python - 使用 Pymunk 和 Pygame 进行横向滚动。如何移动相机/视口以仅查看世界的一部分？

Question

从 pymunk 示例中，我看到 pymunk 坐标和 pygame 坐标之间存在差异。此外，pymunk 仅用于 2D 物理，而 pygame 用于在屏幕上渲染对象/精灵。

所以在寻找如何构建一个摄像机跟随玩家的环境时，人们（包括我）最终会感到困惑。我已经在这里、这里、这里和这里看到了示例（甚至对没有人回答这个问题感到惊讶），但考虑到与同一主题相关的问题被反复询问的数量，老实说，我觉得答案并不能充分解释这个概念和要求向社区展示最简单的示例，其中所有代码都带有注释。

我曾在 OGRE 和 OSG 等 3D 环境中工作，其中相机是一个可以用视锥体定义的适当概念，但我很惊讶 2D 世界没有预定义的功能。所以：

如果不在 pymunk 或 pygame 的官方教程中，至少可以提供一个简单的示例（以 pymunk 身体作为玩家，世界上很少有 pymunk 身体）作为答案，其中玩家在 2D pymunk+ 中移动pygame 世界和相机跟随玩家？

Answer 1

好的，我会尽量简化（我假设有基本的 pygame 知识）。

首先，让我们从一些基本的东西开始。一个可以在世界各地移动的小精灵：

import pygame
import random

class Player(pygame.sprite.Sprite):
    def __init__(self):
        super().__init__()
        self.image = pygame.Surface((32, 32))
        self.image.fill(pygame.Color('dodgerblue'))
        self.rect = self.image.get_rect()
        self.pos = pygame.Vector2((100, 200))

    def update(self, events, dt):
        pressed = pygame.key.get_pressed()
        move = pygame.Vector2((0, 0))
        if pressed[pygame.K_w]: move += (0, -1)
        if pressed[pygame.K_a]: move += (-1, 0)
        if pressed[pygame.K_s]: move += (0, 1)
        if pressed[pygame.K_d]: move += (1, 0)
        if move.length() > 0: move.normalize_ip()
        self.pos += move*(dt/5)
        self.rect.center = self.pos

def main():
    pygame.init()
    screen = pygame.display.set_mode((500, 500))
    clock = pygame.time.Clock()
    dt = 0
    player = Player()
    sprites = pygame.sprite.Group(player)
    background = screen.copy()
    background.fill((30, 30, 30))
    for _ in range(1000):
        x, y = random.randint(0, 1000), random.randint(0, 1000)
        pygame.draw.rect(background, pygame.Color('green'), (x, y, 2, 2))

    while True:
        events = pygame.event.get()
        for e in events:
            if e.type == pygame.QUIT:
                return
        sprites.update(events, dt)
        screen.blit(background, (0, 0))
        sprites.draw(screen)
        pygame.display.update()
        dt = clock.tick(60)

if __name__ == '__main__':
    main()

到目前为止没有什么疯狂的。

---

那么，什么是“相机”？它只是我们用来移动整个“世界”（例如所有非 UI）x的值。y它是我们游戏对象的坐标和屏幕之间的抽象。

在我们上面的例子中，当一个游戏对象（玩家或背景）想要在位置绘制时(x, y)，我们在屏幕上的这个位置绘制它们。

现在，如果我们想在“相机”周围移动，我们只需创建另一个x, y-pair，并将其添加到游戏对象的坐标中以确定屏幕上的实际位置。我们开始区分世界坐标（游戏逻辑认为物体的位置在哪里）和屏幕坐标（物体在屏幕上的实际位置）。

