如何在xamarin表单中手绘现有的图像

using SkiaSharp;
using SkiaSharp.Views.Forms;
using Xamarin.Forms;

public class HandDrawPage : ContentPage
{
    SKCanvasView canvasView;
    SKBitmap bitmap;
    SKPath path;
    SKPaint paint;

    public HandDrawPage()
    {
        canvasView = new SKCanvasView();
        canvasView.PaintSurface += OnCanvasViewPaintSurface;
        canvasView.Touch += OnCanvasViewTouch;

        Content = canvasView;
    }

    protected override void OnAppearing()
    {
        base.OnAppearing();

        // 加载现有图像
        bitmap = SKBitmap.Decode("path_to_existing_image");

        // 初始化画笔
        paint = new SKPaint
        {
            Style = SKPaintStyle.Stroke,
            Color = SKColors.Black,
            StrokeWidth = 5
        };

        // 初始化路径
        path = new SKPath();
    }

    void OnCanvasViewPaintSurface(object sender, SKPaintSurfaceEventArgs args)
    {
        SKSurface surface = args.Surface;
        SKCanvas canvas = surface.Canvas;

        // 清空画布
        canvas.Clear();

        // 绘制现有图像
        canvas.DrawBitmap(bitmap, new SKRect(0, 0, canvasView.Width, canvasView.Height));

        // 绘制手绘路径
        canvas.DrawPath(path, paint);
    }

    void OnCanvasViewTouch(object sender, SKTouchEventArgs args)
    {
        switch (args.ActionType)
        {
            case SKTouchAction.Pressed:
                // 开始手绘
                path.MoveTo(args.Location);
                break;
            case SKTouchAction.Moved:
                // 手指移动时更新手绘路径
                path.LineTo(args.Location);
                break;
            case SKTouchAction.Released:
                // 手指释放时结束手绘
                path.LineTo(args.Location);
                path.Close();
                break;
        }

        // 更新画布
        canvasView.InvalidateSurface();
    }
}