This seems slower than it should work...

We tested on a couple of computers and got different results. On @smokris’s computer, both versions ran steadily at 60 fps, even after 1 hour. On my computer, both versions ran at 10-15 fps.

Is almost seems like it’s working on the CPU instead of GPU.

That could be. Sometimes when we get shader code that runs just fine on one computer and slowly on another, it’s because the one GPU driver doesn’t like something in the GLSL code so it does a software fallback.

Would the built-in Displace 3D Object with Image node work for you? Or are you just using heightfields as an example to test shaders?

Probably related, I get a lot of this in Console:

It was slow on my computer without the Console messages, so I don’t think that’s the problem. These have come up for other compositions, too, so I created public bug reports: “CODE SIGNING: cs_invalid_page” warnings in Console and “Excessive wakeups” warnings in Console.