Event bookend (#837)

Sensor and contact end touch events are now generated whenever a contact is destroyed via user operations, such as: - destroying a body or shape - changing filters - changing body type - disabling a body - connecting bodies via joints Enable hot reloading on MSVC.
erincatto · Nov 10, 2024 · 90c2781 · 90c2781
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commit 90c2781
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diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -35,6 +35,12 @@ if (MSVC OR APPLE)
 			add_compile_options(-fsanitize=address -fsanitize-address-use-after-scope -fsanitize=undefined)
 			add_link_options(-fsanitize=address -fsanitize-address-use-after-scope -fsanitize=undefined)
 		endif()
+	else()
+		if(MSVC)
+			# enable hot reloading
+			add_compile_options("$<$<CONFIG:Debug>:/ZI>")
+			add_link_options("$<$<CONFIG:Debug>:/INCREMENTAL>")
+		endif()
 	endif()
 endif()
 

diff --git a/docs/overview.md b/docs/overview.md
@@ -123,6 +123,7 @@ of the time step:
 
 - body movement events
 - contact begin and end events
+- sensor begin and end events
 - contact hit events
 
 These events allow your application to react to changes in the simulation.

diff --git a/docs/simulation.md b/docs/simulation.md
@@ -1009,21 +1009,34 @@ for (int i = 0; i < sensorEvents.beginCount; ++i)
 }
 ```
 
-And there are events when a shape stops overlapping with a sensor.
+And there are events when a shape stops overlapping with a sensor. Be careful with end
+touch events because they may be generated when shapes are destroyed. Test the shape
+ids with `b2Shape_IsValid`.
 
 ```c
 for (int i = 0; i < sensorEvents.endCount; ++i)
 {
     b2SensorEndTouchEvent* endTouch = sensorEvents.endEvents + i;
-    void* myUserData = b2Shape_GetUserData(endTouch->visitorShapeId);
-    // process end event
+    if (b2Shape_IsValid(endTouch->visitorShapeId))
+    {
+        void* myUserData = b2Shape_GetUserData(endTouch->visitorShapeId);
+        // process end event
+    }
 }
 ```
 
-You will not get end events if a shape is destroyed. Sensor events should
-be processed after the world step and before other game logic. This should
+Sensor events should be processed after the world step and before other game logic. This should
 help you avoid processing stale data.
 
+There are several user operations that can cause sensors to stop touching. Such operations
+include:
+- destroying a body or shape
+- changing the filter on a shape
+- disabling a body
+- setting the body transform
+These may generate end-touch events and these events are included with simulation events available
+after the next call to `b2World_Step`. 
+
 Sensor events are only enabled for a non-sensor shape if `b2ShapeDef::enableSensorEvents`
 is true.
 
@@ -1065,11 +1078,17 @@ contain the two shape ids.
 for (int i = 0; i < contactEvents.endCount; ++i)
 {
     b2ContactEndTouchEvent* endEvent = contactEvents.endEvents + i;
-    ShapesStopTouching(endEvent->shapeIdA, endEvent->shapeIdB);
+
+    // Use b2Shape_IsValid because a shape may have been destroyed
+    if (b2Shape_IsValid(endEvent->shapeIdA) && b2Shape_IsValid(endEvent->shapeIdB))
+    {
+        ShapesStopTouching(endEvent->shapeIdA, endEvent->shapeIdB);
+    }
 }
 ```
 
-The end touch events are not generated when you destroy a shape or the body that owns it.
+Similar to `b2SensorEndTouchEvent`, `b2ContactEndTouchEvent` may be generated due to a user operation,
+such as destroying a body or shape. These events are included with simulation events after the next `b2World_Step`.
 
 Shapes only generate begin and end touch events if `b2ShapeDef::enableContactEvents` is true.
 

diff --git a/include/box2d/types.h b/include/box2d/types.h
@@ -969,16 +969,21 @@ typedef struct b2SensorBeginTouchEvent
 } b2SensorBeginTouchEvent;
 
 /// An end touch event is generated when a shape stops overlapping a sensor shape.
-///	You will not get an end event if you do anything that destroys contacts outside
-///	of the world step. These include things like setting the transform, destroying a body
+///	You will get an end event if you do anything that destroys contacts previous to the last
+///	world step.  These include things like setting the transform, destroying a body
 ///	or shape, or changing a filter or body type.
 typedef struct b2SensorEndTouchEvent
 {
 	/// The id of the sensor shape
+	///	@warning this shape may have been destroyed
+	///	@see b2Shape_IsValid
 	b2ShapeId sensorShapeId;
 
