dust/js/arc.js

import { ENTITIES, RAD } from './enums';
import Random from './random';

const Arc = {
    create: function(bounds, grid) {
        let arc = {
            centerX: Random.num(0, bounds.width),
            centerY: Random.num(0, bounds.height),
            clockwise: Random.bool(),
            endX: 0,
            endY: 0,
            length: Random.num(RAD.t90, RAD.t360),
            prevEndX: 0,
            prevEndY: 0,
            radius: Random.num(100, 200),
            theta: Random.num(RAD.t90, RAD.t360)
        };

        arc.cosTheta = Math.cos(arc.theta);
        arc.sinTheta = Math.sin(arc.theta);

        arc.endX = arc.centerX + arc.radius * arc.cosTheta;
        arc.endY = arc.centerY - arc.radius * arc.sinTheta;

        arc = Arc.overflow(arc, bounds);

        // If starting in a hazard, recurse.
        // if (grid.getPoint({ x: arc.endX, y: arc.endY, type: ENTITIES.HAZARD })) {
        //     arc = Arc.create(bounds, grid);
        // }

        return arc;
    },

    step: function(arc, bounds, speed) {
        // Ensure constant velocity and theta between 0 and 2π.
        const delta = speed / arc.radius;
        arc.length -= delta;

        arc.theta += (arc.clockwise ? -delta : +delta);
        arc.theta = (arc.theta > 0 ? arc.theta % RAD.t360 : RAD.t360 + arc.theta);

        arc.cosTheta = Math.cos(arc.theta);
        arc.sinTheta = Math.sin(arc.theta);

        arc.prevEndX = arc.endX;
        arc.prevEndY = arc.endY;

        arc.endX = arc.centerX + arc.radius * arc.cosTheta;
        arc.endY = arc.centerY - arc.radius * arc.sinTheta;

        // Overflow.
        arc = Arc.overflow(arc, bounds);

        return arc;
    },

    randomize: function(arc) {
        arc.length = Random.num(RAD.t90, RAD.t360);

        arc = Arc.changeRadius(arc, Random.num(100, 200));

        if (Random.bool(0.8)) {
            arc = Arc.reverse(arc);
        }

        return arc;
    },

    overflow: function(arc, bounds) {
        if (arc.endX < 0) {
            arc.endX += bounds.width;
            arc.centerX += bounds.width
        } else if (arc.endX > bounds.width) {
            arc.endX -= bounds.width;
            arc.centerX -= bounds.width
        }

        if (arc.endY < 0) {
            arc.endY += bounds.height;
            arc.centerY += bounds.height
        } else if (arc.endY > bounds.height) {
            arc.endY -= bounds.height;
            arc.centerY -= bounds.height
        }

        return arc;
    },

    changeRadius: function(arc, newRadius) {
        const r0 = arc.radius;
        const r1 = newRadius;

        // Moves arc center to new radius while keeping theta constant.
        arc.centerX -= (r1 - r0) * arc.cosTheta;
        arc.centerY += (r1 - r0) * arc.sinTheta;
        arc.radius = r1;

        return arc;
    },

    reverse: function(arc) {
        arc.clockwise = !arc.clockwise;

        arc.theta = (arc.theta + RAD.t180) % RAD.t360;

        arc.cosTheta = Math.cos(arc.theta);
        arc.sinTheta = Math.sin(arc.theta);

        arc.centerX -= (2 * arc.radius) * arc.cosTheta;
        arc.centerY += (2 * arc.radius) * arc.sinTheta;

        return arc;
    },

    follow: function(arc, arcToFollow) {
        if (arc.clockwise !== arcToFollow.clockwise) {
            arc = Arc.reverse(arc);
        }

        if (Math.abs(arc.theta - arcToFollow.theta) > 0.2) {
            arc = Arc.changeRadius(arc, 50);
        } else {
            arc = Arc.changeRadius(arc, arcToFollow.radius);
        }

        return arc;
    },

    goto: function (arc, x, y, speed) {
        const prevD = Math.pow(Math.pow(x - arc.prevEndX, 2) + Math.pow(y - arc.prevEndY, 2), 0.5);
        const currD = Math.pow(Math.pow(x - arc.endX, 2) + Math.pow(y - arc.endY, 2), 0.5);
        const ratio = (prevD - currD) / speed;

        if (currD < 10) {
            throw new Error(`Arc end of (${arc.endX},${arc.endY}) is within 50px of (${x},${y})`);
        } else if (ratio < 0.8) {
            // arc = (ratio < 0 ? Arc.reverse(arc) : arc);
            arc = Arc.changeRadius(arc, 20);
        } else {
            arc = Arc.changeRadius(arc, 400);
        }

        return arc;
    },

    evade: function(arc) {
        arc = Arc.changeRadius(arc, 20);
        arc.length = 1;

        return arc;
    }
}

export default Arc;