- Qt 6.8
- Qt Quick 3D Physics
- Qt Quick 3D Physics Examples and Tutorials
- Qt Quick 3D Physics - Cannon Example
- Qt Quick 3D Physics | Commercial or GPLv3

# Qt Quick 3D Physics - Cannon Example

Demonstrates how to spawn physical objects.

This example demonstrates how to create and delete physical objects on demand. The scene consists of a number of stacks of boxes. You can move around by using `WASD` and the mouse and shoot a ball by pressing `space`.

The scene is setup with the usual Qt Quick 3D objects like view, camera and light:

     PerspectiveCamera {
         id: camera
         position: Qt.vector3d(-4000, 5000, 10000)
         eulerRotation: Qt.vector3d(-20, -20, 0)
         clipFar: 500000
         clipNear: 100
     }
     DirectionalLight {
         eulerRotation: Qt.vector3d(-45, 45, 0)
         castsShadow: true
         brightness: 1
         shadowMapQuality: Light.ShadowMapQualityVeryHigh
         shadowFactor: 100
     }

We also add a static floor:

     StaticRigidBody {
         eulerRotation: Qt.vector3d(-90, 0, 0)
         collisionShapes: PlaneShape {}
         Model {
             source: "#Rectangle"
             scale: Qt.vector3d(2000, 2000, 1)
             materials: PrincipledMaterial {
                 baseColor: "green"
             }
             castsShadows: false
             receivesShadows: true
         }
     }

We create a Node we use as the spawner of objects and put inside our view:

     Node {
         id: shapeSpawner
         property var instancesBoxes: []
         property var instancesSpheres: []
         property int stackCount: 0
         property var boxComponent: Qt.createComponent("Box.qml")
         property var sphereComponent: Qt.createComponent("Sphere.qml")

         function createStack(stackZ, numStacks) {
             let size = 10
             let extents = 400

             for (var i = 0; i < size; i++) {
                 for (var j = 0; j < size - i; j++) {
                     let x = j * 2 - size + i
                     let y = i * 2 + 1
                     let z = 5 * (stackZ - numStacks)
                     let center = Qt.vector3d(x, y, z).times(0.5 * extents)
                     let box = boxComponent.incubateObject(shapeSpawner, {
                                                               "position": center,
                                                               "xyzExtents": extents
                                                           })
                     instancesBoxes.push(box)
                 }
             }
         }

         function createBall(position, forward) {
             var diameter = 600
             var speed = 20000
             let settings = {
                 "position": position,
                 "sphereDiameter": diameter
             }
             let sphere = sphereComponent.createObject(shapeSpawner, settings)
             sphere.setLinearVelocity(forward.times(speed))
             instancesSpheres.push(sphere)

             if (sphere === null) {
                 console.log("Error creating object")
             }
         }

         function reset() {
             // Only run method if previous stack has been created fully
             for (var i = 0; i < instancesBoxes.length; i++)
                 if (!instancesBoxes[i].object)
                     return

             instancesSpheres.forEach(sphere => {
                                          sphere.collisionShapes = []
                                          sphere.destroy()
                                      })
             instancesBoxes.forEach(box => {
                                        box.object.collisionShapes = []
                                        box.object.destroy()
                                    })
             instancesSpheres = []
             instancesBoxes = []

             for (var stackI = 0; stackI < stackSlider.value; stackI++) {
                 shapeSpawner.createStack(stackI, stackSlider.value)
             }
         }
     }

We have three methods: `createStack` for creating a stack, `createBall` for creating a ball with velocity and `reset` for resetting the scene. The actual box and sphere that is spawn is stored in their own qml files (`box.qml` and `sphere.qml`).

Files:

- cannon/Box.qml
- cannon/CMakeLists.txt
- cannon/Crosshair.qml
- cannon/Sphere.qml
- cannon/cannon.pro
- cannon/main.cpp
- cannon/main.qml
- cannon/qml.qrc