How to draw a circle in a square in python?

Question

I have the following Canvas class for drawing color in a given pixel:

class Canvas:
    def __init__(self,color,pixel):
        self.color = color
        self.pixel = pixel
        
        self.im = np.zeros((pixel,pixel,3))
        self.im[:,:] = color
        
    def show(self):
        plt.imshow(self.im)
        plt.axis("off")
        

This simple class draws a square with color, for example:

purple = np.array([0.5, 0.0, 0.5])
C = Canvas(purple, 2001) # 2001 x 2001 pixels
C.show()

renders:

I want to create add_disk() function with three argument: centroid,radius,color. So that

C.add_disk((1001, 1001), 500, white)
C.show()

renders:

However, I am not sure how to do it using the math formula:

I think I can use np.meshgrid to color white points, but how do I find those points and display on top of the square?

Answer 1

So with meshgrid, using the shape of the self.im, we first find the coordinates of the X and Y values in the 2D image. Then, we find all values whose coordinates follows the circle rule ((X - Ox) ** 2 + (Y - Oy)**2 <= R**2).

import matplotlib.pyplot as plt
import numpy as np

class Canvas:
    def __init__(self,color,pixel):
        self.color = color
        self.pixel = pixel
        
        self.im = np.zeros((pixel,pixel,3))
        self.im[:,:] = color
        
    def show(self):
        plt.imshow(self.im)
        plt.axis("off")
    
    def add_disk(self, centroid,radius,color):
        x, y = np.meshgrid(np.arange(self.im.shape[0]), np.arange(self.im.shape[1]))
        circle_pixels = (x - centroid[0]) ** 2 + (y - centroid[1]) ** 2 <= radius ** 2
        self.im[circle_pixels, ...] = color

purple = np.array([0.5, 0.0, 0.5])
C = Canvas(purple, 2001) # 2001 x 2001 pixels
C.show()       

white = np.array([255, 255, 255])
C.add_disk((1001, 1001), 500, white)
C.show()