Create a Zoomable Canvas Control

   
  
<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:WpfApplication1="clr-namespace:WpfApplication1;assembly="
   Title="WPF" Height="300" Width="300" >

    <Window.Resources>
        <Style TargetType="Button">
            <Setter Property="Width" Value="Auto" />
            <Setter Property="Height" Value="24" />
        </Style>
    </Window.Resources>
    <DockPanel>
        <Slider DockPanel.Dock="Bottom" x:Name="zoomSlider" Minimum="0.1" Maximum="5" Value="1"/>
        <ScrollViewer VerticalScrollBarVisibility="Auto" HorizontalScrollBarVisibility="Auto">
            <WpfApplication1:ZoomableCanvasControl x:Name="zoomControl">
                <Canvas.LayoutTransform>
                    <ScaleTransform ScaleX="{Binding Path=Value, ElementName=zoomSlider}"
                                    ScaleY="{Binding Path=Value, ElementName=zoomSlider}"/>
                </Canvas.LayoutTransform>
                <Rectangle Canvas.Top="0" Canvas.Left="0" StrokeThickness="2" Stroke="Red" Width="50" Height="50"/>
                <Rectangle Canvas.Top="50" Canvas.Left="50" StrokeThickness="2" Stroke="Blue" Width="150" Height="150"/>
                <Rectangle Canvas.Top="200" Canvas.Left="200" StrokeThickness="2" Stroke="Green" Width="200" Height="200"/>
            </WpfApplication1:ZoomableCanvasControl>
        </ScrollViewer>

    </DockPanel>
</Window>
//File:Window.xaml.cs

using System.Windows;
using System;
using System.Windows;
using System.Windows.Controls;
namespace WpfApplication1
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }
    }

    public class ZoomableCanvasControl : Canvas
    {
        static ZoomableCanvasControl()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(ZoomableCanvasControl),new FrameworkPropertyMetadata(typeof(ZoomableCanvasControl)));
        }

        protected override Size MeasureOverride(Size constraint)
        {
            double bottomMost = 0d;
            double rightMost = 0d;

            foreach(object obj in Children)
            {
                FrameworkElement child = obj as FrameworkElement;

                if(child != null)
                {
                    child.Measure(constraint);

                    bottomMost = Math.Max(bottomMost,GetTop(child) +child.DesiredSize.Height);
                    rightMost = Math.Max(rightMost,GetLeft(child) +child.DesiredSize.Width);
                }
            }
            return new Size(rightMost, bottomMost);
        }
    }
}