Use a VisualBrush to magnify a portion of the screen. : Brush « Windows Presentation Foundation « C# / CSharp Tutorial

1. C# / CSharp Tutorial
2. Windows Presentation Foundation
3. Brush

<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
  x:Class="Microsoft.Samples.Graphics.UsingVisualBrush.MagnifyingGlassExample"
  Background="White">
  <Page.Resources>
    <Style TargetType="{x:Type Paragraph}">
      <Setter Property="Margin" Value="10" />
    </Style>
    <DrawingBrush x:Key="MyGridBackgroundBrushResource"
      Viewport="0,0,10,10" ViewportUnits="Absolute" TileMode="Tile">
      <DrawingBrush.Drawing>
        <DrawingGroup>
          <DrawingGroup.Children>
            <GeometryDrawing Brush="White">
              <GeometryDrawing.Geometry>
                <RectangleGeometry Rect="0,0,1,1" />
              </GeometryDrawing.Geometry>
            </GeometryDrawing>
            <GeometryDrawing Brush="#E6E8F6"
              Geometry="M 0,0 L 0,1 0.1,1 0.1,0.1 1,0.1 1,0 Z" />                      
          </DrawingGroup.Children>
        </DrawingGroup>
      </DrawingBrush.Drawing>
    </DrawingBrush>   
    
  </Page.Resources>

  <Grid>  
    <ScrollViewer>
      <StackPanel Name="magnifiedPanel" 
        VerticalAlignment="Stretch"
        MouseMove="updateMagnifyingGlass" 
        Background="{StaticResource MyGridBackgroundBrushResource}">
        
        <FlowDocumentScrollViewer>
        <FlowDocument>
<Paragraph><Button></Button></Paragraph>

<Paragraph><Border BorderBrush="Black" BorderThickness="1"><Image Source="c:\image.jpg" Stretch="None" /></Border></Paragraph>

<Paragraph>this is a test</Paragraph> 
        </FlowDocument>
        </FlowDocumentScrollViewer>
      </StackPanel>
    </ScrollViewer>
    <Canvas Name="magnifyingGlassCanvas">
      <Ellipse Name="magnifyingGlassEllipse" Width="100" Height="100" Stroke="Black">
        <Ellipse.Fill>
          <DrawingBrush>
            <DrawingBrush.Drawing>
              <DrawingGroup>
                <DrawingGroup.Children>
                   <GeometryDrawing Brush="White">
                    <GeometryDrawing.Geometry>
                      <RectangleGeometry Rect="0,0,1,1" />
                    </GeometryDrawing.Geometry>
                  </GeometryDrawing>
                   <GeometryDrawing>
                    <GeometryDrawing.Brush>
                       <VisualBrush x:Name="myVisualBrush" ViewboxUnits="Absolute"
                        Visual="{Binding ElementName=magnifiedPanel}"/>
                    </GeometryDrawing.Brush>
                    <GeometryDrawing.Geometry>
                      <RectangleGeometry Rect="0,0,1,1" />
                    </GeometryDrawing.Geometry>
                  </GeometryDrawing>
                </DrawingGroup.Children>
              </DrawingGroup>
            </DrawingBrush.Drawing>
          </DrawingBrush>
        </Ellipse.Fill>
      </Ellipse>
    </Canvas>
  </Grid>
</Page>

//File:Window.xaml.cs
using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Media;
using System.Windows.Input;

namespace Microsoft.Samples.Graphics.UsingVisualBrush
{
    public partial class MagnifyingGlassExample : Page
    {
        private static readonly double distanceFromMouse = 5;
        
        public MagnifyingGlassExample()
        {
        }
        private void updateMagnifyingGlass(object sender, MouseEventArgs args)
        {
            Mouse.SetCursor(Cursors.Cross);
            Point currentMousePosition = args.GetPosition(this);
            if (this.ActualWidth - currentMousePosition.X > magnifyingGlassEllipse.Width + distanceFromMouse)
            {
                Canvas.SetLeft(magnifyingGlassEllipse, currentMousePosition.X + distanceFromMouse);
            }
            else
            {
                Canvas.SetLeft(magnifyingGlassEllipse, currentMousePosition.X - distanceFromMouse - magnifyingGlassEllipse.Width);
            }
            
            if (this.ActualHeight - currentMousePosition.Y > magnifyingGlassEllipse.Height + distanceFromMouse)
            {
                Canvas.SetTop(magnifyingGlassEllipse, currentMousePosition.Y + distanceFromMouse);
            }
            else
            {
                Canvas.SetTop(magnifyingGlassEllipse, currentMousePosition.Y - distanceFromMouse - magnifyingGlassEllipse.Height);
            }
            myVisualBrush.Viewbox = new Rect(currentMousePosition.X - 10, currentMousePosition.Y  - 10, 20, 20);
        }
    }
}

24.81.Brush
	24.81.1.	Set color for SolidColorBrush
	24.81.2.	Paint with system brushes and colors.
	24.81.3.	Uses a predefined SolidColorBrush, defined by the System.Windows.Media.Brushes class
	24.81.4.	Gradient brushes within a DrawingBrush. Two overlapping gradients are layered
	24.81.5.	OpacityMask, LinearGradientBrush, RenderTransform
	24.81.6.	Brush resource
	24.81.7.	Use a VisualBrush to magnify a portion of the screen.
	24.81.8.	Predefined brush in Brushes Class
	24.81.9.	Solid Color Brush In Code with predefined brush
	24.81.10.	Solid Color Brush In Code with SolidColorBrush
	24.81.11.	Solid Color Brush In Code with SolidColorBrush and RGB color
	24.81.12.	Get all public static properties from Brush
	24.81.13.	Change the Window background with a Brush
	24.81.14.	Using Brushes.AliceBlue
	24.81.15.	Color map Brush
	24.81.16.	Create Vector from width and height