let currentAngle = 0.0;

let x = 0.0;

let y = 0.0;

let smoothSpeed = 0.02;

let scl = 25.0;

const count = 3;

let iToTheta;

​

function setup() {

    createCanvas(400, 400);

    x = width * 0.5;

    y = height * 0.5;

    iToTheta = TWO_PI / count;

}

​

function draw() {

    targetAngle = atan2(mouseY - y, mouseX - x);

    currentAngle = lerpAngle(currentAngle, targetAngle, smoothSpeed);

    background(220);

    noStroke();

    beginShape();

    for (let i = 0; i < count; ++i) {

        const theta = currentAngle + i * iToTheta;

        vertex(x + cos(theta) * scl, y + sin(theta) * scl);

    }

    endShape(CLOSE);

    strokeWeight(1.25);

    stroke(color(255, 0, 0));

    line(x, y, x + cos(targetAngle) * scl,

        y + sin(targetAngle) * scl);

​

    stroke(color(0, 255, 0));

    line(x, y, x + cos(currentAngle) * scl,

        y + sin(currentAngle) * scl);

}

​

// Linear interpolation of an angle.

function lerpAngle(a, b, step) {

    // Prefer shortest distance,

    const delta = b - a;

    if (delta == 0.0) {

        return a;

    } else if (delta < -PI) {

        b += TWO_PI;

    } else if (delta > PI) {

        a += TWO_PI;

    }

    return (1.0 - step) * a + step * b;

}