- Qt 6.4
- Qt Quick 3D
- Qt Quick 3D Examples and Tutorials
- Qt Quick 3D - Quick Ball Example
- Qt Quick 3D | Commercial or GPLv3

# Qt Quick 3D - Quick Ball Example

Demonstrates how to create a simple game using Quick3D.

This example demonstrates how to combine Qt Quick and Qt Quick 3D to create a simple 3D game. The goal of the game is to hit target boxes by throwing a ball. Points are given based on how fast and with how few balls all targets are down. Aim well but be quick!

The source code is in a single QML file to emphasize how compact this example is, considering it being a fully playable game. Let's start by looking at the main properties. These are quite self-explanatory, and you can easily adjust them to see how they affect the game.

     // Scaling helpper
     readonly property real px: 0.2 + Math.min(width, height) / 800
     // This is false until the first game has started
     property bool playingStarted: false
     // This is true whenever game is on
     property bool gameOn: false
     // Sizes of our 3D models
     readonly property real ballSize: 40
     readonly property real targetSize: 120
     // Playing time in seconds
     readonly property real gameTime: 60
     property real currentTime: 0
     // Amount of balls per game
     readonly property int gameBalls: 20
     property int currentBalls: 0
     // Scores
     property int score: 0
     property int timeBonus: 0
     property int ballsBonus: 0

The game logic is implemented with JavaScript. View3D contains a function to start the game, which (re)initializes all required variables and creates the level targets. It also contains a function to calculate the final points when the game ends.

     function createLevel1() {
         // Simple level of target items
         var level1 = [{ "x": 0, "y": 100, "z": -100, "points": 10 },
                       { "x": -300, "y": 100, "z": -400, "points": 10 },
                       { "x": 300, "y": 100, "z": -400, "points": 10 },
                       { "x": -200, "y": 400, "z": -600, "points": 20 },
                       { "x": 0, "y": 400, "z": -600, "points": 20 },
                       { "x": 200, "y": 400, "z": -600, "points": 20 },
                       { "x": 0, "y": 700, "z": -600, "points": 30 }];
         targetsNode.addTargets(level1);
     }

     function startGame() {
         ballModel.resetBall();
         targetsNode.resetTargets();
         createLevel1();
         score = timeBonus = ballsBonus = 0;
         currentBalls = gameBalls;
         gameOn = true;
         playingStarted = true;
     }

     function endGame() {
         if (targetsNode.currentTargets == 0) {
             // If we managed to get all targets down -> bonus points!
             timeBonus = currentTime;
             ballsBonus = currentBalls * 10;
         }
         gameOn = false;
     }

The view also contains a PointLight node to light up the scene. It is positioned above the objects and set to cast shadows. Note how brightness is used to darken the playing area when then game has ended. The ambientColor property is used to soften the light contrast, as without it the bottom parts of the objects would be very dark.

     PointLight {
         x: 400
         y: 1200
         castsShadow: true
         shadowMapQuality: Light.ShadowMapQualityHigh
         shadowFactor: 50
         quadraticFade: 2
         ambientColor: "#202020"
         brightness: gameOn ? 200 : 40
         Behavior on brightness {
             NumberAnimation {
                 duration: 1000
                 easing.type: Easing.InOutQuad
             }
         }
     }

Throwing the ball uses Qt Quick MouseArea item, which is only enabled when game is on, and the ball isn't already moving.

     MouseArea {
         anchors.fill: parent
         enabled: gameOn && !ballModel.ballMoving
         onPressed: {
             ballModel.moveBall(mouseX, mouseY);
         }
         onPositionChanged: {
             ballModel.moveBall(mouseX, mouseY);
         }
         onReleased: {
             ballModel.throwBall();
         }
     }

Then we get into actual 3D models. Ball model is the biggest one, as it contains the logic how the ball behaves, its animations, and hit detection. Let's look into the ball properties first. Ball uses a built-in sphere model, scaled based on `ballSize`. We use DefaultMaterial with a diffuseMap and a normalMap to create tennis ball appearance.

