Re: [Gimp-developer] Warp transform Abyss policy

[Ell <ell_se yahoo com>]

On Tue, 13 Jun 2017 18:39:39 +0200
Julien Hardelin <jm hard wanadoo fr> wrote:

> Hello developers,
>
> I am writing gimp-help-2 doc for warp transform tool and I have 
> difficulty with "Abyss policy". I read the wiki/glossary for these
> items but did not understand what they do.
>
> How to explain these features to users?

Granted, the abyss policy option is a bit on the technical side.

The warp tool moves pixels from one point to another.  Some pixels may
come from outside the layer boundary.  These pixels don't actually
exist anywhere, and therefore don't have any associated color; yet, we
must assign *some* color to them.  The abyss policy specifies how to
determine their color:

  - None:  Assume that all pixels outside the layer boundary are
    transparent.

  - Clamp:  Assume that each edge of the layer stretches out
    indefinitely, so, for example, a pixel to the left of the layer
    boundary has the same color as the leftmost pixel of the layer with
    the same y coordinate.  An alternative way to think of it is that
    each pixel outside the layer boundary has the same color as the
    closest pixel inside the layer boundary.

  - Loop:  Assume that the layer repeats itself in all directions, so
    that, for example, falling off the right edge of the layer takes
    you back to the left edge.

And here's a quick comparison of the three modes:
http://i.imgur.com/R5RKkLF.gif

You'll find an abyss policy option in some of the filters as well, with
a similar function.  In filters, there are additional "black" and
"white" modes, which are similar to "none", but use black and white for
out-of-bounds pixels, instead of transparency.

--
Ell