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

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

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 : captureControls.state === "MobilePortrait" ? -buttonPaneShadow.height/2 : 0
         width : 100
         height: parent.height - (flashControl.visible * flashControl.height)

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

     property Camera cameraDevice
     property bool mIsFlashSupported: (cameraDevice && cameraDevice.active) ? cameraDevice.isFlashModeSupported(Camera.FlashOn) : false
     property bool mIsTorchSupported: (cameraDevice && cameraDevice.active) ? cameraDevice.isTorchModeSupported(Camera.TorchOn) : false

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

         Switch {
             id: flashModeControl
             visible: flashControl.mIsFlashSupported
             opacity: checked ? 0.75 : 0.25
             text: "Flash"
             contentItem: Text {
                 text: flashModeControl.text
                 color: "white"
                 leftPadding: flashModeControl.indicator.width + flashModeControl.spacing
             }

             onPositionChanged: {
                 if (position) {
                     if (torchModeControl.checked)
                         torchModeControl.toggle();
                     flashControl.cameraDevice.flashMode = Camera.FlashOn

                 } else {
                     flashControl.cameraDevice.flashMode = Camera.FlashOff
                 }
             }
         }

Torch control is implemented in a similar way.

Example project @ code.qt.io

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