过年啦，用canvas画个烟花吧

前言：马上过年了，我打算在后台里面偷偷地埋个新春祝福+放烟花的彩蛋。项目是基于react+typescript的，因此最后封装成了一个组件，设置好开启时间就可以显示了。

目录结构

目录结构大致如下

我们将烟花分为两个阶段，一个是未炸开持续上升时期，另一个是炸开后分散的时期。
其中Vector表示一个坐标，Particle表示一个烟花的亮点，Firewor表示烟花未炸开时持续上升的亮点。index.tsx就是组件了，绘制了canvas，并执行了动画。

Vector

这个坐标就很简单，后面涉及到位置的变更都可以使用它的add方法进行偏移操作

export default class Vector {
    constructor(public x: number, public y: number) {}
    add(vec2: {x: number; y: number}) {
        this.x = this.x + vec2.x;
        this.y = this.y + vec2.y;
    }
}

Particle

初始创建的时候给个坐标，后续每次更新的时候控制y坐标下落，gravity变量就是下落的值。timeSpan用于控制烟花展示的时长

import Vector from './Vector';
export default class Particle {
    pos: Vector = null;
    vel: {x: number; y: number} = null;
    dead: boolean = false;
    start: number = 0;
    ctx: CanvasRenderingContext2D = null;
    constructor(pos: {x: number; y: number}, vel: {x: number; y: number}, ctx: CanvasRenderingContext2D) {
        this.pos = new Vector(pos.x, pos.y);
        this.vel = vel;
        this.dead = false;
        this.start = 0;
        this.ctx = ctx;
    }
    update(time: number, gravity: number) {
        let timeSpan = time - this.start;

        if (timeSpan > 500) {
            this.dead = true;
        }

        if (!this.dead) {
            this.pos.add(this.vel);
            this.vel.y = this.vel.y + gravity;
        }
    }

    draw() {
        if (!this.dead) {
            this.drawDot(this.pos.x, this.pos.y, Math.random() > 0.5 ? 1 : 2);
        }
    }
    drawDot(x: number, y: number, size: number) {
        this.ctx.beginPath();
        this.ctx.arc(x, y, size, 0, Math.PI * 2);
        this.ctx.fill();
        this.ctx.closePath();
    }
}

Firework

生成随机的hsl颜色，hsl(' + rndNum(360) + ', 100%, 60%);Firework每次上升的距离是一个递减的过程，我们初始设置一个上升的距离，之后每次绘制的时候，这个距离减gravity，当距离小于零的时候，说明该出现烟花绽放的动画了。

import Vector from './Vector';
import Particle from './Particle';
let rnd = Math.random;
function rndNum(num: number) {
    return rnd() * num + 1;
}
export default class Firework {
    pos: Vector = null;
    vel: Vector = null;
    color: string = null;
    size: number = 0;
    dead: boolean = false;
    start: number = 0;
    ctx: CanvasRenderingContext2D = null;
    gravity: number = null;
    exParticles: Particle[] = [];
    exPLen: number = 100;
    rootShow: boolean = true;
    constructor(x: number, y: number, gravity: number, ctx: CanvasRenderingContext2D) {
        this.pos = new Vector(x, y);
        this.vel = new Vector(0, -rndNum(10) - 3);
        this.color = 'hsl(' + rndNum(360) + ', 100%, 60%)';
        this.size = 4;
        this.dead = false;
        this.start = 0;
        this.ctx = ctx;
        this.gravity = gravity;
    }
    update(time: number, gravity: number) {
        if (this.dead) {
            return;
        }

        this.rootShow = this.vel.y < 0;

        if (this.rootShow) {
            this.pos.add(this.vel);
            this.vel.y = this.vel.y + gravity;
        } else {
            if (this.exParticles.length === 0) {
                for (let i = 0; i < this.exPLen; i++) {
                    let randomR = rndNum(5);
                    let randomX = -rndNum(Math.abs(randomR) * 2) + Math.abs(randomR);
                    let randomY =
                        Math.sqrt(Math.abs(Math.pow(randomR, 2) - Math.pow(randomX, 2))) *
                        (Math.random() > 0.5 ? 1 : -1);
                    this.exParticles.push(new Particle(this.pos, new Vector(randomX, randomY), this.ctx));
                    this.exParticles[this.exParticles.length - 1].start = time;
                }
            }
            let numOfDead = 0;
            for (let i = 0; i < this.exPLen; i++) {
                let p = this.exParticles[i];
                p.update(time, this.gravity);
                if (p.dead) {
                    numOfDead++;
                }
            }

