[Gimp-developer] Some changes to the "Edge" plug-in

[William Skaggs]

I've made a few tweaks to the "Edge" plug-in in the development branch, 
in order to make it easier to use and understand, which I would like to 
explain.

1) Changed the menu entry from "Edge" to "Sharp Edges".  Having an
   entry called "Edge" in the "Edge-detect" category is silly, and the
   thing that distinguishes this plugin is that it detects edges
   between neighboring pixels, that is, sharp edges.

2) Added an "invert" control, so that you can see the edges as dark
   lines on a light background.  Without this, the preview is almost
   useless.  I did some voodoo to make "invert" the default for
   interactive use, but not to change the result when "edge" is called
   from the PDB.  The new "invert" argument is optional.  If it is
   omitted, a value of FALSE is used, which gives the same behavior as
   the plug-in has had previously.  Therefore, no existing script that
   uses this plug-in should change its behavior.

3) Changed the default method to Prewitt, which I believe gives the
   closest match to what users are hoping for.  I renamed the
   method-selector menu from "Algorithm" to "Method", and renamed the
   Prewitt entry to "Default", also putting it at the top.

4) Removed the "wrap-style" radio buttons from the interface, on the
   grounds that the choice between "Wrap", "Smear", and "Black" is
   puzzling to users, and that almost always Smear is the only choice
   that makes sense.  (Smear means that the edge of the image or 
   selection does not get treated as an edge for edge-detection.
   This option is still present in the pdb interface, though, without 
   any changes.

I would like to follow up on this, unless anybody objects, by removing
the Sobel and Laplace entries from the Edge-detect menu (but not from
the PDB).  Both of these methods are available in the Edge plug-in,
and neither is very useful for interactive usage.  They are, however,
potentially quite useful in scripts, so I think they should stay in
the PDB.

  -- Bill