     Model {
         id: ballModel
         property real directionX: 0
         property real directionY: 0
         // How many ms the ball flies
         readonly property real speed: 2000
         readonly property real ballScale: ballSize / 100
         property var moves: []
         readonly property int maxMoves: 5
         readonly property bool ballMoving: ballAnimation.running

         source: "#Sphere"
         scale: Qt.vector3d(ballScale, ballScale, ballScale)

         materials: DefaultMaterial {
             diffuseMap: Texture {
                 source: "images/ball.jpg"
             }
             normalMap: Texture {
                 source: "images/ball_n.jpg"
             }
             bumpAmount: 1.0
         }

When mouse is moved or touch-screen is swiped, last `maxMoves` positions before releasing the ball are stored into `moves` array. When user releases the ball, `throwBall()` gets called, which calculates the ball direction from these latest positions, and starts animating it.

     function resetBall() {
         moves = [];
         x = 0;
         y = ballSize/2;
         z = 400;
     }

     function moveBall(posX, posY) {
         var pos = view3D.mapTo3DScene(Qt.vector3d(posX, posY, ballModel.z + ballSize));
         pos.y = Math.max(ballSize / 2, pos.y);
         var point = {"x": pos.x, "y": pos.y };
         moves.push(point);
         if (moves.length > maxMoves) moves.shift();
         // Apply position into ball model
         ballModel.x = pos.x;
         ballModel.y = pos.y;
     }

     function throwBall() {
         currentBalls--;
         var moveX = 0;
         var moveY = 0;
         if (moves.length >= 2) {
             var first = moves.shift();
             var last = moves.pop();
             moveX = last.x - first.x;
             moveY = last.y - first.y;
             if (moveY < 0) moveY = 0;
         }
         directionX = moveX * 20;
         directionY = moveY * 4;
         ballAnimation.start();
     }

The ball position is animated separately among different axis. These animations use previously assigned `directionX` and `directionY` to define where the ball moves to, as well as `speed` for the ball flying time. Vertical position has two sequential animations, so we can use easing for ball bounce. When position animations finish, we'll check if there are still balls left or should the game end. Finally we animate also rotation of the ball, so user can throw curve balls.

     ParallelAnimation {
         id: ballAnimation
         running: false
         // Move forward
         NumberAnimation {
             target: ballModel
             property: "z"
             duration: ballModel.speed
             to: -ballModel.directionY * 5
             easing.type: Easing.OutQuad
         }
         // Move up & down with a bounce
         SequentialAnimation {
             NumberAnimation {
                 target: ballModel
                 property: "y"
                 duration: ballModel.speed * (1 / 3)
                 to: ballModel.y + ballModel.directionY
                 easing.type: Easing.OutQuad
             }
             NumberAnimation {
                 target: ballModel
                 property: "y"
                 duration: ballModel.speed * (2 / 3)
                 to: ballSize / 4
                 easing.type: Easing.OutBounce
             }
         }
         // Move sideways
         NumberAnimation {
             target: ballModel
             property: "x"
             duration: ballModel.speed
             to: ballModel.x + ballModel.directionX
         }

         onFinished: {
             if (currentBalls <= 0)
                 view3D.endGame();
             ballModel.resetBall();
         }
     }

     NumberAnimation on eulerRotation.z {
         running: ballModel.ballMoving
         loops: Animation.Infinite
         from: ballModel.directionX < 0 ? 0 : 720
         to: 360
         duration: 10000 / (2 + Math.abs(ballModel.directionX * 0.05))
     }

Important part of the game playing is detecting when the ball hits the targets. Whenever ball z position changes, we loop through `targets` array and detect if ball is touching any of them using `fuzzyEquals()`. Whenever we detect a hit, we'll call target `hit()` function and check if all targets are down.

     onZChanged: {
         // Loop through target items and detect collisions
         var hitMargin = ballSize / 2 + targetSize / 2;
         for (var i = 0; i < targetsNode.targets.length; ++i) {
             var target = targetsNode.targets[i];
             var targetPos = target.scenePosition;
             var hit = ballModel.scenePosition.fuzzyEquals(targetPos, hitMargin);
             if (hit) {
                 target.hit();
                 if (targetsNode.currentTargets <= 0)
                     view3D.endGame();
             }
         }
     }

Then we can switch to targets. Those are dynamically generated into a grouping node which contains helper functions and allows e.g. animating all targets as a group. Note that `currentTargets` property is needed because in QML arrays changes are not triggering bindings, so we will update the amount of targets manually.

