/**
 * 引力模拟
 */

const planets = [];
const plantsNumber = 10;
let sun;

function setup() {
    createCanvas(1728, 972);
    noStroke();
    colorMode(HSB);
    sun = createVector(width / 2, height / 2);
    for (let i = 0; i < plantsNumber; i++) {
        const planet = new Planet(random(width), random(height));
        planet.vel = p5.Vector.random2D();
        planets.push(planet);
    }
}

function draw() {
    background(0);
    for (let i = 0; i < plantsNumber; i++) {
        planets[i].update();
        planets[i].drawPath();
    }
    for (let i = 0; i < plantsNumber; i++) {
        planets[i].show();
    }
    fill("#FFFF77");
    circle(sun.x, sun.y, 8);
}

class Planet {
    constructor(x, y) {
        this.pos = createVector(x, y);
        this.vel = createVector(0, 0);
        this.acc = createVector(0, 0);
        this.color = color(random(0, 255), 255, 255);
        this.path = [];
    }
    update() {
        this.acc = p5.Vector.sub(sun, this.pos);
        const dist = this.acc.mag() / 10;
        this.acc.normalize().div(dist * dist);
        this.vel.add(this.acc);
        this.pos.add(this.vel);
        this.path.push(this.pos.copy());
        if (this.path.length > 1024) this.path.shift();
    }
    drawPath() {
        push();
        noFill();
        let h = hue(this.color);
        stroke(color(h, 255, 32));
        strokeWeight(1);
        beginShape();
        this.path.forEach((v, i) => {
            vertex(v.x, v.y);
        });
        endShape();
        pop();
    }
    show() {
        push();
        translate(this.pos.x, this.pos.y);

        push();
        rotate(this.vel.heading());
        const vel = this.vel.copy().mult(10);
        vel.limit(50);
        stroke("#007700");
        line(0, 0, vel.mag(), 0);
        line(vel.mag(), 0, vel.mag() - 2, 2);
        line(vel.mag(), 0, vel.mag() - 2, -2);
        pop();

        push();
        rotate(this.acc.heading());
        const dir = this.acc.copy().mult(1000);
        dir.limit(50);
        stroke("#770000");
        line(0, 0, dir.mag(), 0);
        line(dir.mag(), 0, dir.mag() - 2, 2);
        line(dir.mag(), 0, dir.mag() - 2, -2);
        pop();

        noStroke();
        fill(this.color);
        circle(0, 0, 4);
        pop();
    }
}

function mouseClicked() {}

function switchFullscreen() {
    let fs = fullscreen();
    fullscreen(!fs);
}