QML 攝像機應用程序

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.

運行範例

要運行範例從 Qt Creator ，打開 歡迎 模式，然後選擇範例從 範例 。更多信息，見 Qt Creator：教程：構建並運行 .

應用程序結構

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 像這樣：

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.