Bird flocking is a wonderful example of how simple behaviors can lead to complex, beautiful patterns in nature. We’ll learn the key principles behind this flocking behavior and write a python program to simulate this wonderful phenomenon.
The principles
- Cohesion: Birds want to stay with the group, so they naturally move towards the center of the flock. It’s like friends sticking together at a crowded party.
- Alignment: This continuous adjustment to match their neighbors allows birds to fly in harmony, preventing chaotic changes in the flock.
- Separation: Birds maintain a ‘space’ around themselves to avoid collisions. This is a key rule for safe and coordinated movement within the flock.
Bird Flocking Simulation Algorithm
Setting Up the Simulation
- Define the space (width and height of the simulation area).
- Create the birds:
- Set the desired number of birds.
- Assign random starting positions within the space.
- Give each bird a random initial velocity.
Each Frame of the Simulation
- For each bird in the flock:
- Cohesion: Calculate the center of mass of the flock and adjust the bird’s velocity to move closer to it.
- Alignment: Calculate the average velocity of the flock and adjust the bird’s velocity to align with it.
- Separation: Check for nearby birds and adjust the bird’s velocity to avoid collisions.
- Update Positions: Using the new velocity, calculate each bird’s new position.
- Handle Boundaries: Make sure birds stay within the simulation area.
- Display the updated bird positions on the screen.
The pygame example
import pygame
import sys
import random
from pygame.locals import *
pygame.init()
clock = pygame.time.Clock()
display_x = 1200
display_y = 700
screen = pygame.display.set_mode((display_x, display_y))
lightgreen = (144, 238, 144)
class FlyingBird():
def __init__(self):
self.circle_radius = 2
self.display_position_x = random.randint(self.circle_radius, display_x - self.circle_radius)
self.display_position_y = random.randint(self.circle_radius, display_y - self.circle_radius)
self.horizontal_speed = random.randint(-3, 3)
self.vertical_speed = random.randint(-3, 3)
def show(self):
pygame.draw.circle(screen, (0, 0, 0), (self.display_position_x, self.display_position_y), self.circle_radius)
def update(self, birds):
center_of_mass_x = sum(b.display_position_x for b in birds) / len(birds)
center_of_mass_y = sum(b.display_position_y for b in birds) / len(birds)
self.horizontal_speed += (center_of_mass_x - self.display_position_x) * 0.001
self.vertical_speed += (center_of_mass_y - self.display_position_y) * 0.001
self.display_position_x += self.horizontal_speed
self.display_position_y += self.vertical_speed
if self.display_position_x + self.circle_radius >= display_x or self.display_position_x - self.circle_radius <= 0:
self.horizontal_speed *= -1
if self.display_position_y + self.circle_radius >= display_y or self.display_position_y - self.circle_radius <= 0:
self.vertical_speed *= -1
total_bird_number = 1000
list_of_birds = [FlyingBird() for _ in range(total_bird_number)]
game_running = True
while game_running:
clock.tick(60)
for event in pygame.event.get():
if event.type == QUIT:
pygame.quit()
sys.exit()
screen.fill(lightgreen)
for bird in list_of_birds:
bird.update(list_of_birds)
bird.show()
pygame.display.update()
Practice More pygame example including this example code from github