I often work with instances or deform geometry along splines, and I consistently find myself struggling to control the output of my operations. Blender sometimes changes the spline direction randomly after I move just one of the curve’s control points. Notably, this direction change occurs with previously splited curves that are later merged back together.

This behavior is incredibly frustrating because there is no specific criteria for when Blender decides to reverse any spline. Despite my attempts to establish a control system to prevent these random direction changes, I have not been successful.

Could you please explain Blender’s rules for switching a spline’s direction? Additionally, is there a way to maintain stable spline directions?

Here’s a .blend file demonstrating the issue. It’s part of a large node tree that I’ve simplified to highlight the problem. There may be several elements that could be confusing, and I apologize for that.

  • $\begingroup$ In Edit Mode, you can select all points by pressing A, then right-click, and Switch Direction. It doesn't solve your issue procedurally but it may help. $\endgroup$
    – Lutzi
    Mar 4 at 16:08
  • $\begingroup$ I can't reproduce this.. can you share a misbehaving file on blend-exchange.com ? And describe how to make this happen? The tilt can spin around depending on the shape of a curve, but that seems a different question $\endgroup$
    – Robin Betts
    Mar 4 at 19:32
  • 1
    $\begingroup$ @RobinBetts I have uploaded a blend file $\endgroup$ Mar 6 at 9:57


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