From ec89611d5d02f775ca5971122b212825930799da Mon Sep 17 00:00:00 2001
From: Mariusz Jamro <mariusz.jamro@gmail.com>
Date: Mon, 3 Aug 2015 21:05:12 +0200
Subject: [PATCH] Added methods for performing skew transform on the Matrix
 objects.

---
 src/matrix.js  | 37 +++++++++++++++++++++++++++++++++++++
 test/matrix.js | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 73 insertions(+)

diff --git a/src/matrix.js b/src/matrix.js
index 957beda..1b95144 100644
--- a/src/matrix.js
+++ b/src/matrix.js
@@ -153,6 +153,43 @@ Snap.plugin(function (Snap, Element, Paper, glob, Fragment) {
             this.add(cos, sin, -sin, cos, x, y);
             return this.add(1, 0, 0, 1, -x, -y);
         };
+        /*\
+         * Matrix.skewX
+         [ method ]
+         **
+         * Skews the matrix along the x-axis
+         - x (number) Angle to skew along the x-axis (in degrees).
+        \*/
+        matrixproto.skewX = function (x) {
+            return this.skew(x, 0);
+        };
+        /*\
+         * Matrix.skewY
+         [ method ]
+         **
+         * Skews the matrix along the y-axis
+         - y (number) Angle to skew along the y-axis (in degrees).
+        \*/
+        matrixproto.skewY = function (y) {
+            return this.skew(0, y);
+        };
+        /*\
+         * Matrix.skew
+         [ method ]
+         **
+         * Skews the matrix
+         - y (number) Angle to skew along the y-axis (in degrees).
+         - x (number) Angle to skew along the x-axis (in degrees).
+        \*/
+        matrixproto.skew = function (x, y) {
+            x = x || 0;
+            y = y || 0;
+            x = Snap.rad(x);
+            y = Snap.rad(y);
+            var c = math.tan(x).toFixed(9);
+            var b = math.tan(y).toFixed(9);
+            return this.add(1, b, c, 1, 0, 0);
+        };
         /*\
          * Matrix.x
          [ method ]
diff --git a/test/matrix.js b/test/matrix.js
index e446d7a..02242dd 100644
--- a/test/matrix.js
+++ b/test/matrix.js
@@ -183,6 +183,42 @@ describe("Matrix methods", function () {
             f: 18
         });
     });
+    it("Matrix.skewX", function() {
+        var matrix = new Snap.Matrix(1, 0, 0, 1, 20, 30);
+        matrix.skewX(45);
+        expect(matrix).to.eql({
+            a: 1,
+            b: 0,
+            c: 1,
+            d: 1,
+            e: 20,
+            f: 30
+        });
+    });
+    it("Matrix.skewY", function() {
+        var matrix = new Snap.Matrix(1, 0, 0, 1, 20, 30);
+        matrix.skewY(45);
+        expect(matrix).to.eql({
+            a: 1,
+            b: 1,
+            c: 0,
+            d: 1,
+            e: 20,
+            f: 30
+        });
+    });
+    it("Matrix.skew", function() {
+        var matrix = new Snap.Matrix(1, 0, 0, 1, 20, 30);
+        matrix.skew(45, -45);
+        expect(matrix).to.eql({
+            a: 1,
+            b: -1,
+            c: 1,
+            d: 1,
+            e: 20,
+            f: 30
+        });
+    });
     it("Matrix.x", function() {
         var matrix = new Snap.Matrix(1, 0, 0, 1, 20, 30);
         var result = matrix.x(10, -10);