Changes suggested by Rob Rouhani

* Turned the new Matrix4 properties into methods
* Matrix4.Normalize() now behaves correctly. ExtractRotation() does its
own row normalisation.

Source/OpenTK/Math/Matrix4.cs

@@ -275,9 +275,11 @@ public Matrix4 Normalized()
         /// </summary>
         public void Normalize()
         {
-            Row0.Xyz = Row0.Xyz.Normalized();
-            Row1.Xyz = Row1.Xyz.Normalized();
-            Row2.Xyz = Row2.Xyz.Normalized();
+            var determinant = this.Determinant;
+            Row0 /= determinant;
+            Row1 /= determinant;
+            Row2 /= determinant;
+            Row3 /= determinant;
         }
 
         /// <summary>
@@ -292,71 +294,80 @@ public Matrix4 Inverted()
         }
 
         /// <summary>
-        /// Gets the translation component of this instance.
+        /// Returns the translation component of this instance.
         /// </summary>
-        public Vector3 TranslationPart { get { return Row3.Xyz; } }
+        public Vector3 ExtractTranslation() { return Row3.Xyz; }
 
         /// <summary>
-        /// Gets the scale component of this instance.
+        /// Returns the scale component of this instance.
         /// </summary>
-        public Vector3 ScalePart { get { return new Vector3 (Row0.Length, Row1.Length, Row2.Length); } }
+        public Vector3 ExtractScale() { return new Vector3 (Row0.Length, Row1.Length, Row2.Length); }
 
         /// <summary>
-        /// Gets the rotation component of this instance. The Matrix MUST be normalized first.
+        /// Returns the rotation component of this instance. Quite slow.
         /// </summary>
-        public Quaternion RotationPart
+        /// <param name="row_normalise">Whether the method should operate on a row-normalised (i.e. scale == 1) version of the Matrix. Pass false if you know it's already normalised.</param>
+        public Quaternion ExtractRotation(bool row_normalise = true)
         {
-            get
+            var row0 = Row0.Xyz;
+            var row1 = Row1.Xyz;
+            var row2 = Row2.Xyz;
+
+            if (row_normalise)
             {
-                Quaternion q = new Quaternion();
+                if (row0.LengthSquared != 1) row0 = row0.Normalized();
+                if (row1.LengthSquared != 1) row1 = row1.Normalized();
+                if (row2.LengthSquared != 1) row2 = row2.Normalized();
+            }
 
-                // Adapted from Blender
-                double trace = 0.25 * (Row0[0] + Row1[1] + Row2[2] + 1.0);
+            // code below adapted from Blender
 
-                if (trace > 0.0f)
-                {
-                    double sq = Math.Sqrt(trace);
+            Quaternion q = new Quaternion();
+            double trace = 0.25 * (row0[0] + row1[1] + row2[2] + 1.0);
 
-                    q.W = (float)sq;
-                    sq = 1.0 / (4.0 * sq);
-                    q.X = (float)((Row1[2] - Row2[1]) * sq);
-                    q.Y = (float)((Row2[0] - Row0[2]) * sq);
-                    q.Z = (float)((Row0[1] - Row1[0]) * sq);
-                }
-                else if (Row0[0] > Row1[1] && Row0[0] > Row2[2])
-                {
-                    double sq = 2.0 * Math.Sqrt(1.0 + Row0[0] - Row1[1] - Row2[2]);
+            if (trace > 0)
+            {
+                double sq = Math.Sqrt(trace);
 
-                    q.X = (float)(0.25 * sq);
-                    sq = 1.0 / sq;
-                    q.W = (float)((Row2[1] - Row1[2]) * sq);
-                    q.Y = (float)((Row1[0] + Row0[1]) * sq);
-                    q.Z = (float)((Row2[0] + Row0[2]) * sq);
-                }
-                else if (Row1[1] > Row2[2])
-                {
-                    double sq = 2.0 * Math.Sqrt(1.0 + Row1[1] - Row0[0] - Row2[2]);
+                q.W = (float)sq;
+                sq = 1.0 / (4.0 * sq);
+                q.X = (float)((row1[2] - row2[1]) * sq);
+                q.Y = (float)((row2[0] - row0[2]) * sq);
+                q.Z = (float)((row0[1] - row1[0]) * sq);
+            }
+            else if (row0[0] > row1[1] && row0[0] > row2[2])
+            {
+                double sq = 2.0 * Math.Sqrt(1.0 + row0[0] - row1[1] - row2[2]);
 
-                    q.Y = (float)(0.25 * sq);
-                    sq = 1.0 / sq;
-                    q.W = (float)((Row2[0] - Row0[2]) * sq);
-                    q.X = (float)((Row1[0] + Row0[1]) * sq);
-                    q.Z = (float)((Row2[1] + Row1[2]) * sq);
-                }
-                else
-                {
-                    double sq = 2.0 * Math.Sqrt(1.0 + Row2[2] - Row0[0] - Row1[1]);
+                q.X = (float)(0.25 * sq);
+                sq = 1.0 / sq;
+                q.W = (float)((row2[1] - row1[2]) * sq);
+                q.Y = (float)((row1[0] + row0[1]) * sq);
+                q.Z = (float)((row2[0] + row0[2]) * sq);
+            }
+            else if (row1[1] > row2[2])
+            {
+                double sq = 2.0 * Math.Sqrt(1.0 + row1[1] - row0[0] - row2[2]);
 
-                    q.Z = (float)(0.25 * sq);
-                    sq = 1.0 / sq;
-                    q.W = (float)((Row1[0] - Row0[1]) * sq);
-                    q.X = (float)((Row2[0] + Row0[2]) * sq);
-                    q.Y = (float)((Row2[1] + Row1[2]) * sq);
-                }
+                q.Y = (float)(0.25 * sq);
+                sq = 1.0 / sq;
+                q.W = (float)((row2[0] - row0[2]) * sq);
+                q.X = (float)((row1[0] + row0[1]) * sq);
+                q.Z = (float)((row2[1] + row1[2]) * sq);
+            }
+            else
+            {
+                double sq = 2.0 * Math.Sqrt(1.0 + row2[2] - row0[0] - row1[1]);
 
-                q.Normalize();
-				return q;
+                q.Z = (float)(0.25 * sq);
+                sq = 1.0 / sq;
+                q.W = (float)((row1[0] - row0[1]) * sq);
+                q.X = (float)((row2[0] + row0[2]) * sq);
+                q.Y = (float)((row2[1] + row1[2]) * sq);
             }
+
+            q.Normalize();
+            return q;
         }
 
         #endregion