     Node {
         id: targetsNode

         property var targets: []
         property int currentTargets: 0

         function addTargets(items) {
             items.forEach(function (item) {
                 let instance = targetComponent.createObject(
                         targetsNode, { "x": item.x, "startPosY": item.y, "z": item.z, "points": item.points});
                 targets.push(instance);
             });
             currentTargets = targets.length;
         }

         function removeTarget(item) {
             var index = targets.indexOf(item);
             targets.splice(index, 1);
             currentTargets = targets.length;
         }

         function resetTargets() {
             while (targets.length > 0)
                 targets.pop().destroy();
             currentTargets = targets.length;
         }
     }

Targets are nodes with a cube model and a text element for showing points. Similarly to the ball model, we use diffuseMap and normalMap textures to create cubes with a Qt logo. When the hit is detected, we sequentially animate the cube away and show the points gained from this target. Once the animation is finished, we will dynamically remove the target node.

     Component {
         id: targetComponent
         Node {
             id: targetNode

             property int points: 0
             property real hide: 0
             property real startPosY: 0
             property real posY: 0
             property real pointsOpacity: 0

             function hit() {
                 targetsNode.removeTarget(this);
                 score += points;
                 hitAnimation.start();
                 var burstPos = targetNode.mapPositionToScene(Qt.vector3d(0, 0, 0));
                 hitParticleEmitter.burst(100, 200, burstPos);
             }

             y: startPosY + posY
             SequentialAnimation on posY {
                 running: gameOn && !hitAnimation.running
                 loops: Animation.Infinite
                 NumberAnimation {
                     from: 0
                     to: 150
                     duration: 3000
                     easing.type: Easing.InOutQuad
                 }
                 NumberAnimation {
                     to: 0
                     duration: 1500
                     easing.type: Easing.InOutQuad
                 }
             }

             SequentialAnimation {
                 id: hitAnimation
                 NumberAnimation {
                     target: targetNode
                     property: "hide"
                     to: 1
                     duration: 800
                     easing.type: Easing.InOutQuad
                 }
                 NumberAnimation {
                     target: targetNode
                     property: "pointsOpacity"
                     to: 1
                     duration: 1000
                     easing.type: Easing.InOutQuad
                 }
                 NumberAnimation {
                     target: targetNode
                     property: "pointsOpacity"
                     to: 0
                     duration: 200
                     easing.type: Easing.InOutQuad
                 }
                 ScriptAction {
                     script: targetNode.destroy();
                 }
             }

             Model {
                 id: targetModel

                 readonly property real targetScale: (1 + hide) * (targetSize / 100)

                 source: "#Cube"
                 scale: Qt.vector3d(targetScale, targetScale, targetScale)
                 opacity: 0.99 - hide * 2
                 materials: DefaultMaterial {
                     diffuseMap: Texture {
                         source: "images/qt_logo.jpg"
                     }
                     normalMap: Texture {
                         source: "images/qt_logo_n.jpg"
                     }
                     bumpAmount: 1.0
                 }
                 Vector3dAnimation on eulerRotation {
                     loops: Animation.Infinite
                     duration: 5000
                     from: Qt.vector3d(0, 0, 0)
                     to: Qt.vector3d(360, 360, 360)
                 }
             }
             Text {
                 anchors.centerIn: parent
                 scale: 1 + pointsOpacity
                 opacity: pointsOpacity
                 text: targetNode.points
                 font.pixelSize: 60 * px
                 color: "#808000"
                 style: Text.Outline
                 styleColor: "#f0f000"
             }
         }
     }

We also need some models for the playing area. Ground model is a rectangle with grass textures scaled to fill a larger area.

