This is the amount of shader ISA code the compiler produces for a single atan2(). Avoid using it for time critical code. - ThreadSky

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kostasanagnostou.bsky.social • 145 days ago

This is the amount of shader ISA code the compiler produces for a single atan2(). Avoid using it for time critical code.

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fatlimey.bsky.social•144 days ago

They went with a polynomial ATAN2? But that's the perfect example of CORDIC in action.

https://inria.hal.science/hal-01091138/document

impossible.bsky.social•145 days ago

I see people over use (imo) atan2 a lot. Granted it's mostly in gameplay code, not shader code, but a common pattern is to use atan2 to find the angle between two points and use that angle to rotate a vector to get facing direction, when a simpler normalize would work.

impossible.bsky.social•145 days ago

#pico-8 has weird behavior where this is faster, because sqrt's artificial cost is higher than atan2's artificial cost in the VM. sqrt is 48 "cycles" and atan2 is 4.

srekel.net•145 days ago

Yikes. Is atan2 as bad on the CPU? What are some alternatives?

dneto.dev•145 days ago

And GPU apis allow the implementation to take a lot of shortcuts, so you almost certainly won't get IEEE behaviour. And there are a lot of rough corners on this one.
We had to dumb down WGSL's definition after testing various back ends in our CTS.

https://www.w3.org/TR/WGSL/#atan2-builtin

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