fabric.js/src/intersection.class.js

//= require 'point.class'

(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;
  }
  
  /**
   * @class Intersection
   * @memberOf fabric
   */
  function Intersection(status) {
    if (arguments.length > 0) {
      this.init(status);
    }
  }
  
  fabric.Intersection = Intersection;
  
  fabric.Intersection.prototype = /** @scope fabric.Intersection.prototype */ {
    
    /**
     * @method init
     * @param {String} status
     */
    init: function (status) {
      this.status = status;
      this.points = [];
    },
    
    /**
     * @method appendPoint
     * @param {String} status
     */
    appendPoint: function (point) {
      this.points.push(point);
    },
    
    /**
     * @method appendPoints
     * @param {String} status
     */
    appendPoints: function (points) {
      this.points = this.points.concat(points);
    }
  };
  
  /**
   * @static
   * @method intersectLineLine
   */
  fabric.Intersection.intersectLineLine = function (a1, a2, b1, b2) {
    var result,
        ua_t = (b2.x - b1.x) * (a1.y - b1.y) - (b2.y - b1.y) * (a1.x - b1.x),
        ub_t = (a2.x - a1.x) * (a1.y - b1.y) - (a2.y - a1.y) * (a1.x - b1.x),
        u_b = (b2.y - b1.y) * (a2.x - a1.x) - (b2.x - b1.x) * (a2.y - a1.y);
    if (u_b != 0) {
      var ua = ua_t / u_b,
          ub = ub_t / u_b;
      if (0 <= ua && ua <= 1 && 0 <= ub && ub <= 1) {
        result = new Intersection("Intersection");
        result.points.push(new fabric.Point(a1.x + ua * (a2.x - a1.x), a1.y + ua * (a2.y - a1.y)));
      }
      else {
        result = new Intersection("No Intersection");
      }
    }
    else {
      if (ua_t == 0 || ub_t == 0) {
        result = new Intersection("Coincident");
      }
      else {
        result = new Intersection("Parallel");
      }
    }
    return result;
  };
  
  /**
   * @method intersectLinePolygon
   */
  fabric.Intersection.intersectLinePolygon = function(a1,a2,points){
    var result = new Intersection("No Intersection"),
        length = points.length;
        
    for (var i = 0; i < length; i++) {
      var 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;
  };
  
  /**
   * @method intersectPolygonPolygon
   */
  fabric.Intersection.intersectPolygonPolygon = function (points1, points2) {
    var result = new Intersection("No 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;
  };
  
  /**
   * @method intersectPolygonRectangle
   */
  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("No 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;
  };
  
})(this);