相当于UWP的DrawingVisual

Question

I have a bitmap image of a person and I would like to draw a rectangle over the person's face. I have the coordinates of the rectangle (x, y, width, height). Like this:

If I were using WPF, then I could achieve this using the DrawingVisual and DrawingContext classes. Unfortunately they are not available in UWP. Are there any equivalent API's available or maybe a NuGet package to achieve the same functionality?

Answer 1

I am using the 'WriteableBitmapEx' Nuget Package solved this problem. More information is http://kaki104.tistory.com/517

Sample code:

private async void BrowseButton_Click(object sender, RoutedEventArgs e)
{
    //FileOpePicker
    var openDlg = new FileOpenPicker();
    openDlg.FileTypeFilter.Add(".jpg");
    openDlg.FileTypeFilter.Add(".jpeg");
    openDlg.FileTypeFilter.Add(".png");
    //Open file selection window
    var result = await openDlg.PickSingleFileAsync();
    if (result == null || !result.IsAvailable) return;
    var file = await StorageFile.GetFileFromPathAsync(result.Path);
    var property = await file.Properties.GetImagePropertiesAsync();
    //Create bitmap from image size
    var writeableBmp = BitmapFactory.New((int)property.Width, (int)property.Height);
    using (writeableBmp.GetBitmapContext())
    {
        //Load bitmap from image file
        using (var fileStream = await file.OpenAsync(FileAccessMode.Read))
        {
            writeableBmp = await BitmapFactory.New(1, 1).FromStream(fileStream, BitmapPixelFormat.Bgra8);
        }
    }

    //find face that DetectAsync Face API
    using (var imageFileStream = await file.OpenStreamForReadAsync())
    {
        var faces = await faceServiceClient.DetectAsync(imageFileStream);
        if (faces == null) return;
        //display rect
        foreach (var face in faces)
        {
            writeableBmp.DrawRectangle(face.FaceRectangle.Left, face.FaceRectangle.Top,
            face.FaceRectangle.Left + face.FaceRectangle.Width,
            face.FaceRectangle.Top + face.FaceRectangle.Height, Colors.Red);
        }
    }
    FacePhoto.Source = writeableBmp;
}

Answer 2

A solution I have come up with is encompassing the image in a Grid and placing an ItemsControl on top of it which is bound to a set of rectangles and a Canvas as a panel template:

<Grid>
    <Image Source="{Binding Image}" />
    <ItemsControl ItemsSource="{Binding Rectangles}">
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <Canvas />
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
        <ItemsControl.ItemContainerStyle>
            <Style TargetType="ContentPresenter">
                <Setter Property="Helper:BindingHelper.CanvasLeftBindingPath" Value="Left" />
                <Setter Property="Helper:BindingHelper.CanvasTopBindingPath" Value="Top" />
             </Style>
        </ItemsControl.ItemContainerStyle>
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Rectangle Width="{Binding Width}"
                           Height="{Binding Height}"
                           Stroke="{Binding Color}"
                           StrokeThickness="6">
                </Rectangle>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</Grid>

Since Binding in a style setter is not supported in UWP I had to use a binding helper. More about that can be found here UWP Binding in Style Setter not working