Tree SweepBuilder will now try to output more balanced outputs for pa…

…thological inputs.
FlaXxy1 · Jul 7, 2020 · e7f092c · e7f092c
1 parent 5f9479b
commit e7f092c
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Showing 3 changed files with 11 additions and 4 deletions.
diff --git a/BepuPhysics/BepuPhysics.csproj b/BepuPhysics/BepuPhysics.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
-    <Version>2.3.0-beta0</Version>
+    <Version>2.3.0-beta1</Version>
     <Company>Bepu Entertainment LLC</Company>
     <Authors>Ross Nordby</Authors>
     <Description>Speedy real time physics simulation library.</Description>

diff --git a/BepuPhysics/Trees/Tree_SweepBuilder.cs b/BepuPhysics/Trees/Tree_SweepBuilder.cs
@@ -80,8 +80,15 @@ unsafe void FindPartitionForAxis(BoundingBox* boundingBoxes, BoundingBox* aMerge
                 var subtreeIndex = indexMap[i];
                 BoundingBox.CreateMerged(bMerged, boundingBoxes[subtreeIndex], out bMerged);
 
-                var aCost = i * ComputeBoundsMetric(ref aMerged[aIndex]);
-                var bCost = (count - i) * ComputeBoundsMetric(ref bMerged);
+                //Note the modifications to the cost function compare to raw SAH.
+                //First, we include a very mildly quadratic term for the counts so that skewed distributions are penalized.
+                //This penalty is weak enough that it should effectively never come into play except in pathological cases, like all bounding boxes overlapping.
+                //Second, we include an extremely small (the smallest normal floating point number) baseline to the evaluated bounds metric.
+                //This ensures that even a set of perfectly overlapping zero bounds will use a midpoint split rather than a skewed split.
+                const float normalEpsilon = 1.1754943508e-38f;
+                var aCost = i * (1f + i * 0.001f) * (normalEpsilon + ComputeBoundsMetric(ref aMerged[aIndex]));
+                var bCount = count - i;
+                var bCost = bCount * (1f + bCount * 0.001f) * (normalEpsilon + ComputeBoundsMetric(ref bMerged));
 
                 var totalCost = aCost + bCost;
                 if (totalCost < cost)

diff --git a/BepuUtilities/BepuUtilities.csproj b/BepuUtilities/BepuUtilities.csproj
@@ -3,7 +3,7 @@
     <AssemblyName>BepuUtilities</AssemblyName>
     <RootNamespace>BepuUtilities</RootNamespace>
     <TargetFramework>netstandard2.0</TargetFramework>
-    <Version>2.3.0-beta0</Version>
+    <Version>2.3.0-beta1</Version>
     <Company>Bepu Entertainment LLC</Company>
     <Authors>Ross Nordby</Authors>
     <Description>Supporting utilities library for BEPUphysics v2.</Description>