Line.Extend is a new static function that allows you extend the start and/or end points of a Line by the given amounts.

Author: photonstorm

CHANGELOG.md

@@ -169,6 +169,7 @@ one set of bindings ever created, which makes things a lot cleaner.
 * `CanvasTexture.setPixel` is a new method that sets the given pixel in the CanvasTexture to the color and alpha values provided.
 * `CanvasTexture.getData` is a new method that will extract an ImageData block from the CanvasTexture from the region given.
 * `CanvasTexture.putData` is a new method that will put an ImageData block at the given coordinates in a CanvasTexture.
+* `Line.Extend` is a new static function that allows you extend the start and/or end points of a Line by the given amounts.
 
 ### Updates
 

src/geom/line/Extend.js

@@ -0,0 +1,52 @@
+/**
+ * @author       Richard Davey <rich@photonstorm.com>
+ * @copyright    2018 Photon Storm Ltd.
+ * @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
+ */
+
+var Length = require('./Length');
+
+/**
+ * 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.
+ */
+var 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;
+};
+
+module.exports = Extend;

src/geom/line/index.js

@@ -12,6 +12,7 @@ Line.CenterOn = require('./CenterOn');
 Line.Clone = require('./Clone');
 Line.CopyFrom = require('./CopyFrom');
 Line.Equals = require('./Equals');
+Line.Extend = require('./Extend');
 Line.GetMidPoint = require('./GetMidPoint');
 Line.GetNearestPoint = require('./GetNearestPoint');
 Line.GetNormal = require('./GetNormal');