新年到~用Python安排一场烟花秀

新年伊始，各位同学又给今年定下了什么小目标呢？

本篇文章，我们带给大家一个小案例：用 Python 制作一个炫酷烟花秀，祝大家新年快乐，顺便也提前送上春节祝福。

开始之前先看一下最终效果：

环境介绍：

语言：Python

库：Pygame

原理介绍

在介绍代码之前，先介绍下 Pygame 绘制烟花的基本原理，烟花从发射到绽放一共分为三个阶段：

1，发射阶段：在这一阶段烟花的形状是线性向上，通过设定一组大小不同、颜色不同的点来模拟“向上发射” 的运动运动，运动过程中 5个点被赋予不同大小的加速度，随着时间推移，后面的点会赶上前面的点，最终所有点会汇聚在一起，处于 绽放准备阶段；

2，烟花绽放：烟花绽放这个阶段，是由一个点分散多个点向不同方向发散，并且每个点的移动轨迹可需要被记录，目的是为了追踪整个绽放轨迹。

3，烟花凋零，此阶段负责描绘绽放后烟花的效果，绽放后的烟花，而在每一时刻点的下降速度和亮度（代码中也叫透明度）是不一样的，因此在代码里，将烟花绽放后将每个点赋予两个属性：分别为重力向量和生命周期，来模拟烟花在不同时期时不同的展现效果，

代码实操

代码部分将烟花封装为三个类：

Firework : 烟花整体；

Particle：烟花粒子（包含轨迹）

Trail：烟花轨迹，本质上是一个点 。

三个类之间的关系为：一个Firework 由多个 Particle 构成，而一个 Particle 由多个 Trail 构成

首先设置全局变量，例如重力向量，窗口大小，Trail 的颜色列表（多为灰色或白色）以及不同状态下 Trail 之间间隔

gravity = vector(0, 0.3)
DISPLAY_WIDTH = DISPLAY_HEIGHT = 800


trail_colours = [(45, 45, 45), (60, 60, 60), (75, 75, 75), (125, 125, 125), (150, 150, 150)]
dynamic_offset = 1
static_offset = 3

创建 Trail 类，定义 show 方法绘制轨迹 、get_pos 实时获取轨迹坐标

class Trail:

    def __init__(self, n, size, dynamic):
        self.pos_in_line = n
        self.pos = vector(-10, -10)
        self.dynamic = dynamic

        if self.dynamic:
            self.colour = trail_colours[n]
            self.size = int(size - n / 2)
        else:
            self.colour = (255, 255, 200)
            self.size = size - 2
            if self.size < 0:
                self.size = 0

    def get_pos(self, x, y):
        self.pos = vector(x, y)

    def show(self, win):
        pygame.draw.circle(win, self.colour, (int(self.pos.x), int(self.pos.y)), self.size)

Particle 类核心代码

class Particle:

    def __init__(self, x, y, firework, colour):
        self.firework = firework
        self.pos = vector(x, y)
        self.origin = vector(x, y)
        self.radius = 20
        self.remove = False
        self.explosion_radius = randint(5, 18)
        self.life = 0
        self.acc = vector(0, 0)
        # trail variables
        self.trails = []  # stores the particles trail objects
        self.prev_posx = [-10] * 10  # stores the 10 last positions
        self.prev_posy = [-10] * 10  # stores the 10 last positions

        if self.firework:
            self.vel = vector(0, -randint(17, 20))
            self.size = 5
            self.colour = colour
            for i in range(5):
                self.trails.append(Trail(i, self.size, True))
        else:
            self.vel = vector(uniform(-1, 1), uniform(-1, 1))
            self.vel.x *= randint(7, self.explosion_radius + 2)
            self.vel.y *= randint(7, self.explosion_radius + 2)
            # 向量
            self.size = randint(2, 4)
            self.colour = choice(colour)
            # 5 个 tails总计
            for i in range(5):
                self.trails.append(Trail(i, self.size, False))

    def apply_force(self, force):
        self.acc += force

    def move(self):
        if not self.firework:
            self.vel.x *= 0.8
            self.vel.y *= 0.8
        self.vel += self.acc
        self.pos += self.vel
        self.acc *= 0

