How to make an enemy follow the player in pygame?

Question

I made part of a game. It runs well but I would like to add enemies in my game. So far I add the image of the enemies in pygame sprites.
But how do I make the enemies follow the player? I tried do this but it just made the image of the enemy direct to the player:

def moveEnemy(self):
    enemies.rect.x = player.rect.x
    enemies.rect.y = player.rect.y
    all_sprites_list.add(enemies)
    enemies_list.add(enemies)

I thought this would make the image of the enemy follow the player. Instead it just overlaped the player's image.

I read though many pygame sprites examples but the examples saids to replace the enemies.rect.x = player.rect.x with enemies.rect.x = -5 or something around that. I also tried this but it just move the image up instead of following the player.

Do I have to formulate an equation? If so I do not know how to.
How do I make the enemy move but as well make it follow the player? Can someone help me solve this problem?

Any help would be appreciated.

Answer 1

You need to reduce the distance between the enemy and the player by changing the enemy's position. This can be done by finding the difference between their positions and then using that vector to compute a normalized (unit length) direction vector. With that, change the enemy's position by adding its speed times the direction vector to it.

One way of doing this would be by adding a method like the following to your Enemy class. The mathmatical operations can be done using the built-in math module or the pygame.math module. The latter also has support for a 2D Vector2 class, so it would probably be the better one to actually use.

import math
import pygame
from pygame.locals import *

class Enemy(object):
    ...
    def move_towards_player(self, player):
        # Find direction vector (dx, dy) between enemy and player.
        dx, dy = player.rect.x - self.rect.x, player.rect.y - self.rect.y
        dist = math.hypot(dx, dy)
        dx, dy = dx / dist, dy / dist  # Normalize.
        # Move along this normalized vector towards the player at current speed.
        self.rect.x += dx * self.speed
        self.rect.y += dy * self.speed

    # Same thing using only pygame utilities
    def move_towards_player2(self, player):
        # Find direction vector (dx, dy) between enemy and player.
        dirvect = pygame.math.Vector2(player.rect.x - self.rect.x,
                                      player.rect.y - self.rect.y)
        dirvect.normalize()
        # Move along this normalized vector towards the player at current speed.
        dirvect.scale_to_length(self.speed)
        self.rect.move_ip(dirvect)

You will need to add checks to determine whether the enemy object will overshoot and thereby hit the player along the way if it moves this distance, and react accordingly. Hint: A collision will occur whenever the amount to be moved—the length of the speed vector, i.e. the object's speed—is greater or equal to the distance between them.

Answer 2

At a high level you need to work out the vector from the enemy to the player. The x and y components of the direction vector would look like:

enemies.rect.x - player.rect.x
enemies.rect.y - player.rect.y

You then add a multiple of the direction to the enemy position to make it move towards the player.

However: You'll notice that this vector will have a large magnitude when the player and enemy are far apart and a small magnitude when they are closer together. So to avoid having the enemy move at super-fast speeds, you would could normalise the direction vector and multiply by a speed s to keep it under control.

Answer 3

Getting an enemy to follow a player takes some math. I suggest to use pygame.math.Vector2 for the computation.

Calculate the Euclidean distance between the enemy (follower_x, follower_y) to the player (player_x, player_y) and the unit direction vector from the enemy to the palyer. The Unit Vector can be computed by dividing the direction vector by the distance or by normalizing (normalize()) the direction vector:

target_vector = Vector2(player_x, player_y)
follower_vector = Vector2(follower_x, follower_y)

distance = follower_vector.distance_to(target_vector)
direction_vector = target_vector - follower_vector
if distance > 0:
    direction_vector /= distance

Define an exact step_distance and move in the direction of the sprite along the direction vector from the enemy to the player

if distance > 0:
    new_follower_vector = follower_vector + direction_vector * step_distance.

