GLSL dot function

[tonirandell]

Hi!

I was porting this old seascape-code from shadertoy Shader - Shadertoy BETA and came up with some kind of a tearing problem like in the first picture here.

Somehow I found out that if I change the second part of the dot-function on the line 48 (of the code in the picture) to integers (line 50), the tearing disappears like in the next picture here.

I don’t understand what is happening here, can someone explain it to me?

Toni.

[malcolm]

This has come up a few times. It seems like a defect in that hash function, that results in some artifacts at certain intervals on certain GPUs. It’s not TouchDesigner specific, but different shading languages (CUDA/WebGL/Vulkan etc) have different rules for how floating point precision and the sin() function works.

[malcolm]

More information in this post:

Book of Shaders and TouchDesigner

Here’s a crazy helpful answer that Nvidia gave: The use of sin() here is exactly the issue; graphics APIs in general don’t guarantee that sin() produces consistent results across APIs or platforms. The best practice for random number generators is to use integer-based RNG instead of sin(); this is guaranteed to be consistent, often produces better results, and is sometimes faster. The short answer is that I recommend using one of the “2->1” hashes in Jarzynski and Olano’s “Hash Functions for GP…