Pymunk是一个易于使用的pythonic2d物理库

　　1 说明：
　　=====
　　1.1 中英文介绍：
　　Pymunk is a easy-to-use pythonic 2d physics library
　　pymunk是一个易于使用的pythonic 2d物理库
　　1.2 多基于pygame和pyglet的动画。
　　1.3 官网示意图：
　　图1：index_video.gif，可以实现
　　2 准备：
　　=====
　　2.1 官网：http://www.pymunk.org/en/latest/ https://pypi.org/project/pymunk/ https://github.com/viblo/pymunk
　　2.2 环境：
　　华为笔记本电脑、深度deepin-linux操作系统、谷歌浏览器、python3.8和微软vscode编辑器。
　　2.3 安装：pip install pymunk #本机安装，且推荐国内源安装 sudo pip3.8 install pymunk -i https://mirrors.aliyun.com/pypi/simple
　　3 官方example：
　　arrow
　　bouncing_balls
　　4 拿官网的动画gif来讲解:
　　======================
　　4.1 图1：index_video.gif，也可以实现，代码量太多了，省略，属于example。
　　4.2 蜘蛛网：spiderweb.py对代码进行修改，注释，bug改进。
　　5 spiderweb.py代码：
　　===============
　　提前看看效果图：
　　5.1 第1步：导入模块import math, random import pyglet import pymunk from pymunk.vec2d import Vec2d
　　5.2 第2步：初始化参数设定config = pyglet.gl.Config(sample_buffers=1, samples=2, double_buffer=True) window = pyglet.window.Window(config=config, vsync = False,     #窗口大小和标题名设定     width=800,     height=800,     caption=＂spiderweb＂,     resizable=True)  #pymunk物理参数设定 space = pymunk.Space() space.gravity = 0,-900 space.damping = .999 #中心点坐标 c = Vec2d(window.width /2., window.height / 2.)                  #WEB参数 web_group = 1 bs = [] dist = .3  cb = pymunk.Body(1,1) cb.position = c  #位置中心点坐标 s = pymunk.Circle(cb, 15) # to have something to grab s.filter = pymunk.ShapeFilter(group = web_group) s.ignore_draw = True space.add(cb, s)
　　5.3 第3步：织网#generate each crossing in the net for x in range(0,101):     b = pymunk.Body(1, 1)     v = Vec2d.unit()     v.angle_degrees = x*18     scale = window.height / 2. / 6. * .5          dist += 1/18.      dist = dist ** 1.005          offset = 0     offset = [0.0, -0.80, -1.0, -0.80][((x*18) % 360)//18 % 4]     offset = .8 + offset          offset *= dist**2.8 / 100.          v.length = scale * (dist + offset)           b.position = c + v     s = pymunk.Circle(b, 15)     s.filter = pymunk.ShapeFilter(group = web_group)     s.ignore_draw = True     space.add(b,s)     bs.append(b)  #连接线 def add_joint(a,b):     rl = a.position.get_distance(b.position) * 0.9     stiffness = 5000.     damping = 100     j = pymunk.DampedSpring(a, b, (0,0), (0,0), rl, stiffness, damping)     j.max_bias = 1000     j.max_force = 50000     space.add(j)      for b in bs[:20]:     add_joint(cb,b)      for i in range(len(bs)-1):     add_joint(bs[i], bs[i+1])      i2 = i+20     if len(bs) > i2:         add_joint(bs[i], bs[i2])
　　5.4 网和点的关系static_bs = [] for b in bs[-17::4]:     static_body = pymunk.Body(body_type = pymunk.Body.STATIC)     static_body.position = b.position     static_bs.append(static_body)          j = pymunk.PivotJoint(static_body, b, static_body.position)     j = pymunk.DampedSpring(static_body, b, (0,0), (0,0), 0, 0, 0)     j.damping = 100     j.stiffness = 20000     space.add(j)  #更新 def update(dt):     r = 10     for x in range(r):         space.step(1./30./r)                  pyglet.clock.schedule_interval(update, 1/30.)  selected = None selected_joint = None mouse_body = pymunk.Body(body_type = pymunk.Body.KINEMATIC)
　　5.5 第5步：窗口事件绑定和运行#第5步：窗口时间绑定 @window.event def on_mouse_press(x, y, button, modifiers):     mouse_body.position = x,y     hit = space.point_query_nearest((x,y), 10, pymunk.ShapeFilter())     if hit != None:         global selected         body = hit.shape.body         rest_length = mouse_body.position.get_distance(body.position)         stiffness = 1000         damping = 10         selected = pymunk.DampedSpring(mouse_body, body, (0,0), (0,0), rest_length, stiffness, damping)         space.add(selected)          @window.event def on_mouse_release(x, y, button, modifiers):     global selected     if selected != None:         space.remove(selected)         selected = None      @window.event def on_mouse_drag(x, y, dx, dy, buttons, modifiers):     mouse_body.position = x,y     @window.event def on_key_press(symbol, modifiers):     #保存设置，当按p就是保存     if symbol == pyglet.window.key.P:         pyglet.image.get_buffer_manager().get_color_buffer().save(＂spiderweb.png＂)      fps_display = pyglet.window.FPSDisplay(window)  @window.event def on_draw():     #窗口背景颜色设置，默认为黑色(0,0,0,255)，最后一个255为透明度     #pyglet.gl.glClearColor(240,240,240,255)  #白色     #pyglet.gl.glClearColor(0,0,0,255)  #黑色，不设置也是黑色     window.clear()          fps_display.draw()          # static attach points     pyglet.gl.glColor3f(1,0,1)     pyglet.gl.glPointSize(6)     a = []     for b in static_bs:         a += [b.position.x, b.position.y]         pyglet.graphics.draw(len(a)//2, pyglet.gl.GL_POINTS, (＂v2f＂,a))          # web crossings / bodies     pyglet.gl.glColor3f(.8,.8,.8)     a = []     for b in bs:         a += [b.position.x, b.position.y]     pyglet.gl.glPointSize(4)     pyglet.graphics.draw(len(a)//2, pyglet.gl.GL_POINTS, (＂v2f＂,a))              # web net / constraints     a = []     for j in space.constraints:         a += [j.a.position.x, j.a.position.y, j.b.position.x, j.b.position.y]         pass          pyglet.graphics.draw(len(a)//2, pyglet.gl.GL_LINES, (＂v2f＂,a))       pyglet.app.run()
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