- Qt 6.12
- Qt Multimedia
- Qt Multimedia Examples
- QML Camera Application
- Qt 6.12.0 Reference Documentation

# QML Camera Application

This Qt Quick based application shows how to use the API to capture a still image or video.

This example demonstrates how to access camera functions via QML. It shows how to change settings and capture images or video.

#### Running the Example

You can run the example from:

- Qt Creator

  Open the Welcome mode and select the example from Examples. For more information, see Qt Creator: Tutorial: Build and run.

- Qt Extension for Visual Studio Code

  Run the Qt: Open Qt examples command from the Command Palette, and select the example from the list. For more information, see Qt Extension for Visual Studio Code: Tutorial: Build and run.

#### Application structure

Most of the QML code in this example supports the user interface. Custom types that support the requirements have been implemented using existing Qt Quick controls.

#### Using screen orientation to select layout

The orientation and control layout state logic is encapsulated in a separate Item, `controlLayout` like so:

     Item {
         id: controlLayout

         readonly property bool isMobile: Qt.platform.os === "android" || Qt.platform.os === "ios"
         readonly property bool isLandscape: Screen.desktopAvailableWidth >= Screen.desktopAvailableHeight
         property int buttonsWidth: state === "MobilePortrait" ? Screen.desktopAvailableWidth / 3.4 : 114

         states: [
             State {
                 name: "MobileLandscape"
                 when: controlLayout.isMobile && controlLayout.isLandscape
             },
             State {
                 name: "MobilePortrait"
                 when: controlLayout.isMobile && !controlLayout.isLandscape
             },
             State {
                 name: "Other"
                 when: !controlLayout.isMobile
             }
         ]

         onStateChanged: {
             console.log("State: " + controlLayout.state)
         }
     }

The `stillControls` and `videoControls` objects both bind to the `state` and `buttonsWidth` properties of this Item, as shown in `stillControls`:

     PhotoCaptureControls {
         id: stillControls
         state: controlLayout.state
         anchors.fill: parent
         buttonsWidth: controlLayout.buttonsWidth
         buttonsPanelPortraitHeight: cameraUI.buttonsPanelPortraitHeight
         buttonsPanelWidth: cameraUI.buttonsPanelLandscapeWidth
         captureSession: captureSession
         visible: (cameraUI.state === "PhotoCapture")
         onPreviewSelected: cameraUI.state = "PhotoPreview"
         onVideoModeSelected: cameraUI.state = "VideoCapture"
         previewAvailable: imageCapture.preview.length !== 0
     }

To support debugging, a message about layout state change is logged.

Here is the portrait layout:

You can see the `state` property is initially set as `PhotoCapture`.

Then the `states` themselves are defined like so:

     states: [
         State {
             name: "PhotoCapture"
             StateChangeScript {
                 script: {
                     camera.start()
                 }
             }
         },
         State {
             name: "PhotoPreview"
         },
         State {
             name: "VideoCapture"
             StateChangeScript {
                 script: {
                     camera.start()
                 }
             }
         },
         State {
             name: "VideoPreview"
             StateChangeScript {
                 script: {
                     camera.stop()
                 }
             }
         }
     ]

#### Controls for capturing

Controls for capturing are implemented in `PhotoCaptureControls.qml` and VideoCaptureControls.qml. They each are based on a FocusScope that defines common buttons dimensions and margins that are used by the control buttons and then declares the buttons.

This generates a column on the right hand side of the screen which includes, listed top to bottom, the following controls:

- A `Capture` or `Record` button, which initiates capturing.
- A `capture properties` button that displays the icon of the current white balance mode selected and when pressed uses a pop-up to displays the following option's icons:
  - Flash mode (if available)
  - White balance modes
  - Exposure compensation
- A `View` button, once something has been captured.
- A button which displays the currently selected capture device and when pressed provides a list of available devices to switch to, using a pop-up.
- A `Switch To` button that displays the alternate capture mode (video or photo) depending on the current active selection and switches the mode when pressed.
- A `Quit` button, that exits the application.

