the width paintable could be drawn into or 0.0 if unknown
the height paintable could be drawn into or 0.0 if unknown
the width paintable would be drawn into if no other constraints were given
the height paintable would be drawn into if no other constraints were given
will be set to the concrete width computed
will be set to the concrete height computed
Compute a concrete size for the gdk.paintable.Paintable.
Applies the sizing algorithm outlined in the CSS Image spec
to the given paintable. See that link for more details.
It is not necessary to call this function when both specified_width and specified_height are known, but it is useful to call this function in GtkWidget:measure implementations to compute the other dimension when only one dimension is given.