Interactive Python：Mini-project # 7

gmdzxx

An Introduction to Interactive
Programming in Python

Mini-project description - Spaceship
　　In our last two mini-projects, we will build a 2D space gameRiceRocksthat is inspired by the classic arcade gameAsteroids(1979).Asteroidsis a relatively
simple game by today's standards, but was still immensely popular during its time. (Joe spent countless quarters playing it.) In the game, the player controls a spaceship via four buttons: two buttons that rotate the spaceship clockwise or counterclockwise
(independent of its current velocity), a thrust button that accelerates the ship in its forward direction and a fire button that shoots missiles. Large asteroids spawn randomly on the screen with random velocities. The player's goal is to destroy these asteroids
before they strike the player's ship. In the arcade version, a large rock hit by a missile split into several fast moving small asteroids that themselves must be destroyed. Occasionally, a flying saucer also crosses the screen and attempts to destroy the player's
spaceship. Searching for "asteroids arcade" yields links to multiple versions ofAsteroidsthat are available on the web (including an updated version byAtari, the original creator ofAsteroids).

Mini-project development process

For this mini-project, you will implement a working spaceship plus add a single asteroid and a single missile. We have provided art for your game so its look and feel is that of a more modern game. You should begin by loading theprogram
template.The program template includes all necessary image and audio files. Unfortunately, no audio format is supported by all major browsers so we have decided to provided sounds in themp3format
which is supported by Chrome (but not by Firefox on some systems). (oggversions are also available.)We highly recommend using Chrome for the last two weeks of the class.We
have found that Chrome typically has better performance on games with more substantial drawing requirements and standardization on a common browser will make peer assessing projects more reliable.　　Phase one - Spaceship
　　In this phase, you will implement the control scheme for the spaceship.This includes a complete Spaceship class and the appropriate keyboard handlers to control the spaceship. Your spaceship should behave as follows:

• The left and right arrows should control the orientation of your spaceship. While the left arrow is held down, your spaceship should turn counter-clockwise. While the right arrow is down, your spaceship should turn clockwise. When
  neither key is down, your ship should maintain its orientation. You will need to pick some reasonable angular velocity at which your ship should turn.
  
• The up arrow should control the thrusters of your spaceship. The thrusters should be on when the up arrow is down and off when it is up. When the thrusters are on, you should draw the ship with thrust flames. When the thrusters
  are off, you should draw the ship without thrust flames.
  
• When thrusting, the ship should accelerate in the direction of its forward vector. This vector can be computed from the orientation/angle of the ship using the provided helper functionangle_to_vector.
  You will need to experiment with scaling each component of this acceleration vector to generate a reasonable acceleration.
  
• Remember that while the ship accelerates in its forward direction, but the ship always moves in the direction of its velocity vector. Being able to accelerate in a direction different than the direction that you are moving is a
  hallmark ofAsteroids.
  
• Your ship should always experience some amount of friction. (Yeah, we know, "Why is there friction in the vacuum of space?". Just trust us there is in this game.) This choice means that the velocity should always be multiplied by
  a constant factor less than one to slow the ship down. It will then come to a stop eventually after you stop the thrusters.
  

Now, implement these behaviors above in order. Each step should require just a few lines of code. Here are some hints:

• Modify the draw method for the Ship class to draw the ship image (without thrust flames) instead of a circle. This method should incorporate the ship's position and angle. Note that the angle should be in radians, not degrees. Since
  a call to the ship's draw method already exists in the draw handler, you should now see the ship image. Experiment with different positions and angles for the ship.
  
• Implement an initial version of the update method for the ship. This version should update the position of the ship based on its velocity. Since a call to the update method also already exists in the draw handler, the ship should
  move in response to different initial velocities.
  
• Modify the update method for the ship to increment its angle by its angular velocity.
  
• Make your ship turn in response to the left/right arrow keys. Add keydown and keyup handlers that check the left and right arrow keys. Add methods to the Ship class to increment and decrement the angular velocity by a fixed amount.
  (There is some flexibility in how you structure these methods.) Call these methods in the keyboard handlers appropriately and verify that you can turn your ship as you expect.
  
