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code/entities/DirectionalGravity.cs

@@ -0,0 +1,64 @@
+using Sandbox;
+using System.Linq;
+
+[Library( "directional_gravity", Title = "Directional Gravity", Spawnable = true )]
+public partial class DirectionalGravity : Prop
+{
+	bool enabled = false;
+
+	public override void Spawn()
+	{
+		base.Spawn();
+
+		DeleteOthers();
+
+		SetModel( "models/arrow.vmdl" );
+		SetupPhysicsFromModel( PhysicsMotionType.Dynamic, false );
+
+		enabled = true;
+	}
+
+	private void DeleteOthers()
+	{
+		// Only allow one of these to be spawned at a time
+		foreach ( var ent in All.OfType<DirectionalGravity>()
+			.Where( x => x.IsValid() && x != this ) )
+		{
+			ent.Delete();
+		}
+	}
+
+	protected override void OnDestroy()
+	{
+		base.OnDestroy();
+
+		if ( IsServer )
+		{
+			PhysicsWorld.UseDefaultGravity();
+			PhysicsWorld.WakeAllBodies();
+		}
+
+		enabled = false;
+	}
+
+	[Event.Physics.PostStep]
+	public void OnPostPhysicsStep()
+	{
+		if ( !IsServer )
+			return;
+
+		if ( !enabled )
+			return;
+
+		if ( !this.IsValid() )
+			return;
+
+		var gravity = Rotation.Down * 800.0f;
+
+		if ( gravity != PhysicsWorld.Gravity )
+		{
+			PhysicsWorld.Gravity = gravity;
+			PhysicsWorld.WakeAllBodies();
+		}
+	}
+}