fix missing hit events

add test for null pair task
add manifold to contact begin events

Author: erincatto

include/box2d/box2d.h

@@ -156,6 +156,13 @@ B2_API void b2World_Explode( b2WorldId worldId, b2Vec2 position, float radius, f
 ///	@note Advanced feature
 B2_API void b2World_SetContactTuning( b2WorldId worldId, float hertz, float dampingRatio, float pushVelocity );
 
+/// Adjust joint tuning parameters
+///	@param worldId The world id
+/// @param hertz The contact stiffness (cycles per second)
+/// @param dampingRatio The contact bounciness with 1 being critical damping (non-dimensional)
+///	@note Advanced feature
+B2_API void b2World_SetJointTuning( b2WorldId worldId, float hertz, float dampingRatio );
+
 /// Enable/disable constraint warm starting. Advanced feature for testing. Disabling
 ///	sleeping greatly reduces stability and provides no performance gain.
 B2_API void b2World_EnableWarmStarting( b2WorldId worldId, bool flag );

include/box2d/collision.h

@@ -488,10 +488,11 @@ typedef struct b2ManifoldPoint
 	b2Vec2 point;
 
 	/// Location of the contact point relative to bodyA's origin in world space
-	///	@note When used internally to the Box2D solver, these are relative to the center of mass.
+	///	@note When used internally to the Box2D solver, this is relative to the center of mass.
 	b2Vec2 anchorA;
 
 	/// Location of the contact point relative to bodyB's origin in world space
+	///	@note When used internally to the Box2D solver, this is relative to the center of mass.
 	b2Vec2 anchorB;
 
 	/// The separation of the contact point, negative if penetrating
@@ -504,7 +505,7 @@ typedef struct b2ManifoldPoint
 	float tangentImpulse;
 
 	/// The maximum normal impulse applied during sub-stepping
-	///	todo not sure this is needed
+	///	This could be a bool to indicate the point is confirmed (may be a speculative point)
 	float maxNormalImpulse;
 
 	/// Relative normal velocity pre-solve. Used for hit events. If the normal impulse is

include/box2d/types.h

@@ -928,6 +928,9 @@ typedef struct b2ContactBeginTouchEvent
 
 	/// Id of the second shape
 	b2ShapeId shapeIdB;
+
+	/// The initial contact manifold
+	b2Manifold manifold;
 } b2ContactBeginTouchEvent;
 
 /// An end touch event is generated when two shapes stop touching.

samples/sample_continuous.cpp

@@ -11,14 +11,6 @@
 #include <GLFW/glfw3.h>
 #include <imgui.h>
 
-// This tests continuous collision robustness and also demonstrates the speed limits imposed
-// by b2_maxTranslation and b2_maxRotation.
-struct HitEvent
-{
-	b2Vec2 point;
-	float speed;
-	int stepIndex;
-};
 
 class BounceHouse : public Sample
 {
@@ -30,6 +22,13 @@ class BounceHouse : public Sample
 		e_boxShape
 	};
 
+	struct HitEvent
+	{
+		b2Vec2 point;
+		float speed;
+		int stepIndex;
+	};
+
 	explicit BounceHouse( Settings& settings )
 		: Sample( settings )
 	{
@@ -389,64 +388,8 @@ class SkinnyBox : public Sample
 
 static int sampleSkinnyBox = RegisterSample( "Continuous", "Skinny Box", SkinnyBox::Create );
 
-class SpeculativeBug : public Sample
-{
-public:
-	explicit SpeculativeBug( Settings& settings )
-		: Sample( settings )
-	{
-		if ( settings.restart == false )
-		{
-			g_camera.m_center = { 1.0f, 5.0f };
-			g_camera.m_zoom = 25.0f * 0.25f;
-		}
-
-		{
-			b2BodyDef bodyDef = b2DefaultBodyDef();
-			b2BodyId groundId = b2CreateBody( m_worldId, &bodyDef );
-
-			b2Segment segment = { { -10.0f, 0.0f }, { 10.0f, 0.0f } };
-			b2ShapeDef shapeDef = b2DefaultShapeDef();
-			b2CreateSegmentShape( groundId, &shapeDef, &segment );
-
-			shapeDef.friction = 0.0f;
-			b2Polygon box = b2MakeOffsetBox( 0.05f, 1.0f, { 0.0f, 1.0f }, b2Rot_identity );
-			b2CreatePolygonShape( groundId, &shapeDef, &box );
-		}
-
-		b2BodyDef bodyDef = b2DefaultBodyDef();
-		bodyDef.type = b2_dynamicBody;
-		for (int i = 0; i < 2; ++i)
-		{
-			if (i == 0)
-			{
-				bodyDef.position = { -0.8f, 0.25f };
-				bodyDef.isAwake = false;
-			}
-			else
-			{
-				bodyDef.position = { 0.8f, 2.0f };
-				bodyDef.isAwake = true;
-			}
-
-			b2BodyId bodyId = b2CreateBody( m_worldId, &bodyDef );
-
-			b2ShapeDef shapeDef = b2DefaultShapeDef();
-			b2Capsule capsule = { { -0.5f, 0.0f }, { 0.5f, 0.0f }, 0.25f };
-			b2CreateCapsuleShape( bodyId, &shapeDef, &capsule );
-		}
-	}
-
-	static Sample* Create( Settings& settings )
-	{
-		return new SpeculativeBug( settings );
-	}
-};
-
-static int sampleSpeculativeBug = RegisterSample( "Continuous", "Speculative Bug", SpeculativeBug::Create );
-
-// This sample shows ghost collisions
-class GhostCollision : public Sample
+// This sample shows ghost bumps
+class GhostBumps : public Sample
 {
 public:
 	enum ShapeType
@@ -456,7 +399,7 @@ class GhostCollision : public Sample
 		e_boxShape
 	};
 
