rigidbody, forces and collision testing

PhysicsEngine/Physics/Bodies/Box.cs

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+using System;
+using System.Numerics;
+using Raylib_cs;
+
+namespace PhysicsEngine
+{
+    public class Box : Body
+    {
+        public Vector2 Size;
+
+        public Box(Vector2 position, Vector2 size, float mass)
+        {
+            Position = position;
+            Size = size;
+            Mass = mass;
+            MomentOfInertia = (1.0f / 12.0f) * mass * (size.X * size.X + size.Y * size.Y);
+        }
+
+        public override void Draw(float pixelsPerMeter = 100.0f)
+        {
+            DrawHelper.DrawRotatedBox(Position, Size, Rotation, BaseColor, pixelsPerMeter);
+        }
+
+        private Vector2 RotatePoint(Vector2 point, float radians)
+        {
+            float cos = MathF.Cos(radians);
+            float sin = MathF.Sin(radians);
+            return new Vector2(
+                point.X * cos - point.Y * sin,
+                point.X * sin + point.Y * cos
+            );
+        }
+
+        public override void ApplyAerodynamicDrag(float dt)
+        {
+            if (DragCoefficient <= 0.0f) return;
+
+            const float airDensity = 1.225f;
+            float speed = Velocity.Length();
+            if (speed < 0.01f) return;
+
+            // 1. Oncoming relative wind direction (opposite to velocity)
+            Vector2 windDir = -Velocity / speed;
+
+            float cos = MathF.Cos(Rotation);
+            float sin = MathF.Sin(Rotation);
+
+            // Box local axes transformed into world space (Assuming Size.Y is length/major axis)
+            Vector2 worldAxisY = new Vector2(-sin, cos); // Major axis vector
+            Vector2 worldAxisX = new Vector2(cos, sin);  // Minor axis vector
+
+            // 2. Calculate effective frontal width (projected area in 2D) based on current orientation
+            Vector2 windPerp = new Vector2(-windDir.Y, windDir.X);
+            float projX = MathF.Abs(Vector2.Dot(worldAxisX, windPerp));
+            float projY = MathF.Abs(Vector2.Dot(worldAxisY, windPerp));
+            float effectiveWidth = Size.X * projX + Size.Y * projY;
+
+            // 3. Translational Drag Force (scales with dynamic pressure and current effective width)
+            float dragMagnitude = 0.5f * airDensity * speed * speed * DragCoefficient * effectiveWidth;
+            Vector2 dragForce = windDir * dragMagnitude;
+            ApplyForce(dragForce);
+
+            // 4. Weathercock / Fin-Effect Restoring Torque
+            // Measures angular misalignment between the box's major axis and the wind direction
+            float cross = worldAxisY.X * windDir.Y - worldAxisY.Y * windDir.X;
+            float restoringTorque = cross * 0.5f * airDensity * speed * speed * DragCoefficient * Size.X * Size.Y;
+            ApplyTorque(restoringTorque);
+
+            // 5. Angular Damping (Quadratic Rotational Drag)
+            float angularSpeed = MathF.Abs(AngularVelocity);
+            if (angularSpeed > 0.0001f)
+            {
+                float angularDragTorque = -MathF.Sign(AngularVelocity) * 0.5f * airDensity * angularSpeed * angularSpeed * DragCoefficient * (Size.X + Size.Y);
+                ApplyTorque(angularDragTorque);
+            }
+        }
+    }
+}