Angle from vector proof example

angle_from_vec_proof.py

import math
import pygame
import random
from pygame import Vector2

pygame.init()

class Game:
    def __init__(self):
        self.window_size = Vector2(512)
        self.window = pygame.display.set_mode(self.window_size, pygame.DOUBLEBUF)
        pygame.display.set_caption('playground')
        
        self.screen_scale = 3
        self.screen = pygame.Surface(self.window_size/self.screen_scale)
        self.screen_size = Vector2(self.screen.get_size())
        
        self.clock = pygame.time.Clock()
        self.mpos = Vector2(pygame.mouse.get_pos()) / self.screen_scale

        self.bullet = Bullet(
            self.screen_size/2,
            Vector2(
                random.random() * 2 - 1,
                random.random() * 2 - 1
            ).normalize() * 100
        )

    def run(self):
        while 1:
            self.process_events()
            self.update()
            self.draw()
            
    def process_events(self):
        for event in pygame.event.get():
            if (event.type == pygame.QUIT or
                    (event.type == pygame.KEYDOWN and
                        event.key == pygame.K_ESCAPE)):
                pygame.quit()
                quit()
            elif (event.type == pygame.KEYDOWN and
                  event.key == pygame.K_SPACE):
                self.bullet.vel = Vector2(
                    random.random() * 2 - 1,
                    random.random() * 2 - 1
                ).normalize() * 100
            
    def update(self):
        dt = self.clock.tick(60)*.001
        
        self.bullet.pos += self.bullet.vel * dt
        
        if not (0 < self.bullet.pos.x < self.screen_size.x):
            if self.bullet.pos.x < 0:
                self.bullet.pos.x = 0
            else:
                self.bullet.pos.x = self.screen_size.x
            self.bullet.vel.x *= -1
        if not (0 < self.bullet.pos.y < self.screen_size.y):
            if self.bullet.pos.y < 0:
                self.bullet.pos.y = 0
            else:
                self.bullet.pos.y = self.screen_size.y
            self.bullet.vel.y *= -1
        
    def draw(self):
        self.screen.fill((60,50,60))
        layer = pygame.Surface(self.screen.get_size(), pygame.SRCALPHA)
        
        layer.blit(self.bullet.surf, self.bullet.pos - Vector2(self.bullet.surf.get_size())/2)
        
        mpos = Vector2(pygame.mouse.get_pos()) / self.screen_scale
        center = self.screen_size / 2
        vec = (mpos - center).normalize()
        
        degrees = math.degrees(math.atan2(vec.y, vec.x))
        angle = (360 + degrees) % 360

        pygame.draw.line(layer, (0,200,0), center, center + vec * 10, 1)
        pygame.draw.circle(layer, (0,200,0), center, 2)
        
        if mpos != self.mpos:
            print(angle)
        self.mpos = mpos
        
        self.screen.blit(layer, Vector2())
        pygame.transform.scale(self.screen, self.window_size, self.window)
        pygame.display.flip()


class Bullet:
    def __init__(self, pos, vel):
        self.pos = Vector2(pos)
        self.vel = Vector2(vel)
        surf = pygame.Surface(Vector2(8, 4))
        pygame.draw.rect(surf, (200, 200, 0), (0,0,8,4))
        pygame.draw.rect(surf, (200, 0, 0), (4,0,4,4))
        self._surf = surf

    @property
    def surf(self):
        if not self.vel:
            return self._surf
        vel = self.vel.normalize()
        degrees = math.degrees(math.atan2(vel.y, vel.x))
        angle = (360 + degrees) % 360
        return pygame.transform.rotate(self._surf, -angle)
        

Game().run()