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

In declarative-camera.qml we handle detecting the orientation we're in and select the appropriate layout while also catering for the limitations of small screen mobile devices like so:

Rectangle {
    id : cameraUI

    width: 800
    height: 480
    color: "black"
    state: "PhotoCapture"

    property string platformScreen: ""
    property int buttonsPanelLandscapeWidth: 328
    property int buttonsPanelPortraitHeight: 180

    onWidthChanged: {
        setState()
    }
    function setState() {
        if (Qt.platform.os === "android" || Qt.platform.os === "ios") {
            if (Screen.desktopAvailableWidth < Screen.desktopAvailableHeight) {
                stillControls.state = "MobilePortrait";
            } else {
                stillControls.state  = "MobileLandscape";
            }
        } else {
            stillControls.state = "Other";
        }
        console.log("State: " + stillControls.state);
        stillControls.buttonsWidth = (stillControls.state === "MobilePortrait")
                ? Screen.desktopAvailableWidth/3.4 : 144
    }

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: buttonsWidth
                visible: captureSession.imageCapture.readyForCapture
                onClicked: 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
    signal zoomTo(real target)

    visible: zoomControl.maximumZoom > 1

    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(1, 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-1.0) / (zoomControl.maximumZoom-1.0))
            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 : 0
        width : 100
        height: parent.height

        currentZoom: captureSession.camera.zoomFactor
        maximumZoom: captureSession.camera.maximumZoomFactor
        onZoomTo: captureSession.camera.zoomFactor = target
    }

    states: [
        State {
            name: "MobilePortrait"
            PropertyChanges {
                target: buttonPaneShadow
                width: parent.width
                height: buttonsPanelPortraitHeight
            }
            PropertyChanges {
                target: buttonsColumn
                height: captureControls.buttonsPanelPortraitHeight / 2 - buttonsmargin
            }
            PropertyChanges {
                target: bottomColumn
                height: captureControls.buttonsPanelPortraitHeight / 2 - buttonsmargin
            }
            AnchorChanges {
                target: buttonPaneShadow
                anchors.bottom: parent.bottom
                anchors.left: parent.left
                anchors.right: parent.right
            }
            AnchorChanges {
                target: buttonsColumn
                anchors.left: parent.left
                anchors.right: parent.right
                anchors.top: parent.top
            }
            AnchorChanges {
                target: bottomColumn;
                anchors.bottom: parent.bottom
                anchors.left: parent.left
                anchors.right: parent.right
            }
        },
        State {
            name: "MobileLandscape"
            PropertyChanges {
                target: buttonPaneShadow
                width: buttonsPanelWidth
                height: parent.height
            }
            PropertyChanges {
                target: buttonsColumn
                height: parent.height
                width: buttonPaneShadow.width / 2
            }
            PropertyChanges {
                target: bottomColumn
                height: parent.height
                width: buttonPaneShadow.width / 2
            }
            AnchorChanges {
                target: buttonPaneShadow
                anchors.top: parent.top
                anchors.right: parent.right
            }
            AnchorChanges {
                target: buttonsColumn;
                anchors.top: parent.top
                anchors.bottom: parent.bottom
                anchors.left: parent.left;
            }
            AnchorChanges {
                target: bottomColumn;
                anchors.top: parent.top;
                anchors.bottom: parent.bottom;
                anchors.right: parent.right;
            }
        },
        State {
            name: "Other"
            PropertyChanges {
                target: buttonPaneShadow;
                width: bottomColumn.width + 16;
                height: parent.height;
            }
            AnchorChanges {
                target: buttonPaneShadow;
                anchors.top: parent.top;
                anchors.right: parent.right;
            }
            AnchorChanges {
                target: buttonsColumn;
                anchors.top: parent.top
                anchors.right: parent.right
            }
            AnchorChanges {
                target: bottomColumn;
                anchors.bottom: parent.bottom;
                anchors.right: parent.right;
            }
        }
    ]
}

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:



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




Torch control is implemented in a similar way.


Example project @ code.qt.io








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