 	/// The id of the dynamic shape that stopped touching the sensor shape
+	///	@warning this shape may have been destroyed
+	///	@see b2Shape_IsValid
 	b2ShapeId visitorShapeId;
+
 } b2SensorEndTouchEvent;
 
 /// Sensor events are buffered in the Box2D world and are available
@@ -1013,15 +1018,19 @@ typedef struct b2ContactBeginTouchEvent
 } b2ContactBeginTouchEvent;
 
 /// An end touch event is generated when two shapes stop touching.
-///	You will not get an end event if you do anything that destroys contacts outside
-///	of the world step. These include things like setting the transform, destroying a body
+///	You will get an end event if you do anything that destroys contacts previous to the last
+///	world step. These include things like setting the transform, destroying a body
 ///	or shape, or changing a filter or body type.
 typedef struct b2ContactEndTouchEvent
 {
 	/// Id of the first shape
+	///	@warning this shape may have been destroyed
+	///	@see b2Shape_IsValid
 	b2ShapeId shapeIdA;
 
 	/// Id of the second shape
+	///	@warning this shape may have been destroyed
+	///	@see b2Shape_IsValid
 	b2ShapeId shapeIdB;
 } b2ContactEndTouchEvent;
 

diff --git a/samples/sample_events.cpp b/samples/sample_events.cpp
@@ -14,7 +14,7 @@
 #include <imgui.h>
 #include <vector>
 
-class SensorEvent : public Sample
+class SensorFunnel : public Sample
 {
 public:
 	enum
@@ -24,7 +24,7 @@ class SensorEvent : public Sample
 		e_count = 32
 	};
 
-	explicit SensorEvent( Settings& settings )
+	explicit SensorFunnel( Settings& settings )
 		: Sample( settings )
 	{
 		if ( settings.restart == false )
@@ -56,7 +56,7 @@ class SensorEvent : public Sample
 				{ -8.26825142, 11.906374 },	 { -16.8672504, 17.1978741 },
 			};
 
-			int count = sizeof( points ) / sizeof( points[0] );
+			int count = std::size( points );
 
 			// float scale = 0.25f;
 			// b2Vec2 lower = {FLT_MAX, FLT_MAX};
@@ -101,7 +101,6 @@ class SensorEvent : public Sample
 			float y = 14.0f;
 			for ( int i = 0; i < 3; ++i )
 			{
-				b2BodyDef bodyDef = b2DefaultBodyDef();
 				bodyDef.position = { 0.0f, y };
 				bodyDef.type = b2_dynamicBody;
 
@@ -317,7 +316,7 @@ class SensorEvent : public Sample
 
 	static Sample* Create( Settings& settings )
 	{
-		return new SensorEvent( settings );
+		return new SensorFunnel( settings );
 	}
 
 	Human m_humans[e_count];
@@ -328,7 +327,161 @@ class SensorEvent : public Sample
 	float m_side;
 };
 
