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Lindenmayer / Path turtle: correct coordinate system

What does the merge request do?

Fix https://bugs.launchpad.net/inkscape/+bug/1094627

For Lindenmayer, "Turn left" and "Turn right" were inverted. This was due to an error in turtle.py - the y axis in SVG looks down so a left rotation has a negative sign.

Entering the examples on Wikipedia now gives identically oriented results.

Question: can we change this behavior? turtle is used in 2 extensions in mightyscape, so it's rather rare. But it's still a breaking change without warning.

Answer: We're not changing the API, it's the API being broken. Even if users are affected, a simple Mirror command is all it takes to fix this on user side.

Implementation notes

Added unit tests for a simple Koch snowflake and a Sierpinski triangle to test multiple rules.

Summary for release notes

A bug in the rotation sense of the Lindenmayer extension has been fixed.

Checklist

  • Add unit tests (if applicable)
  • Changes to inkex/ are well documented
  • Clean merge request history
Edited by Jonathan Neuhauser

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