Atomics and Materials (#873)

- shape material
- friction and restitution callbacks from narrow phase
- platform atomic wrappers
- removed experimental:c11atomics flag

#812 #872

CMakeLists.txt

@@ -47,6 +47,7 @@ endif()
 
 # Deterministic math
 # https://box2d.org/posts/2024/08/determinism/
+# todo make this apply to ClangCL
 if (MINGW OR APPLE OR UNIX)
 	add_compile_options(-ffp-contract=off)
 endif()
@@ -100,7 +101,6 @@ if(PROJECT_IS_TOP_LEVEL)
 
 	# enkiTS is used by all the test apps, but not directly by the Box2D library
 	if(BOX2D_UNIT_TESTS OR BOX2D_SAMPLES OR BOX2D_BENCHMARKS)
-		SET(ENKITS_BUILD_EXAMPLES OFF CACHE BOOL "Build enkiTS examples")
 
 		# Emscripten pthread support for enkiTS
 		if(EMSCRIPTEN)
@@ -111,7 +111,8 @@ if(PROJECT_IS_TOP_LEVEL)
 			string(APPEND CMAKE_EXE_LINKER_FLAGS " ${EMSCRIPTEN_PTHREADS_LINKER_FLAGS}")
 		endif()
 
-		# Used in tests and samples
+		# Task system used in tests and samples
+		set(ENKITS_BUILD_EXAMPLES OFF CACHE BOOL "Build enkiTS examples")
 		FetchContent_Declare(
 			enkits
 			GIT_REPOSITORY https://github.com/dougbinks/enkiTS.git

benchmark/CMakeLists.txt

@@ -7,10 +7,6 @@ add_executable(benchmark ${BOX2D_BENCHMARK_FILES})
 
 set_target_properties(benchmark PROPERTIES C_STANDARD 17)
 
-if (MSVC AND CMAKE_C_COMPILER_ID MATCHES "MSVC")
-	target_compile_options(benchmark PRIVATE /experimental:c11atomics)
-endif()
-
 target_link_libraries(benchmark PRIVATE box2d shared enkiTS)
 
 source_group(TREE ${CMAKE_CURRENT_SOURCE_DIR} PREFIX "" FILES ${BOX2D_BENCHMARK_FILES})

benchmark/amd7950x_avx2/joint_grid.csv

@@ -1,9 +1,9 @@
-threads,fps
-1,197.415
-2,338.192
-3,485.363
-4,590.58
-5,678.894
-6,755.337
-7,830.03
-8,889.992
+threads,ms
+1,2565.3
+2,1533.85
+3,1053.01
+4,865.702
+5,748.989
+6,658.623
+7,613.633
+8,578.973

benchmark/amd7950x_avx2/large_pyramid.csv

@@ -1,9 +1,9 @@
-threads,fps
-1,337.398
-2,599.766
-3,853.652
-4,1095.24
-5,1288.22
-6,1467.1
-7,1669.81
-8,1704.72
+threads,ms
+1,1584.03
+2,841.862
+3,598.747
+4,471.697
+5,396.306
+6,347.983
+7,309.086
+8,308.832

benchmark/amd7950x_avx2/many_pyramids.csv

@@ -1,9 +1,9 @@
-threads,fps
-1,82.5412
-2,156.573
-3,233.64
-4,294.31
-5,357.121
-6,420.298
-7,487.163
-8,537.355
+threads,ms
+1,2663.34
+2,1407.85
+3,934.506
+4,725.271
+5,590.288
+6,502.513
+7,422.693
+8,395.369

benchmark/amd7950x_avx2/rain.csv

@@ -1,9 +1,9 @@
-threads,fps
-1,158.379
-2,253.381
-3,337.197
-4,408.427
-5,475.14
-6,530.178
-7,583.798
-8,633.102
+threads,ms
+1,6526.9
+2,4017.74
+3,3052.28
+4,2493.5
+5,2149.12
+6,1911.45
+7,1735.97
+8,1625.71

benchmark/amd7950x_avx2/smash.csv

@@ -1,9 +1,9 @@
-threads,fps
-1,194.531
-2,299.76
-3,389.501
-4,469.022
-5,532.045
-6,580.977
-7,620.559
-8,655.217
+threads,ms
+1,1562.06
+2,1020.55
+3,781.193
+4,661.318
+5,580.115
+6,530.502
+7,489.672
+8,467.998

benchmark/amd7950x_avx2/spinner.csv

@@ -1,9 +1,9 @@
-threads,fps
-1,342.697
-2,549.335
-3,711.477
-4,889.473
-5,1011.82
-6,1141.73
-7,1261.39
-8,1338.51
+threads,ms
+1,4106.89
+2,2635.21
+3,1986.32
+4,1614.21
+5,1420.63
+6,1272.06
+7,1157.16
+8,1091.25

