mesh.py

#!/usr/bin/env python
#
# mesh.py - The TriangleMesh class.
#
# Author: Paul McCarthy <pauldmccarthy@gmail.com>
#
"""This module provides the :class:`TriangleMesh` class, which represents a
3D model made of triangles.

.. note:: I/O support is very limited - currently, the only supported file
          type is the VTK legacy file format, containing the ``POLYDATA``
          dataset. the :class:`TriangleMesh` class assumes that every polygon
          defined in an input file is a triangle (i.e. refers to three
          vertices).

          See http://www.vtk.org/wp-content/uploads/2015/04/file-formats.pdf
          for an overview of the VTK legacy file format.

          In the future, I may or may not add support for more complex meshes.
"""


import logging

import os.path as op
import numpy   as np

import six

import fsl.utils.memoize   as memoize
import fsl.utils.transform as transform

from . import image as fslimage


log = logging.getLogger(__name__)


class TriangleMesh(object):
    """The ``TriangleMesh`` class represents a 3D model. A mesh is defined by a
    collection of ``N`` vertices, and ``M`` triangles.  The triangles are
    defined by ``(M, 3)`` indices into the list of vertices.


    A ``TriangleMesh`` instance has the following attributes:


    ============== ====================================================
    ``name``       A name, typically the file name sans-suffix.

    ``dataSource`` Full path to the mesh file (or ``None`` if there is
                   no file associated with this mesh).

    ``vertices``   A :math:`N\times 3` ``numpy`` array containing
                   the vertices.

    ``indices``    A :meth:`M\times 3` ``numpy`` array containing
                   the vertex indices for :math:`M` triangles

    ``normals``    A :math:`M\times 3` ``numpy`` array containing
                   face normals.

    ``vnormals``   A :math:`N\times 3` ``numpy`` array containing
                   vertex normals.
    ============== ====================================================


    And the following methods:

    .. autosummary::
       :nosignatures:

       getBounds
       loadVertexData
       getVertexData
       clearVertexData
    """


    def __init__(self, data, indices=None, fixWinding=False):
        """Create a ``TriangleMesh`` instance.

        :arg data:       Can either be a file name, or a :math:`N\\times 3`
                         ``numpy`` array containing vertex data. If ``data``
                         is a file name, it is passed to the
                         :func:`loadVTKPolydataFile` function.

        :arg indices:    A list of indices into the vertex data, defining
                         the triangles.

        :arg fixWinding: Defaults to ``False``. If ``True``, the vertex
                         winding order of every triangle is is fixed so they
                         all have outward-facing normal vectors.
        """

        if isinstance(data, six.string_types):
            infile = data
            data, lengths, indices = loadVTKPolydataFile(infile)

            if np.any(lengths != 3):
                raise RuntimeError('All polygons in VTK file must be '
                                   'triangles ({})'.format(infile))

            self.name       = op.basename(infile)
            self.dataSource = infile
        else:
            self.name       = 'TriangleMesh'
            self.dataSource = None

        if indices is None:
            indices = np.arange(data.shape[0])

        self.__vertices     = np.array(data)
        self.__indices      = np.array(indices).reshape((-1, 3))

        self.__vertexData = {}
        self.__faceNormals = None
        self.__vertNormals = None
        self.__loBounds    = self.vertices.min(axis=0)
        self.__hiBounds    = self.vertices.max(axis=0)

        if fixWinding:
            self.__fixWindingOrder()


    def __repr__(self):
        """Returns a string representation of this ``TriangleMesh`` instance.
        """
        return '{}({}, {})'.format(type(self).__name__,
                                   self.name,
                                   self.dataSource)

    def __str__(self):
        """Returns a string representation of this ``TriangleMesh`` instance.
        """
        return self.__repr__()


    def __fixWindingOrder(self):
        """Called by :meth:`__init__` if ``fixWinding is True``.  Fixes the
        mesh triangle winding order so that all face normals are facing
        outwards from the centre of the mesh.
        """

        # Define a viewpoint which is
        # far away from the mesh.
        fnormals = self.normals
        camera   = self.__loBounds - (self.__hiBounds - self.__loBounds)

        # Find the nearest vertex
        # to the viewpoint
        dists = np.sqrt(np.sum((self.vertices - camera) ** 2, axis=1))
        ivert = np.argmin(dists)
        vert  = self.vertices[ivert]

        # Pick a triangle that
        # this vertex in and
        # ges its face normal
        itri = np.where(self.indices == ivert)[0][0]
        n    = fnormals[itri, :]

