[arc in 3D] placing an arc/angle between lines in 3D. #manim #3D #angle #arc

20240524_arc3d.py

from manim import *
# https://discord.com/channels/581738731934056449/1096718885606150154/1096718885606150154

class arc3d(VMobject):
    def __init__(self, A=None, B=None, center=None, radius=1, segments=40, **kwargs):
        super().__init__(**kwargs)
        start = center + (A-center)*radius/np.linalg.norm(A-center) 
        end   = center + (B-center)*radius/np.linalg.norm(B-center) 
        self.set_points([start])
        for i in np.linspace(0,1,segments,endpoint=True):
            dotonline = start + i*(end-start)
            radline = dotonline-center
            dotonarc = center + radline/np.linalg.norm(radline)*radius
            self.add_smooth_curve_to(dotonarc)
            
class threeDarcTestCube(ThreeDScene):
    def construct(self):
        cs = ThreeDAxes()
        self.add(cs)
        corners = np.array([[0,0,0],[1,0,0],[1,1,0],[0,1,0],[0,0,1],[1,0,1],[1,1,1],[0,1,1]])*3-np.array([1,1,1])
        cube = VGroup(
            *[Line(corners[i],corners[(i+1)%4]) for i in range(4)],
            *[Line(corners[4+i],corners[4+(i+1)%4]) for i in range(4)],
            *[Line(corners[i],corners[i+4]) for i in range(4)],
            *[Dot3D(corners[i]) for i in range(8)]
        )
        self.move_camera(phi=75 * DEGREES, theta=25 * DEGREES)
        self.play(Create(cube))

        line1 = Line(corners[1],corners[7]).set_color(RED)
        line2 = Line(corners[3],corners[5]).set_color(BLUE)
        self.play(Create(line1),Create(line2))
        self.wait()

        arc1 = arc3d(A=corners[1],B=corners[3],center=cube.get_center(),radius=1,segments=30).set_color(YELLOW)
        arc2 = arc3d(A=corners[1],B=corners[5],center=cube.get_center(),radius=1.3,segments=30).set_color(TEAL)        

        self.play(Create(arc1))        
        self.play(Create(arc2))
        self.wait()

        arc3 = arc3d(A=corners[1],B=corners[3],center=corners[5],radius=1,segments=30).set_color(ORANGE)
        arc4 = arc3d(A=corners[7],B=corners[3],center=corners[1],radius=0.7,segments=30).set_color(GREEN)        
        line4 = DashedLine(corners[1],corners[3])
        self.play(Create(arc3))        
        self.play(Create(arc4))
        self.play(Create(line4))
        self.wait()        

readme.md

https://discord.com/channels/581738731934056449/1096718885606150154/1096718885606150154