benchmark/amd7950x_avx2/tumbler.csv

@@ -1,9 +1,9 @@
-threads,fps
-1,461.248
-2,726.229
-3,947.347
-4,1152.31
-5,1335.66
-6,1483.59
-7,1613.59
-8,1715.86
+threads,ms
+1,1613.69
+2,1061.88
+3,810.738
+4,670.874
+5,578.959
+6,519.473
+7,479.842
+8,437.851

benchmark/main.c

@@ -394,7 +394,7 @@ int main( int argc, char** argv )
 			continue;
 		}
 
-		fprintf( file, "threads, ms\n" );
+		fprintf( file, "threads,ms\n" );
 		for ( int threadIndex = 1; threadIndex <= maxThreadCount; ++threadIndex )
 		{
 			fprintf( file, "%d,%g\n", threadIndex, minTime[threadIndex - 1] );

include/box2d/box2d.h

@@ -198,6 +198,12 @@ B2_API void b2World_SetUserData( b2WorldId worldId, void* userData );
 /// Get the user data pointer.
 B2_API void* b2World_GetUserData( b2WorldId worldId );
 
+/// Set the friction callback. Passing NULL resets to default.
+B2_API void b2World_SetFrictionCallback( b2WorldId worldId, b2FrictionCallback* callback );
+
+/// Set the restitution callback. Passing NULL resets to default.
+B2_API void b2World_SetRestitutionCallback( b2WorldId worldId, b2RestitutionCallback* callback );
+
 /// Dump memory stats to box2d_memory.txt
 B2_API void b2World_DumpMemoryStats( b2WorldId worldId );
 
@@ -552,6 +558,13 @@ B2_API void b2Shape_SetRestitution( b2ShapeId shapeId, float restitution );
 /// Get the shape restitution
 B2_API float b2Shape_GetRestitution( b2ShapeId shapeId );
 
+/// Set the shape material identifier
+/// @see b2ShapeDef::material
+B2_API void b2Shape_SetMaterial( b2ShapeId shapeId, int material );
+
+/// Get the shape material identifier 
+B2_API int b2Shape_GetMaterial( b2ShapeId shapeId );
+
 /// Get the shape filter
 B2_API b2Filter b2Shape_GetFilter( b2ShapeId shapeId );
 

include/box2d/types.h

@@ -49,6 +49,16 @@ typedef void* b2EnqueueTaskCallback( b2TaskCallback* task, int itemCount, int mi
 /// @ingroup world
 typedef void b2FinishTaskCallback( void* userTask, void* userContext );
 
+/// Optional friction mixing callback. This intentionally provides no context objects because this is called
+/// from a worker thread.
+/// @warning This function should not attempt to modify Box2D state or user application state.
+typedef float b2FrictionCallback( float frictionA, int materialA, float frictionB, int materialB );
+
+/// Optional restitution mixing callback. This intentionally provides no context objects because this is called
+/// from a worker thread.
+/// @warning This function should not attempt to modify Box2D state or user application state.
+typedef float b2RestitutionCallback( float restitutionA, int materialA, float restitutionB, int materialB );
+
 /// Result from b2World_RayCastClosest
 /// @ingroup world
 typedef struct b2RayResult
@@ -62,16 +72,6 @@ typedef struct b2RayResult
 	bool hit;
 } b2RayResult;
 
-/// Mixing rules for friction and restitution
-typedef enum b2MixingRule
-{
-	b2_mixAverage,
-	b2_mixGeometricMean,
-	b2_mixMultiply,
-	b2_mixMinimum,
-	b2_mixMaximum
-} b2MixingRule;
-
 /// World definition used to create a simulation world.
 /// Must be initialized using b2DefaultWorldDef().
 /// @ingroup world
@@ -108,11 +108,11 @@ typedef struct b2WorldDef
 	/// Maximum linear speed. Usually meters per second.
 	float maximumLinearSpeed;
 
-	/// Mixing rule for friction. Default is b2_mixGeometricMean.
-	b2MixingRule frictionMixingRule;
+	/// Optional mixing callback for friction. The default uses sqrt(frictionA * frictionB).
+	b2FrictionCallback* frictionCallback;
 
-	/// Mixing rule for restitution. Default is b2_mixMaximum.
-	b2MixingRule restitutionMixingRule;
+	/// Optional mixing callback for restitution. The default uses max(restitutionA, restitutionB).
+	b2RestitutionCallback* restitutionCallback;
 
 	/// Can bodies go to sleep to improve performance
 	bool enableSleep;
@@ -341,12 +341,18 @@ typedef struct b2ShapeDef
 	/// The Coulomb (dry) friction coefficient, usually in the range [0,1].
 	float friction;
 
-	/// The restitution (bounce) usually in the range [0,1].
+	/// The coefficient of restitution (bounce) usually in the range [0,1].
+	/// https://en.wikipedia.org/wiki/Coefficient_of_restitution
 	float restitution;
 
