Qt Quick 3D - Volumetric Rendering Example

 // Copyright (C) 2023 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 import QtQuick
 import QtQuick3D

 // The rotation math is based on the paper
 // ARCBALL:
 // A User Interface for Specifying Three-Dimensional Orientation Using a Mouse
 // by Ken Shoemake, 1992
 Item {
     id: root
     visible: false

     required property Node controlledObject
     property vector3d lastPos: Qt.vector3d(0, 0, 0)
     property bool moving: false

     // From Shoemake 1992:
     // pt.x <- (screen.x - center.x)/radius;
     // pt.y <- (screen.y - center.y)/radius;
     // r <- pt.x*pt.x + pt.y*pt.y;
     // IF r > 1.0
     //   THEN s <- 1.0/Sqrt[r];
     //     pt.x <- s*pt.x;
     //     pt.y <- s*pt.y;
     //     pt.z <- 0.0;
     //   ELSE pt.z <- Sqrt[1.0 - r] ;
     function pos2DToPos3D(posNDC) {
         var pt = Qt.vector3d(posNDC.x, posNDC.y, 0)
         let r = posNDC.x * posNDC.x + posNDC.y * posNDC.y
         if (r > 1.0) {
             let s = 1.0 / Math.sqrt(r)
             pt.x = s * pt.x
             pt.y = s * pt.y
             pt.z = 0.0
         } else {
             pt.z = Math.sqrt(1.0 - r)
         }

         return pt
     }

     function mousePressed(posNDC) {
         lastPos = pos2DToPos3D(posNDC)
         moving = true
     }

     function mouseReleased(posNDC) {
         moving = false
     }

     function mouseMoved(posNDC) {
         if (!moving)
             return

         let currentPos = pos2DToPos3D(posNDC)

         // From Shoemake 1992:
         // [q.x, q.y, q.z] <- V3_Cross[pO, p1];
         // q.w <- V3_Dot[pO, p1];
         // qnow <- QuatMul[q, qstart];
         let p0 = lastPos
         let p1 = currentPos
         let p0p1 = p0.crossProduct(p1)
         let q = Qt.quaternion(p0.dotProduct(p1), p0p1.x, p0p1.y, p0p1.z)
         let qnow = q.times(controlledObject.rotation)
         controlledObject.rotation = qnow
         lastPos = currentPos
     }
 }