Merge pull request #2 from dabingnn/master

add fromRTS for mat23

Author: jwu

lib/mat23.js

@@ -332,6 +332,35 @@ mat23.fromTranslation = function (out, v) {
   return out;
 };
 
+/**
+ * Creates a matrix from a rotation, vector translation and vector scale
+ * This is equivalent to (but faster than):
+ *
+ *     mat23.identity(dest);
+ *     mat23.translate(dest, vec);
+ *     let tmp = mat23.create();
+ *     mat23.fromRotation(tmp, rot);
+ *     mat23.multiply(dest, dest, tmp);
+ *     mat23.fromScaling(tmp, scale);
+ *     mat23.multiply(dest, dest, tmp);
+ *
+ * @param {mat23} out mat23 receiving operation result
+ * @param {number} r Rotation radian
+ * @param {vec2} v Translation vector
+ * @param {vec2} s Scaling vector
+ * @returns {mat23} out
+ */
+mat23.fromRTS = function (out, r, t, s) {
+  let sr = Math.sin(r), cr = Math.cos(r);
+  out.m00 = cr * s.x;
+  out.m01 = sr * s.x;
+  out.m02 = -sr * s.y;
+  out.m03 = cr * s.y;
+  out.m04 = t.x;
+  out.m05 = t.y;
+  return out;
+};
+
 /**
  * Returns a string representation of a mat23
  *