Slow NES and SNES games using shaders

[Steve_C78]

Hello everyone,
a few weeks ago I bought a Retroflag superpi case for rpi3 to play only nes and snes games.
I installed Retropie 4.8 on a 32 Gb sd and put the nes and snes roms.
I inserted an overlay that covers the black bands on the sides simulating an old nintendo TV and I use the crt-pi shaders to get as close as possible to the old CRTs.
The problem is that when I enable the shaders the nes and snes games run very slow.
If I disable the shaders everything seems to be ok.
After a while sometimes I also notice the thermometer icon at the top right which probably warns me of an overheating of the rpi3 when I stress it with the shaders.
At the moment I don't use cooling fans inside the superpi case but only passive heatsinks. I'm still gearing up with an extra fan.
Can you tell me if I have to set particular settings in the various core settings? Or does the rpi3 have some hardware limitations to support the use of shaders?
I use the superpi on a full HD TV and therefore as the video output of retropie I set 1080.
I am only interested in playing nes and snes titles and I thought the rpi3 was more than enough for these consoles

[Darksavior]

@Steve_C78 I retired my pi3 so I'm not totally sure but I can give you some options.

At the moment I don't use cooling fans inside the superpi case but only passive heatsinks.

I wouldn't continue troubleshooting until you install a fan. The case you're using supports it. Overheating makes the pi slow itself down and shows you the thermometer icon.

I inserted an overlay that covers the black bands on the sides simulating an old nintendo TV and I use the crt-pi shaders to get as close as possible to the old CRTs.

I don't use overlays so I'm not sure if that's causing the slowdowns. You can try it with only the crt-pi shader. You can also try the zfast-crt shader that's more lightweight on resources.

I thought the rpi3 was more than enough for these consoles

No, a pi3 is not enough for the latest version of snes9x. You need a pi4 for that. The default/recommended emulator for the pi3b is lr-snes9x2010 so make sure you're using that. You might still get slowdowns with special chip games.

[dankcushions]

@Steve_C78 which shaders? which specific emulators? please fill out https://retropie.org.uk/forum/topic/3/read-this-first including verbose log

please read https://retropie.org.uk/docs/Shaders-and-Smoothing/

overlays + shaders compound the performance drain, so may not be feasible for all games. reducing resolution will help performance but reduce fidelity such that scanline shaders look awful, for example.

if you're seeing the thermometer icon, your pi is overheating and reducing internal clocks to reduce the temperature. fans/better case will at least allow it to throw as much power as it can at your config.