get_requested_height

This function is only intended to be used when implementing new canvas items, specifically layout items such as CanvasTable.

It gets the requested height of a child item, assuming it is allocated the given width. This is useful for text items whose requested height may change depending on the allocated width.

Parameters:

this	a CanvasItem.
cr	a cairo context.
width	the width that the item may be allocated.

Returns:

the requested height of the item, given the allocated width, or %-1 if the item doesn't support this method or its height doesn't change when allocated different widths.