WPF - Drawing on canvas with mouse events

I'm willing to bet that your canvas isn't receiving mouse events because it's background property is set to transparent

This works fine for me.

enter image description here

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Canvas  Name="paintSurface" MouseDown="Canvas_MouseDown_1" MouseMove="Canvas_MouseMove_1" >
        <Canvas.Background>
            <SolidColorBrush Color="White" Opacity="0"/>
        </Canvas.Background>
    </Canvas>
</Window>


using System;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Input;
using System.Windows.Shapes;

namespace WpfApplication1
{
    public partial class MainWindow : Window
    {

        Point currentPoint = new Point();

        public MainWindow()
        {
            InitializeComponent();
        }

        private void Canvas_MouseDown_1(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            if (e.ButtonState == MouseButtonState.Pressed)
                currentPoint = e.GetPosition(this);
        }

        private void Canvas_MouseMove_1(object sender, System.Windows.Input.MouseEventArgs e)
        {
            if (e.LeftButton == MouseButtonState.Pressed)
            {
                Line line = new Line();

                line.Stroke = SystemColors.WindowFrameBrush;
                line.X1 = currentPoint.X;
                line.Y1 = currentPoint.Y;
                line.X2 = e.GetPosition(this).X;
                line.Y2 = e.GetPosition(this).Y;

                currentPoint = e.GetPosition(this);

                paintSurface.Children.Add(line);
            }
        }

    }
}

Simple use the InkCanvas

 <InkCanvas x:Name="InkCanvas" x:FieldModifier="public" Background="Transparent" Opacity="1" EditingMode="GestureOnly" ForceCursor="True" Cursor="Pen" >
                            <InkCanvas.DefaultDrawingAttributes>
                                <DrawingAttributes Color="White" Width="7" Height="7" />
                            </InkCanvas.DefaultDrawingAttributes>
                        </InkCanvas>

When using Line, thick line(line.StrokeThickness = 20) looks like this:

enter image description here

So I tried PolyLine and works fine.(from this example http://www.c-sharpcorner.com/uploadfile/mahesh/polyline-in-wpf/)

Canvas.MouseMove += (sender, args) =>
{
    if (args.LeftButton == MouseButtonState.Pressed)
    {
        Polyline polyLine;
        if (PathModeCanvas.Children.Count == 0)
        {
            polyLine = new Polyline();
            polyLine.Stroke = new SolidColorBrush(Colors.AliceBlue);
            polyLine.StrokeThickness = 10;

            Canvas.Children.Add(polyLine);
        }

        polyLine = (Polyline)Canvas.Children[0];
        Point currentPoint = args.GetPosition(Canvas);
        polyLine.Points.Add(currentPoint);
   }
};