fabric.js/src/intersection.class.js

(function(global) {

  'use strict';

  /* Adaptation of work of Kevin Lindsey (kevin@kevlindev.com) */
  var fabric = global.fabric || (global.fabric = { });

  if (fabric.Intersection) {
    fabric.warn('fabric.Intersection is already defined');
    return;
  }

  /**
   * Intersection class
   * @class fabric.Intersection
   * @memberOf fabric
   * @constructor
   */
  function Intersection(status) {
    this.status = status;
    this.points = [];
  }

  fabric.Intersection = Intersection;

  fabric.Intersection.prototype = /** @lends fabric.Intersection.prototype */ {

    constructor: Intersection,

    /**
     * Appends a point to intersection
     * @param {fabric.Point} point
     * @return {fabric.Intersection} thisArg
     * @chainable
     */
    appendPoint: function (point) {
      this.points.push(point);
      return this;
    },

    /**
     * Appends points to intersection
     * @param {Array} points
     * @return {fabric.Intersection} thisArg
     * @chainable
     */
    appendPoints: function (points) {
      this.points = this.points.concat(points);
      return this;
    }
  };

  /**
   * Checks if one line intersects another
   * TODO: rename in intersectSegmentSegment
   * @static
   * @param {fabric.Point} a1
   * @param {fabric.Point} a2
   * @param {fabric.Point} b1
   * @param {fabric.Point} b2
   * @return {fabric.Intersection}
   */
  fabric.Intersection.intersectLineLine = function (a1, a2, b1, b2) {
    var result,
        uaT = (b2.x - b1.x) * (a1.y - b1.y) - (b2.y - b1.y) * (a1.x - b1.x),
        ubT = (a2.x - a1.x) * (a1.y - b1.y) - (a2.y - a1.y) * (a1.x - b1.x),
        uB = (b2.y - b1.y) * (a2.x - a1.x) - (b2.x - b1.x) * (a2.y - a1.y);
    if (uB !== 0) {
      var ua = uaT / uB,
          ub = ubT / uB;
      if (0 <= ua && ua <= 1 && 0 <= ub && ub <= 1) {
        result = new Intersection('Intersection');
        result.appendPoint(new fabric.Point(a1.x + ua * (a2.x - a1.x), a1.y + ua * (a2.y - a1.y)));
      }
      else {
        result = new Intersection();
      }
    }
    else {
      if (uaT === 0 || ubT === 0) {
        result = new Intersection('Coincident');
      }
      else {
        result = new Intersection('Parallel');
      }
    }
    return result;
  };

  /**
   * Checks if line intersects polygon
   * TODO: rename in intersectSegmentPolygon
   * fix detection of coincident
   * @static
   * @param {fabric.Point} a1
   * @param {fabric.Point} a2
   * @param {Array} points
   * @return {fabric.Intersection}
   */
  fabric.Intersection.intersectLinePolygon = function(a1, a2, points) {
    var result = new Intersection(),
        length = points.length,
        b1, b2, inter;

    for (var i = 0; i < length; i++) {
      b1 = points[i];
      b2 = points[(i + 1) % length];
      inter = Intersection.intersectLineLine(a1, a2, b1, b2);

      result.appendPoints(inter.points);
    }
    if (result.points.length > 0) {
      result.status = 'Intersection';
    }
    return result;
  };

  /**
   * Checks if polygon intersects another polygon
   * @static
   * @param {Array} points1
   * @param {Array} points2
   * @return {fabric.Intersection}
   */
  fabric.Intersection.intersectPolygonPolygon = function (points1, points2) {
    var result = new Intersection(),
        length = points1.length;

    for (var i = 0; i < length; i++) {
      var a1 = points1[i],
          a2 = points1[(i + 1) % length],
          inter = Intersection.intersectLinePolygon(a1, a2, points2);

      result.appendPoints(inter.points);
    }
    if (result.points.length > 0) {
      result.status = 'Intersection';
    }
    return result;
  };

  /**
   * Checks if polygon intersects rectangle
   * @static
   * @param {Array} points
   * @param {fabric.Point} r1
   * @param {fabric.Point} r2
   * @return {fabric.Intersection}
   */
  fabric.Intersection.intersectPolygonRectangle = function (points, r1, r2) {
    var min = r1.min(r2),
        max = r1.max(r2),
        topRight = new fabric.Point(max.x, min.y),
        bottomLeft = new fabric.Point(min.x, max.y),
        inter1 = Intersection.intersectLinePolygon(min, topRight, points),
        inter2 = Intersection.intersectLinePolygon(topRight, max, points),
        inter3 = Intersection.intersectLinePolygon(max, bottomLeft, points),
        inter4 = Intersection.intersectLinePolygon(bottomLeft, min, points),
        result = new Intersection();

    result.appendPoints(inter1.points);
    result.appendPoints(inter2.points);
    result.appendPoints(inter3.points);
    result.appendPoints(inter4.points);

    if (result.points.length > 0) {
      result.status = 'Intersection';
    }
    return result;
  };

})(typeof exports !== 'undefined' ? exports : this);