dot_in_triangle.js

/**
 * @description check dot whether in a triangle
 * @author zhiyelee
 */

/**
 * for tri like below:
 *        A
 *     *     *
 *   B *  *  * C
 */


 // point is an object like A = [4,5]
 // D is the point to check
 function isInTriangle(A, B, C, D) {

     return isLeftOfLine(A, B, D) && isLeftOfLine(B, C, D) && isLeftOfLine(C, A, D)
     // check whether point `check` is on the left of vector `start-end`
     function isLeftOfLine(start, end, check) {
        return (end[0] - start[0]) * (check[1] - start[1]) - (end[1] - start[1]) * (check[0] - start[0]) > 0;
     }
 }


var A = [1, 3],
    B = [0, 0],
    C = [2, 0],
    check1 = [2, 3],
    check2 = [1, 1];

console.info(isInTriangle(A, B, C, check1));
console.info(isInTriangle(A, B, C, check2));