Add NoEmptyPolygons on Tess instance to remove zero area polygons.

Author: speps

LibTessDotNet/Sources/MeshUtils.cs

@@ -371,5 +371,20 @@ public static void KillFace(Face fDel, Face newLFace)
             fNext._prev = fPrev;
             fPrev._next = fNext;
         }
+
+        /// <summary>
+        /// Return signed area of face.
+        /// </summary>
+        public static float FaceArea(Face f)
+        {
+            float area = 0.0f;
+            var e = f._anEdge;
+            do
+            {
+                area += (e._Org._s - e._Dst._s) * (e._Org._t + e._Dst._t);
+                e = e._Lnext;
+            } while (e != f._anEdge);
+            return area;
+        }
     }
 }

LibTessDotNet/Sources/Tess.cs

@@ -31,6 +31,7 @@
 ** LibTessDotNet: Remi Gillig, https://github.com/speps/LibTessDotNet
 */
 
+using System;
 using System.Diagnostics;
 
 namespace LibTessDotNet
@@ -99,6 +100,8 @@ public partial class Tess
         public float SUnitY = 0.0f;
         public float SentinelCoord = 4e30f;
 
+        public bool NoEmptyPolygons = false;
+
         public ContourVertex[] Vertices { get { return _vertices; } }
         public int VertexCount { get { return _vertexCount; } }
 
@@ -187,15 +190,11 @@ private void CheckOrientation()
             float area = 0.0f;
             for (var f = _mesh._fHead._next; f != _mesh._fHead; f = f._next)
             {
-                var e = f._anEdge;
-                if (e._winding <= 0)
+                if (f._anEdge._winding <= 0)
                 {
                     continue;
                 }
-                do {
-                    area += (e._Org._s - e._Dst._s) * (e._Org._t + e._Dst._t);
-                    e = e._Lnext;
-                } while (e != f._anEdge);
+                area += MeshUtils.FaceArea(f);
             }
             if (area < 0.0f)
             {
@@ -455,6 +454,15 @@ private void OutputPolymesh(ElementType elementType, int polySize)
                 f._n = MeshUtils.Undef;
                 if (!f._inside) continue;
 
+                if (NoEmptyPolygons)
+                {
+                    float area = MeshUtils.FaceArea(f);
+                    if (Math.Abs(area) < float.Epsilon)
+                    {
+                        continue;
+                    }
+                }
+
                 edge = f._anEdge;
                 faceVerts = 0;
                 do {
@@ -500,6 +508,15 @@ private void OutputPolymesh(ElementType elementType, int polySize)
             {
                 if (!f._inside) continue;
 
+                if (NoEmptyPolygons)
+                {
+                    float area = MeshUtils.FaceArea(f);
+                    if (Math.Abs(area) < float.Epsilon)
+                    {
+                        continue;
+                    }
+                }
+
                 // Store polygon
                 edge = f._anEdge;
                 faceVerts = 0;

TessBed/MainForm.Designer.cs

@@ -72,6 +72,12 @@ public MainForm()
                 RefreshAsset(toolStripAssets.SelectedIndex);
             };
 
+            toolStripButtonNoEmpty.CheckedChanged += delegate(object sender, EventArgs e)
+            {
+                _tess.NoEmptyPolygons = toolStripButtonNoEmpty.Checked;
+                RefreshAsset(toolStripAssets.SelectedIndex);
+            };
+
             toolStripButtonBench.Click += delegate(object sender, EventArgs e)
             {
                 new BenchForm().ShowDialog(this);

TessBed/MainForm.cs

@@ -104,6 +104,33 @@ public void Tesselate_WithIssue1Quad_ReturnsSameResultAsLibtess2()
             }
         }
 
+        [Test]
+        // From https://github.com/speps/LibTessDotNet/issues/1
+        public void Tesselate_WithNoEmptyPolygonsTrue_RemovesEmptyPolygons()
+        {
+            string data = "2,0,4\n2,0,2\n4,0,2\n4,0,0\n0,0,0\n0,0,4";
+            var indices = new List<int>();
+            var expectedIndices = new int[] { 0, 1, 2, 2, 3, 4, 3, 1, 5 };
+            using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(data)))
+            {
+                var pset = DataLoader.LoadDat(stream);
+                var tess = new Tess();
+                PolyConvert.ToTess(pset, tess);
+                tess.NoEmptyPolygons = true;
+                tess.Tessellate(WindingRule.EvenOdd, ElementType.Polygons, 3);
+                indices.Clear();
+                for (int i = 0; i < tess.ElementCount; i++)
+                {
+                    for (int j = 0; j < 3; j++)
+                    {
+                        int index = tess.Elements[i * 3 + j];
+                        indices.Add(index);
+                    }
+                }
+                Assert.AreEqual(expectedIndices, indices.ToArray());
+            }
+        }
+
         [Test]
         public void Tesselate_CalledTwiceOnSameInstance_DoesNotCrash()
         {