        # Make sure the angle between the
        # normal, and a vector from the
        # vertex to the camera is positive
        # If it isn't, flip the triangle
        # winding order.
        if np.dot(n, transform.normalise(camera - vert)) < 0:
            self.indices[:, [1, 2]] = self.indices[:, [2, 1]]
            self.__faceNormals     *= -1


    @property
    def vertices(self):
        """The ``(N, 3)`` vertices of this mesh. """
        return self.__vertices


    @property
    def indices(self):
        """The ``(M, 3)`` triangles of this mesh. """
        return self.__indices


    @property
    def normals(self):
        """A ``(M, 3)`` array containing surface normals for every
        triangle in the mesh, normalised to unit length.
        """

        if self.__faceNormals is not None:
            return self.__faceNormals

        v0 = self.vertices[self.indices[:, 0]]
        v1 = self.vertices[self.indices[:, 1]]
        v2 = self.vertices[self.indices[:, 2]]

        n = np.cross((v1 - v0), (v2 - v0))

        self.__faceNormals = transform.normalise(n)

        return self.__faceNormals


    @property
    def vnormals(self):
        """A ``(N, 3)`` array containing normals for every vertex
        in the mesh.
        """
        if self.__vertNormals is not None:
            return self.__vertNormals

        # per-face normals
        fnormals = self.normals
        vnormals = np.zeros((self.vertices.shape[0], 3), dtype=np.float)

        # TODO make fast. I can't figure
        # out how to use np.add.at to
        # accumulate the face normals for
        # each vertex.
        for i in range(self.indices.shape[0]):

            v0, v1, v2 = self.indices[i]

            vnormals[v0, :] += fnormals[i]
            vnormals[v1, :] += fnormals[i]
            vnormals[v2, :] += fnormals[i]

        # normalise to unit length
        self.__vertNormals = transform.normalise(vnormals)

        return self.__vertNormals


    @memoize.Instanceify(memoize.memoize)
    def trimesh(self):
        """Reference to a ``trimesh.Trimesh`` object which can be used for
        geometric operations on the mesh.

        If the ``trimesh`` or ``rtree`` libraries are not available, this
        function returns ``None``
        """

        # trimesh is an optional dependency - rtree
        # is a depedendency of trimesh which is a
        # wrapper around libspatialindex, without
        # which trimesh can't be used for calculating
        # ray-mesh intersections.
        try:
            import trimesh
            import rtree   # noqa
        except ImportError:
            log.warning('trimesh is not available')
            return None

        if hasattr(self, '__trimesh'):
            return self.__trimesh

        self.__trimesh = trimesh.Trimesh(self.__vertices,
                                         self.__indices,
                                         process=False,
                                         validate=False)

        return self.__trimesh


    def rayIntersection(self, origins, directions, vertices=False):
        """Calculate the intersection between the mesh, and the rays defined by
        ``origins`` and ``directions``.

        :arg origins:    Sequence of ray origins
        :arg directions: Sequence of ray directions
        :returns:        A tuple containing:

                           - A ``(n, 3)`` array containing the coordinates
                             where the mesh was intersected by each of the
                             ``n`` rays.

                           - A ``(n,)`` array containing the indices of the
                             triangles that were intersected by each of the
                             ``n`` rays.
        """

        trimesh = self.trimesh()

        if trimesh is None:
            return np.zeros((0, 3)), np.zeros((0,))

        tris, rays, locs = trimesh.ray.intersects_id(
            origins,
            directions,
            return_locations=True,
            multiple_hits=False)

        if tris.size == 0:
            return np.zeros((0, 3)), np.zeros((0,))

        # sort by ray. I'm Not sure if this is
        # needed - does trimesh do it for us?
        rayIdxs = np.asarray(np.argsort(rays), np.int)
        locs    = locs[rayIdxs]
        tris    = tris[rayIdxs]

        return locs, tris


    def getBounds(self):
        """Returns a tuple of values which define a minimal bounding box that
        will contain all vertices in this ``TriangleMesh`` instance. The
        bounding box is arranged like so:

            ``((xlow, ylow, zlow), (xhigh, yhigh, zhigh))``
        """
        return (self.__loBounds, self.__hiBounds)


    def loadVertexData(self, dataSource, vertexData=None):
        """Attempts to load scalar data associated with each vertex of this
        ``TriangleMesh`` from the given ``dataSource``. The data is returned,
        and also stored in an internal cache so it can be retrieved later
        via the :meth:`getVertexData` method.