-	explicit GhostCollision( Settings& settings )
+	explicit GhostBumps( Settings& settings )
 		: Sample( settings )
 	{
 		if ( settings.restart == false )
@@ -671,7 +614,7 @@ class GhostCollision : public Sample
 		ImGui::SetNextWindowPos( ImVec2( 10.0f, g_camera.m_height - height - 50.0f ), ImGuiCond_Once );
 		ImGui::SetNextWindowSize( ImVec2( 180.0f, height ) );
 
-		ImGui::Begin( "Ghost Collision", nullptr, ImGuiWindowFlags_NoResize );
+		ImGui::Begin( "Ghost Bumps", nullptr, ImGuiWindowFlags_NoResize );
 		ImGui::PushItemWidth( 100.0f );
 
 		if ( ImGui::Checkbox( "Chain", &m_useChain ) )
@@ -720,7 +663,7 @@ class GhostCollision : public Sample
 
 	static Sample* Create( Settings& settings )
 	{
-		return new GhostCollision( settings );
+		return new GhostBumps( settings );
 	}
 
 	b2BodyId m_groundId;
@@ -733,7 +676,7 @@ class GhostCollision : public Sample
 	bool m_useChain;
 };
 
-static int sampleGhostCollision = RegisterSample( "Continuous", "Ghost Collision", GhostCollision::Create );
+static int sampleGhostCollision = RegisterSample( "Continuous", "Ghost Collision", GhostBumps::Create );
 
 // Speculative collision failure case suggested by Dirk Gregorius. This uses
 // a simple fallback scheme to prevent tunneling.
@@ -786,6 +729,55 @@ class SpeculativeFallback : public Sample
 
 static int sampleSpeculativeFallback = RegisterSample( "Continuous", "Speculative Fallback", SpeculativeFallback::Create );
 
+// This shows that while Box2D uses speculative collision, it does not lead to speculative ghost collisions at small distances
+class SpeculativeGhost : public Sample
+{
+public:
+	explicit SpeculativeGhost( Settings& settings )
+		: Sample( settings )
+	{
+		if ( settings.restart == false )
+		{
+			g_camera.m_center = { 0.0f, 1.75f };
+			g_camera.m_zoom = 2.0f;
+		}
+
+		{
+			b2BodyDef bodyDef = b2DefaultBodyDef();
+			b2BodyId groundId = b2CreateBody( m_worldId, &bodyDef );
+
+			b2ShapeDef shapeDef = b2DefaultShapeDef();
+			b2Segment segment = { { -10.0f, 0.0f }, { 10.0f, 0.0f } };
+			b2CreateSegmentShape( groundId, &shapeDef, &segment );
+
+			b2Polygon box = b2MakeOffsetBox( 1.0f, 0.1f, { 0.0f, 0.9f }, b2Rot_identity );
+			b2CreatePolygonShape( groundId, &shapeDef, &box );
+		}
+
+		{
+			b2BodyDef bodyDef = b2DefaultBodyDef();
+			bodyDef.type = b2_dynamicBody;
+
+			// The speculative distance is 0.02 meters, so this avoid it
+			bodyDef.position = { 0.015f, 2.515f };
+			bodyDef.linearVelocity = { 0.1f * 1.25f * settings.hertz, -0.1f * 1.25f * settings.hertz };
+			bodyDef.gravityScale = 0.0f;
+			b2BodyId bodyId = b2CreateBody( m_worldId, &bodyDef );
+
+			b2ShapeDef shapeDef = b2DefaultShapeDef();
+			b2Polygon box = b2MakeSquare( 0.25f );
+			b2CreatePolygonShape( bodyId, &shapeDef, &box );
+		}
+	}
+
+	static Sample* Create( Settings& settings )
+	{
+		return new SpeculativeGhost( settings );
+	}
+};
+
+static int sampleSpeculativeGhost = RegisterSample( "Continuous", "Speculative Ghost", SpeculativeGhost::Create );
+
 // This shows a fast moving body that uses continuous collision versus static and dynamic bodies.
 // This is achieved by setting the ball body as a *bullet*.
 class Pinball : public Sample

samples/sample_stacking.cpp

@@ -383,10 +383,16 @@ class VerticalStack : public Sample
 
 static int sampleVerticalStack = RegisterSample( "Stacking", "Vertical Stack", VerticalStack::Create );
 
