Hello SideFX,

I just submitted a RFE which appears to be a bug when trying to use conditional statements in vex to assign a color. This color is going onto a deforming bounding box, and it is based on the normals of the object.

Here is a video describing the issue:
https://vimeo.com/1147066452/90951ee99a [vimeo.com]


Any and all are insights are much appreciated.
Thank you ahead of time!

- Tyler

You may want to try comparing with tolerances -- eg.

Hi Tyler,

The issue is float equality. Normals are approximate, not exact axis vectors. On some frames the components evaluate to values like 0.9999999403953552 rather than 1.0, so the == checks fail. You can see this by enabling full precision in the Details View.

So I would just do this:

malexander
You may want to try comparing with tolerances -- eg.

if(a==0.0) --> if(abs(a) < 1e-6)  
if(a==1.0) --> if(abs(a-1.0) < 1e-6)

Okay, that worked.

Thanks malexander! It looks like the precision was off. Does this approximate precision with the Normal node have to do with the mathematical equation that generates the value? And do you know if the full precision is, by default, turned off?

The normal SOP would be taking 32b point positions and doing the calculation in 64b, then converting to the final 32b normal. The Geometry spreadsheet may be pretty-printing the value, so something like 0.9999998 would appear as 1.0. Floating point precision can be inexact, so unless you absolutely need to be checking against an exact value (often 0.0), use a fuzzy comparison with a small epsilon value. (Integers are exact, so you're fine doing exact comparisons there)

Thanks for the explanation. That makes sense on a technical level.

From a user experience perspective... well... I'm sure about 99% of newer Houdini users won't know what to make of it when the geo spreadsheet values shows them values that aren't the actual value by default. I suppose I'll just need to warn them about it.

Thanks again!