pygame鼠标移动失败

Question

I am working through pygame tutorials and at the moment I am trying to figure out how to select a circle which is firing a ball where a ball hits another ball which in turn knocks a box down. The knocking of the box works fine when the ball hits the box. However, when I add the mouse movement so that I can select the ball again and place it in the same position so that it can be hit again so that the box knocks again. The ball just rolls backwards without firing the second ball to knock the box.Here is the previous code that works with one ball firing another ball but without the mouse movements ie without allowing the ball to be selected and dragged.

import pygame
from pygame.locals import *
from pygame.color import *
import pymunk as pm
from pymunk import Vec2d
import sys
from random import randint

def to_pygame(p):
    """Small hack to convert pymunk to pygame coordinates"""
    return int(p[0]), int(-p[1]+600)


def draw_ball(screen, ball, colour):
    r = ball.radius
    rot = ball.body.rotation_vector
    p = to_pygame(ball.body.position)
    p2 = Vec2d(rot.x, -rot.y) * r * 0.9
    pygame.draw.line(screen, THECOLORS["red"], p, p+p2)
    pygame.draw.circle(screen, colour, p, int(r), 3)


def add_ball(space, x=0, y=130):
    mass = 1.3
    radius = 20
    inertia = pm.moment_for_circle(mass, 0, radius, (0,0))
    body = pm.Body(mass, inertia)
    body.position = (x,y)
    shape = pm.Circle(body, radius, (0,0))
    shape.friction = 10.0
    shape.elasticity = 1.0
    space.add(body, shape)

    return shape


def add_box(space, size, pos, mass=0.3):
    points = [(-size, -size), (-size, size), (size,size), (size, -size)]
    moment = pm.moment_for_poly(int(mass), points, (0,0))

    body = pm.Body(mass, moment)
    body.position = pos

    shape = pm.Poly(body, points, (0,0))
    shape.friction = 1
    space.add(body,shape)

    return shape

def draw_box(screen, box):
    ps = box.get_points()
    ps.append(ps[0])
    newps = [to_pygame(x) for x in ps]
    pygame.draw.polygon(screen, THECOLORS["blue"], newps, 3)


def main():
    pygame.init()
    screen = pygame.display.set_mode((600, 600))
    pygame.display.set_caption("Impulsive balls")
    clock = pygame.time.Clock()

    balls = []
    space = pm.Space()
    space.gravity = (0.0, -300.0)

    # ground
    body = pm.Body()
    shape = pm.Segment(body, (0,100), (450,100), .0)
    shape.friction = 6.0
    space.add(shape)

    # hidden ramp
    body = pm.Body()
    slope = pm.Segment(body, (0,100), (180,150), .0)
    space.add(slope)

    balls.append(add_ball(space, 10, 130))
    balls.append(add_ball(space, 100, 150))
    #joint = pm.PinJoint(balls[0].body, balls[1].body)
    #joint.distance = 90

    mass = 1.0
    size = 20
    box = add_box(space, size, (400,100+size), mass)
    count = 0

    while 1:
        space.step(1/30.0)
        clock.tick(30)

        for event in pygame.event.get():
            if event.type == QUIT:
                pygame.quit()
                sys.exit(0)
            elif event.type == KEYDOWN:
                if event.key == K_ESCAPE:
                    pygame.quit()
                    sys.exit(0)

        if count == 10:
            pm.Body.apply_impulse(balls[0].body, (450,0))

        screen.fill(THECOLORS["white"])
        pygame.draw.line(screen, THECOLORS["red"], to_pygame((0,100)), to_pygame((450,100)), 3)

        pygame.draw.line(screen, THECOLORS["red"], to_pygame((0,100)), to_pygame((180,150)), 3)

        draw_box(screen, box)
        for ball in balls:
            draw_ball(screen, ball, THECOLORS["green"])

        pygame.display.flip()
        count += 1

if __name__ == '__main__':
    main()

