Python Box2D Pygame屏幕坐标到Box2D网格

Question

我无法找出从鼠标坐标获取世界坐标的正确方法。

在这样的问题中： mouseWorld Coords Box2D 有一个方法：box2d.coordPixelsToWorld(x,y);但我在 box2d 的 Python 库中找不到这个方法。

position = pygame.mouse.get_pos() 

position = ??? * ??? 

body.position = position

更多上下文代码：

PPM = 20.0  # pixels per meter
TARGET_FPS = 60
TIME_STEP = 1.0 / TARGET_FPS
SCREEN_WIDTH, SCREEN_HEIGHT = 1280, 720  # 640, 480

# --- pygame setup ---
screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT), 0, 32, display=1)
pygame.display.set_caption('Simple pygame example')
clock = pygame.time.Clock()

body = world.CreateStaticBody(
        position=(i, 1),
        shapes=box2d.b2PolygonShape(box=(1, 1)),
    ))

bodies.append(body)

colors = {
    box2d.b2_staticBody: (255, 255, 255, 255),
    box2d.b2_dynamicBody: (127, 127, 127, 255),
}

# --- main game loop ---
running = True
while running:
    # Check the event queue
    for event in pygame.event.get():
        if event.type == QUIT or (event.type == KEYDOWN and event.key == K_ESCAPE):
            # The user closed the window or pressed escape
            running = False

    screen.fill((0, 0, 0, 0))
    
    position = pygame.mouse.get_pos() 

    position = ??? * ??? 

    body.position = position

    for body in bodies:  # or: world.bodies
        # The body gives us the position and angle of its shapes
        # body
        for fixture in body.fixtures:
            # The fixture holds information like density and friction,
            # and also the shape.
            shape = fixture.shape

            # Naively assume that this is a polygon shape. (not good normally!)
            # We take the body's transform and multiply it with each
            # vertex, and then convert from meters to pixels with the scale
            # factor.
            vertices = [(body.transform * v) * PPM for v in shape.vertices]

            # But wait! It's upside-down! Pygame and Box2D orient their
            # axes in different ways. Box2D is just like how you learned
            # in high school, with positive x and y directions going
            # right and up. Pygame, on the other hand, increases in the
            # right and downward directions. This means we must flip
            # the y components.
            vertices = [(v[0], SCREEN_HEIGHT - v[1]) for v in vertices]

            pygame.draw.polygon(screen, colors[body.type], vertices)

    # Make Box2D simulate the physics of our world for one step.
    # Instruct the world to perform a single step of simulation. It is
    # generally best to keep the time step and iterations fixed.
    # See the manual (Section "Simulating the World") for further discussion
    # on these parameters and their implications.
    world.Step(TIME_STEP, 10, 10)

    # Flip the screen and try to keep at the target FPS
    pygame.display.flip()
    clock.tick(TARGET_FPS)

pygame.quit()

if __name__ == "__main__":
    print('Done!')

编辑：PPM 值是每米的像素数。 如果我将 pygame.mouse.get_pos().x 除以 PPM，它就是正确的值。但 y 值偏离 3 '米'

EDIT2：因为它是 (SCREEN_HEIGHT - y) / PPM

Answer 1

虽然不熟悉 Python 的 Box2d，但如果您正在寻找的是将鼠标 X,Y 转换为世界 X,Y
只需使用 Box2d 转换因子、PIXEL_PER_METERS 或您使用的任何值转换鼠标 x,y，因此 f.ex
浮动 PIXEL_PER_METER = 100.f;
因此，screenpos 1200, 600 是“box2d 单位/米”中的 12,6

• ，您已经完成了该操作，但有些偏离，您是否考虑了浮点/整数转换？
  Python 毕竟会调用 C++ Box2d 函数，因此请确保您没有将任何 floats 转换为 integers ，但仔细检查后，您看起来并没有这样做。
• 相机 ScreenToWorld 或 WorldToScreen ->它们是如何实施的？
  我认为你在某处有类似的东西，
  此问题是相机功能问题的一个相当典型的症状。

但如何将鼠标转换为世界的答案是：
-如果你想要 Box2d 单位的世界：使用比例因子进行转换
-将Camera.Offset值添加到鼠标x,y以获取世界位置

 Camera.MinWorld  <- update this depending on what camera is focused on

 Mouse.x + Camera.MinWorld.x , Mouse.y + Camera.MinWorld.y = world position

world pos到screenpos：
pos.x - Camera.MinWorld.x , pos.y - Camera.MinWorld.y