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[upstream] Contact recycling (erincatto/box2d#1038)
Contact recycling - re-use contact points across time steps when the relative movement is small. This feature improves stability and performance. The performance lift is around 25% on benchmarks. I've tested this a lot and I haven't seen any artifacts. Contact points are not re-computed until shapes move more than 5cm relative to each other. This distance can be accessed with these functions: ```c b2World_GetContactRecycleDistance() b2World_SetContactRecycleDistance() ``` The default value is `B2_CONTACT_RECYCLE_DISTANCE`. You can set this distance to zero to disable contact recycling. Contact recycling skips some updates (i.e. friction, presolve) until the shapes move relative to each other by ~5cm. I identified some contacts between slow moving shapes can be delayed. I addressed this by adjusting the recycle distance for non-touching shapes to use the speculative contact distance. Other stuff: - Build timeouts - `B2_VALIDATE` that asserts only in debug build - Update trees task moved earlier in the step - Moved `constants.h` to the include folder - Contact solver now uses body indices of 0 to indicate null (static body) - AABB margin now considers the shape size to help reduce the number of pairs
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‎.gitignore‎

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@@ -384,6 +384,9 @@ FodyWeavers.xsd
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!.vscode/extensions.json
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*.code-workspace
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# ai
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.claude/
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# Local History for Visual Studio Code
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.history/
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‎src/Box2D.NET.Samples/Box2D.NET.Samples.csproj‎

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</PropertyGroup>
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<PropertyGroup Condition="'$(Configuration)' == 'Debug'">
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<DefineConstants>$(DefineConstants);B2_SNOOP_TOI_COUNTERS;ENABLED;B2_SNOOP_TABLE_COUNTERS;B2_SNOOP_PAIR_COUNTERS</DefineConstants>
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<DefineConstants>$(DefineConstants);B2_SNOOP_TOI_COUNTERS;ENABLED;B2_SNOOP_TABLE_COUNTERS;B2_SNOOP_PAIR_COUNTERS;B2_ENABLE_VALIDATION</DefineConstants>
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</PropertyGroup>
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<ItemGroup>

‎src/Box2D.NET.Samples/SampleApp.cs‎

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@@ -790,24 +790,42 @@ private void UpdateUI()
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ImGui.Checkbox("Sleep", ref _context.enableSleep);
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ImGui.Checkbox("Warm Starting", ref _context.enableWarmStarting);
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ImGui.Checkbox("Continuous", ref _context.enableContinuous);
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ImGui.Checkbox("Contact Recycling", ref _context.enableRecycling);
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ImGui.Separator();
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ImGui.Checkbox("Shapes", ref _context.debugDraw.drawShapes);
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ImGui.Checkbox("Joints", ref _context.debugDraw.drawJoints);
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ImGui.Checkbox("Joint Extras", ref _context.debugDraw.drawJointExtras);
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ImGui.Checkbox("Bounds", ref _context.debugDraw.drawBounds);
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ImGui.Checkbox("Contact Points", ref _context.debugDraw.drawContactPoints);
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ImGui.Checkbox("Contact Normals", ref _context.debugDraw.drawContactNormals);
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ImGui.Checkbox("Contact Features", ref _context.debugDraw.drawContactFeatures);
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ImGui.Checkbox("Contact Forces", ref _context.debugDraw.drawContactForces);
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ImGui.Checkbox("Friction Forces", ref _context.debugDraw.drawFrictionForces);
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ImGui.Checkbox("Mass", ref _context.debugDraw.drawMass);
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ImGui.Checkbox("Body Names", ref _context.debugDraw.drawBodyNames);
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ImGui.Checkbox("Graph Colors", ref _context.debugDraw.drawGraphColors);
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ImGui.Checkbox("Islands", ref _context.debugDraw.drawIslands);
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ImGui.Checkbox("Counters", ref _context.drawCounters);
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ImGui.Checkbox("Profile", ref _context.drawProfile);
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ImGui.Separator();
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ImGui.Separator();
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{
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bool changed = false;
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string[] drawTypes =
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[
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"None", "Clip", "AnchorA", "AnchorB", "Average"
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];
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int drawType = (int)_context.debugDraw.contactDrawType;
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changed = changed || ImGui.Combo("Contact", ref drawType, drawTypes, drawTypes.Length);
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_context.debugDraw.contactDrawType = (B2ContactDrawType)drawType;
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}
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ImGui.Checkbox("Contact Normals", ref _context.debugDraw.drawContactNormals);
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ImGui.Checkbox("Contact Features", ref _context.debugDraw.drawContactFeatures);
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ImGui.Checkbox("Contact Forces", ref _context.debugDraw.drawContactForces);
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ImGui.Checkbox("Friction Forces", ref _context.debugDraw.drawFrictionForces);
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ImGui.Separator();
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ImGui.PushItemWidth(80.0f);
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ImGui.InputFloat("Joint Scale", ref _context.debugDraw.jointScale);

‎src/Box2D.NET.Samples/SampleContext.cs‎

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public bool drawProfile = false;
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public bool enableWarmStarting = true;
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public bool enableContinuous = true;
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public bool enableRecycling = true;
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public bool enableSleep = true;
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public bool showUI = true;
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‎src/Box2D.NET.Samples/Samples/Benchmarks/BenchmarkBarrel.cs‎

