- Qt 6.6
- Qt Quick 3D
- Qt Quick 3D Examples and Tutorials
- Qt Quick 3D - Volumetric Rendering Example
- Qt Quick 3D | Commercial or GPLv3

# Qt Quick 3D - Volumetric Rendering Example

     // Copyright (C) 2023 The Qt Company Ltd.
     // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
     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
         }
     }