使用 MediaCapture 處理裝置方向

當你的應用程式擷取照片或影片用於應用程式外使用時，例如儲存到檔案或分享，你需要用正確的方向元資料編碼圖片，讓內容在其他應用程式和裝置中能正確顯示。 這篇文章說明如何利用輔助類別管理 WinUI 3 桌面應用程式中的相機方向。

先決條件

開始之前，請確定您擁有：

• 一個 WinUI 3 桌面專案（打包或非打包）。
• 連接到你的裝置的相容攝影機。
• 為您的應用程式宣告的相機存取權限：

  • 套裝應用程式：將裝置功能加入webcam：Package.appxmanifest

    <Capabilities>
        <DeviceCapability Name="webcam" />
    </Capabilities>
    

  • 未封裝應用程式：沒有清單功能可以宣告。 相機存取則由使用者裝置上的「設定>>」中「讓桌面應用程式存取你的相機」設定來控制。

使用者仍可在作業系統層級拒絕攝影機存取。 在初始化攝影機前，請檢查存取權限，並優雅地處理被拒絕的案件，詳見「處理 Windows 攝影機隱私設定」的說明。

方向概念

桌面應用程式通常在固定螢幕的裝置上運行，因此你不需要像行動應用程式那樣處理持續旋轉。 不過，你仍然需要考慮以下事項：

• 相機感測器的方向 ——相機感測器的物理安裝角度，依裝置而異。
• 外部攝影機旋轉 — 使用者可旋轉外部攝影機。

關鍵概念是在編碼拍攝的照片或影片時，套用旋轉修正，使輸出與使用者預覽中看到的相符。

建立 CameraRotationHelper 類別

以下輔助類別根據相機感測器的方向與裝置方向感測器來管理旋轉值：

using Windows.Devices.Enumeration;
using Windows.Devices.Sensors;
using Windows.Media.Capture;
using Windows.Storage.FileProperties;

public class CameraRotationHelper
{
    private readonly EnclosureLocation _cameraEnclosureLocation;
    private readonly SimpleOrientationSensor _orientationSensor;
    private SimpleOrientation _deviceOrientation =
        SimpleOrientation.NotRotated;

    public event EventHandler<bool> OrientationChanged;

    public CameraRotationHelper(
        EnclosureLocation cameraEnclosureLocation)
    {
        _cameraEnclosureLocation = cameraEnclosureLocation;

        _orientationSensor =
            SimpleOrientationSensor.GetDefault();

        if (_orientationSensor != null)
        {
            _orientationSensor.OrientationChanged +=
                OrientationSensor_OrientationChanged;
        }
    }

    private void OrientationSensor_OrientationChanged(
        SimpleOrientationSensor sender,
        SimpleOrientationSensorOrientationChangedEventArgs args)
    {
        if (args.Orientation != SimpleOrientation.Faceup &&
            args.Orientation != SimpleOrientation.Facedown)
        {
            _deviceOrientation = args.Orientation;
            OrientationChanged?.Invoke(this, true);
        }
    }

    public static bool IsEnclosureLocationExternal(
        EnclosureLocation enclosureLocation)
    {
        return enclosureLocation == null ||
            enclosureLocation.Panel == Windows.Devices.Enumeration.Panel.Unknown;
    }

    private bool IsCameraMirrored()
    {
        // Front panel cameras are mirrored by convention
        return _cameraEnclosureLocation?.Panel == Windows.Devices.Enumeration.Panel.Front;
    }

    private SimpleOrientation GetCameraOrientation()
    {
        if (IsEnclosureLocationExternal(_cameraEnclosureLocation))
        {
            return SimpleOrientation.NotRotated;
        }

        // Get the sensor orientation from the device
        return _deviceOrientation;
    }

    /// <summary>
    /// Gets the rotation to apply to the camera preview stream.
    /// </summary>
    public VideoRotation GetCameraPreviewOrientation()
    {
        if (IsEnclosureLocationExternal(_cameraEnclosureLocation))
        {
            return VideoRotation.None;
        }

        return ConvertSimpleOrientationToVideoRotation(
            GetCameraOrientation());
    }

