Add an option to preserve tangent.

606f84b7 · Ilya Portnov · a437c3b4 · 606f84b7 · 606f84b7
--- a/nodes/curve/move_nurbs_curve_point.py
+++ b/nodes/curve/move_nurbs_curve_point.py
@@ -18,7 +18,7 @@ from sverchok.utils.curve.nurbs_algorithms import (
            move_curve_point_by_moving_control_point,
            move_curve_point_by_adjusting_one_weight,
            move_curve_point_by_adjusting_two_weights,
-            move_curve_point_by_moving_control_points,
+            move_curve_point_by_moving_control_points, TANGENT_PRESERVE,
            move_curve_point_by_inserting_knot)

 class SvNurbsCurveMovePointNode(bpy.types.Node, SverchCustomTreeNode):
@@ -71,8 +71,15 @@ class SvNurbsCurveMovePointNode(bpy.types.Node, SverchCustomTreeNode):
            default = 1.0,
            update = updateNode)

+    preserve_tangent : BoolProperty(
+            name = "Preserve tangent",
+            default = False,
+            update = updateNode)
+
    def draw_buttons(self, context, layout):
        layout.prop(self, 'method')
+        if self.method == 'MOVE_CPTS':
+            layout.prop(self, 'preserve_tangent')

    def sv_init(self, context):
        self.inputs.new('SvCurveSocket', "Curve")
@@ -120,7 +127,11 @@ class SvNurbsCurveMovePointNode(bpy.types.Node, SverchCustomTreeNode):
                elif self.method == 'TWO_WEIGHTS':
                    curve = move_curve_point_by_adjusting_two_weights(curve, t_value, index, distance=distance)
                elif self.method == 'MOVE_CPTS':
-                    curve = move_curve_point_by_moving_control_points(curve, t_value, vector)
+                    if self.preserve_tangent:
+                        tangent = TANGENT_PRESERVE
+                    else:
+                        tangent = None
+                    curve = move_curve_point_by_moving_control_points(curve, t_value, vector, tangent=tangent)
                elif self.method == 'INSERT_KNOT':
                    curve = move_curve_point_by_inserting_knot(curve, t_value, vector)
                else:

--- a/utils/curve/nurbs_algorithms.py
+++ b/utils/curve/nurbs_algorithms.py
@@ -818,8 +818,9 @@ def move_curve_point_by_adjusting_two_weights(curve, u_bar, k, distance=None, sc

 WEIGHTS_NONE = 'NONE'
 WEIGHTS_EUCLIDIAN = 'EUCLIDIAN'
+TANGENT_PRESERVE = 'PRESERVE'

-def move_curve_point_by_moving_control_points(curve, u_bar, vector, weights_mode = WEIGHTS_NONE):
+def move_curve_point_by_moving_control_points(curve, u_bar, vector, weights_mode = WEIGHTS_NONE, tangent = None):
    """
    Adjust the given curve so that at parameter u_bar it goues through
    the point C[u_bar] + vector instead of C[u_bar].
@@ -886,13 +887,29 @@ def move_curve_point_by_moving_control_points(curve, u_bar, vector, weights_mode
    kv = curve.get_knotvector()
    basis = SvNurbsBasisFunctions(kv)
    alphas = [basis.fraction(k,p, curve_weights)(np.array([u_bar]))[0] for k in range(n)]
-    A = np.zeros((ndim,ndim*n))
+    if tangent is None:
+        A = np.zeros((ndim,ndim*n))
+    else:
+        if tangent == TANGENT_PRESERVE:
+            tangent = curve.tangent(u_bar)
+        A = np.zeros((2*ndim,ndim*n))
+        ns = np.array([basis.derivative(k, p, 1)(np.array([u_bar]))[0] for k in range(n)])
+        numerator = ns * curve_weights#[np.newaxis].T
+        denominator = curve_weights.sum()
+        betas = numerator / denominator
    for i in range(n):
        for j in range(ndim):
-            A[j,ndim*i+j] = alphas[i] * move_weights[i]
+            A[j, ndim*i+j] = alphas[i] * move_weights[i]
+            if tangent is not None:
+                A[ndim + j, ndim*i+j] = betas[i] * move_weights[i]
    A1 = np.linalg.pinv(A)
-    B = np.zeros((ndim,1))
-    B[0:3,0] = vector[np.newaxis]
+    if tangent is None:
+        B = np.zeros((ndim,1))
+        B[0:3,0] = vector[np.newaxis]
+    else:
+        B = np.zeros((2*ndim,1))
+        B[0:3,0] = vector[np.newaxis]
+        #B[3:6,0] = tangent[np.newaxis]
    X = (A1 @ B).T
    W = np.diag(move_weights)
    d_cpts = W @ X.reshape((n,ndim))