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This problem is absolutely driving me crazy for over a week now. All I need is a bezier curve that starts at point with coordinates (x1, y1, z1,) and ends at a point with coordinates (x2, y2, z2).

I attempted to write a function using basic coordinate geometry, and it works pretty well 90% of the times, but fails depending on domain/range of numpy.atan. (It creates a bezier curve between the two points, then scales and rotates it appropriately)

def connect_points(v1, v2):
    midpoint = [(1 / 2) * (v1[0] + v2[0]), (1 / 2) * (v1[1] + v2[1]), (1 / 2) *(v1[2] + v2[2])]
    distance = math.sqrt((v2[0] - v1[0]) ** 2 + (v2[1] - v1[1]) ** 2 + (v2[2] - v1[2]) ** 2)
    z_rotation = math.atan((v2[1] - v1[1]) / ((v2[0] - v1[0]) + 0.00001))
    y_rotation = -math.atan((v2[2] - v1[2]) / math.sqrt((v2[1] - v1[1]) ** 2 + (v2[0] - v1[0]) ** 2))
    bpy.ops.curve.primitive_bezier_curve_add(location=midpoint, radius=distance / 2, rotation=[0, y_rotation, z_rotation])
    bpy.context.object.data.bevel_depth = 0.010

I am not willing to spend another week trying to write different cases for arctan. Is there a simpler way?

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1 Answer 1

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Using API methods rather than operator.

Using methods outlined similar to those in Bezier-Spline with Python adds unwanted point .

Method to create a 2 point bezier curve object, with each end at defined global locations and the origin in the middle. Notice the left and right handles types are set to auto resulting in a straight line.. (perhaps a poly would be simpler in this situation)

import bpy
from mathutils import Vector

def add_bezier(v0 , v1):
    v0, v1 = Vector(v0), Vector(v1)  
    o = (v1 + v0) / 2  

    curve = bpy.data.curves.new('Curve', 'CURVE')
    spline = curve.splines.new('BEZIER')
    bp0 = spline.bezier_points[0]
    bp0.co = v0 - o
    bp0.handle_left_type = bp0.handle_right_type = 'AUTO'

    spline.bezier_points.add(count=1)
    bp1 = spline.bezier_points[1]
    bp1.co = v1 - o
    bp1.handle_left_type = bp1.handle_right_type = 'AUTO'
    ob = bpy.data.objects.new('Curve', curve)
    ob.matrix_world.translation = o
    return ob

As an example of usage, select a mesh object and run script below to add curves matching each edge.

context = bpy.context
scene = context.scene
ob = context.object
mw = ob.matrix_world
me = ob.data

for e in me.edges:
    pts = [mw @ me.vertices[v].co for v in e.vertices]
    o = add_bezier(*pts)
    curve = o.data    
    curve.dimensions = '3D'
    curve.bevel_depth = 0.010
    curve.bevel_resolution = 3
    scene.collection.objects.link(o)

Note should you wish to not use the global coordinates, could make a single axis aligned curve, and align it using the methods outlined in Align Object to Vector using python (consider using an end as origin)

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  • $\begingroup$ I would never use v0, v1 = Vector(v0), Vector(v1) as you're changing the type of v0 and v1. Also if you don't want to calculate handle points, you can set the handle types to AUTO. $\endgroup$
    – dr. Sybren
    Commented Jun 6, 2018 at 21:22
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    $\begingroup$ @dr.Sybren Thankyou, changed to auto handles, using foreach_set on two points was a little overkill.. Changing the type of v0, v1 to Vector is exactly the intended result... could check to see if they are not vector types then convert them to vectors as they are only going to be used as vectors ... confusing. Importantly wanted to point out to OP to use vectors and not reinvent the wheel with Euclidean distance formulae et al. $\endgroup$
    – batFINGER
    Commented Jun 7, 2018 at 7:52

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