Windows Store App放大镜

Question

我正在研究Windows 8.1的绘图应用程序，需要一种简单的方式来显示用户触摸的区域。显然，在使用手指时，很难看到你在哪里画画。我需要做的是能够将目标元素呈现为位图，并将其显示给用户，以便它们可以看到它们在绘制位置。我想到的是在下面的答案。

Answer 1

代码如下。要使用它，只需在XAML（或编程方式）中添加控件，无论您想要哪个，并将目标属性设置为要预览的控件。

例如，在我的情况下，我在webview上绘制，所以我将WebView设置为目标，并将放大镜添加为兄弟姐妹。

public class Magnifier : Grid
{
    public Magnifier() : base()
    {
        this.Canvas = new Canvas();

        Border border = new Border();
        border.HorizontalAlignment = HorizontalAlignment.Left;
        border.VerticalAlignment = VerticalAlignment.Top;
        border.Child = this.Canvas;
        border.BorderBrush = new SolidColorBrush(Colors.Red);
        border.BorderThickness = new Thickness(10);
        border.Background = new SolidColorBrush(Colors.Black);

        this.Children.Add(border);

        this.border = border;
    }

    public async Task<object> Update(int x, int y)
    {
        this.Visibility = Visibility.Visible;

        // changes the amount of magnification
        int magnification = 2;

        // render the preview of the target
        RenderTargetBitmap bitmap = new RenderTargetBitmap();
        await bitmap.RenderAsync(this.Target);

        this.Canvas.Width = this.PreviewWidth;
        this.Canvas.Height = this.PreviewHeight;

        double w = this.PreviewWidth / (2 * magnification);
        double h = this.PreviewHeight / (2 * magnification);

        ImageBrush brush = new ImageBrush();
        brush.ImageSource = bitmap;

        double scaleX = this.Target.ActualWidth / this.PreviewWidth;
        double scaleY = this.Target.ActualHeight / this.PreviewHeight;

        TransformGroup transform = new TransformGroup();
        TranslateTransform translate = new TranslateTransform();
        translate.X = -(x - w) / scaleX;
        translate.Y = -(y - h) / scaleY;
        transform.Children.Add(translate);

        ScaleTransform scale = new ScaleTransform();
        scale.ScaleX = scaleX * magnification;
        scale.ScaleY = scaleY * magnification;

        transform.Children.Add(scale);

        brush.Transform = transform;

        Rectangle rect = new Rectangle();
        rect.Width = this.PreviewWidth;
        rect.Height = this.PreviewHeight;
        rect.Fill = brush;
        this.Canvas.Children.Clear();
        this.Canvas.Children.Add(rect);

        Ellipse centerDot = new Ellipse();
        centerDot.Width = 6;
        centerDot.Height = 6;
        centerDot.Fill = new SolidColorBrush(Colors.Red);

        Canvas.SetLeft(centerDot, this.PreviewWidth / 2 - 3);
        Canvas.SetTop(centerDot, this.PreviewHeight / 2 - 3);

        this.Canvas.Children.Add(centerDot);

        return null;
    }

    public Canvas Canvas { get; set; }
    public int PreviewWidth { get; set; }
    public int PreviewHeight { get; set; }
    private Border border = null;
    public FrameworkElement Target { get; set; }
}

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