Fix for ATOM-15923 : Editor Spends Several Minutes Entering/Ending Play Game Mode (#1846)

* Cut off kd-tree generation if more than 10 percent of triangles straddle split axis

Signed-off-by: amzn-tommy <waltont@amazon.com>

* Switched to aznumeric_cast and added a comment with a JIRA to follow up on

Signed-off-by: amzn-tommy <waltont@amazon.com>

Gems/Atom/RPI/Code/Include/Atom/RPI.Reflect/Model/ModelKdTree.h

@@ -67,7 +67,8 @@ namespace AZ
             void ConstructMeshList(const ModelAsset* model, const AZ::Transform& matParent);
 
             static const int s_MinimumVertexSizeInLeafNode = 3 * 10;
-
+            // Stop splitting the tree if more than 10% of the triangles are straddling the split axis
+            static constexpr float s_MaximumSplitAxisStraddlingTriangles = 1.1;
             AZStd::unique_ptr<ModelKdTreeNode> m_pRootNode;
 
             struct MeshData

Gems/Atom/RPI/Code/Source/RPI.Reflect/Model/ModelKdTree.cpp

@@ -84,7 +84,11 @@ namespace AZ
 
             // If either the top or bottom contain all the input indices, the triangles are too close to cut any
             // further and the split failed
-            return indices.size() != outInfo.m_aboveIndices.size() && indices.size() != outInfo.m_belowIndices.size();
+            // Additionally, if too many triangles straddle the split-axis,
+            // the triangles are too close and the split failed
+            // [ATOM-15944] - Use a more sophisticated method to terminate KdTree generation
+            return indices.size() != outInfo.m_aboveIndices.size() && indices.size() != outInfo.m_belowIndices.size()
+                && aznumeric_cast<float>(outInfo.m_aboveIndices.size() + outInfo.m_belowIndices.size()) / aznumeric_cast<float>(indices.size()) < s_MaximumSplitAxisStraddlingTriangles;
         }
 
         bool ModelKdTree::Build(const ModelAsset* model)