        if self.life == 0 and not self.firework:  # check if particle is outside explosion radius
            distance = math.sqrt((self.pos.x - self.origin.x) ** 2 + (self.pos.y - self.origin.y) ** 2)
            if distance > self.explosion_radius:
                self.remove = True

        self.decay()

        self.trail_update()

        self.life += 1

    def show(self, win):
        pygame.draw.circle(win, (self.colour[0], self.colour[1], self.colour[2], 0), (int(self.pos.x), int(self.pos.y)),
                           self.size)

    def decay(self):  # random decay of the particles
        if 50 > self.life > 10:  # early stage their is a small chance of decay
            ran = randint(0, 30)
            if ran == 0:
                self.remove = True
        elif self.life > 50:
            ran = randint(0, 5)
            if ran == 0:
                self.remove = True

Firework 类核心代码

class Firework:
    def __init__(self):
        # 随机颜色
        self.colour = (randint(0, 255), randint(0, 255), randint(0, 255))
        self.colours = (
            (randint(0, 255), randint(0, 255), randint(0, 255)),
            (randint(0, 255), randint(0, 255), randint(0, 255)),
            (randint(0, 255), randint(0, 255), randint(0, 255)))
        self.firework = Particle(randint(0, DISPLAY_WIDTH), DISPLAY_HEIGHT, True,
                                 self.colour)  # Creates the firework particle
        self.exploded = False
        self.particles = []
        self.min_max_particles = vector(100, 225)

    def update(self, win):  # called every frame
        if not self.exploded:
            self.firework.apply_force(gravity)
            self.firework.move()
            for tf in self.firework.trails:
                tf.show(win)

            self.show(win)

            if self.firework.vel.y >= 0:
                self.exploded = True
                self.explode()
        else:
            for particle in self.particles:
                particle.apply_force(vector(gravity.x + uniform(-1, 1) / 20, gravity.y / 2 + (randint(1, 8) / 100)))
                particle.move()
                for t in particle.trails:
                    t.show(win)
                particle.show(win)

 
    def remove(self):
        if self.exploded:
            for p in self.particles:
                if p.remove is True:
                    self.particles.remove(p)

            if len(self.particles) == 0:
                return True
            else:
                return False

最后，写一个 main 方法来对 pygame 环境进行初始化，例如背景图片，文字，设置页面刷新间隔，程序中设置的每 60ms 刷新一次。

pygame.display.set_caption("Fireworks in Pygame") # 标题
    background = pygame.image.load("img/1.png") # 背景
    myfont = pygame.font.Font("img/simkai.ttf",80)
    myfont1 = pygame.font.Font("img/simkai.ttf", 30)

    testsurface = myfont.render("元旦快乐",False,(255,255,255))
    testsurface1 = myfont1.render("By:小张Python", False, (255, 255, 255))

    # pygame.image.load("")
    win = pygame.display.set_mode((DISPLAY_WIDTH, DISPLAY_HEIGHT))
    # win.blit(background)
    clock = pygame.time.Clock()

    fireworks = [Firework() for i in range(2)]  # create the first fireworks
    running = True

    while running:
        clock.tick(60)
        win.fill((20, 20, 30))  # draw background
        win.blit(background,(0,0))
        win.blit(testsurface,(200,200))
        win.blit(testsurface1, (300,200))

        if randint(0, 20) == 1:  # create new firework
            fireworks.append(Firework())

        update(win, fireworks)

另外程序中会对你的按键命令进行监控：

• 当按下键 1时 ，会立即生成一个新的 “烟花”；
• 当按下键 2时，会同时生成 10 个 “烟花”

        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                running = False
            if event.type == pygame.KEYDOWN:  # Change game speed with number keys
                if event.key == pygame.K_1: # 按下 1
                    fireworks.append(Firework())
                if event.key == pygame.K_2: # 按下 2 加入10个烟花
                    for i in range(10):
                        fireworks.append(Firework())

小结

总的来说，整个小案例的代码量不算很多，一共250行左右，但案例中涉及到较为复杂的绘制逻辑和抽象的类之间的封装关系，因此大家理解代码相对会需要耗费点时间。

本篇文章主要介绍了如何用 Pygame 来模拟一个烟花绽放过程，核心内容大致两点：第一，如何用绘制点的方式来模拟烟花绽放运动轨迹；第二，介绍Pygame 一些基础用法：替换背景，绘制文字，更新状态等功能。