Geometry Nodes: Add Mesh to Curve Node

This node creates poly curve splines from mesh edges. A selection
attribute input allows only using some of the edges from the mesh.
The node builds cyclic splines from branchless groups of edges where
possible, but when there is a three-way intersection, the spline stops.

The node also transfers all attributes from the mesh to the resulting
control points. In the future we could add a way to limit that to a
subset of the attributes to improve performance.

The algorithm is from Animation Nodes, written by @OmarSquircleArt.
I added the ability to use a selection, attribute transferring, and
used different variable names, etc, but other than that the algorithm
is the same.

Differential Revision: https://developer.blender.org/D11265

release/scripts/startup/nodeitems_builtins.py

@@ -503,6 +503,7 @@ geometry_node_categories = [
     GeometryNodeCategory("GEO_CURVE", "Curve", items=[
         NodeItem("GeometryNodeCurveToMesh"),
         NodeItem("GeometryNodeCurveResample"),
+        NodeItem("GeometryNodeMeshToCurve"),
     ]),
     GeometryNodeCategory("GEO_GEOMETRY", "Geometry", items=[
         NodeItem("GeometryNodeBoundBox"),