Pygame Vector2.as_polar（）和Vector2.from_polar（）方法

Question

有人可以给我看一个使用Vector2.as_polar()获得距离和方位角的例子，然后将该信息插回Vector2.from_polar()以获得笛卡尔坐标吗？

假设我们希望(0, 0)和(15, 10)之间的距离和方位角，再插上这些信息纳入Vector2.from_polar()再次生成(15, 10)。

我会准确解释我在做什么，但对我和其他人来说可能会更容易看到一个有效的示例。

Answer 1

您可以将矢量定义为半径和角度 - 极坐标。

让我们在屏幕中心使用一个点向量作为极坐标系的极点。

pole = Vector2(screen_rect.center) 

为了与from_polar方法的帮助下设定的矢量的坐标，先定义一个载体中，然后通过其由半径和角的元组：

vec = Vector2() 
# This updates the cartesian coordinates of vec. 
vec.from_polar((90, 60)) # 90 pixels long, rotated 60 degrees. 

然后使用pygame.draw.line到绘制（添加vec到pole得到目标COORDS）：

pg.draw.line(screen, (200, 90, 20), pole, pole+vec, 3) 

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作为as_polar的演示，将矢量计算为鼠标位置，并将极坐标解压缩到变量r和phi中，我们稍后渲染变量以查看此矢量的当前半径和角度。

r, phi = (mouse_pos-pole).as_polar() 

请注意，pygame的y轴被翻转，因此负角指向上方，正角朝下。

import sys 
import pygame as pg 
from pygame.math import Vector2 


def main(): 
    screen = pg.display.set_mode((640, 480)) 
    screen_rect = screen.get_rect() 
    font = pg.font.Font(None, 30) 
    color = pg.Color(150, 250, 100) 
    clock = pg.time.Clock() 
    pole = Vector2(screen_rect.center) 
    # A zero vector. 
    vec = Vector2() 
    # To set the coordinates of `vec` we can pass the 
    # polar coordinates (radius, angle) to `from_polar`. 
    vec.from_polar((90, 60)) 
    print(vec) # Now take a look at the updated cartesian coordinates. 
    done = False 

    while not done: 
     for event in pg.event.get(): 
      if event.type == pg.QUIT: 
       done = True 

     mouse_pos = pg.mouse.get_pos() 
     # `as_polar` gives us the radius and angle of the vector that 
     # points to the mouse. Unpack it into the `r` and `phi` variables. 
     r, phi = (mouse_pos-pole).as_polar() 

     screen.fill((30, 30, 30)) 
     # Draw the line to the mouse pos. 
     pg.draw.line(screen, color, pole, mouse_pos, 3) 
     # Add the vec to the pole to get the target coordinates. 
     pg.draw.line(screen, (200, 90, 20), pole, pole+vec, 3) 

     # Render the radius and angle. 
     txt = font.render('r: {:.1f}'.format(r), True, color) 
     screen.blit(txt, (30, 30)) 
     txt = font.render('phi: {:.1f}'.format(phi), True, color) 
     screen.blit(txt, (30, 50)) 

     pg.display.flip() 
     clock.tick(30) 


if __name__ == '__main__': 
    pg.init() 
    main() 
    pg.quit() 
    sys.exit() 

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下面是与跟随鼠标（按“W”或“S”，以加速）子画面的另一示例。我将self.speed作为半径，并将as_polar返回的角度作为参数传递给from_polar以设置玩家精灵的vel ocity。

import sys 
import pygame as pg 


class Player(pg.sprite.Sprite): 
    def __init__(self, pos): 
     super().__init__() 
     self.image = pg.Surface((50, 30), pg.SRCALPHA) 
     color = pg.Color('dodgerblue1') 
     pg.draw.polygon(self.image, color, ((1, 1), (49, 15), (1, 29))) 
     self.orig_img = self.image 
     self.rect = self.image.get_rect(center=pos) 
     self.pos = pg.math.Vector2(pos) 
     self.vel = pg.math.Vector2(0, 0) 
     self.speed = 0 

    def update(self): 
     self.rotate() 
     self.pos += self.vel 
     self.rect.center = self.pos 

    def rotate(self): 
     _, angle = (pg.mouse.get_pos()-self.pos).as_polar() 
     self.vel.from_polar((self.speed, angle)) 
     self.image = pg.transform.rotozoom(self.orig_img, -angle, 1) 
     self.rect = self.image.get_rect(center=self.rect.center) 


def main(): 
    screen = pg.display.set_mode((640, 480)) 
    clock = pg.time.Clock() 
    all_sprites = pg.sprite.Group() 
    player = Player((300, 200)) 
    all_sprites.add(player) 

    done = False 
    while not done: 
     for event in pg.event.get(): 
      if event.type == pg.QUIT: 
       done = True 

     keys = pg.key.get_pressed() 
     if keys[pg.K_w]: 
      player.speed += .2 
     elif keys[pg.K_s]: 
      player.speed -= .2 

     all_sprites.update() 
     screen.fill((30, 30, 30)) 
     all_sprites.draw(screen) 

     pg.display.flip() 
     clock.tick(30) 


if __name__ == '__main__': 
    pg.init() 
    main() 
    pg.quit() 
    sys.exit()