Handling Contacts on Collision

using System;
using System.Collections;
using System.Collections.Generic;
using Unigine;
#region Math Variables
#if UNIGINE_DOUBLE
using Vec3 = Unigine.dvec3;
#else
using Vec3 = Unigine.vec3;
#endif
#endregion
// DO NOT CHANGE THE PropertyGuid VALUE
[Component (PropertyGuid = "YOUR_GUID")]

public class ContactsHandler : Component
{
	// For debugging
	public bool debug = true; 
	// A node that will be loaded on contact (a hit effect in our case)
	public AssetLinkNode contactEffect; 

	// Time, position and some info of the last occurred contact
	private DateTime lastContactTime; 
	private Vec3 lastContactPoint;
	private string lastContactInfo;

	private void Init()
	{
		Body body = node.ObjectBody;
		if (body)
		{
			// For debug purposes, we can render certain contacts depending on their type
			body.EventContacts.Connect((b) => b.RenderInternalContacts()); 
			// A handler to be fired when each contact emerges
			body.EventContactEnter.Connect(OnContactEnter);
		}
	}

	// This function takes the body and the index of the contact
	private void OnContactEnter(Body body, int num)
	{
		// Enable Visualizer to see the rendered contact points
		Visualizer.Enabled = true;
		
		if(body.IsContactInternal(num))
		{
			if (debug)
			{
				// The time of the contact
				lastContactTime = DateTime.Now; 
				// The position of the contact
				lastContactPoint = body.GetContactPoint(num); 

				// We get both physical bodies participating in this contact
				Body body0 = body.GetContactBody0(num);
				Body body1 = body.GetContactBody1(num);

				Body touchedBody = null;

				// We check if our object has hit another physical object.
				// If any of the bodies exists and it's not the body of our object
				// then we have found another physics-driven object that hit it
				if (body0 && body0 != body) touchedBody = body0;  
				if (body1 && body1 != body) touchedBody = body1;

				if (touchedBody)
				{
					// Our object has touched a physics-driven object.
					// We save the info about the body
					lastContactInfo = $"body {touchedBody.Name} of {touchedBody.Object.Name}";
					// Render it in the viewport
					Visualizer.RenderObject(touchedBody.Object, vec4.BLUE, 0.5f); 
				}
				else
				{
					// It has touched a surface with Collision enabled
					lastContactInfo = $"surface #{body.GetContactSurface(num)} of {body.GetContactObject(num).Name}";
					// Highlighting the surface
					Visualizer.RenderObjectSurface(body.GetContactObject(num), body.GetContactSurface(num), vec4.BLUE, 0.5f);
				}

				// You can add details you are interested in (e.g., the contact impulse)
				lastContactInfo += $"\nimpulse: {body.GetContactImpulse(num):0.0}";
			}

			// We spawn a hit effect if the impulse is strong enough
			if (body.GetContactImpulse(num) > 0.3f && !contactEffect.IsNull)
			{
				contactEffect.Load(body.GetContactPoint(num), MathLib.RotationFromDir(body.GetContactNormal(num) * MathLib.RotateY(90)));
			}
		}
	}

	private void Update()
	{
		// Here we display the info and create a slow motion effect for one second
		if (debug)
		{
			if((DateTime.Now - lastContactTime).Seconds < 1.0f)
			{
				// Slow motion effect
				Game.Scale = 0.4f; 
				Visualizer.RenderMessage3D(lastContactPoint, vec3.ONE, $"last contact: \n{lastContactInfo}", vec4.GREEN, 2, 24);
			}
			else
			{
				// All the other time the speed will be normal
				Game.Scale = 1.0f;
			}
		}
	}
}