chasing_heart.py

# Import a library of functions called 'pygame'
import pygame
import math

# Initialize the game engine
pygame.init()

# Define the colors we will use in RGB format
black = [0, 0, 0]
white = [255, 255, 255]
blue = [0, 0, 255]
green = [0, 255, 0]
red = [255, 0, 0]

PI = 3.141592653
r = 50
R = 200

# Set the height and width of the screen
size = [800, 480]
screen = pygame.display.set_mode(size)

pygame.display.set_caption("Sansagraphics World")

# Loop until the user clicks the close button.
done = False
clock = pygame.time.Clock()

colour = red
thickness = 0
i = 0

cx = 10
cy = 155
cz = 240

while not done:
    # This limits the while loop to a max of 10 times per second.
    # Leave this out and we will use all CPU we can.
    clock.tick(10)

    for event in pygame.event.get():  # User did something
        if event.type == pygame.QUIT:  # If user clicked close
            done = True  # Flag that we are done so we exit this loop

    # All drawing code happens after the for loop and but
    # inside the main while done==False loop.

    # Clear the screen and set the screen background
    screen.fill(white)
    prevx = 400.0
    prevy = 240.0

    # Draw on the screen several green lines from (0,10) to (100,110)
    # 5 pixels wide using a loop
    if colour == red:
        colour = blue
    elif colour == blue:
        colour = green
    else:
        colour = red

    thickness += 1
    if thickness > 10:
        thickness = 0

    for n in range(1200):
        theta = n * 2 * PI / 120
        y_offset = R * math.cos(theta / 10) + r * math.cos(theta) + 240.0
        x_offset = R * math.sin(theta / 10) + r * math.sin(theta) + 400.0
        if n > 0:
            pygame.draw.line(screen, colour, [prevx, prevy], [x_offset, y_offset], thickness)

        gradient_y = (-R * math.sin(theta / 10) / 10 - r * math.sin(theta))
        gradient_x = (R * math.cos(theta / 10) / 10 + r * math.cos(theta))

        if gradient_x != 0:  # Check to prevent division by zero
            m = gradient_y / gradient_x
        else:
            m = float('inf')

        norm_x = x_offset
        norm_y = y_offset
        norm_x1 = norm_x + gradient_x + 40
        norm_y1 = norm_y + gradient_y + 40

        if n > 0:
            pygame.draw.line(screen, [cx, cy, cz], [norm_x, norm_y], [norm_x1, norm_y1], thickness)
            cx = int(120 * (math.sin(theta) + 1) + 10)
            cy = int(120 * (math.sin(theta / 10) + 1) + 10)
            cz = int(120 * (math.sin(theta - PI) + 1) + 10)

        prevx = x_offset
        prevy = y_offset

    # Go ahead and update the screen with what we've drawn.
    # This MUST happen after all the other drawing commands.
    pygame.display.flip()

# Be IDLE friendly
pygame.quit()