coursera课程上的第四个课程mini-project

设计经典的ponggame

游戏的介绍和说明参见http://www.ponggame.org/

在具体求解过程中的步骤如下

1，初始化各个变量（canvas尺寸，paddle尺寸，中间线，）

2，spawn_ball（）函数的编写，此函数作用可以在初始game中进行调用，同时每次状态结束时怎样产生新的状态，初始变量的设置包括设定小球的起始位置和速度方向

3，new_game()函数的编写，此函数用于游戏处初始状态的说明，全局变两种score1和score2的初始化

4，定义event handler 具体包括以下

4.1 draw（canvas）函数，包括中间线各个paddle1,2,边缘线的画出，更新小球，此时首先分为上下、左右的更新，上下的更新较为简单，只需考虑球的竖直分量，不考虑paddle；左右的更新需要在判断球是否成功碰到paddle，需要在if中内嵌一个条件判断，如果成功碰到，球速增加1.1倍，如果没有碰撞上paddle，在对方的界面处产生新的小球并且对方得分。

draw ball, score显示的draw text()

设计keydown和keyup保证paddle的正常滑行

5，create frame

create frame

frame = simplegui.create_frame(“Pong”, WIDTH, HEIGHT)

frame.set_draw_handler(draw)

frame.set_keydown_handler(keydown)

frame.set_keyup_handler(keyup)

6 开始

new_game()

frame.start()

最后的python 程序如下

# Implementation of classic arcade game Pong

import simplegui

import random

# initialize globals - pos and vel encode vertical info for paddles

WIDTH = 600

HEIGHT = 400

BALL_RADIUS = 20

PAD_WIDTH = 8

PAD_HEIGHT = 80

HALF_PAD_WIDTH = PAD_WIDTH / 2

HALF_PAD_HEIGHT = PAD_HEIGHT / 2

LEFT = False

RIGHT = True

ball_vel=[0,0]

score1=0

score2=0

# initialize ball_pos and ball_vel for new bal in middle of table

# if direction is RIGHT, the ball's velocity is upper right, else upper left

def spawn_ball(direction):

global ball_pos, ball_vel # these are vectors stored as lists

ball_pos=[WIDTH/2,HEIGHT/2]

ball_vel=[random.randrange(120,240),random.randrange(60,180)]

if (direction==LEFT):

ball_vel[0]=-ball_vel[0]

ball_vel[1]=-ball_vel[1]

elif(direction==RIGHT):

ball_vel[1]=-ball_vel[1]

# define event handlers

def new_game():

global paddle1_pos, paddle2_pos, paddle1_vel, paddle2_vel # these are numbers

global score1, score2 # these are ints

paddle1_pos=HEIGHT/2

paddle2_pos=HEIGHT/2

paddle1_vel=0

paddle2_vel=0

spawn_ball(LEFT)

def draw(canvas):

global score1, score2, paddle1_pos, paddle2_pos, ball_pos, ball_vel

# draw mid line and gutters

canvas.draw_line([WIDTH / 2, 0],[WIDTH / 2, HEIGHT], 1, "White")

canvas.draw_line([PAD_WIDTH, 0],[PAD_WIDTH, HEIGHT], 1, "White")

canvas.draw_line([WIDTH - PAD_WIDTH, 0],[WIDTH - PAD_WIDTH, HEIGHT], 1, "White")

# update ball

if (ball_pos[1]<=BALL_RADIUS)or(ball_pos[1]>=HEIGHT-BALL_RADIUS):

ball_vel[1]=-ball_vel[1]

# ball_pos[1]+=ball_vel[1]

if (ball_pos[0]-BALL_RADIUS-PAD_WIDTH<=0):

if ((paddle1_pos-PAD_HEIGHT/2)<=ball_pos[1]<=(PAD_HEIGHT/2+paddle1_pos)):

ball_vel[0]=-ball_vel[0]

ball_vel[0]=1.1*ball_vel[0]

ball_vel[1]=1.1*ball_vel[1]

else:

spawn_ball(RIGHT)

score2+=1

if (WIDTH-BALL_RADIUS-PAD_WIDTH-ball_pos[0]<=0):

if ((paddle2_pos-PAD_HEIGHT/2)<=ball_pos[1]<=(PAD_HEIGHT/2+paddle2_pos)):

##judge the right side whether it correct

ball_vel[0]=-ball_vel[0]

ball_vel[0]=1.1*ball_vel[0]

ball_vel[1]=1.1*ball_vel[1]

else:

spawn_ball(LEFT)

score1+=1

ball_pos[0]+=ball_vel[0]/60

ball_pos[1]+=ball_vel[1]/60

# draw ball

canvas.draw_circle(ball_pos,BALL_RADIUS,2,"Red","White")

# update paddle's vertical position, keep paddle on the screen

if (PAD_HEIGHT/2<=paddle1_pos+paddle1_vel<=HEIGHT-PAD_HEIGHT/2):

paddle1_pos+=paddle1_vel

if (PAD_HEIGHT/2<=paddle2_pos+paddle2_vel<=HEIGHT-PAD_HEIGHT/2):

paddle2_pos+=paddle2_vel

# draw paddles

canvas.draw_line([PAD_WIDTH/2,paddle1_pos-PAD_HEIGHT/2],[PAD_WIDTH/2,paddle1_pos+PAD_HEIGHT/2],PAD_WIDTH,"White")

canvas.draw_line([WIDTH-PAD_WIDTH/2,paddle2_pos-PAD_HEIGHT/2],[WIDTH-PAD_WIDTH/2,paddle2_pos+PAD_HEIGHT/2],PAD_WIDTH,"White")

# determine whether paddle and ball collide

# draw scores

canvas.draw_text(str(score1),(230,80),50,"White")

canvas.draw_text(str(score2),(350,80),50,"White")

def keydown(key):

global paddle1_vel, paddle2_vel

acc=4

if key==simplegui.KEY_MAP["w"]:

paddle1_vel=-acc

elif key==simplegui.KEY_MAP["s"]:

paddle1_vel=acc

elif key==simplegui.KEY_MAP["up"]:

paddle2_vel=-acc

elif key==simplegui.KEY_MAP["down"]:

paddle2_vel=acc

def keyup(key):

global paddle1_vel, paddle2_vel

if (key == simplegui.KEY_MAP['w'] or key == simplegui.KEY_MAP['s']):

paddle1_vel = 0

if (key == simplegui.KEY_MAP['up'] or key == simplegui.KEY_MAP['down']):

paddle2_vel = 0

# create frame

frame = simplegui.create_frame("Pong", WIDTH, HEIGHT)

frame.set_draw_handler(draw)

frame.set_keydown_handler(keydown)

frame.set_keyup_handler(keyup)

# start frame

new_game()

frame.start()