#### Image capturing

The button that triggers this is defined in CameraButton.qml: but its interaction with the camera is in the controls types, lets look at PhotoCaptureControls:

     CameraButton {
         text: "Capture"
         implicitWidth: captureControls.buttonsWidth
         visible: captureControls.captureSession.imageCapture.readyForCapture
         onClicked: captureControls.captureSession.imageCapture.captureToFile("")
     }

#### Zoom control

Implemented in `ZoomControl.qml` the ZoomControl type is based on an Item and creates a bar that represents the zoom level, which can also be dragged. It uses an exponential calculation method to determine the zoom factor given the position of the `grove`.

The bar is only visible if the initialZoom is greater than 1. This means the currently active camera has a zoom function.

     Item {
         id : zoomControl
         property real currentZoom : 1
         property real maximumZoom : 1
         property real minimumZoom : 1
         signal zoomTo(real target)

         visible: zoomControl.maximumZoom > zoomControl.minimumZoom

         MouseArea {
             id : mouseArea
             anchors.fill: parent

             property real initialZoom : 0
             property real initialPos : 0

             onPressed: {
                 initialPos = mouseY
                 initialZoom = zoomControl.currentZoom
             }

             onPositionChanged: {
                 if (pressed) {
                     var target = initialZoom * Math.pow(5, (initialPos-mouseY)/zoomControl.height);
                     target = Math.max(zoomControl.minimumZoom, Math.min(target, zoomControl.maximumZoom))
                     zoomControl.zoomTo(target)
                 }
             }
         }

         Item {
             id : bar
             x : 16
             y : parent.height/4
             width : 24
             height : parent.height/2

             Rectangle {
                 anchors.fill: parent

                 smooth: true
                 radius: 8
                 border.color: "white"
                 border.width: 2
                 color: "black"
                 opacity: 0.3
             }

             Rectangle {
                 id: groove
                 x : 0
                 y : parent.height * (1.0 - (zoomControl.currentZoom-zoomControl.minimumZoom) / (zoomControl.maximumZoom-zoomControl.minimumZoom))
                 width: parent.width
                 height: parent.height - y
                 smooth: true
                 radius: 8
                 color: "white"
                 opacity: 0.5
             }

             Text {
                 id: zoomText
                 anchors {
                     left: bar.right; leftMargin: 16
                 }
                 y: Math.min(parent.height - height, Math.max(0, groove.y - height / 2))
                 text: "x" + Math.round(zoomControl.currentZoom * 100) / 100
                 font.bold: true
                 color: "white"
                 style: Text.Raised; styleColor: "black"
                 opacity: 0.85
                 font.pixelSize: 18
             }
         }
     }

In PhotoCaptureControls.qml and VideoCaptureControls.qml the signal `zoomTo` will set the selected camera's zoomFactor property to the calculated `target` value, as well as updating the ZoomControl bar.

     ZoomControl {
         x : 0
         y : 0
         width : 100
         height: parent.height - (flashControl.visible * flashControl.height) -
                 (captureControls.state === "MobilePortrait" ? buttonPaneShadow.height : 0)

         currentZoom: captureControls.camera.zoomFactor
         maximumZoom: captureControls.camera.maximumZoomFactor
         minimumZoom: captureControls.camera.minimumZoomFactor
         onZoomTo: (target) => captureControls.camera.zoomFactor = target
     }

#### Flash and torch control

Defined in `FlashControl.qml` this enables flash mode selection and torch functionality to be toggled via a Switch. As with the zoom control, the switches are only visible on top of the preview window if the active device supports these functions.

Here we check if the functions are supported:

     required property Camera camera

     property bool mIsFlashSupported: camera.isFlashModeSupported(Camera.FlashOn)
     property bool mIsTorchSupported: camera.isTorchModeSupported(Camera.TorchOn)

Here we implement the `flashModeControl` switch, which also directly controls the Camera device.

     Switch {
         id: flashModeControl
         visible: topItem.mIsFlashSupported
         checked: topItem.camera.flashMode === Camera.FlashOn
         opacity: checked ? 0.75 : 0.25
         text: "Flash"

         contentItem: Text {
             text: flashModeControl.text
             color: "white"
             leftPadding: flashModeControl.indicator.width + flashModeControl.spacing
         }

         onClicked: topItem.camera.flashMode = checked ? Camera.FlashOn : Camera.FlashOff
     }

Torch control is implemented in a similar way.

Example project @ code.qt.io