Add option to allow triangles being excluded from refinement.

src/Triangle.Examples/Examples/Example9.cs

@@ -15,7 +15,7 @@ namespace TriangleNet.Examples
         {
             var pts = new List<Vertex>
             {
-                // The 4 corners of the square.
+                // The 4 corners of the rectangle.
                 new Vertex(1.5, 1.0),
                 new Vertex(1.5, -1.0),
                 new Vertex(-1.5, -1.0),

src/Triangle/Behavior.cs

@@ -25,6 +25,7 @@ namespace TriangleNet
         bool conformDel = false;
 
         Func<ITriangle, double, bool> usertest;
+        Func<ITriangle, bool> exclude;
 
         int noBisect = 0;
 
@@ -177,6 +178,15 @@ namespace TriangleNet
             set { usertest = value; }
         }
 
+        /// <summary>
+        /// Exclude triangles from being refined.
+        /// </summary>
+        public Func<ITriangle, bool> Exclude
+        {
+            get { return exclude; }
+            set { exclude = value; }
+        }
+
         /// <summary>
         /// Enclose the convex hull with segments.
         /// </summary>

src/Triangle/Meshing/QualityMesher.cs

@@ -64,6 +64,7 @@ namespace TriangleNet.Meshing
                 behavior.MaxAngle = quality.MaximumAngle;
                 behavior.MaxArea = quality.MaximumArea;
                 behavior.UserTest = quality.UserTest;
+                behavior.Exclude = quality.Exclude;
                 behavior.VarArea = quality.VariableArea;
 
                 behavior.ConformingDelaunay = behavior.ConformingDelaunay || delaunay;
@@ -250,6 +251,11 @@ namespace TriangleNet.Meshing
 
             double maxangle;
 
+            if (behavior.Exclude != null && behavior.Exclude(testtri.tri))
+            {
+                return;
+            }
+
             torg = testtri.Org();
             tdest = testtri.Dest();
             tapex = testtri.Apex();

src/Triangle/Meshing/QualityOptions.cs

@@ -34,6 +34,15 @@ namespace TriangleNet.Meshing
         /// </remarks>
         public Func<ITriangle, double, bool> UserTest { get; set; }
 
+        /// <summary>
+        /// Gets or sets a test function for excluding triangles from refinement.
+        /// </summary>
+        /// <remarks>
+        /// The exclude test takes higher priority than all other test, i.e. if a
+        /// triangle passes the exclude test, no other test will be executed.
+        /// </remarks>
+        public Func<ITriangle, bool> Exclude { get; set; }
+
         /// <summary>
         /// Gets or sets an area constraint per triangle.
         /// </summary>