-static int sampleSensorEvent = RegisterSample( "Events", "Sensor", SensorEvent::Create );
+static int sampleSensorBeginEvent = RegisterSample( "Events", "Sensor Funnel", SensorFunnel::Create );
+
+class SensorBookend : public Sample
+{
+public:
+	explicit SensorBookend( Settings& settings )
+		: Sample( settings )
+	{
+		if ( settings.restart == false )
+		{
+			g_camera.m_center = { 0.0f, 6.0f };
+			g_camera.m_zoom = 7.5f;
+		}
+
+		{
+			b2BodyDef bodyDef = b2DefaultBodyDef();
+			b2BodyId groundId = b2CreateBody( m_worldId, &bodyDef );
+			b2ShapeDef shapeDef = b2DefaultShapeDef();
+
+			b2Segment groundSegment = { { -10.0f, 0.0f }, { 10.0f, 0.0f } };
+			b2CreateSegmentShape( groundId, &shapeDef, &groundSegment );
+
+			groundSegment = { { -10.0f, 0.0f }, { -10.0f, 10.0f } };
+			b2CreateSegmentShape( groundId, &shapeDef, &groundSegment );
+
+			groundSegment = { { 10.0f, 0.0f }, { 10.0f, 10.0f } };
+			b2CreateSegmentShape( groundId, &shapeDef, &groundSegment );
+
+			m_isVisiting = false;
+		}
+
+		CreateSensor();
+
+		CreateVisitor();
+	}
+
+	void CreateSensor()
+	{
+		b2BodyDef bodyDef = b2DefaultBodyDef();
+
+		bodyDef.position = { 0.0f, 1.0f };
+		m_sensorBodyId = b2CreateBody( m_worldId, &bodyDef );
+
+		b2ShapeDef shapeDef = b2DefaultShapeDef();
+		shapeDef.isSensor = true;
+		b2Polygon box = b2MakeSquare( 1.0f );
+		m_sensorShapeId = b2CreatePolygonShape( m_sensorBodyId, &shapeDef, &box );
+	}
+
+	void CreateVisitor()
+	{
+		b2BodyDef bodyDef = b2DefaultBodyDef();
+		bodyDef.position = { -4.0f, 1.0f };
+		bodyDef.type = b2_dynamicBody;
+
+		m_visitorBodyId = b2CreateBody( m_worldId, &bodyDef );
+
+		b2ShapeDef shapeDef = b2DefaultShapeDef();
+		shapeDef.enableSensorEvents = true;
+
+		b2Circle circle = { { 0.0f, 0.0f }, 0.5f };
+		m_visitorShapeId = b2CreateCircleShape( m_visitorBodyId, &shapeDef, &circle );
+	}
+
+	void UpdateUI() override
+	{
+		float height = 90.0f;
+		ImGui::SetNextWindowPos( ImVec2( 10.0f, g_camera.m_height - height - 50.0f ), ImGuiCond_Once );
+		ImGui::SetNextWindowSize( ImVec2( 140.0f, height ) );
+
+		ImGui::Begin( "Sensor Bookend", nullptr, ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoResize );
+
+		if ( B2_IS_NULL( m_visitorBodyId ) )
+		{
+			if ( ImGui::Button( "create visitor" ) )
+			{
+				CreateVisitor();
+			}
+		}
+		else
+		{
+			if ( ImGui::Button( "destroy visitor" ) )
+			{
+				b2DestroyBody( m_visitorBodyId );
+				m_visitorBodyId = b2_nullBodyId;
+				m_visitorShapeId = b2_nullShapeId;
+			}
+		}
+
+		if ( B2_IS_NULL( m_sensorBodyId ) )
+		{
+			if ( ImGui::Button( "create sensor" ) )
+			{
+				CreateSensor();
+			}
+		}
+		else
+		{
+			if ( ImGui::Button( "destroy sensor" ) )
+			{
+				b2DestroyBody( m_sensorBodyId );
+				m_sensorBodyId = b2_nullBodyId;
+				m_sensorShapeId = b2_nullShapeId;
+			}
+		}
+
+		ImGui::End();
+	}
+
+	void Step( Settings& settings ) override
+	{
+		Sample::Step( settings );
+
+		b2SensorEvents sensorEvents = b2World_GetSensorEvents( m_worldId );
+		for ( int i = 0; i < sensorEvents.beginCount; ++i )
+		{
+			b2SensorBeginTouchEvent event = sensorEvents.beginEvents[i];
+
+			if ( B2_ID_EQUALS( event.visitorShapeId, m_visitorShapeId ) )
+			{
+				assert( m_isVisiting == false );
+				m_isVisiting = true;
+			}
+		}
+
+		for ( int i = 0; i < sensorEvents.endCount; ++i )
+		{
+			b2SensorEndTouchEvent event = sensorEvents.endEvents[i];
+
+			bool wasVisitorDestroyed = b2Shape_IsValid( event.visitorShapeId ) == false;
+			if ( B2_ID_EQUALS( event.visitorShapeId, m_visitorShapeId ) || wasVisitorDestroyed )
+			{
+				assert( m_isVisiting == true );
+				m_isVisiting = false;
+			}
+		}
+
+		g_draw.DrawString( 5, m_textLine, "visiting == %s", m_isVisiting ? "true" : "false" );
+		m_textLine += m_textIncrement;
+	}
+
+	static Sample* Create( Settings& settings )
+	{
+		return new SensorBookend( settings );
+	}
+
+	b2BodyId m_sensorBodyId;
+	b2ShapeId m_sensorShapeId;
+
+	b2BodyId m_visitorBodyId;
+	b2ShapeId m_visitorShapeId;
+	bool m_isVisiting;
+};
+
+static int sampleSensorBookendEvent = RegisterSample( "Events", "Sensor Bookend", SensorBookend::Create );
 
 struct BodyUserData
 {
@@ -927,7 +1080,8 @@ class Platformer : public Sample
 
 		b2ContactData contactData = {};
 		int contactCount = b2Body_GetContactData( m_platformId, &contactData, 1 );
-		g_draw.DrawString( 5, m_textLine, "Platform contact count = %d, point count = %d", contactCount, contactData.manifold.pointCount );
+		g_draw.DrawString( 5, m_textLine, "Platform contact count = %d, point count = %d", contactCount,
+						   contactData.manifold.pointCount );
 		m_textLine += m_textIncrement;
 
 		g_draw.DrawString( 5, m_textLine, "Movement: A/D/Space" );