    /// <summary>
    /// Gets the rotation to apply when encoding a photo.
    /// </summary>
    public PhotoOrientation GetCapturePhotoOrientation()
    {
        if (IsEnclosureLocationExternal(_cameraEnclosureLocation))
        {
            return PhotoOrientation.Normal;
        }

        int encodingRotation = ConvertDeviceOrientationToDegrees(
            GetCameraOrientation());

        if (IsCameraMirrored())
        {
            encodingRotation = (360 - encodingRotation) % 360;
        }

        return ConvertDegreesToPhotoOrientation(encodingRotation);
    }

    /// <summary>
    /// Gets the clockwise rotation to apply when encoding a video.
    /// </summary>
    public int GetCaptureVideoOrientation()
    {
        if (IsEnclosureLocationExternal(_cameraEnclosureLocation))
        {
            return 0;
        }

        int rotation = ConvertDeviceOrientationToDegrees(
            GetCameraOrientation());

        if (IsCameraMirrored())
        {
            rotation = (360 - rotation) % 360;
        }

        return rotation;
    }

    public void Dispose()
    {
        if (_orientationSensor != null)
        {
            _orientationSensor.OrientationChanged -=
                OrientationSensor_OrientationChanged;
        }
    }

    private static int ConvertDeviceOrientationToDegrees(
        SimpleOrientation orientation)
    {
        // TODO: This mapping from counterclockwise SimpleOrientation values
        // to clockwise degree values (for example, mapping
        // Rotated90DegreesCounterclockwise to 90) was carried over from the
        // original UWP sample this article is based on. Verify this mapping
        // against physical devices before relying on it in production; do
        // not change these values without hardware verification.
        return orientation switch
        {
            SimpleOrientation.Rotated90DegreesCounterclockwise => 90,
            SimpleOrientation.Rotated180DegreesCounterclockwise => 180,
            SimpleOrientation.Rotated270DegreesCounterclockwise => 270,
            _ => 0,
        };
    }

    private static VideoRotation ConvertSimpleOrientationToVideoRotation(
        SimpleOrientation orientation)
    {
        // TODO: See the verification note on ConvertDeviceOrientationToDegrees
        // above — this CCW-to-CW mapping needs the same device verification
        // before the values are changed.
        return orientation switch
        {
            SimpleOrientation.Rotated90DegreesCounterclockwise =>
                VideoRotation.Clockwise90Degrees,
            SimpleOrientation.Rotated180DegreesCounterclockwise =>
                VideoRotation.Clockwise180Degrees,
            SimpleOrientation.Rotated270DegreesCounterclockwise =>
                VideoRotation.Clockwise270Degrees,
            _ => VideoRotation.None,
        };
    }

    private static PhotoOrientation ConvertDegreesToPhotoOrientation(
        int degrees)
    {
        return degrees switch
        {
            90 => PhotoOrientation.Rotate90,
            180 => PhotoOrientation.Rotate180,
            270 => PhotoOrientation.Rotate270,
            _ => PhotoOrientation.Normal,
        };
    }
}

使用輔助類別

在建立 MediaCapture 實例並得知攝影機外殼的位置後，請初始化輔助程式：

private CameraRotationHelper _rotationHelper;
private MediaCapture _mediaCapture;

private async Task InitializeCameraAsync()
{
    _mediaCapture = new MediaCapture();
    await _mediaCapture.InitializeAsync();

    var cameraDevice = _mediaCapture.MediaCaptureSettings;

    // Find the camera device info to get enclosure location
    var devices = await DeviceInformation.FindAllAsync(
        DeviceClass.VideoCapture);
    var deviceInfo = devices.FirstOrDefault(
        d => d.Id == cameraDevice.VideoDeviceId);

    _rotationHelper = new CameraRotationHelper(
        deviceInfo?.EnclosureLocation);

    _rotationHelper.OrientationChanged += (s, e) =>
    {
        // Update preview rotation when device orientation changes
        DispatcherQueue.TryEnqueue(UpdatePreviewRotation);
    };
}

對預覽套用旋轉

當方向變更時，在你的 MediaCapture 實例上設定預覽畫面的旋轉：

private void UpdatePreviewRotation()
{
    var rotation = _rotationHelper.GetCameraPreviewOrientation();
    _mediaCapture.SetPreviewRotation(rotation);
}

拍照時套用旋轉設定

儲存拍攝照片時設定方向元資料：

using System.Collections.Generic;
using Windows.Storage;
using Windows.Storage.FileProperties;

private async Task CapturePhotoWithOrientationAsync()
{
    var file = await ApplicationData.Current.LocalFolder
        .CreateFileAsync("photo.jpg",
            CreationCollisionOption.GenerateUniqueName);

    await _mediaCapture.CapturePhotoToStorageFileAsync(
        ImageEncodingProperties.CreateJpeg(), file);

    // Set the orientation metadata. ImageProperties.Orientation is
    // read-only, so save the EXIF orientation value directly through
    // the file's property store instead.
    var photoOrientation =
        _rotationHelper.GetCapturePhotoOrientation();

    var propertiesToSave = new List<KeyValuePair<string, object>>
    {
        new KeyValuePair<string, object>(
            "System.Photo.Orientation", photoOrientation)
    };
    await file.Properties.SavePropertiesAsync(propertiesToSave);
}

相關內容

• 相機預覽存取
• 使用 MediaCapture 擷取基本相片、視訊和音訊
• 相機