"NURBS Curve Nodes" node.

a5dc101f · Ilya Portnov · ebe4f681 · a5dc101f · a5dc101f · a5dc101f
--- a/docs/nodes/curve/curve_index.rst
+++ b/docs/nodes/curve/curve_index.rst
@@ -33,6 +33,7 @@ Curves
   length_rebuild
   curvature
   torsion
+   nurbs_curve_nodes
   deconstruct_curve
   curve_frame
   curve_frame_on_surface

--- a/docs/nodes/curve/nurbs_curve_nodes.rst
+++ b/docs/nodes/curve/nurbs_curve_nodes.rst
+NURBS Curve Nodes
+=================
+
+Functionality
+-------------
+
+This node calculates so-called *node* points (also known as Greville points or
+average knot points) of the NURBS curve.
+NURBS curve *nodes* (or Greville abscissaes) are defined as:
+``t[i] = sum(u[i+j] for j from 1 to p) / p``, where ``u`` is curve's knotvector, and
+``p`` is curve's degree.
+NURBS curve *node points* (or Greville points) are points at the curve at
+parameter values equal to node values.
+The number of curve's nodes is equal to the number of curve's control points.
+Node points of the curve are positioned on the curve near corresponding control
+points. So in many NURBS algorithms, node points are used to define the shape
+of NURBS curve, instead of control points.
+
+Inputs
+------
+
+This node has the following input:
+
+* **Curve**. The NURBS Curve object to calculate nodes for. This input is mandatory.
+
+Outputs
+-------
+
+This node has the following outputs:
+
+* **Points**. The calculated node points on the curve.
+* **T**. The calculated node values (values of curve's T parameter corresponding to node points).
+
+Example of Usage
+----------------
+
--- a/index.md
+++ b/index.md
@@ -68,6 +68,7 @@
    SvApproxNurbsCurveMk2Node
    SvExInterpolateNurbsCurveNode
    SvDeconstructCurveNode
+    SvNurbsCurveNodesNode
    ---
    SvCurveInsertKnotNode
    SvCurveRemoveKnotNode

--- a/nodes/curve/nurbs_curve_nodes.py
+++ b/nodes/curve/nurbs_curve_nodes.py
+# This file is part of project Sverchok. It's copyrighted by the contributors
+# recorded in the version control history of the file, available from
+# its original location https://github.com/nortikin/sverchok/commit/master
+#
+# SPDX-License-Identifier: GPL3
+# License-Filename: LICENSE
+
+import numpy as np
+
+import bpy
+from bpy.props import FloatProperty, EnumProperty, BoolProperty, IntProperty
+
+from sverchok.node_tree import SverchCustomTreeNode
+from sverchok.data_structure import (updateNode, zip_long_repeat, ensure_nesting_level,
+                                     get_data_nesting_level)
+from sverchok.utils.curve import SvCurve
+from sverchok.utils.curve.nurbs import SvNurbsCurve
+
+class SvNurbsCurveNodesNode(bpy.types.Node, SverchCustomTreeNode):
+    """
+    Triggers: NURBS curve nodes (Greville points)
+    Tooltip: Display nodes (a.k.a edit points or Greville points) of a NURBS curve
+    """
+    bl_idname = 'SvNurbsCurveNodesNode'
+    bl_label = 'NURBS Curve Nodes'
+    bl_icon = 'OUTLINER_OB_EMPTY'
+    sv_icon = 'SV_DECONSTRUCT_CURVE'
+
+    def sv_init(self, context):
+        self.inputs.new('SvCurveSocket', "Curve")
+        self.outputs.new('SvVerticesSocket', "Points")
+        self.outputs.new('SvStringsSocket', "T")
+
+    def process(self):
+        if not any(socket.is_linked for socket in self.outputs):
+            return
+
+        curve_s = self.inputs['Curve'].sv_get()
+
+        curves_level = get_data_nesting_level(curve_s, data_types=(SvCurve,))
+        curve_s = ensure_nesting_level(curve_s, 2, data_types=(SvCurve,))
+
+        points_out = []
+        t_out = []
+        for curves in curve_s:
+            point_list = []
+            t_list = []
+            for curve in curves:
+                ts = curve.calc_greville_ts()
+                pts = curve.evaluate_array(ts)
+                t_list.append(ts.tolist())
+                point_list.append(pts.tolist())
+
+            if curves_level == 2:
+                points_out.append(point_list)
+                t_out.append(t_list)
+            else:
+                points_out.extend(point_list)
+                t_out.extend(t_list)
+
+        self.outputs['Points'].sv_set(points_out)
+        self.outputs['T'].sv_set(t_out)
+                
+def register():
+    bpy.utils.register_class(SvNurbsCurveNodesNode)
+
+def unregister():
+    bpy.utils.unregister_class(SvNurbsCurveNodesNode)
+