WPF canvas draw lines via brush with default stroke, and implement simple color picker such as palette

//xaml
<Window x:Class="WpfApp11.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:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp11"
        mc:Ignorable="d" WindowState="Maximized"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Canvas Background="White" Name="cvs" MouseDown="cvs_MouseDown"
                MouseMove="cvs_MouseMove" MouseUp="cvs_MouseUp"/>
    </Grid>
</Window>


//xaml.cs
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.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp11
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        Point _pos;
        bool _isDrawing;
        Brush _stroke=Brushes.Black;
        public MainWindow()
        {
            InitializeComponent();
        }

　　　　　　private void cvs_MouseDown(object sender, MouseButtonEventArgs e)
　　　　　　{
　　　　　　　　_isDrawing = true;
　　　　　　　　_pos = e.GetPosition(cvs);
　　　　　　　　cvs.CaptureMouse();
　　　　　　}

        private void cvs_MouseMove(object sender, MouseEventArgs e)
        {
            if(_isDrawing)
            {
                Line line = new Line();
                line.X1 = _pos.X;
                line.Y1 = _pos.Y;
                _pos=e.GetPosition(cvs);
                line.X2 = _pos.X;
                line.Y2= _pos.Y;
                line.Stroke = _stroke;
                line.StrokeThickness = 10;
                cvs.Children.Add(line);
            }
        }         

        private void cvs_MouseUp(object sender, MouseButtonEventArgs e)
        {
            _isDrawing=false;
            cvs.ReleaseMouseCapture();
        }
    }
}

 

 

 

 

 

 

 

 

 

 

//xaml
<Window x:Class="WpfApp11.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:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp11"
        mc:Ignorable="d" WindowState="Maximized"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        
        <Canvas Background="White" Name="cvs"  MouseDown="cvs_MouseDown"
                MouseMove="cvs_MouseMove" MouseUp="cvs_MouseUp">
            <Rectangle Stroke="Black" Width="25" Height="25" Canvas.Left="5" Canvas.Top="5"
                       Fill="Red"/>
            <Rectangle Stroke="Black" Width="25" Height="25" Canvas.Left="35" Canvas.Top="5"
                               Fill="Blue"/>
            <Rectangle Stroke="Black" Width="25" Height="25" Canvas.Left="65" Canvas.Top="5"
                       Fill="Yellow"/>
            <Rectangle Stroke="Black" Width="25" Height="25" Canvas.Left="95" Canvas.Top="5"
                               Fill="Green"/>
            <Rectangle Stroke="Black" Width="25" Height="25" Canvas.Left="125" Canvas.Top="5"
                               Fill="Black"/>
        </Canvas>
    </Grid>
</Window>




//xaml.cs
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.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp11
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        Point _pos;
        bool _isDrawing;
        Brush _stroke = Brushes.Black;
        public MainWindow()
        {
            InitializeComponent();
        }

        private void cvs_MouseDown(object sender, MouseButtonEventArgs e)
        {
            var rect = e.Source as Rectangle;
            if(rect!=null)
            {
                _stroke = rect.Fill;
            }
            else
            {
                _isDrawing = true;
                _pos=e.GetPosition(cvs);
                cvs.CaptureMouse();
            }
        }

        private void cvs_MouseMove(object sender, MouseEventArgs e)
        {
            if (_isDrawing)
            {
                Line line = new Line();
                line.X1 = _pos.X;
                line.Y1 = _pos.Y;
                _pos = e.GetPosition(cvs);
                line.X2 = _pos.X;
                line.Y2 = _pos.Y;
                line.Stroke = _stroke;
                line.StrokeThickness = 10;
                cvs.Children.Add(line);
            }
        }

        private void cvs_MouseUp(object sender, MouseButtonEventArgs e)
        {
            _isDrawing = false;
            cvs.ReleaseMouseCapture();
        }


    }
}

 

 

 

 

 

The key part of simple palette located at choose stroke from rectange fill color ,if hit the listed rectange and set  the stroke  as the hit rectangle color,else stayed as the default black stroke 

 private void cvs_MouseDown(object sender, MouseButtonEventArgs e)
 {
     var rect = e.Source as Rectangle;
     if(rect!=null)
     {
         _stroke = rect.Fill;
     }
     else
     {
         _isDrawing = true;
         _pos=e.GetPosition(cvs);
         cvs.CaptureMouse();
     }
 }