>>Hi,
>>
>>Simplest way to explain my requirements will be a simple example. So:

<Window x:Class="WpfApplication1.Window23"
>>    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
>>      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" >
>>    <StackPanel Orientation="Vertical">
>>    <Canvas x:Name="Outer" Height="500" Width="500" Background="AliceBlue">
>>        <Canvas x:Name="Main" Height="200" Width="200" Background="Red" Canvas.Top="200" ClipToBounds="True" >
>>                <Canvas.RenderTransform>
>>                    <RotateTransform Angle="345" />
>>                </Canvas.RenderTransform>
>>                    <Canvas x:Name="Contained" Height="300" Width="300" Background="Yellow" Canvas.Top="50" Canvas.Left="50">
>>                <Canvas.RenderTransform>
>>                    <RotateTransform Angle="345"/>
>>                </Canvas.RenderTransform>
>>            </Canvas>
>>        </Canvas>
>>    </Canvas>
>>        <Border BorderBrush="Black" BorderThickness="2" Width="96" Height="96">
>>        <Viewbox x:Name="VBox"  >
>>        </Viewbox>
>>            </Border>
>>        <Button Click="Button_Click">Thumbnail it</Button>
>>  </StackPanel>
>></Window>

Code:

using System.Windows;
>>using System.Windows.Controls;
>>using System.Windows.Media;
>>
>>namespace WpfApplication1
>>{
>>  
>>    public partial class Window23 : Window
>>    {
>>        public Window23()
>>        {
>>            InitializeComponent();
>>        }
>>
>>        private void Button_Click(object sender, RoutedEventArgs e)
>>        {
>>            Outer.Children.Remove(Main);
>>            Main.LayoutTransform = Main.RenderTransform;
>>            Main.RenderTransform = Transform.Identity;
>>            VBox.Child = Main;
>>        }
>>    }
>>}

This does what I want. However if ClipToBounds is not set on Main then the sizing is obviously wrong. Whats the simplest way of getting this right?
>>
>>I originally did this without using a ViewBox by using GetDescendantBounds, adding a ScaleTransform etc. It worked OK but got pretty ugly - basing the operation around a ViewBox should be much simpler.
>>
>>Any suggestions,
>>Viv
>
>I played with this for a bit and so far, no matter what I try, I cannot get GetDescendantBounds to calculate a correct width. I'm close, within a few pixels, but I am still off. Frustrating!
>
>Heres what I got, I think this is close to what you wanted, but it is still off!
>
>

<Window x:Class="WpfApplication2.Window1"
>        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
>        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" SizeToContent="WidthAndHeight">
>  <StackPanel Orientation="Vertical">
>    <Canvas x:Name="Outer" Height="500" Width="500" Background="AliceBlue">
>      <Canvas x:Name="cvsMeasure" Height="0" Width="0" Canvas.Top="200" >
>        <Canvas x:Name="Main" Height="200" Width="200" Background="Red" >
>        <Canvas.RenderTransform>
>          <RotateTransform Angle="345" />
>        </Canvas.RenderTransform>
>        <Canvas x:Name="Contained" Height="300" Width="300" Background="Yellow" Canvas.Top="50" Canvas.Left="50" >
>          <Canvas.RenderTransform>
>            <RotateTransform Angle="345"/>
>          </Canvas.RenderTransform>
>        </Canvas>
>      </Canvas>
>      </Canvas>
>    </Canvas>
>    <Border BorderBrush="Black" BorderThickness="2" Width="96" Height="96"> 
>      <Viewbox x:Name="VBox" >
>        <Canvas x:Name="VBoxCanvas" Background="AliceBlue" ></Canvas>
>      </Viewbox>
>    </Border>
>    <Button Click="Button_Click">Thumbnail it</Button>
>  </StackPanel>
></Window>

>

using System;
>using System.Collections.Generic;
>using System.Linq;
>using System.Text;
>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 WpfApplication2
>  {
>  /// <summary>
>  /// Interaction logic for Window1.xaml
>  /// </summary>
>  public partial class Window1 : Window
>    {
>    public Window1()
>      {
>      InitializeComponent();
>      }
>
>    private void Button_Click(object sender, RoutedEventArgs e)
>      {
>      //Main.LayoutTransform = Main.RenderTransform;
>      //Main.RenderTransform = Transform.Identity;
>      Rect bounds = VisualTreeHelper.GetDescendantBounds(cvsMeasure);
>      Double size = Math.Max(bounds.Size.Width + (bounds.Left*2) , bounds.Size.Height + bounds.Top);
>      cvsMeasure.Children.Remove(Main);
>      Main.SetValue(Canvas.TopProperty, 0-bounds.Top );
>      Main.SetValue(Canvas.LeftProperty, 0 - bounds.Left);
>      VBoxCanvas.Width = size;
>      VBoxCanvas.Height = size;
>      VBoxCanvas.Children.Add(Main);
>      //VBox.Child = Main;
>      }
>
>    }
>  }
>

Hi,
Thx. I was out all day today so only had time to quickly paste in and run your code. Looks pretty good to me. The C# is, I think, very similar to the solution I came up with when *not* using a ViewBox. I hardcoded a canvas to the required size and used the size value for an additional ScaleTransform. I'll take a closer look at this tomorrow.
Best,
Viv