如何在 WPF 中使用 Circle 绘制相机的视野？

在我的旧代数教科书中度过了一段美好的时光后，我为您提供了一个完整的解决方案。

这使用WpfLib Nuget 包（免责声明：我是该包的作者）作为INotifyPropertyChanged支持，但您应该能够轻松更改您想要的任何更改事件系统。完整的解决方案可以从BitBucket下载。

XAML：

<Window
    x:Class="ViewingAngle.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="clr-namespace:ViewingAngle"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    Title="MainWindow"
    Width="525"
    Height="350"
    d:DataContext="{d:DesignInstance local:MainWindowVm}"
    mc:Ignorable="d">
    <DockPanel Margin="4">
        <StackPanel DockPanel.Dock="Bottom">
            <TextBlock Margin="4,4,4,0" Text="{Binding Path=FieldOfView, StringFormat='Field of View: {0}'}" />
            <Slider
                Margin="4"
                Maximum="360"
                Minimum="0"
                TickFrequency="5"
                TickPlacement="Both"
                Value="{Binding Path=FieldOfView}" />
            <TextBlock Margin="4,4,4,0" Text="{Binding Path=TargetAngle, StringFormat='Target Angle: {0}'}" />
            <Slider
                Margin="4"
                Maximum="360"
                Minimum="0"
                TickFrequency="5"
                TickPlacement="Both"
                Value="{Binding Path=TargetAngle}" />
        </StackPanel>

        <Viewbox Margin="4" Stretch="Uniform">
            <Canvas Width="500" Height="500">
                <Path
                    Fill="Blue"
                    Stroke="Blue"
                    StrokeThickness="1">
                    <Path.Data>
                        <PathGeometry>
                            <PathGeometry.Figures>
                                <PathFigure StartPoint="250,250">
                                    <LineSegment Point="{Binding Path=StartPoint}" />
                                    <ArcSegment
                                        IsLargeArc="{Binding Path=IsLargeArc}"
                                        Point="{Binding Path=EndPoint}"
                                        Size="250,250"
                                        SweepDirection="Clockwise" />
                                    <LineSegment Point="250,250" />
                                </PathFigure>
                            </PathGeometry.Figures>
                        </PathGeometry>
                    </Path.Data>
                </Path>
            </Canvas>
        </Viewbox>
    </DockPanel>
</Window>

视图模型：

using System;
using System.Windows;
using AgentOctal.WpfLib;

namespace ViewingAngle
{
    class MainWindowVm : ViewModel
    {
        private const int Radius = 250;
        private const int CenterX = 250;
        private const int CenterY = 250;


        public MainWindowVm()
        {
            FieldOfView = 45;
            TargetAngle = 90;
        }

        private int _fieldOfView;
        public int FieldOfView
        {
            get { return _fieldOfView; }
            set
            {
                SetValue(ref _fieldOfView, value);
                RecalculateArc();
            }
        }

        private int _targetAngle;
        public int TargetAngle
        {
            get { return _targetAngle; }
            set
            {
                SetValue(ref _targetAngle, value);
                RecalculateArc();
            }
        }

        private double GetRadians(int angle)
        {
            return angle * Math.PI / 180;
        }

        private void RecalculateArc()
        {
            var targetAngle = GetRadians(_targetAngle);
            var fieldOfView = GetRadians(_fieldOfView);
            var halfFieldOfView = fieldOfView / 2;

            var startAngle = targetAngle - halfFieldOfView;
            var endAngle = targetAngle + halfFieldOfView;
            double angleDiff = endAngle - startAngle;
            IsLargeArc = angleDiff >= Math.PI;

            StartPoint = new Point(CenterX + Radius * Math.Cos(startAngle), CenterY + Radius * Math.Sin(startAngle));
            EndPoint = new Point(CenterX + Radius * Math.Cos(endAngle), CenterY + Radius * Math.Sin(endAngle));
        }

        private Point _startPoint;
        public Point StartPoint
        {
            get { return _startPoint; }
            set { SetValue(ref _startPoint, value); }
        }

        private Point _endPoint;
        public Point EndPoint
        {
            get { return _endPoint; }
            set { SetValue(ref _endPoint, value); }
        }

        private bool _isLargeArc;
        public bool IsLargeArc
        {
            get { return _isLargeArc; }
            set { SetValue(ref _isLargeArc, value); }
        }
    }
}

所有的魔法都发生在RecalculateArc每当TargetAngle或被FieldOfView改变时被调用。所有的数学运算都必须以弧度表示，所以它做的第一件事就是转换值。它使用一些涉及正弦和余弦的相当简单的代数计算新的StartPoint和EndPoint值ArcSegment（尽管我仍然需要查数学，因为高中毕业后谁还记得这些东西？）。

在 XAML 中，我放置了一些绑定到 的滑块TargetAngle，并FieldOfView允许您控制角度。它还包含Canvas绘制图形的位置，这是在 a 中ViewBox，只是为了使指标填充可用空间。

该Canvas包含Path，这是由一个高达PathFigure。所述PathFigure在250250（500×500的中心开始Canvas），绘制LineSegment出到弧的起点，这势必会StartPoint。一个ArcSegment然后加入，即在端部EndPoint。IsLargeArc只是用来让绘图系统知道要绘制弧的“一半”。添加另一个LineSegment在中心结束的PathFigure.