Qt Quick 3D - XR Simple Input Example

This example shows how to use the low-level input APIs in Qt Quick 3D XR to interact with 2D and 3D objects in the scene. It follows the basic structure of the xr_simple example.

Controller Input

In this example, we do ray picking from the position of the XrController:

 XrController {
     id: rightController
     controller: XrController.ControllerRight
     poseSpace: XrController.AimPose

     property QtObject hitObject

     onRotationChanged: {
         const pickResult = xrView.rayPick(scenePosition, forward)
         if (pickResult.hitType !== PickResult.Null) {
             pickRay.hit = true
             pickRay.length = pickResult.distance
             hitObject = pickResult.objectHit
         } else {
             pickRay.hit = false
             pickRay.length = 50
             hitObject = null
         }
     }

     Node {
         id: pickRay
         property real length: 50
         property bool hit: false

         z: -length/2
         Model {
             eulerRotation.x: 90
             scale: Qt.vector3d(0.02, pickRay.length/100, 0.02)
             source: "#Cylinder"
             materials: PrincipledMaterial { baseColor: pickRay.hit ? "green" : "gray" }
             opacity: 0.5
         }
     }

     Node {
         z: 5
         Model {
             eulerRotation.x: 90
             scale: Qt.vector3d(0.05, 0.10, 0.05)
             source: "#Cylinder"
             materials: PrincipledMaterial {
                 baseColor: "black"
                 roughness: 0.2
             }
         }
     }

 }

This performs two functions:

1. If we hit anything, we change the color of the pickRay to green, and we set its length so it touches the thing we hit. The pickRay is a semi-transparent cylinder that shows where the user is aiming.
2. We set the property hitObject to the object that we hit.

We also use a black cylinder as a generic representation of the controller.

For this example, we have made a simple 3D push button in the file ExampleButton.qml. (The details of how the button works are not explained here.) We create an XrInputAction to react to trigger presses:

 XrInputAction {
     id: rightTrigger
     hand: XrInputAction.RightHand
     actionId: [XrInputAction.TriggerPressed, XrInputAction.TriggerValue, XrInputAction.IndexFingerPinch]
     onTriggered: {
         const button = rightController.hitObject as ExampleButton
         if (button && button !== panel.activeButton) {
             panel.activeButton = button
         }
     }
 }

The rightTrigger action reacts to several different IDs in order to support both hand tracking and different types of controllers. When the action is triggered, it checks if the hitObject we set above is of the type ExampleButton. In that case, the button is activated.

To allow a 3D controller to interact with 2D content, we need to add an XrVirtualMouse to map between them:

 XrInputAction {
     id: rightThumbstickX
     hand: XrInputAction.RightHand
     actionId: [XrInputAction.ThumbstickX]
 }
 XrInputAction {
     id: rightThumbstickY
     hand: XrInputAction.RightHand
     actionId: [XrInputAction.ThumbstickY]
 }

 XrVirtualMouse {
     view: xrView
     source: rightController
     leftMouseButton: rightTrigger.pressed
     scrollWheelX: rightThumbstickX.value
     scrollWheelY: rightThumbstickY.value
 }

First we add two more actions to detect horizontal and vertical thumbstick position. Then we create an XrVirtualMouse, using the XrController as a position source. We use the rightTrigger action we made earlier to generate mouse presses/releases and use the thumbstick actions to generate mouse wheel events.

XrItem

The normal way to embed 2D user interfaces in 3D scenes also works in XR, but since the unit size is one centimeter, those user interfaces will have to be scaled to be useful. The XrItem type provides a convenient way to do the scaling automatically by setting the physical size of the 3D item and the logical size of the 2D surface.

 XrItem {
     width: 75
     height: 100
     x: -100
     y: height + table.height + 5
     z: 40
     eulerRotation.y: 45
     color: "transparent"
     contentItem: Rectangle {
         color: Qt.rgba(1, 1, 1, 0.5)
         border.width: 5
         border.color: "lightblue"
         height: 400
         width: 300
         radius: 25
     ...
         }
     }

We position the XrItem in three dimensions and set it to be 75 cm wide and 100 cm tall. Then add a rectangle as a content item, and set it to be 300 x 400 units. The rest of the Qt Quick UI elements are added as children of the rectangle in the normal way and are not shown here. The 2D content is automatically scaled so it fills the XrItem.

Example project @ code.qt.io