• Modify the keyboard handlers to turn the ship's thrusters on/off. Add a method to the Ship class to turn the thrusters on/off (you can make it take a Boolean argument which is True or False to decide if they should be on or off).
  
• Modify the ship's draw method to draw the thrust image when it is on. (The ship image is tiled and contains both images of the ship.)
  
• Modify the ship's thrust method to play the thrust sound when the thrust is on. Rewind the sound when the thrust turns off.
  
• Add code to the ship's update method to use the given helper functionangle_to_vectorto
  compute the forward vector pointing in the direction the ship is facing based on the ship's angle.
  
• Next, add code to the ship's update method to accelerate the ship in the direction of this forward vector when the ship is thrusting. You will need to update the velocity vector by a small fraction of the forward acceleration vector
  so that the ship does not accelerate too fast.
  
• Then, modify the ship's update method such that the ship's position wraps around the screen when it goes off the edge (use modular arithmetic!).
  
• Up to this point, your ship will never slow down. Finally, add friction to the ship's update method as shown in the "Acceleration and Friction" video by multiplying each component of the velocity by a number slightly less than 1
  during each update.
  

You should now have a ship that flies around the screen,as you would like forRiceRocks. Adjust the constants as you would like to get it to fly how you want.　　Phase two - Rocks
　　To implement rocks, we will use the provided Sprite class. Note that the update method for the sprite will be very similar to the update method for the ship. The primary difference is that the ship's velocity and rotation are controlled by keys, whereas
sprites have these set randomly when they are created. Rocks should screen wrap in the same manner as the ship.
　　In the template, the global variablea_rockis
created at the start with zero velocity. Instead, we want to create version ofa_rockonce
every second in the timer handler. Next week, we will add multiple rocks. This week, the ship will not die if it hits a rock. We'll add that next week. To implement rocks, we suggest the following:

• Complete the Sprite class (as shown in the "Sprite class" video) by modifying the draw handler to draw the actual image and the update handler to make the sprite move and rotate. Rocks do not accelerate or experience friction, so
  the sprite update method should be simpler than the ship update method. Test this by givinga_rockdifferent
  starting parameters and ensuring it behaves as you expect.
  
• Implement the timer handlerrock_spawner.
  In particular, seta_rockto
  be a new rock on every tick. (Don't forget to declarea_rockas
  a global in the timer handler.) Choose a velocity, position, and angular velocity randomly for the rock. You will want to tweak the ranges of these random numbers, as that will affect how fun the game is to play. Make sure you generated rocks that spin in
  both directions and, likewise, move in all directions.
  

Phase three - Missiles　　To implement missiles, we will use the same sprite class as for rocks. Missiles will always have a zero angular velocity. They will also have a lifespan (they should disappear after a certain amount of time or you will eventually have missiles all over the
place), but we will ignore that this week. Also, for now, we will only allow a single missile and it will not yet blow up rocks. We'll add more next week.
　　Your missile should be created when you press the spacebar, not on a timer like rocks. They should screen wrap just as the ship and rocks do. Otherwise, the process is very similar:

• Add ashootmethod
  to your ship class. This should spawn a new missile (for now just replace the old missile ina_missile).
  The missile's initial position should be the tip of your ship's "cannon". Its velocity should be the sum of the ship's velocity and a multiple of the ship's forward vector.
  
• Modify the keydown handler to call this shoot method when the spacebar is pressed.
  
• Make sure that the missile sound is passed to the sprite initializer so that the shooting sound is played whenever you shoot a missile.
  

Phase four - User interface　　Our user interface forRiceRockssimply shows the number of lives remaining and the score. This week neither of those elements ever change, but they will next week. Add code to the draw event handler to draw these on the
canvas. Use thelivesandscoreglobal
variables as the current lives remaining and score.
　　代码链接：点击打开链接
　　代码如下：

# program template for Spaceship
import simplegui
import math
import random
# globals for user interface
WIDTH = 800
HEIGHT = 600
score = 0
lives = 3
time = 0.5
class ImageInfo:
def __init__(self, center, size, radius = 0, lifespan = None, animated = False):
self.center = center
self.size = size
self.radius = radius
if lifespan:
self.lifespan = lifespan
else:
self.lifespan = float('inf')
self.animated = animated
def get_center(self):
return self.center
def get_size(self):
return self.size
def get_radius(self):
return self.radius
def get_lifespan(self):
return self.lifespan
def get_animated(self):
return self.animated

