C# WPF 使用多边形裁剪控件

Question

我正在尝试制作一个自定义的 ContentControl，它采用圆角多边形的形状。出于某种原因，当我在控件上设置 Clip 属性时，没有显示任何内容。感谢任何帮助...

PageHost.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.Windows;
using System.Windows.Media;
using System.Windows.Shapes;
using System.Windows.Controls;

namespace DtcInvoicer.Controls
{
    public class PageHost:UserControl
    {
        #region public ImageSource Icon;
        public static readonly DependencyProperty IconProperty = DependencyProperty.Register("Icon", typeof(ImageSource), typeof(PageHost));
        public ImageSource Icon
        {
            get { return GetValue(IconProperty) as ImageSource; }
            set { SetValue(IconProperty, value); }
        }
        #endregion

        #region public string Title;
        public static readonly DependencyProperty TitleProperty = DependencyProperty.Register("Title", typeof(string), typeof(PageHost));
        public string Title
        {
            get { return GetValue(TitleProperty).ToString(); }
            set { SetValue(TitleProperty, value); }
        }
        #endregion

        #region public double Radius;
        public static readonly DependencyProperty RadiusProperty = DependencyProperty.Register("Radius", typeof(double), typeof(PageHost));
        public double Radius
        {
            get { return (double)GetValue(RadiusProperty); }
            set 
            { 
                SetValue(RadiusProperty, value); 
                DoClip(); 
            }
        }
        #endregion

        public PageHost()
        {
            Loaded += new RoutedEventHandler(PageHost_Loaded);
            SizeChanged += new SizeChangedEventHandler(PageHost_SizeChanged);
        }

        #region Event Handlers
        private void PageHost_Loaded(object sender, RoutedEventArgs e)
        {
            DoClip();
        }

        private void PageHost_SizeChanged(object sender, SizeChangedEventArgs e)
        {
            DoClip();
        }
        #endregion

        private void DoClip()
        {
            Polygon p = new Polygon()
            { 
                Points = new PointCollection()
                {
                    new Point(0, 0),
                    new Point(ActualWidth - 30, 0),
                    new Point(ActualWidth, 30),
                    new Point(ActualWidth, ActualHeight),
                    new Point(0, ActualHeight)
                }
            };

            Geometry g1 = new RectangleGeometry(new Rect(0, 0, ActualWidth, ActualHeight), Radius, Radius);
            Geometry g2 = p.RenderedGeometry;

            // Clip = g1; this works, the control shows up with the rounded corners
            // Clip = g2; this does not work, nothing shows up

            // this is what I want to do, I want to combine the two geometries
            // but this does not work either
            Clip = new CombinedGeometry(GeometryCombineMode.Intersect, g1, g2);
        }
    }
}

HomePage.xaml

<control:PageHost x:Class="DtcInvoicer.Pages.HomePage"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:control="clr-namespace:DtcInvoicer.Controls"
         Width="500" Height="250" Radius="20" Background="Aqua">
</control:PageHost>

Answer 1

在这种情况下，将剪辑设置为 RenderedGeometry 会失败，因为 RenderedGeometry 尚未实际渲染，因此不可用。对于常规几何图形，在 DoClip 中使用它:

Dispatcher.BeginInvoke(DispatcherPriority.Background, new ThreadStart(delegate
{
    Clip = new CombinedGeometry(GeometryCombineMode.Intersect, g1, g2); 
}));

对于 RenderedGeometry，您需要将它添加到可视化树中的某处，然后在设置 Clip 区域之前使用它的 Loaded 事件，这会很困难。尝试使用具有相同点的常规 Geometry 而不是 RenderedGeometry，例如 A path geometry .这是我使用 PathGeometry 绘制三角形的示例:

double leftPoint = cellRect.Right - 12;
if (leftPoint < cellRect.Left)
    leftPoint = cellRect.Left;
double topPoint = cellRect.Top + (cellRect.Height - 4.0) / 2;
if (topPoint < cellRect.Top)
    topPoint = cellRect.Top;
double rightPoint = leftPoint + 7;
if (rightPoint > cellRect.Right)
    rightPoint = cellRect.Right;
double bottomPoint = topPoint + 4;
if (bottomPoint > cellRect.Bottom)
    bottomPoint = cellRect.Bottom;
double middlePoint = leftPoint + 3;
if (middlePoint > cellRect.Right)
    middlePoint = cellRect.Right;

PathFigure figure = new PathFigure();
figure.StartPoint = new Point(middlePoint, bottomPoint);
PathFigureCollection figCollection = new PathFigureCollection();
figCollection.Add(figure);

PathSegmentCollection segCollection = new PathSegmentCollection();
LineSegment topSeg = new LineSegment();
topSeg.Point = new Point(rightPoint, topPoint);
segCollection.Add(topSeg);
LineSegment midRightSeg = new LineSegment();
midRightSeg.Point = new Point(leftPoint, topPoint);
segCollection.Add(midRightSeg);
LineSegment midLeftSeg = new LineSegment();
midLeftSeg.Point = new Point(middlePoint+1, bottomPoint);
segCollection.Add(midLeftSeg);
figure.Segments = segCollection;

PathGeometry geo = new PathGeometry();
geo.Figures = figCollection;