Fixed by implementing Massimo's two findings:
gimp_operation_cage_transform_process(): if aux_buf is NULL, bail out
after initializing out_buf with identity vectors, fixes the crash.
gimp_cage_tool_create_filter(): set the drawable filter's region to
GIMP_FILTER_REGION_DRAWABLE, fixes offset when there is a selection.
... instead of gegl_buffer_sample()
GEGL commit 26f13cbfe9aaaa8c176162e54fdbb8af6876538e got rid of the
per-buffer cached samplers, making gegl_buffer_sample() much more
expensive, suitable primarily for one-off samples.
Use a sampler object instead.
It seems gegl_buffer_sample() crashes with the first parameter being
NULL so let's just test its value first. This will output a huge
quantity of CRITICALs in this edge case but that's much better than a
crash. :-)
See also bug 793371 where this bug is being processed.
When checking the Cage Transform operation code, I saw some ifdef meant
to be switched to when bug 645810 is fixed. It also says in a comment:
> /* When Gegl bug #645810 will be solved,
> this should be a good optimisation */
Checking said bug, it appears it has been fixed since 2012!
I also fixed a bit the parameters in gegl_buffer_sample() call since it
seems the function signature has changed quite a bit.
Keep multi-threading disable on the cage transform operation. It is now
fixed but is a lot much slower than when single-threaded, making it
painful to use on bigger images.
So let's reenable later if we can improve this. See bug 787663.
More than 2000 lines of code less in app/, instead of
if (instance->member)
{
g_object_unref/g_free/g_whatever (instance->member);
instance->member = NULL;
}
we now simply use
g_clear_object/pointer (&instance->member);
Use a proper "progress" signal instead of a property "notify" one
to update the on-canvas progress widget.
This way the graph is not invalidated while processing it
