Re: [Gimp-developer] Cage transform and Warp transform


On Tue, Nov 28, 2017 at 3:54 PM, Elle Stone
<ellestone ninedegreesbelow com> wrote:
Hi All,

I wanted to somewhat reshape some curved lines in a drawing, and tried the
Cage transform, which I remember using a long time ago. After selecting the
points, it took a long time for the cage transform to calculate the cage.
But when trying to move a point on the cage, nothing happened. During all of
this calculating plus "nothing happened", these lines were printed over and
over to the terminal:

(gimp-2.9:30657): GEGL-CRITICAL **: gegl_buffer_get: assertion
'GEGL_IS_BUFFER (buffer)' failed

Is there a bug? Or maybe I did something wrong? I reread through the on-line
documentation (, but maybe
I misunderstood what it says.

Well if it doesn't work and if there is a GEGL-critical, yes there is
definitely a bug. ;-)
You should run gimp with --gtk-g-fatal-warnings to force it to crash
when it gets a warning. Doing this inside gdb will get you a
stacktrace which led to this warning so that you can copy-paste it in
a bug report. :-)

So I switched to the Warp transform, which worked very smoothly, quickly,
responsively. It's like using a paint brush to warp the lines. The only
catch was that after moving all the lines to where you want them, then you
have to hit Return to actually apply the transform, which makes sense, but
it took me a couple tries to figure this out.

Whoever programmed the warp transform, thank you!! This is such a nice way
to gently reshape curved lines!

Jehan, is there any possibility that this warp transform could be made to
work symmetrically, perhaps via the symmetric painting dialog? Or maybe it
already does, but somehow I did something wrong?

No. The symmetries work for paint tools (children of GimpPaintTool
class), but the warp transform is not a paint tool (I mean, not in our
code; it is derived directly from GimpDrawTool, which is lower level
Of course, in theory, that could be changed. But this is not how it is
implemented currently.

Anyway, I made the transformed lines symmetric by duplicating the warped
layer, flipping it around the horizontal axis, and applying a mask to hide
the untranformed half of the image, which worked out just fine.

Cool. That's old style how it would have been done with paint tools as
well. I guess this still has to be done for other tools until someone
make symmetries even more generic.


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