adjusted allowed clip fraction usage

samples/sample_continuous.cpp

@@ -226,6 +226,7 @@ class ChainDrop : public Sample
 		m_bodyId = b2_nullBodyId;
 		m_yOffset = -0.1f;
 		m_speed = -42.0f;
+		m_clipFraction = 0.1f;
 
 		Launch();
 	}
@@ -241,24 +242,38 @@ class ChainDrop : public Sample
 		bodyDef.type = b2_dynamicBody;
 		bodyDef.linearVelocity = { 0.0f, m_speed };
 		bodyDef.position = { 0.0f, 10.0f + m_yOffset };
-		bodyDef.gravityScale = 1.0f;
+		bodyDef.rotation = b2MakeRot( 0.5f * B2_PI );
+		bodyDef.fixedRotation = true;
 		m_bodyId = b2CreateBody( m_worldId, &bodyDef );
 
 		b2ShapeDef shapeDef = b2DefaultShapeDef();
-		b2Circle circle = { { 0.0f, 0.0f }, 0.5f };
-		b2CreateCircleShape( m_bodyId, &shapeDef, &circle );
+		shapeDef.allowedClipFraction = m_clipFraction;
+
+		//b2Circle circle = { { 0.0f, 0.0f }, 0.5f };
+		//m_shapeId = b2CreateCircleShape( m_bodyId, &shapeDef, &circle );
+
+		//b2Capsule capsule = { { -0.5f, 0.0f }, { 0.5f, 0.0 }, 0.25f };
+		//m_shapeId = b2CreateCapsuleShape( m_bodyId, &shapeDef, &capsule );
+
+		float h = 0.5f;
+		b2Polygon box = b2MakeBox( h, h );
+		m_shapeId = b2CreatePolygonShape( m_bodyId, &shapeDef, &box );
 	}
 
 	void UpdateUI() override
 	{
-		float height = 120.0f;
+		float height = 140.0f;
 		ImGui::SetNextWindowPos( ImVec2( 10.0f, g_camera.m_height - height - 50.0f ), ImGuiCond_Once );
 		ImGui::SetNextWindowSize( ImVec2( 240.0f, height ) );
 
 		ImGui::Begin( "Chain Drop", nullptr, ImGuiWindowFlags_NoResize );
 
 		ImGui::SliderFloat( "Speed", &m_speed, -100.0f, 0.0f, "%.0f" );
 		ImGui::SliderFloat( "Y Offset", &m_yOffset, -1.0f, 1.0f, "%.1f" );
+		if (ImGui::SliderFloat( "Clip Fraction", &m_clipFraction, 0.0f, 1.0f, "%.1f" ))
+		{
+			b2Shape_SetAllowedClipFraction( m_shapeId, m_clipFraction );
+		}
 
 		if ( ImGui::Button( "Launch" ) )
 		{
@@ -274,8 +289,10 @@ class ChainDrop : public Sample
 	}
 
 	b2BodyId m_bodyId;
+	b2ShapeId m_shapeId;
 	float m_yOffset;
 	float m_speed;
+	float m_clipFraction;
 };
 
 static int sampleChainDrop = RegisterSample( "Continuous", "Chain Drop", ChainDrop::Create );

src/shape.h

@@ -15,6 +15,7 @@ typedef struct b2Shape
 	int bodyId;
 	int prevShapeId;
 	int nextShapeId;
+	int sensorIndex;
 	b2ShapeType type;
 	float density;
 	float friction;
@@ -66,6 +67,18 @@ typedef struct b2ShapeExtent
 	float maxExtent;
 } b2ShapeExtent;
 
+// Sensors are shapes that live in the broad-phase but never have contacts.
+// At the end of the time step all sensors are queried for overlap with any other shapes.
+// Sensors ignore body type and sleeping.
+// Sensors generate events when there is a new overlap or and overlap disappears.
+// The sensor overlaps don't get cleared until the next time step regardless of the overlapped
+// shapes being destroyed.
+// When a sensor is destroyed.
+typedef struct 
+{
+	b2IntArray overlaps;
+} b2SensorOverlaps;
+
 void b2CreateShapeProxy( b2Shape* shape, b2BroadPhase* bp, b2BodyType type, b2Transform transform, bool forcePairCreation );
 void b2DestroyShapeProxy( b2Shape* shape, b2BroadPhase* bp );
 

src/solver.c

@@ -289,7 +289,7 @@ static bool b2ContinuousQueryCallback( int proxyId, int shapeId, void* context )
 			b2Vec2 c2 = continuousContext->centroid2;
 			float offset2 = b2Cross( b2Sub( c2, p1 ), e );
 
-			if ( offset1 < 0.0f || offset2 > (1.0f - fastShape->allowedClipFraction) * fastBodySim->minExtent )
+			if ( offset1 < 0.0f || offset1 - offset2 < fastShape->allowedClipFraction * fastBodySim->minExtent )
 			{
 				// Minimal clipping
 				return true;

src/world.h

@@ -92,6 +92,9 @@ typedef struct b2World
 	b2ShapeArray shapes;
 	b2ChainShapeArray chainShapes;
 
+	// Array of all sensor shape indices
+	b2IntArray sensors;
+
 	// Per thread storage
 	b2TaskContextArray taskContexts;