Thinking off the top of my head, you could make a histogram call to
the selection "channel" at 255 (fully selected) and see if the
returned pixel count equals the number of pixels (width x height).

On 10/9/10, Ofnuts <> wrote:
>   On 10/10/2010 00:22, David Gowers (kampu) wrote:
>> On Sun, Oct 10, 2010 at 7:47 AM, Ofnuts<>  wrote:
>>>   Assume I have a selection on small area (for instance a 20px circle),
>>> and I invert it. Now, if I grow the selection by a sufficient amount
>>> (10px in this case), everything gets selected.
>>> Is there a practical, fast way, to detect this case, i.e, that the
>>> selection covers the whole layer (or image?) and that no pixels remain
>>> unselected? I assume that inverting the selection again and testing for
>>> empty would work, but that would be two selection inversions in the
>>> normal case and that may be a bit costly.
>> Testing for empty and for full are the same operation (an empty sel is
>> equivalent to a full one)
>> HTH
> There are indeed many tools that behave the same way if the selection is
> empty of complete, but gimp_selection_is_empty
> <>()
> return False when the selection is complete, alas.
> --
> Bertrand
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