Triangle2D = function(_a, _b, _c) {
            if (arguments.length === 3) {
              this.a = _a.copy();
              this.b = _b.copy();
              this.c = _c.copy();
            }
          }
@class
@member toxi
@param {toxi.Vec2D} a
@param {toxi.Vec2D} b
@param {toxi.Vec2D} c