这是我们使用“camera”（引号中的“camera”）的示例，因为它实际上只有两个值：

import pygame
import random

class Player(pygame.sprite.Sprite):
    def __init__(self):
        super().__init__()
        self.image = pygame.Surface((32, 32))
        self.image.fill(pygame.Color('dodgerblue'))
        self.rect = self.image.get_rect()
        self.pos = pygame.Vector2((100, 200))

    def update(self, events, dt):
        pressed = pygame.key.get_pressed()
        move = pygame.Vector2((0, 0))
        if pressed[pygame.K_w]: move += (0, -1)
        if pressed[pygame.K_a]: move += (-1, 0)
        if pressed[pygame.K_s]: move += (0, 1)
        if pressed[pygame.K_d]: move += (1, 0)
        if move.length() > 0: move.normalize_ip()
        self.pos += move*(dt/5)
        self.rect.center = self.pos

def main():
    pygame.init()
    screen = pygame.display.set_mode((500, 500))
    clock = pygame.time.Clock()
    dt = 0
    player = Player()
    sprites = pygame.sprite.Group(player)
    # the "world" is now bigger than the screen
    # so we actually have anything to move the camera to
    background = pygame.Surface((1500, 1500))
    background.fill((30, 30, 30))

    # a camera is just two values: x and y
    # we use a vector here because it's easier to handle than a tuple
    camera = pygame.Vector2((0, 0))

    for _ in range(3000):
        x, y = random.randint(0, 1000), random.randint(0, 1000)
        pygame.draw.rect(background, pygame.Color('green'), (x, y, 2, 2))

    while True:
        events = pygame.event.get()
        for e in events:
            if e.type == pygame.QUIT:
                return

        # copy/paste because I'm lazy
        # just move the camera around
        pressed = pygame.key.get_pressed()
        camera_move = pygame.Vector2()
        if pressed[pygame.K_UP]: camera_move += (0, 1)
        if pressed[pygame.K_LEFT]: camera_move += (1, 0)
        if pressed[pygame.K_DOWN]: camera_move += (0, -1)
        if pressed[pygame.K_RIGHT]: camera_move += (-1, 0)
        if camera_move.length() > 0: camera_move.normalize_ip()
        camera += camera_move*(dt/5)

        sprites.update(events, dt)

        # before drawing, we shift everything by the camera's x and y values
        screen.blit(background, camera)
        for s in sprites:
            screen.blit(s.image, s.rect.move(*camera))

        pygame.display.update()
        dt = clock.tick(60)

if __name__ == '__main__':
    main()

现在您可以使用箭头键移动相机。

就是这样。我们只是将所有内容移动一点，然后将其传送到屏幕上。

有关更完整的示例（支持精灵、在世界边缘停止、平滑移动），请参阅此问题。

---

而对于使用 pymunk：它只是工作。它不受将东西绘制到另一个位置的影响，因为它适用于世界坐标，而不是屏幕坐标。唯一的缺陷是 pymunk 的 y 轴与 pygame 的 y 轴相比是翻转的，但您可能已经知道这一点。

这是一个例子：

import pygame
import random
import pymunk

class Player(pygame.sprite.Sprite):
    def __init__(self, space):
        super().__init__()
        self.space = space
        self.image = pygame.Surface((32, 32))
        self.image.fill(pygame.Color('dodgerblue'))
        self.rect = self.image.get_rect()
        self.pos = pygame.Vector2((100, 200))
        self.body = pymunk.Body(1,1666)
        self.body.position = self.pos
        self.poly = pymunk.Poly.create_box(self.body)
        self.space.add(self.body, self.poly)

    def update(self, events, dt):
        pressed = pygame.key.get_pressed()
        move = pygame.Vector2((0, 0))
        if pressed[pygame.K_w]: move += (0, 1)
        if pressed[pygame.K_a]: move += (-1, 0)
        if pressed[pygame.K_s]: move += (0, -1)
        if pressed[pygame.K_d]: move += (1, 0)
        if move.length() > 0: move.normalize_ip()
        self.body.apply_impulse_at_local_point(move*5)

        # if you used pymunk before, you'll probably already know
        # that you'll have to invert the y-axis to convert between
        # the pymunk and the pygame coordinates.
        self.pos = pygame.Vector2(self.body.position[0], -self.body.position[1]+500)
        self.rect.center = self.pos

def main():
    pygame.init()
    screen = pygame.display.set_mode((500, 500))
    clock = pygame.time.Clock()
    dt = 0

    space = pymunk.Space()
    space.gravity = 0,-100

    player = Player(space)
    sprites = pygame.sprite.Group(player)