 	/// The rolling resistance usually in the range [0,1].
+	/// todo
 	float rollingResistance;
 
+	/// User material identifier. This is passed with query results and to friction and restitution
+	/// combining functions. It is not used internally.
+	int material;
+
 	/// The density, usually in kg/m^2.
 	float density;
 

samples/sample.cpp

@@ -108,8 +108,6 @@ Sample::Sample( Settings& settings )
 	worldDef.userTaskContext = this;
 	worldDef.enableSleep = settings.enableSleep;
 
-	worldDef.restitutionMixingRule = b2_mixMaximum;
-
 	m_worldId = b2CreateWorld( &worldDef );
 	m_textLine = 30;
 	m_textIncrement = 22;
@@ -345,6 +343,7 @@ void Sample::Step( Settings& settings )
 		char buffer[256] = { 0 };
 		static_assert( std::size( s.colorCounts ) == 12 );
 
+		// todo fix this
 		int offset = snprintf( buffer, 256, "colors: " );
 		for ( int i = 0; i < 12; ++i )
 		{

samples/sample_bodies.cpp

@@ -468,6 +468,16 @@ class Character : public Sample
 
 static int sampleCharacter = RegisterSample( "Bodies", "Character", Character::Create );
 
+float FrictionCallback( float, int, float, int )
+{
+	return 0.1f;
+}
+
+float RestitutionCallback( float, int, float, int )
+{
+	return 1.0f;
+}
+
 class Weeble : public Sample
 {
 public:
@@ -480,6 +490,10 @@ class Weeble : public Sample
 			g_camera.m_zoom = 25.0f * 0.5f;
 		}
 
+		// Test friction and restitution callbacks
+		b2World_SetFrictionCallback( m_worldId, FrictionCallback );
+		b2World_SetRestitutionCallback( m_worldId, RestitutionCallback );
+
 		b2BodyId groundId = b2_nullBodyId;
 		{
 			b2BodyDef bodyDef = b2DefaultBodyDef();
@@ -892,7 +906,7 @@ class Pivot : public Sample
 			m_lever = 3.0f;
 			b2Vec2 r = { 0.0f, -m_lever };
 
-			float omega = b2Cross(v, r) / b2Dot(r, r);
+			float omega = b2Cross( v, r ) / b2Dot( r, r );
 			b2Body_SetAngularVelocity( m_bodyId, omega );
 
 			b2Polygon box = b2MakeBox( 0.1f, m_lever );
@@ -911,7 +925,7 @@ class Pivot : public Sample
 		b2Vec2 r = b2Body_GetWorldVector( m_bodyId, { 0.0f, -m_lever } );
 
 		b2Vec2 vp = v + b2CrossSV( omega, r );
-		g_draw.DrawString( 5, m_textLine, "pivot velocity = (%g, %g)", vp.x, vp.y);
+		g_draw.DrawString( 5, m_textLine, "pivot velocity = (%g, %g)", vp.x, vp.y );
 		m_textLine += m_textIncrement;
 	}
 

samples/sample_events.cpp

@@ -13,6 +13,7 @@
 
 #include <GLFW/glfw3.h>
 #include <imgui.h>
+#include <stdio.h>
 #include <vector>
 
 class SensorFunnel : public Sample
@@ -1600,6 +1601,7 @@ class SensorTypes : public Sample
 				continue;
 			}
 
+			// todo fix this
 			start += snprintf( buffer + start, sizeof( buffer ) - start, "%s, ", name );
 		}
 

samples/settings.h

@@ -10,14 +10,8 @@ struct Settings
 	void Load();
 
 	int sampleIndex = 0;
-	// int windowWidth = 3840;
-	// int windowHeight = 2160;
 	int windowWidth = 1920;
 	int windowHeight = 1080;
-	// int windowWidth = 1280;
-	// int windowHeight = 720;
-	// int windowWidth = 800;
-	// int windowHeight = 600;
 	float hertz = 60.0f;
 	int subStepCount = 4;
 	int workerCount = 1;

src/CMakeLists.txt

@@ -5,6 +5,7 @@ set(BOX2D_SOURCE_FILES
 	arena_allocator.h
 	array.c
 	array.h
+	atomic.h
 	bitset.c
 	bitset.h
 	body.c
@@ -137,11 +138,6 @@ if (MSVC)
 	# Enable asserts in release with debug info
 	target_compile_definitions(box2d PUBLIC "$<$<CONFIG:RELWITHDEBINFO>:B2_ENABLE_ASSERT>")
 
-	# Atomics are still considered experimental in Visual Studio 17.8
-	if (CMAKE_C_COMPILER_ID MATCHES "MSVC")
-		target_compile_options(box2d PRIVATE /experimental:c11atomics)
-	endif()
-
 	# All warnings
 	target_compile_options(box2d PRIVATE /W4)