wip

Author: ikpil

src/Box2D.NET.Samples/Samples/Stackings/CircleImpulse.cs

@@ -0,0 +1,164 @@
+// SPDX-FileCopyrightText: 2025 Erin Catto
+// SPDX-FileCopyrightText: 2025 Ikpil Choi(ikpil@naver.com)
+// SPDX-License-Identifier: MIT
+
+using System.Collections.Generic;
+using System.Numerics;
+using System.Runtime.InteropServices;
+using ImGuiNET;
+using static Box2D.NET.B2Types;
+using static Box2D.NET.B2Bodies;
+using static Box2D.NET.B2Shapes;
+using static Box2D.NET.B2Ids;
+using static Box2D.NET.B2Worlds;
+using static Box2D.NET.B2Contacts;
+using static Box2D.NET.Samples.Graphics.Draws;
+
+namespace Box2D.NET.Samples.Samples.Stackings;
+
+public class CircleImpulse : Sample
+{
+    private static readonly int SampleCircleImpulse = SampleFactory.Shared.RegisterSample("Stacking", "Circle Impulse", Create);
+
+    public struct Event
+    {
+        public float impulse;
+        public float totalImpulse;
+        public float speed;
+    };
+
+    private float m_mass;
+    private List<Event> m_events = new List<Event>();
+    private B2BodyId m_bodyId;
+    private float m_gravity;
+    private float m_restitution;
+    private bool m_useGravity;
+    private bool m_useRestitution;
+
+    private static Sample Create(SampleContext context)
+    {
+        return new CircleImpulse(context);
+    }
+
+    public CircleImpulse(SampleContext context) : base(context)
+    {
+        if (m_context.restart == false)
+        {
+            m_context.camera.center = new B2Vec2(0.0f, 2.7f);
+            m_context.camera.zoom = 3.4f;
+        }
+
+        {
+            B2BodyDef bodyDef = b2DefaultBodyDef();
+            B2BodyId groundId = b2CreateBody(m_worldId, bodyDef);
+
+            B2ShapeDef shapeDef = b2DefaultShapeDef();
+
+            B2Segment segment = new B2Segment(new B2Vec2(-10.0f, 0.0f), new B2Vec2(10.0f, 0.0f));
+            b2CreateSegmentShape(groundId, shapeDef, segment);
+        }
+
+        m_gravity = 10.0f;
+        m_restitution = 0.25f;
+        m_useGravity = false;
+        m_useRestitution = false;
+        m_mass = 1.0f;
+        m_bodyId = b2_nullBodyId;
+
+        Spawn();
+    }
+
+    void Spawn()
+    {
+        if (B2_IS_NON_NULL(m_bodyId))
+        {
+            b2DestroyBody(m_bodyId);
+            m_bodyId = b2_nullBodyId;
+        }
+
+        m_events.Clear();
+
+        B2BodyDef bodyDef = b2DefaultBodyDef();
+        bodyDef.type = B2BodyType.b2_dynamicBody;
+        bodyDef.gravityScale = m_useGravity ? 1.0f : 0.0f;
+        bodyDef.linearVelocity.Y = -25.0f;
+        bodyDef.position.Y = 5.5f;
+
+        B2Circle circle = new B2Circle();
+        circle.radius = 0.25f;
+
+        B2ShapeDef shapeDef = b2DefaultShapeDef();
+        shapeDef.enableHitEvents = true;
+        shapeDef.material.friction = 0.0f;
+        shapeDef.material.restitution = m_useRestitution ? m_restitution : 0.0f;
+
+        m_bodyId = b2CreateBody(m_worldId, bodyDef);
+
+        b2CreateCircleShape(m_bodyId, shapeDef, circle);
+
+        // Override mass
+        B2MassData massData = b2Body_GetMassData(m_bodyId);
+        float ratio = m_mass / massData.mass;
+        massData.mass = m_mass;
+        massData.rotationalInertia *= ratio;
+        b2Body_SetMassData(m_bodyId, massData);
+    }
+
+    public override void UpdateGui()
+    {
+        float fontSize = ImGui.GetFontSize();
+        float height = 6.0f * fontSize;
+        ImGui.SetNextWindowPos(new Vector2(0.5f * fontSize, m_camera.height - height - 2.0f * fontSize), ImGuiCond.Once);
+        ImGui.SetNextWindowSize(new Vector2(10.0f * fontSize, height));
+
+        ImGui.Begin("Circle Impulse", ImGuiWindowFlags.NoMove | ImGuiWindowFlags.NoResize);
+
+        if (ImGui.Checkbox("gravity", ref m_useGravity))
+        {
+            Spawn();
+        }
+
+        if (ImGui.Checkbox("restitution", ref m_useRestitution))
+        {
+            Spawn();
+        }
+
+        ImGui.End();
+    }
+
+    public override void Step()
+    {
+        base.Step();
+
+        B2ContactEvents events = b2World_GetContactEvents(m_worldId);
+        for (int i = 0; i < events.hitCount; ++i)
+        {
+            ref readonly B2ContactHitEvent @event = ref events.hitEvents[i];
+
+            DrawPoint(m_draw, @event.point, 10.0f, B2HexColor.b2_colorWhite);
+
+            B2ContactData data = b2Contact_GetData(@event.contactId);
+
+            Event e = new Event();
+            e.speed = @event.approachSpeed;
+
+            if (data.manifold.pointCount > 0)
+            {
+                e.impulse = data.manifold.points[0].normalImpulse;
+                e.totalImpulse = data.manifold.points[0].totalNormalImpulse;
+            }
+
+            m_events.Add(e);
+        }
+
+        DrawTextLine($"mass = {m_mass}, gravity = {(m_useGravity ? 10.0f : 0.0f)}, restitution = {(m_useRestitution ? m_restitution : 0.0f)}");
+
+        int eventCount = m_events.Count;
+        var eventsSpan = CollectionsMarshal.AsSpan(m_events);
+        for (int i = 0; i < eventCount; ++i)
+        {
+            ref readonly Event e = ref eventsSpan[i];
+            DrawTextLine($"hit speed = {e.speed}, hit momentum = {m_mass * e.speed}, final impulse = {e.impulse}, total impulse = {e.totalImpulse}");
+        }
+    }
+}

src/Box2D.NET.Shared/Benchmarks.cs

@@ -185,7 +185,7 @@ public static void CreateManyPyramids(B2WorldId worldId)
             for (int i = 0; i < rowCount; ++i)
             {
                 B2Segment segment = new B2Segment(new B2Vec2(-0.5f * 2.0f * groundWidth, groundY), new B2Vec2(0.5f * 2.0f * groundWidth, groundY));
-                b2CreateSegmentShape(groundId, ref shapeDef, ref segment);
+                b2CreateSegmentShape(groundId, shapeDef, segment);
                 groundY += groundDeltaY;
             }