# art assets created by Kim Lathrop, may be freely re-used in non-commercial projects, please credit Kim
# debris images - debris1_brown.png, debris2_brown.png, debris3_brown.png, debris4_brown.png
#                 debris1_blue.png, debris2_blue.png, debris3_blue.png, debris4_blue.png, debris_blend.png
debris_info = ImageInfo([320, 240], [640, 480])
debris_image = simplegui.load_image("http://commondatastorage.googleapis.com/codeskulptor-assets/lathrop/debris2_blue.png")
# nebula images - nebula_brown.png, nebula_blue.png
nebula_info = ImageInfo([400, 300], [800, 600])
nebula_image = simplegui.load_image("http://commondatastorage.googleapis.com/codeskulptor-assets/lathrop/nebula_blue.png")
# splash image
splash_info = ImageInfo([200, 150], [400, 300])
splash_image = simplegui.load_image("http://commondatastorage.googleapis.com/codeskulptor-assets/lathrop/splash.png")
# ship image
ship_info = ImageInfo([45, 45], [90, 90], 35)
ship_image = simplegui.load_image("http://commondatastorage.googleapis.com/codeskulptor-assets/lathrop/double_ship.png")
# missile image - shot1.png, shot2.png, shot3.png
missile_info = ImageInfo([5,5], [10, 10], 3, 50)
missile_image = simplegui.load_image("http://commondatastorage.googleapis.com/codeskulptor-assets/lathrop/shot2.png")
# asteroid images - asteroid_blue.png, asteroid_brown.png, asteroid_blend.png
asteroid_info = ImageInfo([45, 45], [90, 90], 40)
asteroid_image = simplegui.load_image("http://commondatastorage.googleapis.com/codeskulptor-assets/lathrop/asteroid_blue.png")
# animated explosion - explosion_orange.png, explosion_blue.png, explosion_blue2.png, explosion_alpha.png
explosion_info = ImageInfo([64, 64], [128, 128], 17, 24, True)
explosion_image = simplegui.load_image("http://commondatastorage.googleapis.com/codeskulptor-assets/lathrop/explosion_alpha.png")
# sound assets purchased from sounddogs.com, please do not redistribute
soundtrack = simplegui.load_sound("http://commondatastorage.googleapis.com/codeskulptor-assets/sounddogs/soundtrack.mp3")
missile_sound = simplegui.load_sound("http://commondatastorage.googleapis.com/codeskulptor-assets/sounddogs/missile.ogg")
missile_sound.set_volume(.5)
ship_thrust_sound = simplegui.load_sound("http://commondatastorage.googleapis.com/codeskulptor-assets/sounddogs/thrust.ogg")
explosion_sound = simplegui.load_sound("http://commondatastorage.googleapis.com/codeskulptor-assets/sounddogs/explosion.mp3")
# helper functions to handle transformations
def angle_to_vector(ang):
return [math.cos(ang), math.sin(ang)]
def dist(p,q):
return math.sqrt((p[0] - q[0]) ** 2+(p[1] - q[1]) ** 2)

