Mini projects #7 ---- Spaceship

课程全名：An Introduction to Interactive Programming in Python，来自 Rice University

授课教授：Joe Warren, Scott Rixner, John Greiner, Stephen Wong

工具：http://www.codeskulptor.org/， simplegui 模块

最后两周就要结束了~~~

第七周：

先上图，这周完成Spaceship游戏的一部分。

在这图里面有什么？飞船，陨石，子弹，背景图….

用OO的对象来看，他们都对应一幅图像，那么抽象一个类ImageInfo来操作这些图像信息，它包括图像的center(中心位置)，size(图像大小)，radius(半径)，lifespan(时间周期)，animated(动画)。可能有些属性比较陌生，有些针对到具体的对象才有用。

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

有了图像的表示，那么我们还需要飞船，用Ship来表示

Ship有什么属性和方法呢？

pos：位置

vel：加速度

thrust：冲刺状态

angle：飞船旋转的角度

angle_vel：飞船旋转角速度

image：飞船图像

image_cener：飞船图像的中心位置

image_size：飞船图像的大小

image_radius：飞船半径？(这周作业没用到，不知道干嘛的)

飞船的方法：

draw(canvas): 绘制飞船，要求绘制根据是否在冲刺状态，绘制图像不同。所给的飞船image是tiled图像，所以绘制时候计算一下偏移就好

update()：更新当前飞船位置以及角度。基本所有涉及到简单数学计算的公式，课上以及相关ppt都给出来，都比较简单，直接拿来用。对于角度的更新和Pong那周一样，用左右按键按下增加旋转角速度，放开减少旋转角速度，每次更新的时候就只用把飞船的角度加上旋转角速度。

飞船的位置更新同理，使用位置加上加速度，但是要考虑飞出边界，所以对WIDTH和HEIGHT分别取模。

这边与Pong不同的是加速度的计算，Pong只有上下方向，但这里飞船可以旋转指向各个方向，所以加速度修改飞船向着它转角的方向，原理还是一样，把转角方向向水平和垂直方向做投影乘以常量，然后加到原有的加速度上。

最后剩下的一个问题就是，外太空有<阻力>，所以飞船会不断减速直到速度为0，那么不断按照一定的比例缩小飞船的加速度，直到加速度为0，飞船的位置就不更新了。

update()的代码如下:

def update(self):
    self.angle += self.angle_vel
    self.pos[0] = (self.pos[0] + self.vel[0]) % WIDTH
    self.pos[1] = (self.pos[1] + self.vel[1]) % HEIGHT
    c = 0.05
    self.vel[0] *= (1 - c)
    self.vel[1] *= (1 - c)
    forward = angle_to_vector(self.angle)
    if self.thrust:
        self.vel[0] += forward[0] * 1.2
        self.vel[1] += forward[1] * 1.2

change_angle_vel(ori, key_state)：根据按键是left或者right和按键当前状态是按下或者松开，来改变飞船的旋转角速度

set_thruster(thruster_state)：根据up按键来改变飞船的冲刺状态，并且播放和暂停响应的声音效果

shoot(): 飞船发子弹，初始化子弹，它的位置在飞船的炮孔位置，然后子弹的加速度等于，飞船的加速度，加上飞船角度在水平垂直分量的常量倍，这与飞船的加速思路一样的，子弹的角度和旋转角速度设置成0就好。

飞船处理完了，剩下的就是陨石和子弹，给的template中用sprite来抽象表示他们。

基本的属性和飞船差不多，pos, vel, angle, angle_vel, image, image_center, image_size, radius，多了lifespan, animated, age还有sound

主要方法：

draw(canvas): 直接根据image的信息进行绘制

update(canvas): 更新角度和位置，与飞船类似。超出边界要取模

其他的部分就是frame的draw事件模板里已经写好，key_up，key_down事件，上面也都提到处理方法。

这周的任务也就这样完工了。

完整的代码如下：

# 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.f2014.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.mp3")
missile_sound.set_volume(.5)
ship_thrust_sound = simplegui.load_sound("http://commondatastorage.googleapis.com/codeskulptor-assets/sounddogs/thrust.mp3")
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:
            center = (self.image_center[0]+self.image_size[0], self.image_center[1])
            canvas.draw_image(self.image, center, self.image_size, self.pos, self.image_size, self.angle)
        else:
            canvas.draw_image(self.image, self.image_center, self.image_size, self.pos, self.image_size, self.angle)

