"Outset/inset path" act erratically if input path is small

Reproduced with Inkscape 0.48+devel r9701 on OS X 10.5.8

Perhaps one should optionally be able to specify a percentage for outset/inset step size.

Is this bug related to https://bugs.launchpad.net/inkscape/+bug/180708 ?

Still present with Inkscape trunk revision 12010 on Windows XP.

Still present with Inkscape 0.91+devel r14159 (on OS X 10.7.5).

Still present with 0.92 (on linux). It's an annoying bug, and limits me from using Inkscape for preprocessing laser cutting tasks.

I started to debug this, and everything works correctly if I remove "res->Simplify(1.0)" in "sp_selected_path_do_offset" function. I understand neither the MakeOffset's logic, nor Simplify's logic. I'll dig deeper.

 Peter

I have two proposals:

1. Remove the "Simplify" call completely from Inset/Outset commands. (You can call it manually with Ctrl+L anyway.)
2. Call "Simplify" with "simplifythreshold" value (instead of capping it with an arbitrary 1.0). We might need to adjust it with "size" just as in "sp_selected_path_simplify_item" function. This way the Inset/Outset command would be just the pure Inset/Outset function + a regular call of Simplify.

What do you think?

 Peter

(1) makes sense, I think.

Hi,

 I collected and counted all the votes, it looks like option (1) has the majority (thanks Mc). I created a patch, please find it attached.

 Please note that I have no idea what else I could ruin with this patch. It solves this issue, please merge it only if it looks ok.

 Thanks,
  Peter

pushed to trunk r15619, thanks for the patch!

The fix committed in r15619 produces regressions when outsetting curves multiple times.

To reproduce:
1) launch trunk, default template (mm-based)
   set inset/outset step to 1mm
2) draw a circle (no fill, thin stroke), with about 5cm diameter
3) duplicate ( Ctrl+D ) and outset ( Ctrl+) )
4) repeat step (3) several times (10-12)

The resulting outset paths quickly divert from the original shape into ... nothing even close to the original circle.

Does not reproduce if the commit is reverted.

AFAICT the commit also tends to produce rather large numbers of nodes for in-/outset curves (compared to results with the commit reverted).

Proposing to revert the commit for now (and not to consider it for backporting to stable - testing it with 0.92.x was how I noticed the changed behavior).

Demonstration of a circle outset multiple times with current git master (4a5430720).

I see. Then I guess the inset/outset algorithm is not perfect (maybe that was the reason for applying simplify), and we should have a deeper look into the code to find out how to fix these issues. I'm a little bit busy these days, I'll try to come back when I have some time.

still present in Windows 10, Inkscape 0.92.2 (5c3e80d, 2017-08-06)

still present in Windows 10, Inkscape trunk, Inkscape 0.92+devel (177a8e8, 2017-12-08)

(the nature of the defect in trunk is significantly different than in 0.92.2, but both defects are still clearly observable)

in view of the fact that trunk sometimes crashes randomly when performing this test, especially when insetting multiple times, I think it would be a good idea to revert rev 15619
http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/15619

I have created a file which should be suitable for debugging this.

This bug is critical for CNC machines with small parts. I'm trying to do a linked-offset of a 5mm hole with a 3mm bit (inkscape:radius 5.3).

The resulting circles are all misshaped.

Messing with the Behavior->Steps "scale by" or "inset/offset by" do not fix this bug. (Why should they? Those are for keyboard steps).

I suspect many others are hitting this bug but haven't said anything.

Going through the example files, this is fixed in 1.0.

However, there is still some problem at small input sizes (similar to https://bugs.launchpad.net/inkscape/+bug/616469/comments/12 except doesn't affect those sample files). This is being tracked in https://gitlab.com/inkscape/inbox/-/issues/3371

Thanks for reporting!