How to slowly draw a circle in Pygame?

Question

I want to slowly draw a circle in pygame so the act of drawing is actually visible to the naked eye. I got a function on stackoverflow to draw a straight line by incrementing the end point and keeping the starting point same but couldn't figure out how to slowly draw a circle in the pygame screen.

Answer 1

You can use the standard sine and cos circle formula:

• x = r * cos(radians(i)) + a
• y = r * sin(radians(i)) + b

Where a is the x coordinate of the center of the circle, and b is the y coordinate of the center of the circle r is the radius of the circle.

To slow down the animation, use a Clock object. You can access the functions sin and cos from the built-in math module (note that you'll need to pass in the values as radians, hence the importance of the radians function).

The implementation:

import pygame
from math import sin, cos, radians

pygame.init()
wn = pygame.display.set_mode((600, 600))

r = 100
a = 300
b = 200

clock = pygame.time.Clock()
for i in range(1, 361):
    clock.tick(30)
    pygame.draw.circle(wn, (255, 255, 255), (int(r * cos(radians(i)) + a), int(r * sin(radians(i)) + b)), 2)
    pygame.display.update()

Output:

If you prefer to use standard lines as the outline instead of overlapping dots, use the pygame.draw.line function like so:

import pygame
from math import sin, cos, radians

pygame.init()
wn = pygame.display.set_mode((600, 600))

r = 100
a = 300
b = 200

def x_y(r, i, a, b):
    return (int(r * cos(radians(i)) + a), int(r * sin(radians(i)) + b))

clock = pygame.time.Clock()
for i in range(0, 360, 2):
    clock.tick(30)
    pygame.draw.line(wn, (255, 255, 255), x_y(r, i, a, b), x_y(r, i+1, a, b), 2)
    pygame.display.update()