-// This shows how to handle high gravity and small shapes using a small time step
+// A simple circle stack that also shows how to collect hit events
 class CircleStack : public Sample
 {
 public:
+
+	struct Event
+	{
+		int indexA, indexB;
+	};
+
 	explicit CircleStack( Settings& settings )
 		: Sample( settings )
 	{
@@ -396,11 +402,16 @@ class CircleStack : public Sample
 			g_camera.m_zoom = 6.0f;
 		}
 
+		int shapeIndex = 0;
+
 		{
 			b2BodyDef bodyDef = b2DefaultBodyDef();
 			b2BodyId groundId = b2CreateBody( m_worldId, &bodyDef );
 
 			b2ShapeDef shapeDef = b2DefaultShapeDef();
+			shapeDef.userData = reinterpret_cast<void*>( intptr_t( shapeIndex ) );
+			shapeIndex += 1;
+
 			b2Segment segment = { { -10.0f, 0.0f }, { 10.0f, 0.0f } };
 			b2CreateSegmentShape( groundId, &shapeDef, &segment );
 		}
@@ -409,9 +420,11 @@ class CircleStack : public Sample
 		b2World_SetContactTuning( m_worldId, 0.25f * 360.0f, 10.0f, 3.0f );
 
 		b2Circle circle = {};
-		circle.radius = 0.5f;
+		circle.radius = 0.25f;
 
 		b2ShapeDef shapeDef = b2DefaultShapeDef();
+		shapeDef.enableHitEvents = true;
+
 		b2BodyDef bodyDef = b2DefaultBodyDef();
 		bodyDef.type = b2_dynamicBody;
 
@@ -422,16 +435,48 @@ class CircleStack : public Sample
 			bodyDef.position.y = y;
 
 			b2BodyId bodyId = b2CreateBody( m_worldId, &bodyDef );
+
+			shapeDef.userData = reinterpret_cast<void*>( intptr_t( shapeIndex ) );
+			shapeIndex += 1;
 			b2CreateCircleShape( bodyId, &shapeDef, &circle );
 
-			y += 1.0f;
+			y += 2.0f;
+		}
+	}
+
+	void Step( Settings& settings ) override
+	{
+		Sample::Step( settings );
+
+		b2ContactEvents events = b2World_GetContactEvents( m_worldId );
+		for ( int i = 0; i < events.hitCount; ++i )
+		{
+			b2ContactHitEvent* event = events.hitEvents + i;
+
+			void* userDataA = b2Shape_GetUserData( event->shapeIdA );
+			void* userDataB = b2Shape_GetUserData( event->shapeIdB );
+			int indexA = static_cast<int>( reinterpret_cast<intptr_t>( userDataA ) );
+			int indexB = static_cast<int>( reinterpret_cast<intptr_t>( userDataB ) );
+
+			g_draw.DrawPoint( event->point, 10.0f, b2_colorWhite );
+
+			m_events.push_back( { indexA, indexB } );
+		}
+
+		int eventCount = m_events.size();
+		for (int i = 0; i < eventCount; ++i)
+		{
+			g_draw.DrawString( 5, m_textLine, "%d, %d", m_events[i].indexA, m_events[i].indexB );
+			m_textLine += m_textIncrement;
 		}
 	}
 
 	static Sample* Create( Settings& settings )
 	{
 		return new CircleStack( settings );
 	}
+
+	std::vector<Event> m_events;
 };
 
 static int sampleCircleStack = RegisterSample( "Stacking", "Circle Stack", CircleStack::Create );

src/broad_phase.c

@@ -360,8 +360,11 @@ void b2UpdateBroadPhasePairs( b2World* world )
 
 	int minRange = 64;
 	void* userPairTask = world->enqueueTaskFcn( &b2FindPairsTask, moveCount, minRange, world, world->userTaskContext );
-	world->finishTaskFcn( userPairTask, world->userTaskContext );
-	world->taskCount += 1;
+	if (userPairTask != NULL)
+	{
+		world->finishTaskFcn( userPairTask, world->userTaskContext );
+		world->taskCount += 1;
+	}
 
 	b2TracyCZoneNC( create_contacts, "Create Contacts", b2_colorGold, true );
 

src/core.h

@@ -139,7 +139,7 @@ extern float b2_lengthUnitsPerMeter;
 #define b2_maxWorkers 64
 
 // Maximum number of colors in the constraint graph. Constraints that cannot
-//	find a color are added to the overflow set which are solved single-threaded.
+// find a color are added to the overflow set which are solved single-threaded.
 #define b2_graphColorCount 12
 
 // A small length used as a collision and constraint tolerance. Usually it is

src/solver.c

@@ -1721,7 +1721,9 @@ void b2Solve( b2World* world, b2StepContext* stepContext )
 				{
 					b2ManifoldPoint* mp = contactSim->manifold.points + k;
 					float approachSpeed = -mp->normalVelocity;
-					if ( approachSpeed > event.approachSpeed && mp->normalImpulse > 0.0f )
+
+					// Need to check max impulse because the point may be speculative and not colliding
+					if ( approachSpeed > event.approachSpeed && mp->maxNormalImpulse > 0.0f )
 					{
 						event.approachSpeed = approachSpeed;
 						event.point = mp->point;