How to get the bounding box of the children of a WPF visual, excluding the parent

Question

From the MSDN documentation for VisualTreeHelper.GetDescendantBounds():

// Return the bounding rectangle of the parent visual object and all of its descendants.
Rect rectBounds = VisualTreeHelper.GetDescendantBounds(parentVisual);

I get this and it works, but I do not want to include the parent's bounds, the reason is that my parent is a page of an XPS document, and so calling this just returns the page boundaries, which is not what I want. I want the bounding box of everything on the page, i.e. just of the children of the page visual.

// snippet of my code
Visual visual = paginator.GetPage(0).Visual;
Rect contentBounds = VisualTreeHelper.GetDescendantBounds(visual);
// above call returns the page boundaries
// is there a way to get the bounding box of just the children of the page?

The reason I need this is that I'm saving the XPS page to a bitmap and need to include as little white space as possible, to limit the bitmap to only the 'used' area of the page.

Do I need to iterate over all the children of the visual myself and call VisualTreeHelper.GetContentBounds() on each one? I thought there would be a better way than doing this...

Answer 1

I've come up with a workable solution by enumerating over all the child visuals of the parent (page) visual. A more efficient and/or library solution would be better, but this works for now.

// enumerate all the child visuals
List<Visual> children = new List<Visual>();
EnumVisual(visual, children);

// loop over each child and call GetContentBounds() on each one
Rect? contentBounds = null;
foreach (Visual child in children)
{
    Rect childBounds = VisualTreeHelper.GetContentBounds(child);
    if (childBounds != Rect.Empty)
    {
        if (contentBounds.HasValue)
        {
            contentBounds.Value.Union(childBounds);
        }
        else
        {
            contentBounds = childBounds;
        }
    }
}

/// <summary>
/// Enumerate all the descendants (children) of a visual object.
/// </summary>
/// <param name="parent">Starting visual (parent).</param>
/// <param name="collection">Collection, into which is placed all of the descendant visuals.</param>
public static void EnumVisual(Visual parent, List<Visual> collection)
{
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)
    {
        // Get the child visual at specified index value.
        Visual childVisual = (Visual)VisualTreeHelper.GetChild(parent, i);

        // Add the child visual object to the collection.
        collection.Add(childVisual);

        // Recursively enumerate children of the child visual object.
        EnumVisual(childVisual, collection);
    }
}