            if (numOfDead === this.exPLen) {
                this.dead = true;
            }
        }
    }

    draw() {
        if (this.dead) {
            return;
        }

        this.ctx.fillStyle = this.color;
        if (this.rootShow) {
            this.drawDot(this.pos.x, this.pos.y, this.size);
        } else {
            for (let i = 0; i < this.exPLen; i++) {
                let p = this.exParticles[i];
                p.draw();
            }
        }
    }
    drawDot(x: number, y: number, size: number) {
        this.ctx.beginPath();

        this.ctx.arc(x, y, size, 0, Math.PI * 2);
        this.ctx.fill();

        this.ctx.closePath();
    }
}

FireworkComponent

组件本身就很简单了，生成和绘制Firework。我们在这里面可以额外加一些文字

import React from 'react';
import Firework from './Firework';
import {autobind} from 'core-decorators';
let rnd = Math.random;
function rndNum(num: number) {
    return rnd() * num + 1;
}
interface PropTypes {
    onClick?: () => void;
}
@autobind
class FireworkComponent extends React.Component<PropTypes> {
    canvas: HTMLCanvasElement = null;
    ctx: CanvasRenderingContext2D = null;
    snapTime: number = 0;
    fireworks: Firework[] = [];
    gravity: number = 0.1;
    componentDidMount() {
        this.canvas = document.querySelector('#fireworks');
        this.canvas.width = window.innerWidth;
        this.canvas.height = window.innerHeight;
        this.ctx = this.canvas.getContext('2d');
        this.init();
        this.draw();
    }

    init() {
        let numOfFireworks = 20;
        for (let i = 0; i < numOfFireworks; i++) {
            this.fireworks.push(new Firework(rndNum(this.canvas.width), this.canvas.height, this.gravity, this.ctx));
        }
    }

    update(time: number) {
        for (let i = 0, len = this.fireworks.length; i < len; i++) {
            let p = this.fireworks[i];
            p.update(time, this.gravity);
        }
    }
    draw(time?: number) {
        this.update(time);

        this.ctx.fillStyle = 'rgba(0,0,0,0.3)';

        this.ctx.fillStyle = 'rgba(0,0,0,0)';
        this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);

        this.ctx.font = 'bold 30px cursive';
        this.ctx.fillStyle = '#e91818';
        let text = 'XX项目组给您拜个早年！';
        let textWidth = this.ctx.measureText(text);
        this.ctx.fillText(text, this.canvas.width / 2 - textWidth.width / 2, 200);
        text = '在新年来临之际，祝您：';
        textWidth = this.ctx.measureText(text);
        this.ctx.fillText(text, this.canvas.width / 2 - textWidth.width / 2, 260);
        text = '工作顺利，新春快乐!';
        this.ctx.font = 'bold 48px STCaiyun';
        this.ctx.fillStyle = 'orangered';
        textWidth = this.ctx.measureText(text);
        this.ctx.fillText(text, this.canvas.width / 2 - textWidth.width / 2, 340);
        this.ctx.fillStyle = 'gray';
        this.ctx.font = '18px Arial';
        text = '点击任意处关闭';
        textWidth = this.ctx.measureText(text);
        this.ctx.fillText(text, this.canvas.width - 20 - textWidth.width, 60);
        this.snapTime = time;

        this.ctx.fillStyle = 'blue';
        for (let i = 0, len = this.fireworks.length; i < len; i++) {
            let p = this.fireworks[i];
            if (p.dead) {
                p = this.fireworks[i] = new Firework(
                    rndNum(this.canvas.width),
                    this.canvas.height,
                    this.gravity,
                    this.ctx
                );
                p.start = time;
            }
            p.draw();
        }

        window.requestAnimationFrame(this.draw);
    }

    render() {
        return (
            <canvas
                id="fireworks"
                onClick={this.props.onClick}
                style={{position: 'fixed', zIndex: 99, background: 'rgba(0,0,0, 0.8)'}}
                width="400"
                height="400"></canvas>
        );
    }
}
export default FireworkComponent;

大致效果