Merge shape pair contacts into body-pair contacts

benchmark/main.c

@@ -16,6 +16,7 @@
 #include <ctype.h>
 #include <stdbool.h>
 #include <stdio.h>
+
 #include <stdlib.h>
 #include <string.h>
 
@@ -46,6 +47,7 @@ static void MinProfile( b3Profile* p1, const b3Profile* p2 )
 	p1->step = b3MinFloat( p1->step, p2->step );
 	p1->pairs = b3MinFloat( p1->pairs, p2->pairs );
 	p1->collide = b3MinFloat( p1->collide, p2->collide );
+	p1->solve = b3MinFloat( p1->solve, p2->solve );
 	p1->constraints = b3MinFloat( p1->constraints, p2->constraints );
 	p1->transforms = b3MinFloat( p1->transforms, p2->transforms );
 	p1->refit = b3MinFloat( p1->refit, p2->refit );
@@ -161,6 +163,7 @@ int main( int argc, char** argv )
 		{ "trees50", NULL, CreateTrees50, DestroyTrees, NULL, 500 },
 		{ "trees25", NULL, CreateTrees25, DestroyTrees, NULL, 500 },
 		{ "washer", GetWasherCapacity, CreateWasher, NULL, NULL, 1000 },
+		{ "wheel_stack", NULL, CreateWheelStack, NULL, NULL, 500 },
 		//{ "smash", CreateSmash, NULL, 300 },
 		//{ "spinner", CreateSpinner, StepSpinner, 1400 },
 		//{ "tumbler", CreateTumbler, NULL, 750 },
@@ -412,8 +415,13 @@ int main( int argc, char** argv )
 			}
 		}
 
-		printf( "body %d / shape %d / contact %d / joint %d / stack %d\n\n", counters.bodyCount, counters.shapeCount,
+		printf( "body %d / shape %d / contact %d / joint %d / stack %d\n", counters.bodyCount, counters.shapeCount,
 				counters.contactCount, counters.jointCount, counters.stackUsed );
+		{
+			b3Profile last = profiles[stepCount - 1];
+			printf( "profile(min last step): step %.3f / collide %.3f / solve %.3f ms\n\n", last.step, last.collide,
+					last.solve );
+		}
 
 		char fileName[64] = { 0 };
 		snprintf( fileName, 64, "%s.csv", benchmarks[benchmarkIndex].name );

samples/CMakeLists.txt

@@ -179,6 +179,7 @@ set(SAMPLE_FILES
     sample_shapes.cpp
     sample_stacking.cpp
     sample_tree.cpp
+    sample_wheel_stack.cpp
     sample_world.cpp
 )
 

samples/sample_wheel_stack.cpp

@@ -0,0 +1,93 @@
+// SPDX-FileCopyrightText: 2026 Erin Catto
+// SPDX-License-Identifier: MIT
+
+#include "gfx/debug_adapter.h"
+#include "sample.h"
+
+#include "box3d/box3d.h"
+
+#include "metal_wheel1_hulls.h"
+
+#include <stdio.h>
+
+// 30 metal_wheel1 props (37-piece convex decompositions) stacked. Body-pair contact merging
+// lets them settle and sleep instead of wobbling.
+class WheelStack : public Sample
+{
+public:
+	explicit WheelStack( SampleContext* context )
+		: Sample( context )
+	{
+		if ( context->restart == false )
+		{
+			m_camera->SetView( 0.0f, 12.0f, 5.0f, { 0.0f, 0.85f, 0.0f } );
+		}
+
+		AddGroundBox( 10.0f );
+
+		for ( int h = 0; h < s_metalWheel1HullCount; ++h )
+		{
+			const WheelHullSpan& span = s_metalWheel1Hulls[h];
+			m_hulls[h] = b3CreateHull( &s_metalWheel1Verts[span.offset], span.count, span.count );
+		}
+
+		const float height = 0.171f;
+		const float spacing = height + 0.006f;
+		const float startY = 0.5f * height + 0.004f;
+
+		b3ShapeDef shapeDef = b3DefaultShapeDef();
+		shapeDef.baseMaterial.friction = 0.6f;
+
+		for ( int i = 0; i < m_wheelCount; ++i )
+		{
+			b3BodyDef bodyDef = b3DefaultBodyDef();
+			bodyDef.type = b3_dynamicBody;
+			bodyDef.name = "wheel";
+			bodyDef.position = { 0.0f, startY + i * spacing, 0.0f };
+			b3BodyId bodyId = b3CreateBody( m_worldId, &bodyDef );
+
+			for ( int h = 0; h < s_metalWheel1HullCount; ++h )
+			{
+				b3CreateHullShape( bodyId, &shapeDef, m_hulls[h] );
+			}
+		}
+
+		b3World_SetContactTuning( m_worldId, 240.0f, 10.0f, 3.0f );
+	}
+
+	~WheelStack() override
+	{
+		for ( int h = 0; h < s_metalWheel1HullCount; ++h )
+		{
+			b3DestroyHull( m_hulls[h] );
+		}
+	}
+
+	void Step() override
+	{
+		Sample::Step();
+
+		b3Profile p = b3World_GetProfile( m_worldId );
+		float substepRate = m_context->hertz * m_context->subStepCount;
+
+		DrawTextLine( "wheels %d, hull pieces/wheel %d (%d total shapes)", m_wheelCount, s_metalWheel1HullCount,
+					  m_wheelCount * s_metalWheel1HullCount );
+		DrawTextLine( "step %.0f hz, sub-steps %d -> substep rate %.0f hz", m_context->hertz, m_context->subStepCount,
+					  substepRate );
+		DrawTextLine( "eff contact hz = min(240, %.0f) = %.0f", 0.125f * substepRate,
+					  b3MinFloat( 240.0f, 0.125f * substepRate ) );
+		DrawTextLine( "step %.3f ms | collide %.3f ms (%.0f%%) | solve %.3f ms (%.0f%%)", p.step, p.collide,
+					  p.step > 0.0f ? 100.0f * p.collide / p.step : 0.0f, p.solve,
+					  p.step > 0.0f ? 100.0f * p.solve / p.step : 0.0f );
+	}
+
+	static Sample* Create( SampleContext* context )
+	{
+		return new WheelStack( context );
+	}
+
+	b3HullData* m_hulls[s_metalWheel1HullCount];
+	static constexpr int m_wheelCount = 30;
+};
+
+static int sampleWheelStack = RegisterSample( "Stacking", "Wheel Stack (PHX)", WheelStack::Create );

