From a655234cc394e0db71799d5d30c9ab9bc775cf77 Mon Sep 17 00:00:00 2001
From: Tim Schaub <tim.schaub@gmail.com>
Date: Fri, 24 Jun 2016 10:03:13 -0600
Subject: [PATCH] Convenience function for common composite transform

---
 src/ol/transform.js            | 26 ++++++++++++++++++++++++++
 test/spec/ol/transform.test.js | 23 +++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/src/ol/transform.js b/src/ol/transform.js
index cdd9e13377..b028d13158 100644
--- a/src/ol/transform.js
+++ b/src/ol/transform.js
@@ -166,6 +166,32 @@ ol.transform.translate = function(transform, dx, dy) {
 };
 
 
+/**
+ * Creates a composite transform given an initial translation, scale, rotation, and
+ * final translation (in that order only, not commutative).
+ * @param {!ol.Transform} transform The transform (will be modified in place).
+ * @param {number} dx1 Initial translation x.
+ * @param {number} dy1 Initial translation y.
+ * @param {number} sx Scale factor x.
+ * @param {number} sy Scale factor y.
+ * @param {number} angle Rotation (in counter-clockwise radians).
+ * @param {number} dx2 Final translation x.
+ * @param {number} dy2 Final translation y.
+ * @return {!ol.Transform} The composite transform.
+ */
+ol.transform.compose = function(transform, dx1, dy1, sx, sy, angle, dx2, dy2) {
+  var sin = Math.sin(angle);
+  var cos = Math.cos(angle);
+  transform[0] = sx * cos;
+  transform[1] = sy * sin;
+  transform[2] = -sx * sin;
+  transform[3] = sy * cos;
+  transform[4] = dx2 * sx * cos - dy2 * sx * sin + dx1;
+  transform[5] = dx2 * sy * sin + dy2 * sy * cos + dy1;
+  return transform;
+};
+
+
 /**
  * Invert the given transform.
  * @param {!ol.Transform} transform Transform.
diff --git a/test/spec/ol/transform.test.js b/test/spec/ol/transform.test.js
index 0a9906b764..b838a91ae9 100644
--- a/test/spec/ol/transform.test.js
+++ b/test/spec/ol/transform.test.js
@@ -72,6 +72,29 @@ describe('ol.transform', function() {
     });
   });
 
+  describe('ol.transform.compose()', function() {
+    it('composes a translate, scale, rotate, translate transform', function() {
+      var dx1 = 3;
+      var dy1 = 4;
+      var sx = 1.5;
+      var sy = -1.5;
+      var angle = Math.PI / 3;
+      var dx2 = -dx1 / 2;
+      var dy2 = -dy1 / 2;
+
+      var expected = ol.transform.create();
+      ol.transform.translate(expected, dx1, dy1);
+      ol.transform.scale(expected, sx, sy);
+      ol.transform.rotate(expected, angle);
+      ol.transform.translate(expected, dx2, dy2);
+
+      var composed = ol.transform.create();
+      var composedReturn = ol.transform.compose(composed, dx1, dy1, sx, sy, angle, dx2, dy2);
+      expect(composed).to.equal(composedReturn);
+      expect(composed).to.eql(expected);
+    });
+  });
+
   describe('ol.transform.invert()', function() {
     it('inverts a transform', function() {
       var transform = [1, 0, 1, 0, 1, 0];