autoRotateMaya.py

"""
autoRotate
==========

Align the selected edge to the world X axis of the scene by rotating the whole mesh.

Usage
-----

Select exactly one edge, then run the script.

License
-------

Copyright (c) 2017 Elie Michel -- ATI (Universite Paris 8)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
"""

from maya import cmds
import maya.api.OpenMaya as om

def objectFromEdge(edge):
    """Convert edge identifier into its matching shape identifier.
    I'm not sure whether this is always correct, but could not find
    a proper way to do so using maya's API"""
    return '.'.join(edge.split('.')[:-1])

def alignEdgeToXAxis():
    """Align the selected edge to the world X axis of the scene"""
    edgeList = cmds.ls(sl=True)
    if len(edgeList) != 1:
        cmds.error("[alignEdgeToXAxis] You must select exactly one edge")
        return
    
    # Get the  position of the vertices of the selected edge
    edge = edgeList[0]
    verts = cmds.ls(cmds.polyListComponentConversion(edge, tv=True), flatten=True)
    assert(len(verts) == 2)
    p = [cmds.xform(v, query=True, translation=True, worldSpace=True) for v in verts]
    assert(len(p) == 2 and len(p[0]) == 3)
    
    p = [om.MVector(u) for u in p]
    
    # Reconstruct rotation matrix from the target X vector
    y = om.MVector(0, 1, 0)
    x = (p[1] - p[0]).normalize()
    z = (x ^ y).normalize()
    y = (z ^ x).normalize()
    
    c = -(p[0] + p[1]) / 2.0
    
    # Transpose the matrix to get a transformation back to the aligned object
    mat = om.MMatrix([
        [x[0], y[0], z[0], 0],
        [x[1], y[1], z[1], 0],
        [x[2], y[2], z[2], 0],
        [   0,    0,    0, 1]
    ])
    
    # Translation matrices, in order to rotate around the center of the edge instead of the origin point
    t1 = om.MMatrix([
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [c.x, c.y, c.z, 1]
    ])
    
    t2 = om.MMatrix([
        [1, 0, 0, 0],
        [0, 1, 0, 0],
        [0, 0, 1, 0],
        [-c.x, -c.y, -c.z, 1]
    ])
    
    # Apply the rotation matrix
    currentMat = om.MMatrix(cmds.xform(objectFromEdge(edge), q=True, m=True))
    currentMat = cmds.xform(objectFromEdge(edge), m=currentMat*t1*mat*t2)
    
alignEdgeToXAxis()