Powerstroke LPE lib2geom error

Bug #986394 reported by AstromanPete on 2012-04-20
This bug affects 1 person
Affects Status Importance Assigned to Milestone
Johan Engelen

Bug Description

I'm having some fun throwing script-generated SVG at the new Powerstroke live path-effect. It's worked like a champ until recently. I get the following error in the console, as many times as I have paths. It doesn't stop Inkscape from running, but the LPE doesn't render. The error is:

** (inkscape:17852): WARNING **: Exception during LPE [Unstable!] Power stroke execution.
 lib2geom exception: rx2 < 0, while computing 'rx' coefficient (2geom/ellipse.cpp:87)

I saw on the mailing list that extensive changes were recently made to the math of Powerstroke.

I've attached the SVG file, and a raster of the image when it worked below for your use.

I'm using Inkscape 0.48+devel r11266 (Apr 20 2012) on Kubuntu 11.10

Adding the new "linejoin_type" attribute to the effect definition yields the same result. This is not reflected in the attached SVG.


AstromanPete (peter-f-smith) wrote :
su_v (suv-lp) on 2012-04-21
tags: added: livepatheffects
removed: powerstroke
su_v (suv-lp) wrote :

Reproduced with Inkscape 0.48+devel r11265 on OS X 10.7.2 (64bit).

Attaching reduced test case with one path extracted from the large test file (1.7 MB).

Other ways to reproduce:
1) switch to the pencil tool
2) reduce smoothness to a very low value
3) choose one of the 'Triangle' shapes (uses Powerstroke)
4) draw a curved path with the pencil (freehand) tool

-> powerstroke path effect often doesn't apply correctly, and produces the same error messages:

** (inkscape:99678): WARNING **: Exception during LPE [Unstable!] Power stroke execution.
 lib2geom exception: rx2 < 0, while computing 'rx' coefficient (../../src/2geom/ellipse.cpp:87)

Changed in inkscape:
importance: Undecided → Medium
status: New → Confirmed
assignee: nobody → Johan Engelen (johanengelen)
su_v (suv-lp) wrote :

Attaching backtrace (full) from opening reduced test case with debug build of r11265 (breakpoint set to 'throw')

Johan Engelen (johanengelen) wrote :

fixed partly in r11295. the ellipse exception is caught now.
but another error pops up... working on it

Changed in inkscape:
status: Confirmed → In Progress
Johan Engelen (johanengelen) wrote :

while I wait for compilation:
Thank you very very very very much for testing Powerstroke so rigorously! Keep it going! :-)

Johan Engelen (johanengelen) wrote :

Now I get this exception when loading the test svg:

** (inkscape.exe:6520): WARNING **: Exception during LPE [Unstable!] Power stroke execution. lib2geom exception: Invariants violation (src/2geom/piecewise.h:144)

It is thrown somewhere in the reverse method of this line:
Piecewise<D2<SBasis> > mirrorpath = reverse(compose(pwd2_in,x) - y*compose(n,x));

Johan Engelen (johanengelen) wrote :

note: happens only for the "Linear" interpolator type

Johan Engelen (johanengelen) wrote :

Fixed in r11297.

Thanks again! :) Waiting for your next bug report ;-)

Changed in inkscape:
status: In Progress → Fix Released
AstromanPete (peter-f-smith) wrote :

No, THANK YOU for working on such an awesome feature. To make my thanks more tangible, I kicked some money into the project.

su_v (suv-lp) on 2012-06-14
tags: added: 2geom
removed: lib2geom
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