Shooting a bullet in pygame in the direction of mouse

问题

I just cant figure out why my bullet is not working. I made a bullet class and here it is:

class Bullet:
    def __init__(self):
        self.x = player.x
        self.y = player.y
        self.height = 7
        self.width = 2
        self.bullet = pygame.Surface((self.width, self.height))
        self.bullet.fill((255, 255, 255))

Now i added several function in my game class and here it is:

class Game:
    def __init__(self):
        self.bullets = []

    def shoot_bullet(self):
         if self.bullets:
            for bullet in self.bullets:
                rise = mouse.y - player.y
                run = mouse.x - player.x
                angle = math.atan2(rise, run)

                bullet.x += math.cos(angle)
                bullet.y += math.sin(angle)

                pygame.transform.rotate(bullet.bullet, -math.degrees(angle))
                D.blit(bullet.bullet, (bullet.x, bullet.y))


    def generate_bullet(self):
        if  mouse.is_pressed():
            self.bullets.append(Bullet())

What i was expecting the code to do was a Bullet() would get added to game.bullets everytime i pressed mouse button, then game.shoot_bullet would calculate the angle between the player and the mouse and shoot the bullet accordingly in the direction of the mouse. However the result is a complete mess and the bullets actually dont rotate dont move they get generated and move weirdly to the left of the screen. I am not sure if i have messed up something or the method i have used is completely wrong. Thanks for helping.

回答1:

First of all pygame.transform.rotate does not transform the object self, it creates a new rotated surface and returns it.

What you want to do is to fire a bullet in a certain direction. The direction is defined when the bullet spawns, but it doe not change continuously.
Set the start position of the bullet and compute the direction vector to the mouse position:

self.pos = (x, y)
mx, my = pygame.mouse.get_pos()
self.dir = (mx - x, my - y)

The direction vector should not depend on the distance to the mouse, it has to be a Unit vector. Normalize the vector be dividing by the Euclidean distance

length = math.hypot(*self.dir)
if length == 0.0:
    self.dir = (0, -1)
else:
    self.dir = (self.dir[0]/length, self.dir[1]/length)

Compute the angle of the vector and rotate the bullet:

angle = math.degrees(math.atan2(-self.dir[1], self.dir[0]))

self.bullet = pygame.Surface((7, 2)).convert_alpha()
self.bullet.fill((255, 255, 255))
self.bullet = pygame.transform.rotate(self.bullet, angle)

To update the position of the bullet, it is sufficient to scale the direction (by a velocity) and add it to its position:

self.pos = (self.pos[0]+self.dir[0]*self.speed, 
            self.pos[1]+self.dir[1]*self.speed)

When you draw the bullet, the get the rectangle of the bullet surface and set the center by self.pos

bullet_rect = self.bullet.get_rect(center = self.pos)
surf.blit(self.bullet, bullet_rect)

See the example:

import pygame
import math

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

class Bullet:
    def __init__(self, x, y):
        self.pos = (x, y)
        mx, my = pygame.mouse.get_pos()
        self.dir = (mx - x, my - y)
        length = math.hypot(*self.dir)
        if length == 0.0:
            self.dir = (0, -1)
        else:
            self.dir = (self.dir[0]/length, self.dir[1]/length)
        angle = math.degrees(math.atan2(-self.dir[1], self.dir[0]))

        self.bullet = pygame.Surface((7, 2)).convert_alpha()
        self.bullet.fill((255, 255, 255))
        self.bullet = pygame.transform.rotate(self.bullet, angle)
        self.speed = 2

    def update(self):  
        self.pos = (self.pos[0]+self.dir[0]*self.speed, 
                    self.pos[1]+self.dir[1]*self.speed)

    def draw(self, surf):
        bullet_rect = self.bullet.get_rect(center = self.pos)
        surf.blit(self.bullet, bullet_rect)  

bullets = []
pos = (250, 250)
run = True
while run:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
        if event.type == pygame.MOUSEBUTTONDOWN:
            bullets.append(Bullet(*pos))

    for bullet in bullets[:]:
        bullet.update()
        if not window.get_rect().collidepoint(bullet.pos):
            bullets.remove(bullet)

    window.fill(0)
    pygame.draw.circle(window, (0, 255, 0), pos, 10)
    for bullet in bullets:
        bullet.draw(window)
    pygame.display.flip()

来源：https://stackoverflow.com/questions/59977052/shooting-a-bullet-in-pygame-in-the-direction-of-mouse

标签

python

pygame