<Window x:Class="WPF_InkCanvas.ROI_InkCanvas"
    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:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:WPF_InkCanvas"
    mc:Ignorable="d"
    Title="ROI_InkCanvas" Height="450" Width="800">
  <Grid>
    <Grid.RowDefinitions>
      <RowDefinition/>
      <RowDefinition Height="auto"/>
    </Grid.RowDefinitions>
    <Image Name="imgMeasure" HorizontalAlignment="Center" Stretch="Uniform"/>
    <InkCanvas Name="inkCanvasMeasure" EditingMode="None" Background="Transparent" Strokes="{Binding InkStrokes, Mode=TwoWay}" HorizontalAlignment="Center" 
          Width="{Binding ElementName=imgMeasure, Path=ActualWidth}" Height="{Binding ElementName=imgMeasure, Path=ActualHeight}"
          MouseDown="InkCanvasMeasure_MouseDown" MouseMove="InkCanvasMeasure_MouseMove">
      <Label Content="{Binding MeaInfo}" Background="Transparent" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="10" 
          FontSize="18" Foreground="Red" IsHitTestVisible="False"/>
    </InkCanvas>
    <StackPanel Grid.Row="1" Orientation="Horizontal">
      <Button Content="OpenFile" Margin="5" HorizontalAlignment="Left" FontSize="20" Click="OpenFile_Click"/>
      <ToggleButton Name="btnSquare" Content="Draw Square" Margin="5" HorizontalAlignment="Left" FontSize="20" Click="DrawSquare_Click"/>
      <ToggleButton Name="btnEllipse" Content="Draw Ellipse" Margin="5" HorizontalAlignment="Left" FontSize="20" Click="DrawEllipse_Click"/>
    </StackPanel>
  </Grid>
</Window>

using Microsoft.Win32;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
 
namespace WPF_InkCanvas
{
  /// <summary>
  /// ROI_InkCanvas.xaml 的交互邏輯
  /// </summary>
  public partial class ROI_InkCanvas : Window
  {
    private ViewModel viewModel;
    private System.Windows.Point iniP;
    public ROI_InkCanvas()
    {
      InitializeComponent();
 
      DrawingAttributes drawingAttributes = new DrawingAttributes
      {
        Color = Colors.Red,
        Width = 2,
        Height = 2,
        StylusTip = StylusTip.Rectangle,
        //FitToCurve = true,
        IsHighlighter = false,
        IgnorePressure = true,
 
      };
      inkCanvasMeasure.DefaultDrawingAttributes = drawingAttributes;
 
      viewModel = new ViewModel
      {
        MeaInfo = "測(cè)試······",
        InkStrokes = new StrokeCollection(),
      };
 
      DataContext = viewModel;
    }
 
    private void OpenFile_Click(object sender, RoutedEventArgs e)
    {
      OpenFileDialog openDialog = new OpenFileDialog
      {
        Filter = "Image Files (*.jpg)|*.jpg|Image Files (*.png)|*.png|Image Files (*.bmp)|*.bmp",
        Title = "Open Image File"
      };
      if (openDialog.ShowDialog() == true)
      {
        BitmapImage image = new BitmapImage();
        image.BeginInit();
        image.UriSource = new Uri(openDialog.FileName, UriKind.RelativeOrAbsolute);
        image.EndInit();
        imgMeasure.Source = image;
      }
    }
 
    private void DrawSquare_Click(object sender, RoutedEventArgs e)
    {
      if (btnSquare.IsChecked == true)
      {
        btnEllipse.IsChecked = false;
      }
    } 
 
    private void DrawEllipse_Click(object sender, RoutedEventArgs e)
    {
      if (btnEllipse.IsChecked == true)
      {
        btnSquare.IsChecked = false;
      }
    }
 
    private List<System.Windows.Point> GenerateEclipseGeometry(System.Windows.Point st, System.Windows.Point ed)
    {
      double a = 0.5 * (ed.X - st.X);
      double b = 0.5 * (ed.Y - st.Y);
      List<System.Windows.Point> pointList = new List<System.Windows.Point>();
      for (double r = 0; r <= 2 * Math.PI; r = r + 0.01)
      {
        pointList.Add(new System.Windows.Point(0.5 * (st.X + ed.X) + a * Math.Cos(r), 0.5 * (st.Y + ed.Y) + b * Math.Sin(r)));
      }
      return pointList;
    }
    private void InkCanvasMeasure_MouseDown(object sender, MouseButtonEventArgs e)
    {
      if (e.LeftButton == MouseButtonState.Pressed)
      {
        iniP = e.GetPosition(inkCanvasMeasure);
      }
    }
 
    private void InkCanvasMeasure_MouseMove(object sender, MouseEventArgs e)
    {
      if (e.LeftButton == MouseButtonState.Pressed)
      {
        // Draw square
        if (btnSquare.IsChecked == true)
        {
          System.Windows.Point endP = e.GetPosition(inkCanvasMeasure);
          List<System.Windows.Point> pointList = new List<System.Windows.Point>
          {
            new System.Windows.Point(iniP.X, iniP.Y),
            new System.Windows.Point(iniP.X, endP.Y),
            new System.Windows.Point(endP.X, endP.Y),
            new System.Windows.Point(endP.X, iniP.Y),
            new System.Windows.Point(iniP.X, iniP.Y),
          };
          StylusPointCollection point = new StylusPointCollection(pointList);
          Stroke stroke = new Stroke(point)
          {
            DrawingAttributes = inkCanvasMeasure.DefaultDrawingAttributes.Clone()
          };
          viewModel.InkStrokes.Clear();
          viewModel.InkStrokes.Add(stroke);
        }
        // Draw Eclipse
        else if (btnEllipse.IsChecked == true)
        {
          System.Windows.Point endP = e.GetPosition(inkCanvasMeasure);
          List<System.Windows.Point> pointList = GenerateEclipseGeometry(iniP, endP);
          StylusPointCollection point = new StylusPointCollection(pointList);
          Stroke stroke = new Stroke(point)
          {
            DrawingAttributes = inkCanvasMeasure.DefaultDrawingAttributes.Clone()
          };
          viewModel.InkStrokes.Clear();
          viewModel.InkStrokes.Add(stroke);
        }
      }
    }
  }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Ink;
 
namespace WPF_InkCanvas
{
  class ViewModel : INotifyPropertyChanged
  {
    public event PropertyChangedEventHandler PropertyChanged;
 
    protected virtual void OnPropertyChanged(string propertyName = null)
    {
      if (PropertyChanged != null)
        PropertyChanged.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
 
    private string meaInfo;
    public string MeaInfo
    {
      get => meaInfo;
      set
      {
        meaInfo = value;
        OnPropertyChanged("MeaInfo");
      }
    }
 
    private StrokeCollection inkStrokes;
    public StrokeCollection InkStrokes
    {
      get { return inkStrokes; }
      set
      {
        inkStrokes = value;
        OnPropertyChanged("InkStrokes");
      }
    }
  }
}