Merge topic 'fix-CoplanarTriangleIntersection'

b13f713e Add tests for triangle intersection fixes.
caa51b1a Fix for CoplanarTrianglesIntersect
Acked-by: Kitware Robot <kwrobot@kitware.com>
Reviewed-by: T.J. Corona <tj.corona@kitware.com>
Merge-request: !4532

Common/DataModel/Testing/Cxx/UnitTestTriangleIntersection.cxx

@@ -580,6 +580,51 @@ int TestReciprocalResult(vtkRandom* seq, unsigned nTests)
   return EXIT_SUCCESS;
 }
 
+int TestIssue17092()
+{
+  // An instance where triangle intersection failed was reported here:
+  // https://gitlab.kitware.com/vtk/vtk/issues/17092. It was fixed here:
+  // https://gitlab.kitware.com/vtk/vtk/merge_requests/3886
+
+  double t1[3][3] = {{ 0., 0., 0.}, {5., 0., 0.}, {0., 5., 0.}};
+  double t2[3][3] = {{ 10., 5., 0.}, {5., 10., 0.}, {1., 1., 0.}};
+
+  int returnValue = vtkTriangle::TrianglesIntersect( t1[0], t1[1], t1[2],
+                                                     t2[0], t2[1], t2[2] );
+
+  if (returnValue != VTK_YES_INTERSECTION)
+  {
+    std::cout<<"Triangle "<<TriangleToString(t1[0],t1[1],t1[2])<<std::endl;
+    std::cout<<" does not intersect "<<TriangleToString(t2[0],t2[1],t2[2])
+             <<" and should."<<std::endl;
+    return EXIT_FAILURE;
+  }
+
+  return EXIT_SUCCESS;
+}
+
+int TestMR4529()
+{
+  // An instance where triangle intersection failed (along with its fix) was
+  // reported here: https://gitlab.kitware.com/vtk/vtk/merge_requests/4529
+
+  double t1[3][3] = {{ 1.751, -.993, 0.}, {-3.021, 2.885, 0.}, {4.14, -4.025, 0.}};
+  double t2[3][3] = {{ 1.751, -.5, 0.}, {1.751, 1.326, 0.}, {-3.382, 2.276, 0.}};
+
+  int returnValue = vtkTriangle::TrianglesIntersect( t1[0], t1[1], t1[2],
+                                                     t2[0], t2[1], t2[2] );
+
+  if (returnValue != VTK_YES_INTERSECTION)
+  {
+    std::cout<<"Triangle "<<TriangleToString(t1[0],t1[1],t1[2])<<std::endl;
+    std::cout<<" does not intersect "<<TriangleToString(t2[0],t2[1],t2[2])
+             <<" and should."<<std::endl;
+    return EXIT_FAILURE;
+  }
+
+  return EXIT_SUCCESS;
+}
+
 int TestTriangleIntersection(vtkRandom* seq, unsigned nTests)
 {
   if (TestPositiveResult(seq,nTests) == EXIT_FAILURE)
@@ -602,6 +647,14 @@ int TestTriangleIntersection(vtkRandom* seq, unsigned nTests)
   {
     return EXIT_FAILURE;
   }
+  if (TestIssue17092() == EXIT_FAILURE)
+  {
+    return EXIT_FAILURE;
+  }
+  if (TestMR4529() == EXIT_FAILURE)
+  {
+    return EXIT_FAILURE;
+  }
   return EXIT_SUCCESS;
 }
 }

Common/DataModel/vtkTriangle.cxx

@@ -1056,22 +1056,42 @@ int CoplanarTrianglesIntersect(double p1[2], double q1[2], double r1[2],
     return 1;
   }
 
-  // If we have reached this point, then either
-  // 1. Two orientations are counterclockwise and one is clockwise, or
-  // 2. Two orientations are clockwise and one is counterclockwise.
+  // If we have reached this point, then
+  // 1.  Two orientations are counterclockwise and one is clockwise, or
+  // 2.a Two orientations are clockwise and one is counterclockwise, or
+  // 2.b One orientation is counterclockwise, one is clockwise and one colinear.
   // Equivalently, from "Faster Triangle-Triangle Intersection Tests":
-  // 1. p1 belongs to region R1
-  // 2. p1 belongs to region R2
-  // We permute T2 so that we have the following orienatation pattern:
-  // (counterclockwise, either orientation, clockwise).
-  // This orientation corresponds to p1 lying in either region R1 or R2
+  // 1.  p1 belongs to region R1
+  // 2.a p1 belongs to region R2
+  // 2.b p1 belongs to boundary of R2
+  // We permute T2 so that we have the following orientation pattern:
+  // (counterclockwise, either orientation, clockwise/colinear).
+  // This orientation corresponds to p1 lying in either region R1 or R2/boundary
   int index;
   for (index = 0; index < 3; index++)
   {
-    if (p1Orientation[index] == Counterclockwise &&
-        p1Orientation[(index+2)%3] == Clockwise)
+    if (p1Orientation[index] == Counterclockwise)
     {
-      break;
+      if (p1Orientation[(index+1)%3] == Counterclockwise &&
+          p1Orientation[(index+2)%3] == Clockwise)
+      {
+        break; // R1 ++-
+      }
+      if (p1Orientation[(index+1)%3] == Clockwise &&
+          p1Orientation[(index+2)%3] == Clockwise)
+      {
+        break; // R2 +--
+      }
+      if (p1Orientation[(index+1)%3] == Colinear &&
+          p1Orientation[(index+2)%3] == Clockwise)
+      {
+        break; // R2 boundary +0-
+      }
+      if (p1Orientation[(index+1)%3] == Clockwise &&
+          p1Orientation[(index+2)%3] == Colinear)
+      {
+        break; // R2 boundary +-0
+      }
     }
   }