What is the fastest way to add vertices to a curve at a specific point?

Question

For example, in inkscape you can double click to add a new control vertex:

Is there a way to do that in Blender?

The closest thing I have found so far is CtrlLMB, but it just adds an unconnected vertex under the cursor.

Is there a way to add a connected vertex at a specific point along the curve, preferably without deforming the curve?

Answer 1

You can script this functionality with python and install it as an addon. I have created such a script.

Curve Edit Tools

Github download link

To use the addon, press I in the Edit Mode of a curve. You'll be prompted into a modal operation where you can slide a new control point along the curve.

The original answer is below, it doesn't cover all the features of the current addon, even the point sampling will be replaced soon. The revision history shows the old addon for 2.7x.

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The first step is to import some modules.

• bpy Interaction with Blenders data and operations
• bgl Blenders OpenGL wrapper
• blf Module for font drawing
• numpy as np Matrix handling, used for mathematical vector operations
• mathutils Use to create the mathutils.Vector

Create a Bezier class

A Cubic Bézier is a very simple mathematical construct.

It needs four points.

0. first control point.
1. first handle (right_handle)
2. second handle (left_handle of second point)
3. second control point

$$ b(t) = \sum_{i=0}^{3} \binom{3}{i} t^i (1-t)^{3-i} b_i \\ = (1-t)^3 b_0 + 3t(1-t)^2 b_1 + 3t^2(1-t) b_2 + t^3 b_3 \\ = (-b_0 + 3b_1 - 3b_2 + b_3)t^3 + (3b_0 - 6b_1 + 3b_2)t^2 + (-3b_0 + 3b_1)t + b_0, \quad t \in [0,1] $$

The De Casteljau's algorithm illustrates how points on the curve are found. The formula takes a $t$ in $[0,1]$.

To split the curve at a specific $t$, we can use the method from this answer. Since we use numpy, we can use the points as points.

class CubicBezier(object):
    def __init__(self, points):
        self.points = np.array(points).astype(np.float32)

    def at(self, t):
        pt =  1 *        (1 - t)**3 * self.points[0]
        pt += 3 * t**1 * (1 - t)**2 * self.points[1]
        pt += 3 * t**2 * (1 - t)**1 * self.points[2]
        pt += 1 * t**3              * self.points[3]
        return pt

    def split(self, t):
        p1, p2, p3, p4 = self.points
        
        p12 = (p2-p1)*t+p1
        p23 = (p3-p2)*t+p2
        p34 = (p4-p3)*t+p3
        p123 = (p23-p12)*t+p12
        p234 = (p34-p23)*t+p23
        p1234 = (p234-p123)*t+p123

        return [p1,p12,p123,p1234,p234,p34,p4]

Next, we need to sample the point closest to the mouse position. Using this algorithm, pick discrete samples and convert them into the 2d region

Thats basically everything from the maths side, now just wrap it in a modal operator.

Here is an example of a modal operator drawing in the 3D View.

Answer 2

According to the Blender documentation for Bezier curves and NURBS curves there is no way to add a new point between two existing points without using the subdivide mechanism (selecting two or more points on the curve, W, Subdivide.

I too wish that there were. Perhaps sometime in the future.

Answer 3

With the last vector in the curve selected, press E for Extrude.

Blender will produce a new vector and attach itself to the cursor. You can move the new vector and left-click to place it.