How do you point the barrel towards mouse in pygame?

Question

I have fixed the problem pointed out in this post, but now I am confused on how to point the gray rectangle (barrel) towards my mouse. Could somebody please help? Thanks!

Here is my code:

import pygame
import math

pygame.init()

screen = pygame.display.set_mode((400, 400))

pygame.display.set_caption("diep.io")

screen.fill((255,255,255))

auto_shoot = False

class Bullet:
  def __init__(self, x_move, y_move, x_loc, y_loc):
    self.image = pygame.image.load("C:\\Users\\ender\\OneDrive\\Documents\\repos\\Bullet.png")
    self.x_move = x_move
    self.y_move = y_move
    self.x_loc = x_loc
    self.y_loc = y_loc
    self.bullet_rect = self.image.get_rect()
  
  def update(self):
    self.x_loc += self.x_move
    self.y_loc += self.y_move   
    self.bullet_rect.center = round(self.x_loc), round(self.y_loc)

    rect = screen.blit(self.image, self.bullet_rect)
    if not screen.get_rect().contains(rect):
      bullets.remove(self)

    if self.x_loc > 400 or self.y_loc > 400:
      bullets.remove(self)

bullet = None
bullets = []

while True:
  screen.fill((255, 255, 255))
  pygame.draw.rect(screen, (100, 100, 100), (205, 193, 25, 15)) # This is the rectangle I want to point at my mouse
  pygame.draw.circle(screen, (82, 219, 255), (200, 200), 15)
  for event in pygame.event.get():
    if event.type == pygame.MOUSEBUTTONUP:
      x = pygame.mouse.get_pos()[0] - 200
      y = pygame.mouse.get_pos()[1] - 200
      pythag = float(math.sqrt(x**2 + y**2))
      bullets.append(Bullet(x/pythag, y/pythag, 200, 200))
  for bullet in bullets:
    bullet.update()
  pygame.display.update()
  pygame.time.delay(10)

Note: This is different from other problems because I am trying to point a rectangle at my mouse, and other posts are pointing an image at the mouse. That is not what I want to do. Secondly, pygame rectangles are defined by their bottom left corner, so this further complicates things.

Answer 1

For the rotation of the bullets see How to move a sprite according to an angle in Pygame and calculating direction of the player to shoot PyGmae.
Compute the angle of the direction vector grees(math.atan2(-y_move, x_move)) and rotate the bullet image:

class Bullet:
    def __init__(self, x_move, y_move, x_loc, y_loc):
        self.image = pygame.image.load("C:\\Users\\ender\\OneDrive\\Documents\\repos\\Bullet.png")
        self.image = pygame.transform.rotate(self.image, math.degrees(math.atan2(-y_move, x_move)))

Rotating the rectangle is a little trickier. Draw the cannon on a pygame.Surface:

cannon = pygame.Surface((50, 50), pygame.SRCALPHA)
pygame.draw.rect(cannon, (100, 100, 100), (30, 17, 25, 15))
pygame.draw.circle(cannon, (82, 219, 255), (25, 25), 15)

See How do I rotate an image around its center using PyGame?. Write a function to rotate and blit a Surface:

def blitRotateCenter(surf, image, center, angle):
    rotated_image = pygame.transform.rotate(image, angle)
    new_rect = rotated_image.get_rect(center = image.get_rect(center = center).center)
    surf.blit(rotated_image, new_rect)

Use the function in the application loop to draw the cannon:

while True:
    # [...]
    
    x = pygame.mouse.get_pos()[0] - 200
    y = pygame.mouse.get_pos()[1] - 200
    angle = math.degrees(math.atan2(-y, x)) 
    blitRotateCenter(screen, cannon, (200, 200), angle)
    
    # [...]

See also How to rotate an image(player) to the mouse direction? and How can you rotate the sprite and shoot the bullets towards the mouse position?.

---

Complete example:

import pygame
import math

pygame.init()
screen = pygame.display.set_mode((400, 400))
pygame.display.set_caption("diep.io")
screen.fill((255,255,255))
clock = pygame.time.Clock()

class Bullet:
    def __init__(self, x_move, y_move, x_loc, y_loc):
        #self.image = pygame.image.load("C:\\Users\\ender\\OneDrive\\Documents\\repos\\Bullet.png")
        self.image = pygame.Surface((20, 5), pygame.SRCALPHA)
        self.image.fill((255, 0, 0))
        self.image = pygame.transform.rotate(self.image, math.degrees(math.atan2(-y_move, x_move)))
        self.x_move = x_move
        self.y_move = y_move
        self.x_loc = x_loc
        self.y_loc = y_loc
        self.bullet_rect = self.image.get_rect()
    
    def update(self):
        self.x_loc += self.x_move
        self.y_loc += self.y_move   
        self.bullet_rect.center = round(self.x_loc), round(self.y_loc)
        rect = screen.blit(self.image, self.bullet_rect)
        if not screen.get_rect().contains(rect):
            bullets.remove(self)
        if self.x_loc > 400 or self.y_loc > 400:
            bullets.remove(self)

cannon = pygame.Surface((50, 50), pygame.SRCALPHA)
pygame.draw.rect(cannon, (100, 100, 100), (30, 17, 25, 15))
pygame.draw.circle(cannon, (82, 219, 255), (25, 25), 15)

def blitRotateCenter(surf, image, center, angle):
    rotated_image = pygame.transform.rotate(image, angle)
    new_rect = rotated_image.get_rect(center = image.get_rect(center = center).center)
    surf.blit(rotated_image, new_rect)

bullet = None
bullets = []
auto_shoot = False
run = True
while run:
    x = pygame.mouse.get_pos()[0] - 200
    y = pygame.mouse.get_pos()[1] - 200
    angle = math.degrees(math.atan2(-y, x))  
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
        if event.type == pygame.MOUSEBUTTONUP:
            pythag = float(math.sqrt(x**2 + y**2))
            bullets.append(Bullet(x/pythag, y/pythag, 200, 200))
    
    screen.fill((255, 255, 255))
    for bullet in bullets:
        bullet.update()
    blitRotateCenter(screen, cannon, (200, 200), angle)
    pygame.display.update()
    clock.tick(100)

pygame.quit()
exit()