New year’s day, draw a fireworks with canvas

Time:2020-3-16

The Spring Festival is coming soon. I plan to bury a new year’s blessing + fireworks egg in the background. The project is based on react + typescript, so it is finally encapsulated as a component, which can be displayed after the opening time is set.

directory structure

The directory structure is roughly as follows
New year's day, draw a fireworks with canvas
We divide fireworks into two stages, one is the period of continuous rise without explosion, the other is the period of dispersion after explosion.
Among them, vector represents a coordinate, particle represents a bright spot of fireworks, and Firewor represents a bright spot that keeps rising when fireworks are not exploded. Index. TSX is the component, drawing canvas and executing animation.

Vector

This coordinate is very simple, and its add method can be used to offset any later change of position

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

At the initial creation, a coordinate is given, and the Y coordinate is controlled to fall every time it is updated. The gravity variable is the value of the fall. Timespan is used to control the duration of fireworks display

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

Generate random HSL colors,hsl(' + rndNum(360) + ', 100%, 60%); the distance of each rise of firework is a decreasing process. We initially set a rising distance, and then each time we draw, the distance decreases gravity. When the distance is less than zero, it means that the animation of fireworks should appear.

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

The component itself is simple, generating and drawing firework. We can add some extra words here

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 project team wishes you a happy New Year! ';
        let textWidth = this.ctx.measureText(text);
        this.ctx.fillText(text, this.canvas.width / 2 - textWidth.width / 2, 200);
        Text = 'on the new year's Eve, I wish you:';
        textWidth = this.ctx.measureText(text);
        this.ctx.fillText(text, this.canvas.width / 2 - textWidth.width / 2, 260);
        Text: 'work well, happy New Year!';
        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 = 'click anywhere to close';
        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;

General effectNew year's day, draw a fireworks with canvas

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