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 GdkPaintable.
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.