Hi,

I have a Canvas contained within another Canvas. I'm using an adorner with Thumbs to resize the inner canvas. In the relevant Thumbs DragDelta() I have the usual:

adornedElement.Width = adornedElement.Width + args.HorizontalChange;

and all works as expected. Now I want to Zoom the containing Canvas. If I use a ScaleTransform as the RenderTransform again all is fine. But if I apply this to the LayoutTransform instead (which is my preference) then the DeltaEventArgs.HorizontalChange returns weird values.

As a rough example assume I am (fairly steadily) increasing the width of the inner canvas then tracing the successive HorizontalChange values shows something like: -8,10,-7,16,-15,19,-19,27,-28,35,-38,46,-50 etc. (These are obviously actually double values - I've just rounded them here for readability).

So the absolute values are continually increasing and are alternatively negative/positive.
What can cause this behaviour? What can prevent it?

UPDATE: I've discovered that if I adjust the HorizontalChange based on the current LayoutTransform before adding it to the canvas width then everything is OK. But I must admit I'm unclear as to why this should be neccessary with a LayoutTransform but not with a RenderTransform ?

Thx,
Viv