title: ViewBox default width and height
body: <p>i've created usercontrol with viewbox as a main container.
  If i add this usercontrol to a window it will place all area of it.
  How to set up default width and height for the control?</p>
  
  <pre><code>&lt;UserControl&gt;
      ...
      &lt;Viewbox&gt;
          &lt;Grid Height="167" Width="178"&gt;
              &lt;ed:RegularPolygon Fill="#FFF4F4F5" InnerRadius="1" PointCount="3" Stroke="Black" RenderTransformOrigin="0.5,0.5" Margin="-39,52,69,52" &gt;
                  &lt;ed:RegularPolygon.RenderTransform&gt;
                      &lt;TransformGroup&gt;
                          &lt;ScaleTransform/&gt;
                          &lt;SkewTransform/&gt;
                          &lt;RotateTransform Angle="90"/&gt;
                          &lt;TranslateTransform/&gt;
                      &lt;/TransformGroup&gt;
                  &lt;/ed:RegularPolygon.RenderTransform&gt;
              &lt;/ed:RegularPolygon&gt;            
          &lt;/Grid&gt;
      &lt;/Viewbox&gt;
  &lt;/UserControl&gt;
  </code></pre>