Define a minimum_distance and a maximum_distance between the player and the enemy. The minimum distance can be 0 and the maximum distance can be very large:

minimum_distance = 0
maximum_distance = 10000

Use this minimum and maximum to restrict the movement of the enemy:

min_step = max(0, distance - maximum_distance)
max_step = distance - minimum_distance

The enemy's movement speed can be constant

VELOCITY = 5
step_distance = min(max_step, max(min_step, VELOCITY))

or smoothed with an interpolation factor:

LERP_FACTOR = 0.05
step_distance = min_step + (max_step - min_step) * LERP_FACTOR

---

Minimal example:

repl.it/@Rabbid76/PyGame-FollowMouseSmoothly

import pygame

VELOCITY         = 5
LERP_FACTOR      = 0.05
minimum_distance = 25
maximum_distance = 100

def FollowMe(pops, fpos):
    target_vector       = pygame.math.Vector2(*pops)
    follower_vector     = pygame.math.Vector2(*fpos)
    new_follower_vector = pygame.math.Vector2(*fpos)

    distance = follower_vector.distance_to(target_vector)
    if distance > minimum_distance:
        direction_vector    = (target_vector - follower_vector) / distance
        min_step            = max(0, distance - maximum_distance)
        max_step            = distance - minimum_distance
        #step_distance       = min(max_step, max(min_step, VELOCITY))
        step_distance       = min_step + (max_step - min_step) * LERP_FACTOR
        new_follower_vector = follower_vector + direction_vector * step_distance

    return (new_follower_vector.x, new_follower_vector.y) 

pygame.init()
window = pygame.display.set_mode((500, 500))
clock = pygame.time.Clock()

follower = (100, 100)
run = True
while run:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    player   = pygame.mouse.get_pos()
    follower = FollowMe(player, follower)

    window.fill(0)  
    pygame.draw.circle(window, (0, 0, 255), player, 10)
    pygame.draw.circle(window, (255, 0, 0), (round(follower[0]), round(follower[1])), 10)
    pygame.display.flip()

pygame.quit()
exit()

Answer 4

Here, px & py are the position (globals) of the object the enemy is following/chasing.

class Enemy(object):
    def __init__(self,x,y):  # initial position
        self.x = x 
        self.y = y
    def move(self, speed=5): # chase movement
        # Movement along x direction
        if self.x > px:
            self.x -= speed
        elif self.x < px:
            self.x += speed
        # Movement along y direction
        if self.y < py:
            self.y += speed
        elif self.y > py:
            self.y -= speed

If you want, you can customize the speed along x & y directions too.

Answer 5

A very simple method is

    if x_player > x_enemy:
        x_enemy = x_enemy + 0.1
    if x_player < x_enemy:
        x_enemy = x_enemy - 0.1
    if y_player > y_enemy:
        y_enemy = y_enemy + 0.1
    if y_player < y_enemy:
        y_enemy = y_enemy - 0.1

Obviously, change the variables to the variables you are using and change the value you are changing the x and y to change the speed at which the enemy moves.

Answer 6

I know this post is a little old but In the answers abobve the enemy goes in a strange way, If you want the enemy to move smoothly across a straight line from the enemy coordinates and player coordinates you can use this code:

    class Enemy:
        def __init__(self,x,y):
            self.x = x
            self.y = y
            self.width = 20
            self.height = 24
            self.hitbox = pygame.Rect(self.x, self.y, self.width, self.height)#Hitbox is a rectangle not important for this
        #Basic enemy class variables

        def move(self): # chase movement
        self.xdiff = abs(px - self.x)
        self.ydiff = abs(py - self.y)
        self.limitx = 0
        self.limity = 0
        if self.ydiff > self.xdiff:
            self.limitx = self.xdiff/(self.ydiff /30)
            self.limity = 30
        elif self.xdiff > self.ydiff:
            self.limity = self.ydiff/(self.xdiff /30)
            self.limitx = 30

        if self.x > px:
            self.x -= self.limitx/30
        elif self.x < px:
            self.x += self.limitx/30
        if self.y > py:
            self.y -= self.limity/30
        elif self.y < py:
            self.y += self.limity/30 #The 30 here is how many times it runs inside the while loop for example, check the while loop.

enemy = Enemy(100,100) #spawn enemy at 100, 100 coordinates
timer = 0

#PYGAME 
while True:
    #PYGAME INITILIZE
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            exit()
    #PYGAME INIT OVER
    if timer > 200:
        enemy.move
    if timer == 230:  #THE ENEMY MOVES 30 PIXELS IN 230 MS' DONT FORGET
        timer = 0 
    enemy.Draw()
    timer += 1
    pygame.display.update() # ^ Give off test values for developers
    clock.tick(60) # ^ Update the screen frame-by-frame