Extend = function (line, left, right)
{
    if (right === undefined) { right = left; }

    var length = Length(line);

    var slopX = line.x2 - line.x1;
    var slopY = line.y2 - line.y1;

    if (left)
    {
        line.x1 = line.x1 - slopX / length * left;
        line.y1 = line.y1 - slopY / length * left;
    }

    if (right)
    {
        line.x2 = line.x2 + slopX / length * right;
        line.y2 = line.y2 + slopY / length * right;
    }

    return line;
}
Extends the start and end points of a Line by the given amounts.

The amounts can be positive or negative. Positive points will increase the length of the line,
while negative ones will decrease it.

If no `right` value is provided it will extend the length of the line equally in both directions.

Pass a value of zero to leave the start or end point unchanged.

@function Phaser.Geom.Line.Extend
@since 3.16.0

@param {Phaser.Geom.Line} line - The line instance to extend.
@param {number} left - The amount to extend the start of the line by.
@param {number} [right] - The amount to extend the end of the line by. If not given it will be set to the `left` value.

@return {Phaser.Geom.Line} The modified Line instance.