Use physics in scene

Description

We will use physics in the scene. i.e gravity.

To do this we add a 2d horizontal plane to the scene and set PhysicsBody = SCNPhysicsBody.CreateKinematicBody().

Then we add 3d cubes at the location the user touches the screen and make it so they mimic gravity using PhysicsBody = SCNPhysicsBody.CreateDynamicBody().

We can see that the cubes are able to fall off the 2d plane.

Video

Code

using ARKit;
using Foundation;
using SceneKit;
using System;
using System.Linq;
using UIKit;

namespace XamarinArkitSample
{
    public partial class ViewController : UIViewController
    {
        private readonly ARSCNView sceneView;

        public ViewController(IntPtr handle) : base(handle)
        {
            this.sceneView = new ARSCNView();
            this.View.AddSubview(this.sceneView);
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();
            this.sceneView.Frame = this.View.Frame;
        }

        public override void ViewDidAppear(bool animated)
        {
            base.ViewDidAppear(animated);

            this.sceneView.Session.Run(new ARWorldTrackingConfiguration
            {
                LightEstimationEnabled = true,
                WorldAlignment = ARWorldAlignment.Gravity
            });

            var light = SCNLight.Create();
            light.LightType = SCNLightType.Directional;
            light.Intensity = 2000f;
            light.ShadowColor = UIColor.Black.ColorWithAlpha(0.5f);
            light.ShadowRadius = 4;
            light.ShadowSampleCount = 4;
            light.CastsShadow = true;

            var lightNode = new SCNNode();
            lightNode.Position = new SCNVector3(0, 1f, 0);
            lightNode.Light = light;
            lightNode.EulerAngles = new SCNVector3((float)-Math.PI / 2, 0, 0);
            lightNode.Opacity = 0;

            this.sceneView.Scene.RootNode.AddChildNode(lightNode);

            var planeNode = new PlaneNode(width:0.5f, length:0.5f, UIColor.DarkGray);

            this.sceneView.Scene.RootNode.AddChildNode(planeNode);
        }

        public override void TouchesEnded(NSSet touches, UIEvent evt)
        {
            base.TouchesEnded(touches, evt);

            if (!(touches.AnyObject is UITouch touch))
                return;

            var point = touch.LocationInView(this.sceneView);
            var hits = this.sceneView.HitTest(point, new SCNHitTestOptions());
            var hit = hits.FirstOrDefault();

            if (hit == null)
                return;

            var node = hit.Node;

            if (node == null)
                return;

            var cubeNode = new CubeNode(0.05f, UIColor.Green)
            {
                Position = new SCNVector3(
                    hit.WorldCoordinates.X,
                    hit.WorldCoordinates.Y + 0.1f,
                    hit.WorldCoordinates.Z
                )
            };

            this.sceneView.Scene.RootNode.AddChildNode(cubeNode);
        }

        public override void ViewDidDisappear(bool animated)
        {
            base.ViewDidDisappear(animated);
            this.sceneView.Session.Pause();
        }

        public override void DidReceiveMemoryWarning()
        {
            base.DidReceiveMemoryWarning();
        }
    }

    public class PlaneNode : SCNNode
    {
        public PlaneNode(float width, float length, UIColor color)
        {
            Geometry = CreateGeometry(width, length, color);
            PhysicsBody = SCNPhysicsBody.CreateKinematicBody();
            EulerAngles = new SCNVector3((float)(-Math.PI / 2), 0, 0);
            CastsShadow = true;
        }

        private static SCNGeometry CreateGeometry(float width, float length, UIColor color)
        {
            var material = new SCNMaterial();
            material.Diffuse.Contents = color;
            material.DoubleSided = true;

            var geometry = SCNPlane.Create(width, length);
            geometry.Materials = new[] { material };
            return geometry;
        }
    }

    public class CubeNode : SCNNode
    {
        public CubeNode(float size, UIColor color)
        {
            Geometry = CreateGeometry(size, color);
            Position = new SCNVector3(0, size / 2, 0);
            PhysicsBody = SCNPhysicsBody.CreateDynamicBody();
        }

        private static SCNGeometry CreateGeometry(float size, UIColor color)
        {
            var material = new SCNMaterial();
            material.Diffuse.Contents = color;

            var geometry = SCNBox.Create(size, size, size, 0);
            geometry.Materials = new[] { material };
            return geometry;
        }
    }
}