calculating direction of the player to shoot pygame

Question

This is my player class

class Player:
    def  __init__(self, image):
        self.rotation_angle = 0

    def rotate(self, keys, left, right):
        if keys[right]:
            self.rotation_angle -= 0.5
        if keys[left]:
            self.rotation_angle += 0.5
        self.rotated_player = pygame.transform.rotate(self.player, (self.rotation_angle))

Now based onself.rotation_angle, i need to shoot the bullet. So i did the following.

class Bullet:
    def __init__(self):
        self.pos = [player1.pos[0], player1.pos[1]]
        self.direction = math.radians(player1.rotation_angle)
        self.bullet = pygame.Surface((5, 20))
        self.rotated_bullet = pygame.transform.rotate(self.bullet, (self.direction))
        self.bullet.fill((100, 200, 120))
        self.time = 0

    def shoot(self):
        self.pos[0] += math.cos(self.direction) * self.time
        self.pos[1] += math.sin(self.direction) * self.time
        self.time += 0.5

But this dosent work and the resulting bullet just moves in some random direction. I tried not converting the angle to radians and changing the self.direction value for y-axis to negative but it just isn't working. How would i accurately calculate the direction for bullet? Thanks for any help.

Rabbid76 · Accepted Answer · 2020-10-11T18:38:42.970

The unit of the angle for the mathematical operations math.sin and math.cos is radian, but the unit of the angel for pygame.transform.rotate() is degrees. Furthermore you have to create a pygame.Surface with the flag SRCALPHA and to fill the surface with the bullet color, before it is rotated:

class Bullet:
    def __init__(self):
        self.pos = [player1.pos[0], player1.pos[1]]
        self.direction = math.radians(player1.rotation_angle)
        self.bullet = pygame.Surface((10, 5), pygame.SRCALPHA)
        self.bullet.fill((100, 200, 120))
        self.rotated_bullet = pygame.transform.rotate(self.bullet, player1.rotation_angle)
        self.time = 0

In pygame the y axis points form the top to the bottom. That is the opposite direction than in a usual Cartesian coordinate system. Because of that the y coordinate of the direction has to be inverted:

class Bullet:
    # [...]

    def shoot(self):
        self.pos[0] += math.cos(self.direction) * self.time
        self.pos[1] -= math.sin(self.direction) * self.time
        self.time += 0.5

See the example:

import pygame
import math

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

class Player():
    def  __init__(self):
        self.rotation_angle = 0
        self.player = pygame.Surface((20, 20), pygame.SRCALPHA)
        self.player.fill((0, 255, 0))
        self.rotated_player = self.player
        self.pos = (WIDTH//2, HEIGHT//2)
        
    def rotate(self, keys, left, right):
        if keys[right]:
            self.rotation_angle -= 0.5
        if keys[left]:
            self.rotation_angle += 0.5
        self.rotated_player = pygame.transform.rotate(self.player, (self.rotation_angle))

class Bullet:
    def __init__(self):
        self.pos = [player1.pos[0], player1.pos[1]]
        self.direction = math.radians(player1.rotation_angle)
        self.bullet = pygame.Surface((10, 5), pygame.SRCALPHA)
        self.bullet.fill((100, 200, 120))
        self.rotated_bullet = pygame.transform.rotate(self.bullet, player1.rotation_angle)
        self.time = 0

    def shoot(self):
        self.pos[0] += math.cos(self.direction) * self.time
        self.pos[1] -= math.sin(self.direction) * self.time
        self.time += 0.5

player1 = Player()

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.KEYDOWN and event.key == pygame.K_SPACE:
            bullets.append(Bullet())

    keys = pygame.key.get_pressed()
    player1.rotate(keys, pygame.K_LEFT, pygame.K_RIGHT)       

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

    window.fill(0)
    window.blit(player1.rotated_player, player1.rotated_player.get_rect(center=player1.pos))
    for bullet in bullets:
        window.blit(bullet.rotated_bullet, bullet.rotated_bullet.get_rect(center=bullet.pos))
    pygame.display.flip()

_{See also
Why aren't any bullets appearing on screen? - pygame

Shooting a bullet in pygame in the direction of mouse}

Hi thanks for answering. Just a quick question, is "pygame.SCRALPHA" the same as "convert_alpha"? — , Feb 29 '20 at 13:28
@hippozhipos It has the same effect. If you use `pygame.SCRALPHA`, then a surface with per pixel alpha is generated. If you use `convert_alpha`, the surface is generated with out alpha and after that it is converted. — Rabbid76, Feb 29 '20 at 13:30

calculating direction of the player to shoot pygame

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