ‘downsample’, I think.