Every 3D modelling software simply uses a series of flat polygons, small enough to appear curved, to created spheres etc. Why? Why can technology even today find it easier to render literally millions of little triangles, than just one curve?
In: Technology
As other people have mentioned you can use curves in 3D modelling software.
If you want to put your 3D model into a game though, most games don’t render curves, so the modelling software will convert your curves into a series of polygons.
Most games don’t render curves because triangles are much easier and still good enough.
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