# Ship class
class Ship:
def __init__(self, pos, vel, angle, image, info):
self.pos = [pos[0],pos[1]]
self.vel = [vel[0],vel[1]]
self.thrust = False
self.angle = angle
self.angle_vel = 0
self.image = image
self.image_center = info.get_center()
self.image_size = info.get_size()
self.radius = info.get_radius()
def draw(self,canvas):
if self.thrust:
self.image_center[0]=135
else:
self.image_center[0]=45
canvas.draw_image(self.image, self.image_center, self.image_size, self.pos, self.image_size,self.angle)
def update(self):
self.vel[0]*=0.98
self.vel[1]*=0.98
self.pos[0]+=self.vel[0]
self.pos[0]%=WIDTH
self.pos[1]+=self.vel[1]
self.pos[1]%=HEIGHT
self.angle+=self.angle_vel
if self.thrust:
ship_thrust_sound.play()
else:
ship_thrust_sound.rewind()
if self.thrust:
foward=angle_to_vector(self.angle)
self.vel[0]+=foward[0]/10
self.vel[1]+=foward[1]/10
def shoot(self):
global a_missile
foward=angle_to_vector(self.angle)
tmppos=[self.pos[0]+45*foward[0],self.pos[1]+45*foward[1]]
tmpvel=[self.vel[0]+foward[0]*3,self.vel[1]+foward[1]*3]
a_missile = Sprite(tmppos, tmpvel, 0, 0, missile_image, missile_info, missile_sound)
missile_sound.play()
# Sprite class
class Sprite:
def __init__(self, pos, vel, ang, ang_vel, image, info, sound = None):
self.pos = [pos[0],pos[1]]
self.vel = [vel[0],vel[1]]
self.angle = ang
self.angle_vel = ang_vel
self.image = image
self.image_center = info.get_center()
self.image_size = info.get_size()
self.radius = info.get_radius()
self.lifespan = info.get_lifespan()
self.animated = info.get_animated()
self.age = 0
if sound:
sound.rewind()
sound.play()
def draw(self, canvas):
canvas.draw_image(self.image, self.image_center, self.image_size, self.pos, self.image_size,self.angle)
def update(self):
self.pos[0]+=self.vel[0]
self.pos[0]%=WIDTH
self.pos[1]+=self.vel[1]
self.pos[1]%=HEIGHT
self.angle+=self.angle_vel

def draw(canvas):
global time
# animiate background
time += 1
center = debris_info.get_center()
size = debris_info.get_size()
wtime = (time / 8) % center[0]
canvas.draw_image(nebula_image, nebula_info.get_center(), nebula_info.get_size(), [WIDTH / 2, HEIGHT / 2], [WIDTH, HEIGHT])
canvas.draw_image(debris_image, [center[0] - wtime, center[1]], [size[0] - 2 * wtime, size[1]],
[WIDTH / 2 + 1.25 * wtime, HEIGHT / 2], [WIDTH - 2.5 * wtime, HEIGHT])
canvas.draw_image(debris_image, [size[0] - wtime, center[1]], [2 * wtime, size[1]],
[1.25 * wtime, HEIGHT / 2], [2.5 * wtime, HEIGHT])
# draw ship and sprites
my_ship.draw(canvas)
a_rock.draw(canvas)
a_missile.draw(canvas)
canvas.draw_text('lives:'+str(lives), (50, 50), 24, "Red")
canvas.draw_text('score:'+str(score), (50, 100), 24, "Red")
# update ship and sprites
my_ship.update()
a_rock.update()
a_missile.update()
# timer handler that spawns a rock   
def rock_spawner():
global a_rock
a_rock = Sprite([random.random()*WIDTH, random.random()*HEIGHT], [random.random(), random.random()], random.random()*2*math.pi, random.random()*0.1, asteroid_image, asteroid_info)
def keydown(key):
if key==simplegui.KEY_MAP['left']:
my_ship.angle_vel=-0.1
elif key==simplegui.KEY_MAP['right']:
my_ship.angle_vel=0.1
elif key==simplegui.KEY_MAP['up']:
my_ship.thrust=True
elif key==simplegui.KEY_MAP['space']:
my_ship.shoot()
def keyup(key):
if key==simplegui.KEY_MAP['left']:
my_ship.angle_vel=0
elif key==simplegui.KEY_MAP['right']:
my_ship.angle_vel=0
elif key==simplegui.KEY_MAP['up']:
my_ship.thrust=False
# initialize frame
frame = simplegui.create_frame("Asteroids", WIDTH, HEIGHT)
# initialize ship and two sprites
my_ship = Ship([WIDTH / 2, HEIGHT / 2], [0, 0], 0, ship_image, ship_info)
a_rock = Sprite([WIDTH / 3, HEIGHT / 3], [1, 1], 0, 0, asteroid_image, asteroid_info)
a_missile = Sprite([2 * WIDTH / 3, 2 * HEIGHT / 3], [-1,1], 0, 0, missile_image, missile_info, missile_sound)
# register handlers
frame.set_draw_handler(draw)
frame.set_keydown_handler(keydown)  
frame.set_keyup_handler(keyup)  
timer = simplegui.create_timer(1000.0, rock_spawner)
# get things rolling
timer.start()
frame.start()