poly2tri/src/utils.js

A 2D constrained Delaunay triangulation library

/*
 * Poly2Tri Copyright (c) 2009-2014, Poly2Tri Contributors
 * http://code.google.com/p/poly2tri/
 * 
 * poly2tri.js (JavaScript port) (c) 2009-2014, Poly2Tri Contributors
 * https://github.com/r3mi/poly2tri.js
 * 
 * All rights reserved.
 * 
 * Distributed under the 3-clause BSD License, see LICENSE.txt
 */

"use strict";

/**
 * Precision to detect repeated or collinear points
 * @private
 * @const {number}
 * @default
 */
var EPSILON = 1e-12;
exports.EPSILON = EPSILON;

/**
 * @private
 * @enum {number}
 * @readonly
 */
var Orientation = {
    "CW": 1,
    "CCW": -1,
    "COLLINEAR": 0
};
exports.Orientation = Orientation;


/**
 * Formula to calculate signed area<br>
 * Positive if CCW<br>
 * Negative if CW<br>
 * 0 if collinear<br>
 * <pre>
 * A[P1,P2,P3]  =  (x1*y2 - y1*x2) + (x2*y3 - y2*x3) + (x3*y1 - y3*x1)
 *              =  (x1-x3)*(y2-y3) - (y1-y3)*(x2-x3)
 * </pre>
 *
 * @private
 * @param {!XY} pa  point object with {x,y}
 * @param {!XY} pb  point object with {x,y}
 * @param {!XY} pc  point object with {x,y}
 * @return {Orientation}
 */
function orient2d(pa, pb, pc) {
    var detleft = (pa.x - pc.x) * (pb.y - pc.y);
    var detright = (pa.y - pc.y) * (pb.x - pc.x);
    var val = detleft - detright;
    if (val > -(EPSILON) && val < (EPSILON)) {
        return Orientation.COLLINEAR;
    } else if (val > 0) {
        return Orientation.CCW;
    } else {
        return Orientation.CW;
    }
}
exports.orient2d = orient2d;


/**
 *
 * @private
 * @param {!XY} pa  point object with {x,y}
 * @param {!XY} pb  point object with {x,y}
 * @param {!XY} pc  point object with {x,y}
 * @param {!XY} pd  point object with {x,y}
 * @return {boolean}
 */
function inScanArea(pa, pb, pc, pd) {
    var oadb = (pa.x - pb.x) * (pd.y - pb.y) - (pd.x - pb.x) * (pa.y - pb.y);
    if (oadb >= -EPSILON) {
        return false;
    }

    var oadc = (pa.x - pc.x) * (pd.y - pc.y) - (pd.x - pc.x) * (pa.y - pc.y);
    if (oadc <= EPSILON) {
        return false;
    }
    return true;
}
exports.inScanArea = inScanArea;


/**
 * Check if the angle between (pa,pb) and (pa,pc) is obtuse i.e. (angle > π/2 || angle < -π/2)
 *
 * @private
 * @param {!XY} pa  point object with {x,y}
 * @param {!XY} pb  point object with {x,y}
 * @param {!XY} pc  point object with {x,y}
 * @return {boolean} true if angle is obtuse
 */
function isAngleObtuse(pa, pb, pc) {
    var ax = pb.x - pa.x;
    var ay = pb.y - pa.y;
    var bx = pc.x - pa.x;
    var by = pc.y - pa.y;
    return (ax * bx + ay * by) < 0;
}
exports.isAngleObtuse = isAngleObtuse;