I wanted to play with the Bezier curve

at first

I wanted to draw a Bezier curve using python, and I was able to draw it immediately. After that, I wanted to play with the Bezier curve interactively, but I couldn't find the code, so I'll post it including a memorandum for myself.

Bezier curve

For the three-dimensional Bezier curve, I referred to the formula of this person.

matplotlib For the part to be displayed interactively, I referred to this person. Every time the control point is updated, the calculation is recalculated and the curve is displayed again.

easy explanation

On the left are control points and Bezier curves. The radius of curvature is displayed on the right. The x-axis of the graph on the right is t (0 <= t <= 1) and the y-axis is the radius of curvature.

code

bezier.py

from scipy import integrate
import matplotlib.pyplot as plt
import numpy as np

class Coo():
    def __init__(self,_x,_y):
        self.x = _x
        self.y = _y

class Bezier():
    def __init__(self,_p0,_p1,_p2,_p3):
        self.p = [0]*4
        self.p[0] = _p0
        self.p[1] = _p1
        self.p[2] = _p2
        self.p[3] = _p3

        self.fig = plt.figure(figsize=(10,5))
        self.ax = self.fig.add_subplot(121)#111 1x1 
        self.ax.set_xlim(-1.0 , 11.0)
        self.ax.set_ylim(-1.0 , 11.0)

        self.dax = self.fig.add_subplot(122)#111 1x1 

        self.t = np.arange(0,1,0.01)
        
        self.x = (self.t**3)*self.p[3].x + 3*(self.t**2)*(1-self.t)*self.p[2].x + 3*self.t*((1-self.t)**2)*self.p[1].x + ((1-self.t)**3)*self.p[0].x
        self.y = (self.t**3)*self.p[3].y + 3*(self.t**2)*(1-self.t)*self.p[2].y + 3*self.t*((1-self.t)**2)*self.p[1].y + ((1-self.t)**3)*self.p[0].y
        
        self.dx = 3*((self.t**2)*(self.p[3].x-self.p[2].x)+2*self.t*(1-self.t)*(self.p[2].x-self.p[1].x)+((1-self.t)**2)*(self.p[1].x-self.p[0].x))
        self.dy = 3*((self.t**2)*(self.p[3].y-self.p[2].y)+2*self.t*(1-self.t)*(self.p[2].y-self.p[1].y)+((1-self.t)**2)*(self.p[1].y-self.p[0].y))

        self.ddx = 6*(self.t*(self.p[3].x-2*self.p[2].x+self.p[1].x)+(1-self.t)*(self.p[2].x-2*self.p[1].x+self.p[0].x))
        self.ddy = 6*(self.t*(self.p[3].y-2*self.p[2].y+self.p[1].y)+(1-self.t)*(self.p[2].y-2*self.p[1].y+self.p[0].y))

        self.artists = [0]*4
        self.artists[0], = self.ax.plot([self.p[0].x],[self.p[0].y],marker='.',markersize=10,picker=15,label='p[0]')
        self.artists[1], = self.ax.plot([self.p[1].x],[self.p[1].y],marker='.',markersize=10,picker=15,label='p[1]')
        self.artists[2], = self.ax.plot([self.p[2].x],[self.p[2].y],marker='.',markersize=10,picker=15,label='p[2]')
        self.artists[3], = self.ax.plot([self.p[3].x],[self.p[3].y],marker='.',markersize=10,picker=15,label='p[3]')
        self.ax_artist, = self.ax.plot(self.x,self.y)

        dp = [((x_a-x_b)**2 + (y_a-y_b)**2)*100 for x_a,x_b,y_a,y_b in zip(self.x[:-1],self.x[1:],self.y[:-1],self.y[1:])]
        adp = [(i**2 + j**2)**0.5 for i,j in zip(self.dx,self.dy)]
        addp = [(i**2 + j**2)**0.5 for i,j in zip(self.ddx,self.ddy)]
        R = ((self.dx**2 + self.dy**2)**1.5)/((self.dx*self.ddy - self.ddx*self.dy)**2)**0.5

        self.dax.set_xlim(-0.1 , 1.5)
        self.dax.set_ylim(-1.0 , 40)
        dp.append(0.0)

        integrate_simps = integrate.simps(self.y, self.x)
        self.dax_artist, = self.dax.plot(self.t,R)

        dp_max_index = [i for i, x in enumerate(dp) if x == max(dp)]
        adp_max_index = [i for i, x in enumerate(adp) if x == max(adp)]

    def change(self):
        self.x = (self.t**3)*self.p[3].x + 3*(self.t**2)*(1-self.t)*self.p[2].x + 3*self.t*((1-self.t)**2)*self.p[1].x + ((1-self.t)**3)*self.p[0].x
        self.y = (self.t**3)*self.p[3].y + 3*(self.t**2)*(1-self.t)*self.p[2].y + 3*self.t*((1-self.t)**2)*self.p[1].y + ((1-self.t)**3)*self.p[0].y
        
        self.dx = 3*((self.t**2)*(self.p[3].x-self.p[2].x)+2*self.t*(1-self.t)*(self.p[2].x-self.p[1].x)+((1-self.t)**2)*(self.p[1].x-self.p[0].x))
        self.dy = 3*((self.t**2)*(self.p[3].y-self.p[2].y)+2*self.t*(1-self.t)*(self.p[2].y-self.p[1].y)+((1-self.t)**2)*(self.p[1].y-self.p[0].y))

        self.ddx = 6*(self.t*(self.p[3].x-2*self.p[2].x+self.p[1].x)+(1-self.t)*(self.p[2].x-2*self.p[1].x+self.p[0].x))
        self.ddy = 6*(self.t*(self.p[3].y-2*self.p[2].y+self.p[1].y)+(1-self.t)*(self.p[2].y-2*self.p[1].y+self.p[0].y))
        
        dp = [((x_a-x_b)**2 + (y_a-y_b)**2)*100 for x_a,x_b,y_a,y_b in zip(self.x[:-1],self.x[1:],self.y[:-1],self.y[1:])]
        adp = [(i**2 + j**2)**0.5 for i,j in zip(self.dx,self.dy)]
        addp = [(i**2 + j**2)**0.5 for i,j in zip(self.ddx,self.ddy)]
        R = ((self.dx**2 + self.dy**2)**1.5)/((self.dx*self.ddy - self.ddx*self.dy)**2)**0.5

        self.ax_artist.set_data(self.x,self.y)
        self.dax_artist.set_data(self.t,R)

    def sets(self,_gco,_event):
        for i,j in zip(self.artists,self.p):
            if i == _gco:
                i.set_data(_event.xdata,_event.ydata)
                j.x = _event.xdata
                j.y = _event.ydata
                break
        self.change()


gco = None

if __name__ == '__main__':
    a = Coo(1,1)
    b = Coo(10,1)
    c = Coo(1,5)
    d = Coo(10,5)

    B = Bezier(a,b,c,d)
    
    def motion(event):
        global gco
        if gco is None:
            return
        B.sets(gco,event)
        plt.draw()

    def onpick(event):
        global gco
        gco = event.artist


    def release(event):
        global gco
        gco = None

    plt.connect('motion_notify_event', motion)
    plt.connect('pick_event', onpick)
    plt.connect('button_release_event', release)
    
    plt.show()

I'm using only major libraries, so I think it will work soon.