如何在SkiaSharp中任意在屏幕上从SVG字符串直接绘制SKPath？

如何解决如何在SkiaSharp中任意在屏幕上从SVG字符串直接绘制SKPath？

我正在构建一个应用程序，可以发送和接收 Skia 锐利的图纸。 SKPath 被序列化为 SVG 格式并发送。然后接收端必须反序列化并从 SVG 字符串中绘制 SKPath。但是，在 OnCanvasViewPaintSurface 事件之外执行此操作似乎是不可能的。

我目前正尝试在 Xamarin 示例解决方案的手指绘画示例中执行此操作。 DrawTestLine 方法应该绘制一条我绘制并序列化为 SVG 的手绘线。实际上，它无一例外地运行，但在屏幕上什么也不画。

非常感谢您对此提供的任何帮助。

在下面查看我的修改：

using System;
using System.Collections.Generic;

using Xamarin.Forms;

using TouchTracking;

using SkiaSharp;
using SkiaSharp.Views.Forms;

namespace SkiaSharpFormsDemos.Paths
{
    public partial class FingerPaintPage : ContentPage
    {
        Dictionary<long,SKPath> inProgressPaths = new Dictionary<long,SKPath>();
        List<SKPath> completedPaths = new List<SKPath>();
        SKBitmap bitmap;

        SKPaint paint = new SKPaint
        {
            Style = SKPaintStyle.Stroke,Color = SKColors.Blue,StrokeWidth = 10,StrokeCap = SKStrokeCap.Round,StrokeJoin = SKStrokeJoin.Round
        };

        public FingerPaintPage()
        {
            InitializeComponent();
            DrawTestLine();
        }

        private void DrawTestLine()
        {
            var svgPath = "M851.953 371.006L865.957 438.527L874.922 462.995L880.957 453.997L884.941 441.011L893.965 427.874L895.957 418.233L900.938 415.006L902.93 405.02L898.945 403.998";
            var testPath = SKPath.ParseSvgPathData(svgPath);
            bitmap = new SKBitmap(1920,1080);// (int)canvasView.CanvasSize.Width,(int)canvasView.CanvasSize.Height);
            var canvas = new SKCanvas(bitmap);
            canvas.Clear();
            canvas.DrawPath(testPath,paint);
            canvasView.InvalidateSurface();
        }

        void OnTouchEffectAction(object sender,TouchActionEventArgs args)
        {
            switch (args.Type)
            {
                case TouchActionType.Pressed:
                    if (!inProgressPaths.ContainsKey(args.Id))
                    {
                        SKPath path = new SKPath();
                        path.MoveTo(ConvertToPixel(args.Location));
                        inProgressPaths.Add(args.Id,path);
                        canvasView.InvalidateSurface();
                    }
                    break;

                case TouchActionType.Moved:
                    if (inProgressPaths.ContainsKey(args.Id))
                    {
                        SKPath path = inProgressPaths[args.Id];
                        path.LineTo(ConvertToPixel(args.Location));
                        canvasView.InvalidateSurface();
                    }
                    break;

                case TouchActionType.Released:
                    if (inProgressPaths.ContainsKey(args.Id))
                    {
                        completedPaths.Add(inProgressPaths[args.Id]);
                        inProgressPaths.Remove(args.Id);
                        canvasView.InvalidateSurface();
                    }
                    break;

                case TouchActionType.Cancelled:
                    if (inProgressPaths.ContainsKey(args.Id))
                    {
                        inProgressPaths.Remove(args.Id);
                        canvasView.InvalidateSurface();
                    }
                    break;
            }
        }

        void OnCanvasViewPaintSurface(object sender,SKPaintSurfaceEventArgs args)
        {
            args.Surface.Canvas.DrawBitmap(bitmap,0);

            SKCanvas canvas = args.Surface.Canvas;
            canvas.Clear();

            foreach (SKPath path in completedPaths)
            {
                canvas.DrawPath(path,paint);
            }

            foreach (SKPath path in inProgressPaths.Values)
            {
                canvas.DrawPath(path,paint);
            }
        }

        SKPoint ConvertToPixel(Point pt)
        {
            return new SKPoint((float)(canvasView.CanvasSize.Width * pt.X / canvasView.Width),(float)(canvasView.CanvasSize.Height * pt.Y / canvasView.Height));
        }
    }   
}

解决方法

using System;
using System.Collections.Generic;

using Xamarin.Forms;

using TouchTracking;

using SkiaSharp;
using SkiaSharp.Views.Forms;

namespace SkiaSharpFormsDemos.Paths
{
    public partial class FingerPaintPage : ContentPage
    {
        Dictionary<long,SKPath> inProgressPaths = new Dictionary<long,SKPath>();
        List<SKPath> completedPaths = new List<SKPath>();
        SKBitmap bitmap;

        SKPaint paint = new SKPaint
        {
            Style = SKPaintStyle.Stroke,Color = SKColors.Blue,StrokeWidth = 10,StrokeCap = SKStrokeCap.Round,StrokeJoin = SKStrokeJoin.Round
        };

        SKPath testPath = SKPath.ParseSvgPathData("M851.953 371.006L865.957 438.527L874.922 462.995L880.957 453.997L884.941 441.011L893.965 427.874L895.957 418.233L900.938 415.006L902.93 405.02L898.945 403.998");

        public FingerPaintPage()
        {
            InitializeComponent();
            DrawTestLine();
        }

        private void DrawTestLine()
        {
            canvasView.InvalidateSurface();
        }

        void OnTouchEffectAction(object sender,TouchActionEventArgs args)
        {
            switch (args.Type)
            {
                case TouchActionType.Pressed:
                    if (!inProgressPaths.ContainsKey(args.Id))
                    {
                        SKPath path = new SKPath();
                        path.MoveTo(ConvertToPixel(args.Location));
                        inProgressPaths.Add(args.Id,path);
                        canvasView.InvalidateSurface();
                    }
                    break;

                case TouchActionType.Moved:
                    if (inProgressPaths.ContainsKey(args.Id))
                    {
                        SKPath path = inProgressPaths[args.Id];
                        path.LineTo(ConvertToPixel(args.Location));
                        canvasView.InvalidateSurface();
                    }
                    break;

                case TouchActionType.Released:
                    if (inProgressPaths.ContainsKey(args.Id))
                    {
                        completedPaths.Add(inProgressPaths[args.Id]);
                        inProgressPaths.Remove(args.Id);
                        canvasView.InvalidateSurface();
                    }
                    break;

                case TouchActionType.Cancelled:
                    if (inProgressPaths.ContainsKey(args.Id))
                    {
                        inProgressPaths.Remove(args.Id);
                        canvasView.InvalidateSurface();
                    }
                    break;
            }
        }

        void OnCanvasViewPaintSurface(object sender,SKPaintSurfaceEventArgs args)
        {           
            bitmap = new SKBitmap((int)canvasView.CanvasSize.Width,(int)canvasView.CanvasSize.Height);
            var canvas = new SKCanvas(bitmap);
            canvas.Clear();
            canvas.DrawPath(testPath,paint);

            args.Surface.Canvas.DrawBitmap(bitmap,0);

            canvas.Clear();

            foreach (SKPath path in completedPaths)
            {
                canvas.DrawPath(path,paint);
            }

            foreach (SKPath path in inProgressPaths.Values)
            {
                canvas.DrawPath(path,paint);
            }
        }

        SKPoint ConvertToPixel(Point pt)
        {
            return new SKPoint((float)(canvasView.CanvasSize.Width * pt.X / canvasView.Width),(float)(canvasView.CanvasSize.Height * pt.Y / canvasView.Height));
        }
    }
}