Add distance-preserving alignment #33
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* Don't compare against numeric constants with 'is' -- those should be checked for equality and not identity * Remove explicit comparisons against True and False Also remove some redundant parentheses
The previous data collection/manipulation done in lists_of_verts tracks BMLoopUV objects, and as far as I can tell, these don't store any references to the corresponding BMLoops. I need to perform a graph traversal of the selected UV vertices, which necessitates using the link information in the BMLoop objects -- so build new mappings storing BMLoops.
I don't know why I thought it was necessary or appropriate to traverse loops in their *entirety* to find the selected neighbors of a vertex in UV space, but this definitely isn't appropriate. We just need to look at the previous and next links.
The direction of vertices isn't stable; successive runs of this flipt he directionality of the vertices. This is worth fixing, but not for my immediate usage.
Quick-and-dirty heuristic: choose the vertex order with minimum total L1 distance
Sequence doesn't imply mutability.
Also deduplicate code that chooses new coordinate directions based on minimum total L1 distance
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First, thanks for the addon! I've found it quite useful in manipulating UV unwrapping.
After using this addon a few times, I realized that what I really wanted to do isn't implemented: aligning vertices to the U or V axis while preserving the distance between them in UV space. As far as I can tell, the existing code paths use
BMLoopUVobjects to move vertices in UV space, but I needed to access the parentBMLoopobjects to walk the edges between vertices. I didn't see a way to access theBMLoopobject from aBMLoopUV, so I had to build entirely separate data structures to map vertex coordinates toBMLoops (see 0c9f0c5). (I consider myself very fluent in Python, and I've written a lot of Python code in the last decade or so, but this is my first exposure to the Blender API.)The new code in this PR requires NumPy and Python 3.7 or newer -- Blender 2.82 on Windows already includes both, so this version of the addon can be installed and used as-is. On Ubuntu, I had to install the
python3-numpysystem package, which is now described in the README (ebdad46).This functionality uses two BFS graph traversals to find a linear ordering of vertices:
Vertices can overlap in both U and V coordinates; this is handled properly:
Disconnected sets of vertices are aligned independently:
If it's not possible to find a simple linear ordering of selected vertices, the addon exits with an error:
I also modernized the code a bit and fixed some
SyntaxWarnings that are shown by Python 3.8 -- for example,Noneis usually the only constant that should be compared against with identity and not equality. There is now amath.isclosemethod that handles the hand-crafted comparison of vertex positions, too. The code formatting was inconsistent in a lot of places, and I cleaned that up with theblackformatter.I understand if you don't want to merge this due to the not-strictly-necessary changes included in this PR, but I couldn't resist making small cleanups while stepping through the code with the debugger to get a feel for the Blender API.
Thanks again for the addon; it was great as an introduction to the Blender API!