Gestures

Description

Gesture Recognisers give us the ability to interact with our virtual objects in different ways such as moving them (pan), rotating them or scaling them (pinch).

There are a number of built in gestures we can make use of:

• UITapGestureRecognizer
• UIPinchGestureRecognizer
• UIRotationGestureRecognizer
• UISwipeGestureRecognizer
• UIPanGestureRecognizer
• UIScreenEdgePanGestureRecognizer
• UILongPressGestureRecognizer

In this lesson we will only use UIPanGestureRecognizer, UIPinchGestureRecognizer and UIRotationGestureRecognizer.

I have really struggled to find Xamarin C# implementations using these in ARKit so I am pleased to show you the code below that I have translated from swift.

One caveat with these gestures is that they can only detect movement in 2 dimensions (as your device screen is only 2D so therefore you can only move your finger across the screen in 2 dimensions).
Therefore whilst it is possible to pan an object up and down (y axis) and left and right (x axis) we cannot detect a pan gesture forwards and backwards (z axis).

However there may be times when we may want this restricted movement in 2 dimensions, for example moving something on a plane/surface like a table or a wall.

Whilst the gestures/interactions in the video don't seem remarkable, they allow us to do some more advanced things later.

Video

Code

using ARKit;
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
            {
                AutoenablesDefaultLighting = true
            };

            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
            {
                AutoFocusEnabled = true,
                PlaneDetection = ARPlaneDetection.None,
                LightEstimationEnabled = true,
                WorldAlignment = ARWorldAlignment.GravityAndHeading

            }, ARSessionRunOptions.ResetTracking | ARSessionRunOptions.RemoveExistingAnchors);

            var panGesture = new UIPanGestureRecognizer(HandlePanGesture);
            this.sceneView.AddGestureRecognizer(panGesture);

            var rotateGesture = new UIRotationGestureRecognizer(HandleRotateGesture);
            this.sceneView.AddGestureRecognizer(rotateGesture);

            var pinchGesture = new UIPinchGestureRecognizer(HandlePinchGesture);
            this.sceneView.AddGestureRecognizer(pinchGesture);

            var tapGesture = new UITapGestureRecognizer(HandleTapGesture);
            this.sceneView.AddGestureRecognizer(tapGesture);

            var swipeGesture = new UISwipeGestureRecognizer(HandleSwipeGesture);
            this.sceneView.AddGestureRecognizer(swipeGesture);

            var longPressGesture = new UILongPressGestureRecognizer(HandleLongPressGesture);
            this.sceneView.AddGestureRecognizer(longPressGesture);

            this.sceneView.Scene.RootNode.AddChildNode(CreateModelNodeFromFile("art.scnassets/mam-tor-1-2.dae"));
        }

        float currentAngleZ;
        float newAngleZ;

        private void HandleTapGesture(UITapGestureRecognizer sender)
        {
            var areaTapped = sender.View as SCNView;
            var location = sender.LocationInView(areaTapped);
            var hitTestResults = areaTapped.HitTest(location, new SCNHitTestOptions());

            var hitTest = hitTestResults.FirstOrDefault();

            if (hitTest == null)
                return;

            var node = hitTest.Node;

            var material = new SCNMaterial();
            material.Diffuse.Contents = UIColor.Black;
            node.Geometry.FirstMaterial = material;
        }

        private void HandleSwipeGesture(UISwipeGestureRecognizer sender)
        {
            var areaSwiped = sender.View as SCNView;
            var location = sender.LocationInView(areaSwiped);
            var hitTestResults = areaSwiped.HitTest(location, new SCNHitTestOptions());

            var hitTest = hitTestResults.FirstOrDefault();

            if (hitTest == null)
                return;

            var node = hitTest.Node;

            var material = new SCNMaterial();
            material.Diffuse.Contents = UIColor.SystemPinkColor;
            node.Geometry.FirstMaterial = material;
        }

        private void HandleLongPressGesture(UILongPressGestureRecognizer sender)
        {
            var areaPressed = sender.View as SCNView;
            var location = sender.LocationInView(areaPressed);
            var hitTestResults = areaPressed.HitTest(location, new SCNHitTestOptions());

            var hitTest = hitTestResults.FirstOrDefault();

            if (hitTest == null)
                return;

            var node = hitTest.Node;

            var material = new SCNMaterial();
            material.Diffuse.Contents = UIColor.Orange;
            node.Geometry.FirstMaterial = material;
        }

        private void HandlePinchGesture(UIPinchGestureRecognizer sender)
        {
            var areaPinched = sender.View as SCNView;
            var location = sender.LocationInView(areaPinched);
            var hitTestResults = areaPinched.HitTest(location, new SCNHitTestOptions());

            var hitTest = hitTestResults.FirstOrDefault();

            if (hitTest == null)
                return;

            var node = hitTest.Node;

            var scaleX = (float)sender.Scale * node.Scale.X;
            var scaleY = (float)sender.Scale * node.Scale.Y;
            var scaleZ = (float)sender.Scale * node.Scale.Z;

            node.Scale = new SCNVector3(scaleX, scaleY, scaleZ);
            sender.Scale = 1;
        }

        private void HandleRotateGesture(UIRotationGestureRecognizer sender)
        {
            var areaTouched = sender.View as SCNView;
            var location = sender.LocationInView(areaTouched);
            var hitTestResults = areaTouched.HitTest(location, new SCNHitTestOptions());

            var hitTest = hitTestResults.FirstOrDefault();

            if (hitTest == null)
                return;

            var node = hitTest.Node;

            newAngleZ = (float)(-sender.Rotation);
            newAngleZ += currentAngleZ;
            node.EulerAngles = new SCNVector3(node.EulerAngles.X, newAngleZ , node.EulerAngles.Z);
        }

        private void HandlePanGesture(UIPanGestureRecognizer sender)
        {
            var areaPanned = sender.View as SCNView;
            var location = sender.LocationInView(areaPanned);
            var hitTestResults = areaPanned.HitTest(location, new SCNHitTestOptions());

            var hitTest = hitTestResults.FirstOrDefault();

            if (hitTest == null)
                return;

            var node = hitTest.Node;

            if (sender.State == UIGestureRecognizerState.Changed)
            {
                var translate = sender.TranslationInView(areaPanned);

                // Only allow movement vertically or horizontally
                node.LocalTranslate(new SCNVector3((float)translate.X / 10000f, (float)-translate.Y / 10000, 0.0f));
            }
        }

        public static SCNNode CreateModelNodeFromFile(string filePath)
        {
            var sceneFromFile = SCNScene.FromFile(filePath);

            var material = new SCNMaterial();
            material.Diffuse.Contents = UIColor.Red;

            var model = sceneFromFile.RootNode.FindChildNode("EXPORT_GOOGLE_SAT_WM", true);
            model.Scale = new SCNVector3(0.1f, 0.1f, 0.1f);
            model.Position = new SCNVector3(0, -0.2f, 0);

            return model;
        }

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

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