Shaders 101

sad_muso

Hi,

I've posted elsewhere on here about shaders, but thought it could be handy to have a n00b thread up for people like me that are new to this.

I am currently trying to get shaders working (specifically ones that emulate CRT curve and scanlines), but have straight away run into performance issues with framerate drops/input lag. I'm currently using the Genesis as the test bed. I've even tried Z_PI_CRT which claims to run at 60fps @ 1080p, yet still had issues in Sonic 2.

I have a few questions about shaders in general:

Are they CPU/RAM intensive or both? Does the Pi 4 cope with shaders better than the 3 B?
Do overlays cause any hit on performance, specifically when used in conjunction with shaders?
What is the least expensive way to implement curve and scanlines that is currently in existence?

SETUP DETAILS
Model: Pi 3 B
Power Supply: Official 5.1v 2.5A
RetroPie Version: 4.6
Built From: Pre made SD Image on RetroPie website (Pi 2/3) - md5: 2e082ef5fc2d7cf7d910494cf0f7185b

Thank you!

dankcushions

@sad_muso you didn't say what emulator you're using. afaik even simple shaders are often very system bus intensive, so they're constantly fighting for bandwidth with the GPU, CPU, etc. afair, lr-genesis-plus-gx really hammers the system bus, so try using lr-picodrive instead, if you're using the former.

Are they CPU/RAM intensive or both? Does the Pi 4 cope with shaders better than the 3 B?

first part answered above. pi 4 will cope better.

Do overlays cause any hit on performance, specifically when used in conjunction with shaders?

yes, for whatever reason they seem to.

What is the least expensive way to implement curve and scanlines that is currently in existence?

the way you're doing it already - z_pi_crt.