Here is the second version where I add the mouse movement code

import pygame
from pygame.locals import *
from pygame.color import *
import pymunk as pm
from pymunk import Vec2d
import sys
from random import randint

def to_pygame(p):
    """Small hack to convert pymunk to pygame coordinates"""
    return int(p[0]), int(-p[1]+600)
def from_pygame(p):
    return to_pygame(p)

def draw_ball(screen, ball, colour):
    r = ball.radius
    rot = ball.body.rotation_vector
    p = to_pygame(ball.body.position)
    p2 = Vec2d(rot.x, -rot.y) * r * 0.9
    pygame.draw.line(screen, THECOLORS["blue"], p, p+p2)
    pygame.draw.circle(screen, colour, p, int(r), 3)


def add_ball(space, x=0, y=130):
    mass = 1.3 #1.5
    radius = 20
    inertia = pm.moment_for_circle(mass, 0, radius, (0,0))
    body = pm.Body(mass, inertia)
    body.position = (x,y)
    shape = pm.Circle(body, radius, (0,0))
    shape.friction = 10.0
    shape.elasticity = 1.0
    space.add(body, shape)

    return shape


def add_box(space, size, pos, mass=0.3):
    points = [(-size, -size), (-size, size), (size,size), (size, -size)]
    moment = pm.moment_for_poly(int(mass), points, (0,0))

    body = pm.Body(mass, moment)
    body.position = pos

    shape = pm.Poly(body, points, (0,0))
    shape.friction = 1
    space.add(body,shape)

    return shape

def draw_box(screen, box):
    ps = box.get_points()
    ps.append(ps[0])
    newps = [to_pygame(x) for x in ps]
    pygame.draw.polygon(screen, THECOLORS["blue"], newps, 3)


def main():
    pygame.init()
    screen = pygame.display.set_mode((600, 600))
    pygame.display.set_caption("Impulsive balls")
    clock = pygame.time.Clock()
    body = []
    selected = None
    balls = []
    space = pm.Space()
    space.gravity = (0.0, -300.0)

    # ground
    body = pm.Body()
    shape = pm.Segment(body, (0,100), (450,100), .0)
    shape.friction = 6.0
    space.add(shape)

    # hidden ramp
    body = pm.Body()
    slope = pm.Segment(body, (0,100), (180,150), .0)
    space.add(slope)

    balls.append(add_ball(space, 10, 130))
    balls.append(add_ball(space, 100, 150))
    #joint = pm.PinJoint(balls[0].body, balls[1].body)
    #joint.distance = 90

    mass = 1.0
    size = 20
    box = add_box(space, size, (400,100+size), mass)
    count = 0

    while 1:
        space.step(1/30.0)
        clock.tick(30)

        for event in pygame.event.get():
            if event.type == QUIT:
                pygame.quit()
                sys.exit(0)
            elif event.type == KEYDOWN:
                if event.key == K_ESCAPE:
                    pygame.quit()
                    sys.exit(0)
                if count == 10:
                    pm.Body.apply_impulse(balls[0].body, (450,0))
                if event.key == K_p:
                    balls[0].body.apply_impulse((450,0))
                if event.key == K_s:
                    balls[0].body.apply_impulse((-450,0))



            elif event.type == MOUSEBUTTONDOWN:
                p = from_pygame(Vec2d(event.pos))
                selected = space.point_query_first(p)
            elif event.type == MOUSEBUTTONUP:
                if selected != None:
                    selected = None
            elif event.type == MOUSEMOTION:
                if selected != None:
                    selected.body.position = from_pygame(event.pos)

        screen.fill(THECOLORS["white"])
        pygame.draw.line(screen, THECOLORS["red"], to_pygame((0,100)), to_pygame((450,100)), 3)

        pygame.draw.line(screen, THECOLORS["red"], to_pygame((0,100)), to_pygame((180,150)), 3)

        draw_box(screen, box)
        for ball in balls:
            draw_ball(screen, ball, THECOLORS["green"])

        pygame.display.flip()
        count += 1

if __name__ == '__main__':
    main()

