python - sge-pygame 旋转父子 Sprite

Question

我一直在研究并试图解决这个问题很长一段时间。我正在尝试创建一个父/子附加系统，以便当父移动时，附加到它的子移动/旋转/缩放相同。我遇到的主要问题是轮换。

这是我目前为 children 使用的代码:

def _rotate(self, origin, point, angle):
  ox, oy = origin
  px, py = point

  qx = ox + math.cos(angle) * (px - ox) - math.sin(angle) * (py - oy)
  qy = oy + math.sin(angle) * (px - ox) + math.cos(angle) * (py - oy)

  return qx, qy

_rotate 代码将 2D 点旋转我在搜索问题答案时找到的原点周围的角度。我使用的点是每个盒子/ Sprite 的中心。

旋转父对象时，我使用 sge-pygame image_rotation，然后继续进行子对象定位。之后我需要根据新的位置和新的角度计算出 child 的旋转来旋转 child 。

发生的事情的图像:

初始

和

旋转 10 度

父级是大矩形，盒子是子级。

我遇到的第二个问题是弄清楚子项的旋转角度是多少，以使其与父项保持一致。我通过 stackflow 发现 math.atan2 的使用应该用于此但是我似乎无法弄清楚如何使用它。

如有任何帮助，我们将不胜感激。

谢谢

Answer 1

您首先将父项和子项旋转相同的量(在此示例中，假设应控制父项而子项不应该)。然后你只需将 child 移动到 parent 的枢轴点(在本例中为它的中心)，并在 parent 面对的方向上额外偏移(偏移当然是可选的)。

from math import cos, sin, radians
import pygame
pygame.init()

SIZE = WIDTH, HEIGHT = 720, 480
BACKGROUND_COLOR = pygame.Color('black')
FPS = 60

screen = pygame.display.set_mode(SIZE)
clock = pygame.time.Clock()


def update_child_rotation(parent, child, degrees, offset):
    # Rotate the parent and child with the same angle.
    parent.rotate(degrees)
    child.rotate(degrees)

    # Calculate the direction the parent is pointing. If you remember the unit circle then you'll
    # know that cos(angle) represent the x value and sin(angle) the y value. At angle = 0 the direction
    # is to the right (which is what your sprite should be pointing, otherwise you'll have to add an angle
    # offset), and it rotates counterclockwise. The minus in '-sin' is because pygame uses positive y as downwards.
    angle_in_radians = radians(parent.angle)
    direction = pygame.math.Vector2(cos(angle_in_radians), -sin(angle_in_radians))

    # Update the child's position to the parent's position but with an added offset in the direction the parent
    # is pointing.
    child.position = parent.position + direction * offset


class Entity(pygame.sprite.Sprite):

    def __init__(self, position, size):
        super().__init__()

        self.original_image = pygame.Surface(size)
        self.original_image.fill((255, 0, 0))
        self.original_image.set_colorkey(BACKGROUND_COLOR)

        self.image = self.original_image
        self.rect = self.image.get_rect(center=position)

        self.angle = 0
        self.position = pygame.math.Vector2(position)
        self.velocity = pygame.math.Vector2(0, 0)

    def rotate(self, degrees):
        self.angle = (self.angle + degrees) % 360
        self.image = pygame.transform.rotate(self.original_image, self.angle)
        self.rect = self.image.get_rect(center=self.position)

    def update(self, dt):
        self.position += self.velocity
        self.rect.center = self.position


def main():
    parent = Entity(position=(200, 200), size=(128, 32))
    child = Entity(position=(356, 200), size=(32, 32))
    all_sprites = pygame.sprite.Group(parent, child)

    running = True
    while running:

        dt = clock.tick(FPS) / 1000

        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                running = False
            elif event.type == pygame.KEYDOWN:
                if event.key == pygame.K_q:
                    update_child_rotation(parent, child, 10, 156)
                elif event.key == pygame.K_e:
                    update_child_rotation(parent, child, -10, 156)
            elif event.type == pygame.KEYUP:
                if event.key == pygame.K_RIGHT or event.key == pygame.K_LEFT:
                    parent.velocity.x = 0
                elif event.key == pygame.K_DOWN or event.key == pygame.K_UP:
                    parent.velocity.y = 0

        all_sprites.update(dt)

        screen.fill(BACKGROUND_COLOR)
        all_sprites.draw(screen)
        pygame.display.update()


if __name__ == '__main__':
    main()