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

[Jehan Pagès <jehan marmottard gmail com>]

Hi!

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 (https://docs.gimp.org/2.9/en/gimp-tool-cage.html), 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
class).
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.

Jehan

> Best,
> Elle
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