Also, how can I have the ball at the same position so that I can drag it and push the other ball to knock the box instead of making the ball roll back, so later I can select the fired ball again and place it next to the ball without rolling back

Answer 1

For your first issue, where the ball is not firing in the second file. The problem is that you have put that code into the event block, which only happens when an external event is fired (like pressing a key). To fix it, that chunk needs to be moved out of that for loop as shown below:

...

while 1:
    space.step(1/30.0)
    clock.tick(30)

    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit(0)
        elif event.type == KEYDOWN:
            if event.key == K_ESCAPE:
                pygame.quit()
                sys.exit(0)
            if event.key == K_p:
                balls[0].body.apply_impulse((450,0))
            if event.key == K_s:
                balls[0].body.apply_impulse((-450,0))
        elif event.type == MOUSEBUTTONDOWN:
            p = from_pygame(Vec2d(event.pos))
            selected = space.point_query_first(p)
        elif event.type == MOUSEBUTTONUP:
            if selected != None:
                selected = None
        elif event.type == MOUSEMOTION:
            if selected != None:
                selected.body.position = from_pygame(event.pos)

    if count == 10:
        pm.Body.apply_impulse(balls[0].body, (450,0))

...

To keep the ball from moving, what I would recommend is to place them on flat ground. I've made the following changes to main to show what I mean. Please note that I disabled the ball firing so that you can see that the balls stay in position. I'd also recommend that you put some invisible walls off the screen on to keep all of the objects stuck inside the frame.

...

def main():
    pygame.init()
    screen = pygame.display.set_mode((600, 600))
    pygame.display.set_caption("Impulsive balls")
    clock = pygame.time.Clock()
    body = []
    selected = None
    balls = []
    space = pm.Space()
    space.gravity = (0.0, -300.0)

    # ground
    body = pm.Body()
    shape = pm.Segment(body, (0,100), (450,100), .0)
    shape.friction = 6.0
    space.add(shape)

    # hidden ramp
    body = pm.Body()
    slope = pm.Segment(body, (20,100), (180,150), .0)
    space.add(slope)
    body = pm.Body()
    slopetop = pm.Segment(body, (180,150), (190,150), .0)
    space.add(slopetop)

    balls.append(add_ball(space, 10, 130))
    balls.append(add_ball(space, 185, 170))
    #joint = pm.PinJoint(balls[0].body, balls[1].body)
    #joint.distance = 90

    mass = 1.0
    size = 20
    box = add_box(space, size, (400,100+size), mass)
    count = 0

    while 1:
        space.step(1/30.0)
        clock.tick(30)

        for event in pygame.event.get():
            if event.type == QUIT:
                pygame.quit()
                sys.exit(0)
            elif event.type == KEYDOWN:
                if event.key == K_ESCAPE:
                    pygame.quit()
                    sys.exit(0)
                if event.key == K_p:
                    balls[0].body.apply_impulse((450,0))
                if event.key == K_s:
                    balls[0].body.apply_impulse((-450,0))
            elif event.type == MOUSEBUTTONDOWN:
                p = from_pygame(Vec2d(event.pos))
                selected = space.point_query_first(p)
            elif event.type == MOUSEBUTTONUP:
                if selected != None:
                    selected = None
            elif event.type == MOUSEMOTION:
                if selected != None:
                    selected.body.position = from_pygame(event.pos)

        if count == 10 and 0:
            pm.Body.apply_impulse(balls[0].body, (450,0))

        screen.fill(THECOLORS["white"])
        pygame.draw.line(screen, THECOLORS["red"], to_pygame((0,100)), to_pygame((450,100)), 3)
        pygame.draw.line(screen, THECOLORS["red"], to_pygame((20,100)), to_pygame((180,150)), 3)
        pygame.draw.line(screen, THECOLORS["red"], to_pygame((180,150)), to_pygame((190,150)), 3)

        draw_box(screen, box)
        for ball in balls:
            draw_ball(screen, ball, THECOLORS["green"])

        pygame.display.flip()
        count += 1
...