        This method may be overridden by sub-classes.

        :arg dataSource: Path to the vertex data to load
        :arg vertexData: The vertex data itself, if it has already been
                         loaded.

        :returns: A ``(M, N)``) array, which contains ``N`` data points
                  for ``M`` vertices.
        """

        nvertices = self.vertices.shape[0]

        # Currently only white-space delimited
        # text files are supported
        if vertexData is None:
            vertexData = np.loadtxt(dataSource)
            vertexData.reshape(nvertices, -1)

        if vertexData.shape[0] != nvertices:
            raise ValueError('Incompatible size: {}'.format(dataSource))

        self.__vertexData[dataSource] = vertexData

        return vertexData


    def getVertexData(self, dataSource):
        """Returns the vertex data for the given ``dataSource`` from the
        internal vertex data cache. If the given ``dataSource`` is not
        in the cache, it is loaded via :meth:`loadVertexData`.
        """

        try:             return self.__vertexData[dataSource]
        except KeyError: return self.loadVertexData(dataSource)


    def clearVertexData(self):
        """Clears the internal vertex data cache - see the
        :meth:`loadVertexData` and :meth:`getVertexData`  methods.
        """

        self.__vertexData = {}


ALLOWED_EXTENSIONS     = ['.vtk']
"""A list of file extensions which could contain :class:`TriangleMesh` data.
"""


EXTENSION_DESCRIPTIONS = ['VTK polygon model file']
"""A description for each of the extensions in :data:`ALLOWED_EXTENSIONS`."""


def loadVTKPolydataFile(infile):
    """Loads a vtk legacy file containing a ``POLYDATA`` data set.

    :arg infile: Name of a file to load from.

    :returns: a tuple containing three values:

                - A :math:`N\\times 3` ``numpy`` array containing :math:`N`
                  vertices.
                - A 1D ``numpy`` array containing the lengths of each polygon.
                - A 1D ``numpy`` array containing the vertex indices for all
                  polygons.
    """

    lines = None

    with open(infile, 'rt') as f:
        lines = f.readlines()

    lines = [l.strip() for l in lines]

    if lines[3] != 'DATASET POLYDATA':
        raise ValueError('Only the POLYDATA data type is supported')

    nVertices = int(lines[4].split()[1])
    nPolygons = int(lines[5 + nVertices].split()[1])
    nIndices  = int(lines[5 + nVertices].split()[2]) - nPolygons

    vertices       = np.zeros((nVertices, 3), dtype=np.float32)
    polygonLengths = np.zeros( nPolygons,     dtype=np.uint32)
    indices        = np.zeros( nIndices,      dtype=np.uint32)

    for i in range(nVertices):
        vertLine       = lines[i + 5]
        vertices[i, :] = [float(w) for w in vertLine.split()]

    indexOffset = 0
    for i in range(nPolygons):

        polyLine          = lines[6 + nVertices + i].split()
        polygonLengths[i] = int(polyLine[0])

        start              = indexOffset
        end                = indexOffset + polygonLengths[i]
        indices[start:end] = [int(w) for w in polyLine[1:]]

        indexOffset        += polygonLengths[i]

    return vertices, polygonLengths, indices


def getFIRSTPrefix(modelfile):
    """If the given ``vtk`` file was generated by `FIRST
    <https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FIRST>`_, this function
    will return the file prefix. Otherwise a ``ValueError`` will be
    raised.
    """

    if not modelfile.endswith('first.vtk'):
        raise ValueError('Not a first vtk file: {}'.format(modelfile))

    modelfile = op.basename(modelfile)
    prefix    = modelfile.split('-')
    prefix    = '-'.join(prefix[:-1])

    return prefix


def findReferenceImage(modelfile):
    """Given a ``vtk`` file, attempts to find a corresponding ``NIFTI``
    image file. Return the path to the image, or ``None`` if no image was
    found.

    Currently this function will only return an image for ``vtk`` files
    generated by `FIRST <https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FIRST>`_.
    """

    try:

        dirname  = op.dirname(modelfile)
        prefixes = [getFIRSTPrefix(modelfile)]
    except ValueError:
        return None

    if prefixes[0].endswith('_first'):
        prefixes.append(prefixes[0][:-6])

    for p in prefixes:
        try:
            return fslimage.addExt(op.join(dirname, p), mustExist=True)
        except fslimage.PathError:
            continue

    return None