RotateAroundXY = function (triangle, x, y, angle)
{
    var c = Math.cos(angle);
    var s = Math.sin(angle);

    var tx = triangle.x1 - x;
    var ty = triangle.y1 - y;

    triangle.x1 = tx * c - ty * s + x;
    triangle.y1 = tx * s + ty * c + y;

    tx = triangle.x2 - x;
    ty = triangle.y2 - y;

    triangle.x2 = tx * c - ty * s + x;
    triangle.y2 = tx * s + ty * c + y;

    tx = triangle.x3 - x;
    ty = triangle.y3 - y;

    triangle.x3 = tx * c - ty * s + x;
    triangle.y3 = tx * s + ty * c + y;

    return triangle;
}
Rotates an entire Triangle at a given angle about a specific point.

@function Phaser.Geom.Triangle.RotateAroundXY
@since 3.0.0

@generic {Phaser.Geom.Triangle} O - [triangle,$return]

@param {Phaser.Geom.Triangle} triangle - The Triangle to rotate.
@param {number} x - The X coordinate of the point to rotate the Triangle about.
@param {number} y - The Y coordinate of the point to rotate the Triangle about.
@param {number} angle - The angle by which to rotate the Triangle, in radians.

@return {Phaser.Geom.Triangle} The rotated Triangle.