private Rect ComputeBounds(Viewport3D viewport)
{
double x = 0;
double y = 0;
Window w = FindContainingWindow(viewport);
if (w != null)
{
// NOTE! Any changes made to viewport.RenderTransform will not be reflected by TransformToAncestor
// until you re-render the viewport with that new RenderTransform. Composition team says it's by design.
GeneralTransform gt = viewport.TransformToAncestor(w);
Point p = gt.Transform(new Point(0, 0));
// Because of the above behavior, we must manually undo the RenderTransform
// because we don't want to factor in the RenderTransform just yet.
// It is handled like an effect at the end of the rendering pass.
if (viewport.RenderTransform != null)
{
p = viewport.RenderTransform.Inverse.Transform(p);
}
x = p.X;
y = p.Y;
}
double width = MathEx.FallbackIfNaN(viewport.Width, viewport.ActualWidth);
double height = MathEx.FallbackIfNaN(viewport.Height, viewport.ActualHeight);
return(new Rect(x, y, width, height));
}