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InkCanvasForClass/Helpers/RectangleSelectionViewer.cs

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+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Windows;
+using System.Windows.Ink;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Animation;
+
+namespace Ink_Canvas.Helpers
+{
+    
+    public class RectangleSelectionViewer : FrameworkElement
+    {
+        private VisualCollection _children;
+        private DrawingVisual _layer = new DrawingVisual();
+        private Pen defaultPen = new Pen();
+        private Pen lassoPen = new Pen();
+
+        public RectangleSelectionViewer()
+        {
+            _children = new VisualCollection(this) {
+                _layer // 初始化DrawingVisual
+            };
+            defaultPen.Thickness = 2;
+            defaultPen.Brush = new SolidColorBrush(Color.FromRgb(37, 99, 235));
+            defaultPen.DashStyle = DashStyles.Dash;
+
+            lassoPen.Thickness = 6;
+            lassoPen.Brush = new SolidColorBrush(Color.FromRgb(37, 99, 235));
+            lassoPen.DashStyle = new DashStyle(new double[]{0,2},0);
+            lassoPen.DashCap = PenLineCap.Round;
+            lassoPen.StartLineCap = PenLineCap.Round;
+            lassoPen.EndLineCap = PenLineCap.Round;
+        }
+
+        protected override int VisualChildrenCount => _children.Count;
+
+        protected override Visual GetVisualChild(int index)
+        {
+            if (index < 0 || index >= _children.Count) throw new ArgumentOutOfRangeException();
+            return _children[index];
+        }
+
+        public void DrawSelectionBox(Rect rect) {
+            DrawingContext context = _layer.RenderOpen();
+            context.DrawRoundedRectangle(new SolidColorBrush(Color.FromArgb(78, 96, 165, 250)), defaultPen, rect, 4, 4);
+            context.Close();
+        }
+
+        public void DrawLassoLine(PointCollection pts) {
+            DrawingContext context = _layer.RenderOpen();
+            if (pts.Count > 2) {
+                StreamGeometry geometry = new StreamGeometry();
+                var _pts = pts.Clone();
+                _pts.RemoveAt(0);
+                using (StreamGeometryContext ctx = geometry.Open()) {
+                    ctx.BeginFigure(pts[0], true , false);
+                    ctx.PolyLineTo(_pts,true, true);
+                }
+                context.DrawGeometry(new SolidColorBrush(Colors.Transparent), lassoPen, geometry);
+            } else if (pts.Count == 2) {
+                context.DrawLine(defaultPen, pts[0], pts[1]);
+            } else if (pts.Count == 1) {
+                context.DrawLine(defaultPen, pts[0], pts[0]);
+            }
+            context.Close();
+        }
+
+        public void ClearDrawing() {
+            DrawingContext context = _layer.RenderOpen();
+            context.Close();
+        }
+    }
+}