Boolean union of two different colored objects doesn't retain color?

Rhino Rhino for Windows
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I’m surprised by this in Rhino 8. Could have sworn someone from McNeel said that they would become per face colors in an old Serengeti (Rhino WIP) topic, but now I can’t find mention of it…

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I know it was requested, but I don’t believe it was implemented. IIRC if both (all) objects have per-face colors set, it should work. (Edit: just checked, and it does.) I think I made a script to convert objects to per-face color at that time, let me see if I can find it and if it works…

Here it is:
ConvertToPerFaceColors.py (1.6 KB)

Ah, what’s interesting is that it works to preserve the per-face colors on the surfaces, however, the result still has one single “object color” which is applied to all the edges. So the results can be funny.

1 Like
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Thanks for the script! Your observations are unfortunately correct.

Here’s what I think Rhino should do, and maybe the script can be modified to do it:

  1. Check if the selection contains objects of different color.
  2. If so, convert all but one of those objects to per face colors instead.
  3. Boolean union them to get a correctly colored result.

Unfortunately I haven’t learned scripting well enough to modify it, but maybe one of these days I’ll take my time to try.

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Well, it is possible that people will want to have the result be one single object with one single color. So that means we would need a PreservePerFaceColors=Yes/No command line switch on all the Boolean operations - but also Join etc.! - or something That’s a pretty extensive modification and who knows what else it might break…

If you don’t have a lot of objects, mouse pick select the object you want to retain the object color first, then the rest. I think the result will take on the object color of the first picked object.