    def update(self):
        self.angle += self.angle_vel
        self.pos[0] = (self.pos[0] + self.vel[0]) % WIDTH
        self.pos[1] = (self.pos[1] + self.vel[1]) % HEIGHT
        c = 0.05
        self.vel[0] *= (1 - c)
        self.vel[1] *= (1 - c)
        forward = angle_to_vector(self.angle)
        if self.thrust:
            self.vel[0] += forward[0] * 1.2
            self.vel[1] += forward[1] * 1.2

    def change_angle_vel(self, ori, key_state):
        if ((ori == "right" and key_state == "keyup") or
            (ori == "left" and key_state == "keydown")):
            self.angle_vel -= 0.1
        elif ((ori == "right" and key_state == "keydown") or
            (ori == "left" and key_state == "keyup")):
            self.angle_vel += 0.1

    def set_thruster(self, thruster_state):
        self.thrust = thruster_state
        if self.thrust:
            ship_thrust_sound.rewind()
            ship_thrust_sound.play()
        else:
            ship_thrust_sound.rewind()

    def shoot(self):
        global a_missile
        offset = self.image_size[0] / 2.0
        forward = angle_to_vector(self.angle)
        pos = [self.pos[0] + offset * forward[0], self.pos[1] + offset * forward[1]]
        vel = [self.vel[0] + 4 * forward[0], self.vel[1] + 4 * forward[1]]
        ang = 0
        ang_vel = 0
        a_missile = Sprite(pos, vel, ang, ang_vel, missile_image, missile_info, missile_sound)

# 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.angle += self.angle_vel
        self.pos[0] = (self.pos[0] + self.vel[0]) % WIDTH
        self.pos[1] = (self.pos[1] + self.vel[1]) % HEIGHT

def draw(canvas):
    global time

    # animiate background
    time += 1
    wtime = (time / 4) % WIDTH
    center = debris_info.get_center()
    size = debris_info.get_size()
    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, size, (wtime - WIDTH / 2, HEIGHT / 2), (WIDTH, HEIGHT))
    canvas.draw_image(debris_image, center, size, (wtime + WIDTH / 2, HEIGHT / 2), (WIDTH, HEIGHT))

    # draw ship and sprites
    my_ship.draw(canvas)
    a_rock.draw(canvas)
    a_missile.draw(canvas)

    # update ship and sprites
    my_ship.update()
    a_rock.update()
    a_missile.update()

    # draw lives
    canvas.draw_text("Lives", [WIDTH / 12, HEIGHT / 12], 30, "White")
    canvas.draw_text(str(lives), [WIDTH / 12, HEIGHT / 12 + 40], 30, "White")

    # draw score
    canvas.draw_text("Score", [10 * WIDTH / 12, HEIGHT/12], 30, "White")
    canvas.draw_text(str(score), [10 * WIDTH /12, HEIGHT/12 + 40], 30, "White")

# timer handler that spawns a rock
def rock_spawner():
    global a_rock
    pos = [random.randint(0, WIDTH-1), random.randint(0, HEIGHT-1)]
    vel = [random.randrange(1, 5, 1)*random.choice([1, -1]), random.randrange(1, 5, 1)*random.choice([1, -1])]
    ang = 0
    ang_vel = random.randrange(5, 10, 1) / 100.0 * random.choice([1, -1])
    a_rock = Sprite(pos, vel, ang, ang_vel, asteroid_image, asteroid_info)

def key_up(key):
    if simplegui.KEY_MAP['left'] == key:
        my_ship.change_angle_vel("left", "keyup")
    elif simplegui.KEY_MAP['right'] == key:
        my_ship.change_angle_vel("right", "keyup")
    elif simplegui.KEY_MAP['up'] == key:
        my_ship.set_thruster(False)

def key_down(key):
    if simplegui.KEY_MAP['left'] == key:
        my_ship.change_angle_vel("left", "keydown")
    elif simplegui.KEY_MAP['right'] == key:
        my_ship.change_angle_vel("right", "keydown")
    elif simplegui.KEY_MAP['up'] == key:
        my_ship.set_thruster(True)
    elif simplegui.KEY_MAP['space'] == key:
        my_ship.shoot()

# 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(key_down)
frame.set_keyup_handler(key_up)

timer = simplegui.create_timer(1000.0, rock_spawner)

# get things rolling
timer.start()
frame.start()

期待着最后一周，游戏完整的代码。就要完成Coursera的一门这么有意思的课，课程难度很小，乐趣十足。