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@@ -69,7 +69,7 @@ public BenchmarkBarrel(SampleContext context) : base(context)
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float x = -40.0f * gridSize;
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for (int i = 0; i < 81; ++i)
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{
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B2Polygon box = b2MakeOffsetBox(0.5f * gridSize, 0.5f * gridSize, new B2Vec2(x, y), b2Rot_identity);
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B2Polygon box = b2MakeOffsetBox(0.55f * gridSize, 0.5f * gridSize, new B2Vec2(x, y), b2Rot_identity);
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b2CreatePolygonShape(groundId, shapeDef, box);
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x += gridSize;
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}
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x = -40.0f * gridSize;
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for (int i = 0; i < 100; ++i)
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{
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B2Polygon box = b2MakeOffsetBox(0.5f * gridSize, 0.5f * gridSize, new B2Vec2(x, y), b2Rot_identity);
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B2Polygon box = b2MakeOffsetBox(0.5f * gridSize, 0.55f * gridSize, new B2Vec2(x, y), b2Rot_identity);
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b2CreatePolygonShape(groundId, shapeDef, box);
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y += gridSize;
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}
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x = 40.0f * gridSize;
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for (int i = 0; i < 100; ++i)
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{
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B2Polygon box = b2MakeOffsetBox(0.5f * gridSize, 0.5f * gridSize, new B2Vec2(x, y), b2Rot_identity);
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B2Polygon box = b2MakeOffsetBox(0.5f * gridSize, 0.55f * gridSize, new B2Vec2(x, y), b2Rot_identity);
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b2CreatePolygonShape(groundId, shapeDef, box);
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y += gridSize;
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}

‎src/Box2D.NET.Samples/Samples/Collisions/Manifold.cs‎

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@@ -189,7 +189,7 @@ void DrawManifold(in B2Manifold manifold, B2Vec2 origin1, B2Vec2 origin2)
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{
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ref B2ManifoldPoint mp = ref manifold.points[i];
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B2Vec2 p1 = mp.point;
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B2Vec2 p1 = mp.clipPoint;
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B2Vec2 p2 = b2MulAdd(p1, 0.5f, manifold.normal);
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DrawLine(m_draw, p1, p2, B2HexColor.b2_colorViolet);
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‎src/Box2D.NET.Samples/Samples/Collisions/ShapeCast.cs‎

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@@ -105,7 +105,8 @@ public ShapeCast(SampleContext context) : base(context)
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}
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#endif
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m_box = b2MakeOffsetBox(0.5f, 0.5f, new B2Vec2(0.0f, 0.0f), b2Rot_identity);
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//m_box = b2MakeOffsetBox(0.5f, 0.5f, new B2Vec2(0.0f, 0.0f), b2Rot_identity);
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m_box = b2MakeBox( 8.984375f, 0.5f );
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#if ZERO
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{

‎src/Box2D.NET.Samples/Samples/Collisions/SmoothManifold.cs‎

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{
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ref B2ManifoldPoint mp = ref manifold.points[i];
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B2Vec2 p1 = mp.point;
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B2Vec2 p1 = mp.clipPoint;
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B2Vec2 p2 = b2MulAdd(p1, 0.5f, manifold.normal);
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DrawLine(m_draw, p1, p2, B2HexColor.b2_colorWhite);
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‎src/Box2D.NET.Samples/Samples/Events/ContactEvent.cs‎

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for (int k = 0; k < manifold.pointCount; ++k)
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{
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B2ManifoldPoint point = manifold.points[k];
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DrawLine(m_draw, point.point, point.point + point.totalNormalImpulse * normal, B2HexColor.b2_colorBlueViolet);
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DrawPoint(m_draw, point.point, 10.0f, B2HexColor.b2_colorWhite);
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DrawLine(m_draw, point.clipPoint, point.clipPoint + point.totalNormalImpulse * normal, B2HexColor.b2_colorBlueViolet);
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DrawPoint(m_draw, point.clipPoint, 10.0f, B2HexColor.b2_colorWhite);
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}
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}
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}
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for (int k = 0; k < manifold.pointCount; ++k)
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{
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B2ManifoldPoint point = manifold.points[k];
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DrawLine(m_draw, point.point, point.point + point.totalNormalImpulse * normal, B2HexColor.b2_colorYellowGreen);
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DrawPoint(m_draw, point.point, 10.0f, B2HexColor.b2_colorWhite);
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DrawLine(m_draw, point.clipPoint, point.clipPoint + point.totalNormalImpulse * normal, B2HexColor.b2_colorYellowGreen);
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DrawPoint(m_draw, point.clipPoint, 10.0f, B2HexColor.b2_colorWhite);
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}
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}
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}

‎src/Box2D.NET.Samples/Samples/Events/PersistentContact.cs‎

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for (int i = 0; i < data.manifold.pointCount; ++i)
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{
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ref readonly B2ManifoldPoint manifoldPoint = ref data.manifold.points[i];
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B2Vec2 p1 = manifoldPoint.point;
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B2Vec2 p1 = manifoldPoint.clipPoint;
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B2Vec2 p2 = p1 + manifoldPoint.totalNormalImpulse * data.manifold.normal;
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DrawLine(m_draw, p1, p2, B2HexColor.b2_colorCrimson);
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DrawPoint(m_draw, p1, 6.0f, B2HexColor.b2_colorCrimson);

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