File: src/Line.js
var Scalar = require('./Scalar');
module.exports = Line;
/**
* Container for line-related functions
* @class Line
*/
function Line(){};
/**
* Compute the intersection between two lines.
* @static
* @method lineInt
* @param {Array} l1 Line vector 1
* @param {Array} l2 Line vector 2
* @param {Number} precision Precision to use when checking if the lines are parallel
* @return {Array} The intersection point.
*/
Line.lineInt = function(l1,l2,precision){
precision = precision || 0;
var i = [0,0]; // point
var a1, b1, c1, a2, b2, c2, det; // scalars
a1 = l1[1][1] - l1[0][1];
b1 = l1[0][0] - l1[1][0];
c1 = a1 * l1[0][0] + b1 * l1[0][1];
a2 = l2[1][1] - l2[0][1];
b2 = l2[0][0] - l2[1][0];
c2 = a2 * l2[0][0] + b2 * l2[0][1];
det = a1 * b2 - a2*b1;
if (!Scalar.eq(det, 0, precision)) { // lines are not parallel
i[0] = (b2 * c1 - b1 * c2) / det;
i[1] = (a1 * c2 - a2 * c1) / det;
}
return i;
};
/**
* Checks if two line segments intersects.
* @method segmentsIntersect
* @param {Array} p1 The start vertex of the first line segment.
* @param {Array} p2 The end vertex of the first line segment.
* @param {Array} q1 The start vertex of the second line segment.
* @param {Array} q2 The end vertex of the second line segment.
* @return {Boolean} True if the two line segments intersect
*/
Line.segmentsIntersect = function(p1, p2, q1, q2){
var dx = p2[0] - p1[0];
var dy = p2[1] - p1[1];
var da = q2[0] - q1[0];
var db = q2[1] - q1[1];
// segments are parallel
if(da*dy - db*dx == 0)
return false;
var s = (dx * (q1[1] - p1[1]) + dy * (p1[0] - q1[0])) / (da * dy - db * dx)
var t = (da * (p1[1] - q1[1]) + db * (q1[0] - p1[0])) / (db * dx - da * dy)
return (s>=0 && s<=1 && t>=0 && t<=1);
};