Easy layer access for rgb8 filters.

[Boudewijn Rempt]

On Monday 17 January 2005 14:44, Casper Boemann wrote:
> On Monday 17 January 2005 13:50, Boudewijn Rempt wrote:
> > On Monday 17 January 2005 13:34, Casper Boemann wrote:
> > > I might be able to make an exact fit if we believe that an iterator is
> > > always walked all the way through. That way I could update the extent
> > > whenever an iterator is created. My first thought of an exact fit was
> > > to update the extent whenever the iterator moves a single pixel (thus
> > > the huge overhead I feared). Should I do this ??
> >
> > No, I don't think so... I think it's time for some decisions.
>
> I don't think you know what you turned down. please read again


I thought you intended to update the extent whenever the iterator moves
a single pixel? I'm not sure that the precondition for the other option
does exist? Can we be sure that an iterator will always be walked all the
way through? That's a contract that we cannot enforce.

> yes. Easily done actually. The decision lies in if we extend with
> background color or transparent pixels. Easy any way.

Depends on the layer properties: some layers have a background colour, others
are defined as transparent.

> Sure, but with the above suggestioon of mine - that you turned down, we
> would gain both performance (better than current) AND exact fit. But it
> does mean that iterators (in write mode) are assumed to truly affect every
> pixel.

But how can we make sure that that condition holds? If you think it won't be  
a problem, we can give it a try. As long as we can guarantee consistent 
behaviour for the user, I'm satisfied.

> With you last suggestion we would have a problem if it is based on
> transparency and we have a background color.

Even a layer with a background colour doesn't need to exactly coincide with 
tile boundaries, does it?

-- 
Boudewijn Rempt 
http://www.valdyas.org/fading/index.cgi
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