    # the "world" is now bigger than the screen
    # so we actually have anything to move the camera to
    background = pygame.Surface((1500, 1500))
    background.fill((30, 30, 30))

    # a camera is just two values: x and y
    # we use a vector here because it's easier to handle than a tuple
    camera = pygame.Vector2((0, 0))

    for _ in range(3000):
        x, y = random.randint(0, 1000), random.randint(0, 1000)
        pygame.draw.rect(background, pygame.Color('green'), (x, y, 2, 2))

    while True:
        events = pygame.event.get()
        for e in events:
            if e.type == pygame.QUIT:
                return

        # copy/paste because I'm lazy
        # just move the camera around
        pressed = pygame.key.get_pressed()
        camera_move = pygame.Vector2()
        if pressed[pygame.K_UP]: camera_move += (0, 1)
        if pressed[pygame.K_LEFT]: camera_move += (1, 0)
        if pressed[pygame.K_DOWN]: camera_move += (0, -1)
        if pressed[pygame.K_RIGHT]: camera_move += (-1, 0)
        if camera_move.length() > 0: camera_move.normalize_ip()
        camera += camera_move*(dt/5)

        sprites.update(events, dt)

        # before drawing, we shift everything by the camera's x and y values
        screen.blit(background, camera)
        for s in sprites:
            screen.blit(s.image, s.rect.move(*camera))

        pygame.display.update()
        dt = clock.tick(60)
        space.step(dt/1000)

if __name__ == '__main__':
    main()

---

请注意，当您使用 时pymunk.Space.debug_draw，您将无法将世界坐标转换为屏幕坐标，因此最好将 pymunk 的东西简单地绘制到另一个Surface上，然后将其转换为Surface.

pygame_util_demo.py这是带有移动相机的pymunk ：

import sys

import pygame
from pygame.locals import *

import pymunk
from pymunk.vec2d import Vec2d
import pymunk.pygame_util

import shapes_for_draw_demos

def main():
    pygame.init()
    screen = pygame.display.set_mode((1000,700)) 
    pymunk_layer = pygame.Surface((1000,700))
    pymunk_layer.set_colorkey((12,12,12))
    pymunk_layer.fill((12,12,12))
    camera = pygame.Vector2((0, 0))
    clock = pygame.time.Clock()
    font = pygame.font.SysFont("Arial", 16)

    space = pymunk.Space()

    captions = shapes_for_draw_demos.fill_space(space)

    # Info
    color = pygame.color.THECOLORS["black"]

    options = pymunk.pygame_util.DrawOptions(pymunk_layer)

    while True:
        for event in pygame.event.get():
            if event.type == QUIT or \
                event.type == KEYDOWN and (event.key in [K_ESCAPE, K_q]):  
                return 
            elif event.type == KEYDOWN and event.key == K_p:
                pygame.image.save(screen, "pygame_util_demo.png")                

        # copy/paste because I'm lazy
        pressed = pygame.key.get_pressed()
        camera_move = pygame.Vector2()
        if pressed[pygame.K_UP]: camera_move += (0, 1)
        if pressed[pygame.K_LEFT]: camera_move += (1, 0)
        if pressed[pygame.K_DOWN]: camera_move += (0, -1)
        if pressed[pygame.K_RIGHT]: camera_move += (-1, 0)
        if camera_move.length() > 0: camera_move.normalize_ip()
        camera += camera_move*5

        screen.fill(pygame.color.THECOLORS["white"])
        pymunk_layer.fill((12,12,12))
        space.debug_draw(options)
        screen.blit(pymunk_layer, camera)
        screen.blit(font.render("Demo example of pygame_util.DrawOptions()", 1, color), (205, 680))
        for caption in captions:
            x, y = caption[0]
            y = 700 - y
            screen.blit(font.render(caption[1], 1, color), camera + (x,y))
        pygame.display.flip()

        clock.tick(30)

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