shared/benchmarks.c

@@ -4,6 +4,7 @@
 #include "benchmarks.h"
 
 #include "human.h"
+#include "metal_wheel1_hulls.h"
 #include "utils.h"
 
 #include "box3d/box3d.h"
@@ -673,6 +674,54 @@ void CreateWasher( b3WorldId worldId )
 	}
 }
 
+// A stack of 30 metal_wheel1 props (37-piece convex decompositions): the contact-reduction stress case.
+void CreateWheelStack( b3WorldId worldId )
+{
+	b3World_EnableSleeping( worldId, false );
+
+	{
+		b3BodyDef bodyDef = b3DefaultBodyDef();
+		bodyDef.position = (b3Pos){ 0.0f, -1.0f, 0.0f };
+		b3BodyId groundId = b3CreateBody( worldId, &bodyDef );
+
+		b3BoxHull box = b3MakeBoxHull( 10.0f, 1.0f, 10.0f );
+		b3ShapeDef shapeDef = b3DefaultShapeDef();
+		g_groundShapeId = b3CreateHullShape( groundId, &shapeDef, &box.base );
+	}
+
+	b3HullData* hulls[s_metalWheel1HullCount];
+	for ( int h = 0; h < s_metalWheel1HullCount; ++h )
+	{
+		const WheelHullSpan span = s_metalWheel1Hulls[h];
+		hulls[h] = b3CreateHull( &s_metalWheel1Verts[span.offset], span.count, span.count );
+	}
+
+	const float height = 0.171f; // y extent of the wheel
+	const float spacing = height + 0.006f;
+	const float startY = 0.5f * height + 0.004f;
+
+	b3ShapeDef shapeDef = b3DefaultShapeDef();
+	shapeDef.baseMaterial.friction = 0.6f;
+
+	for ( int i = 0; i < 30; ++i )
+	{
+		b3BodyDef bodyDef = b3DefaultBodyDef();
+		bodyDef.type = b3_dynamicBody;
+		bodyDef.position = (b3Pos){ 0.0f, startY + i * spacing, 0.0f };
+		b3BodyId bodyId = b3CreateBody( worldId, &bodyDef );
+
+		for ( int h = 0; h < s_metalWheel1HullCount; ++h )
+		{
+			b3CreateHullShape( bodyId, &shapeDef, hulls[h] );
+		}
+	}
+
+	for ( int h = 0; h < s_metalWheel1HullCount; ++h )
+	{
+		b3DestroyHull( hulls[h] );
+	}
+}
+
 struct
 {
 	b3MeshData* meshData;

shared/benchmarks.h

@@ -40,6 +40,7 @@ void StepLargeWorld( b3WorldId worldId, int stepCount );
 void GetWasherCapacity( b3Capacity* capacity );
 void CreateWasher( b3WorldId worldId );
 void CreateConvexPile( b3WorldId worldId );
+void CreateWheelStack( b3WorldId worldId );
 
 // void CreateSpinner( b3WorldId worldId );
 // float StepSpinner( b3WorldId worldId, int stepCount );