From 4f4d7479688645533dd1c4cb03c06890a236efbc Mon Sep 17 00:00:00 2001
From: wmayer <wmayer@users.sourceforge.net>
Date: Mon, 16 Nov 2015 11:59:41 +0100
Subject: [PATCH] + fix undefined behaviour in determining grid length for
 planar meshes

---
 src/Mod/Mesh/App/Core/Grid.cpp | 78 +++++++++++++++++-----------------
 1 file changed, 40 insertions(+), 38 deletions(-)

diff --git a/src/Mod/Mesh/App/Core/Grid.cpp b/src/Mod/Mesh/App/Core/Grid.cpp
index fb8654640..063add3a2 100644
--- a/src/Mod/Mesh/App/Core/Grid.cpp
+++ b/src/Mod/Mesh/App/Core/Grid.cpp
@@ -261,48 +261,50 @@ void MeshGrid::Position (const Base::Vector3f &rclPoint, unsigned long &rulX, un
 
 void MeshGrid::CalculateGridLength (unsigned long ulCtGrid, unsigned long ulMaxGrids)
 {
-  // Grid Laengen bzw. Anzahl der Grids pro Dimension berechnen
-  // pro Grid sollen ca. 10 (?!?!) Facets liegen
-  // bzw. max Grids sollten 10000 nicht ueberschreiten
-  Base::BoundBox3f clBBMeshEnlarged = _pclMesh->GetBoundBox();
-  float fVolElem;
+    // Grid Laengen bzw. Anzahl der Grids pro Dimension berechnen
+    // pro Grid sollen ca. 10 (?!?!) Facets liegen
+    // bzw. max Grids sollten 10000 nicht ueberschreiten
+    Base::BoundBox3f clBBMeshEnlarged = _pclMesh->GetBoundBox();
+    float fGridLen = 0;
 
-  // Stelle sicher, dass die Bounding box ein Volumen > 0 besitzt
-  float fLenX = clBBMeshEnlarged.LengthX();
-  float fLenY = clBBMeshEnlarged.LengthY();
-  float fLenZ = clBBMeshEnlarged.LengthZ();
-  float fMax = 0.005 * std::max<float>(std::max<float>(fLenX, fLenY), fLenZ);
-  // Falls Bounding box zu einem Punkt degeneriert ist
-  if (fMax == 0) {
-      _ulCtGridsX = 1;
-      _ulCtGridsY = 1;
-      _ulCtGridsZ = 1;
-      return;
-  }
-  if (fLenX == 0) {
-      clBBMeshEnlarged.MinX -= fMax;
-      clBBMeshEnlarged.MaxX += fMax;
-  }
-  if (fLenY == 0) {
-      clBBMeshEnlarged.MinY -= fMax;
-      clBBMeshEnlarged.MaxY += fMax;
-  }
-  if (fLenZ == 0) {
-      clBBMeshEnlarged.MinZ -= fMax;
-      clBBMeshEnlarged.MaxZ += fMax;
-  }
+    float fLenX = clBBMeshEnlarged.LengthX();
+    float fLenY = clBBMeshEnlarged.LengthY();
+    float fLenZ = clBBMeshEnlarged.LengthZ();
 
-  if (_ulCtElements > (ulMaxGrids * ulCtGrid))
-    fVolElem = (clBBMeshEnlarged.LengthX() * clBBMeshEnlarged.LengthY() * clBBMeshEnlarged.LengthZ()) / float(ulMaxGrids * ulCtGrid);
-  else
-    fVolElem = (clBBMeshEnlarged.LengthX() * clBBMeshEnlarged.LengthY() * clBBMeshEnlarged.LengthZ()) / float(_ulCtElements);
+    float fVolume = fLenX * fLenY * fLenZ;
+    if (fVolume > 0.0f) {
+        float fVolElem;
+        if (_ulCtElements > (ulMaxGrids * ulCtGrid))
+            fVolElem = (fLenX * fLenY * fLenZ) / float(ulMaxGrids * ulCtGrid);
+        else
+            fVolElem = (fLenX * fLenY * fLenZ) / float(_ulCtElements);
 
-  float fVol     = fVolElem * float(ulCtGrid);
-  float fGridLen = float(pow((float)fVol,(float) 1.0f / 3.0f));
+        float fVol = fVolElem * float(ulCtGrid);
+        fGridLen = float(pow(fVol, 1.0f / 3.0f));
+    }
+    else {
+        // Planare Bounding box
+        float fArea = fLenX * fLenY + fLenX * fLenZ + fLenY * fLenZ;
+        float fAreaElem;
+        if (_ulCtElements > (ulMaxGrids * ulCtGrid))
+            fAreaElem = fArea / float(ulMaxGrids * ulCtGrid);
+        else
+            fAreaElem = fArea / float(_ulCtElements);
 
-  _ulCtGridsX = std::max<unsigned long>((unsigned long)(clBBMeshEnlarged.LengthX() / fGridLen), 1);
-  _ulCtGridsY = std::max<unsigned long>((unsigned long)(clBBMeshEnlarged.LengthY() / fGridLen), 1);
-  _ulCtGridsZ = std::max<unsigned long>((unsigned long)(clBBMeshEnlarged.LengthZ() / fGridLen), 1);
+        fGridLen = sqrt(fAreaElem * float(ulCtGrid));
+    }
+
+    if (fGridLen > 0) {
+        _ulCtGridsX = std::max<unsigned long>(static_cast<unsigned long>(fLenX / fGridLen), 1);
+        _ulCtGridsY = std::max<unsigned long>(static_cast<unsigned long>(fLenY / fGridLen), 1);
+        _ulCtGridsZ = std::max<unsigned long>(static_cast<unsigned long>(fLenZ / fGridLen), 1);
+    }
+    else {
+        // Degenerated grid
+        _ulCtGridsX = 1;
+        _ulCtGridsY = 1;
+        _ulCtGridsZ = 1;
+    }
 }
 
 void MeshGrid::CalculateGridLength (int iCtGridPerAxis)