     Model {
         source: "#Rectangle"
         scale: Qt.vector3d(50, 50, 1)
         eulerRotation.x: -90
         materials: DefaultMaterial {
             diffuseMap: Texture {
                 source: "images/grass.jpg"
                 tilingModeHorizontal: Texture.Repeat
                 tilingModeVertical: Texture.Repeat
                 scaleU: 25.0
                 scaleV: 25.0
             }
             normalMap: Texture {
                 source: "images/grass_n.jpg"
             }
             bumpAmount: 0.6
         }
     }

Sky model is further back, and we don't want shadows cast into the sky, so we set receivesShadows to false. For the sky we also add some stars using Qt Quick Particles module. Similarly to other 2D Qt Quick elements, also particles can be directly added inside 3D nodes.

     Model {
         id: sky
         property real scaleX: 100
         property real scaleY: 20
         source: "#Rectangle"
         scale: Qt.vector3d(sky.scaleX, sky.scaleY, 1)
         position: Qt.vector3d(0, 960, -2000)
         // We don't want shadows casted into sky
         receivesShadows: false
         materials: DefaultMaterial {
             diffuseMap: Texture {
                 source: "images/sky.jpg"
             }
         }
         // Star particles
         Node {
             z: 500
             y: 30
             // Stars are far away, scale up to half the resolution
             scale: Qt.vector3d(2 / sky.scaleX, 2 / sky.scaleY, 1)
             ParticleSystem {
                 anchors.horizontalCenter: parent.horizontalCenter
                 anchors.top: parent.top
                 width: 3000
                 height: 400
                 ImageParticle {
                     source: "qrc:///particleresources/star.png"
                     rotationVariation: 360
                     color: "#ffffa0"
                     colorVariation: 0.1
                 }
                 Emitter {
                     anchors.fill: parent
                     emitRate: 4
                     lifeSpan: 6000
                     lifeSpanVariation: 4000
                     size: 30
                     sizeVariation: 20
                 }
             }
         }
     }

When we combine the above ground and sky models we get a 3D world like this:

Finally we add some sparkles for the targets, this time using the QtQuick3D.Particles3D module. ParticleSystem3D contains a SpriteParticle3D and we allocate `200` or them, which is enough for two simultaneous `100` particle bursts. ParticleEmitter3D defines the emitting properties for the particles like scale, rotation, velocity and lifeSpan. We also add Gravity3D affector to drag the particles down with a suitable magnitude.

     ParticleSystem3D {
         id: psystem
         SpriteParticle3D {
             id: sprite
             sprite: Texture {
                 source: "images/particle.png"
             }
             color: Qt.rgba(1.0, 1.0, 0.0, 1.0)
             colorVariation: Qt.vector4d(0.4, 0.6, 0.0, 0.0)
             unifiedColorVariation: true
             maxAmount: 200
         }
         ParticleEmitter3D {
             id: hitParticleEmitter
             particle: sprite
             particleScale: 4.0
             particleScaleVariation: 2.0
             particleRotationVariation: Qt.vector3d(0, 0, 180)
             particleRotationVelocityVariation: Qt.vector3d(0, 0, 250)
             velocity: VectorDirection3D {
                 direction: Qt.vector3d(0, 300, 0)
                 directionVariation: Qt.vector3d(200, 150, 100)
             }
             lifeSpan: 800
             lifeSpanVariation: 200
             depthBias: 100
         }
         Gravity3D {
             magnitude: 600
         }
     }

This ends the 3D parts of our game. There are still some 2D Qt Quick elements to show the time, scores, start button etc. which are important for the game, but not relevant for this Quick 3D documentation.

Now the ball is on your side (pun intended). Feel free to extend the game in different ways and generate new wacky levels!

Files:

- quickball/CMakeLists.txt
- quickball/main.cpp
- quickball/main.qml
- quickball/qml.qrc
- quickball/quickball.pro

Images:

- quickball/images/ball.jpg
- quickball/images/ball_icon.png
- quickball/images/ball_n.jpg
- quickball/images/grass.jpg
- quickball/images/grass_n.jpg
- quickball/images/particle.png
- quickball/images/qt_logo.jpg
- quickball/images/qt_logo_n.jpg
- quickball/images/quickball.png
- quickball/images/sky.jpg