init

2026-02-12 23:22:11 +08:00
parent 7b09eb3d89
commit 89660bba4e
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+"""
+permutate.py
+-------------
+
+Randomly deform meshes in different ways.
+"""
+
+import numpy as np
+
+from . import transformations, util
+from . import triangles as triangles_module
+from .typed import Number
+
+
+def transform(mesh, translation_scale: Number = 1000.0):
+    """
+    Return a permutated variant of a mesh by randomly reordering faces
+    and rotatating + translating a mesh by a random matrix.
+
+    Parameters
+    ----------
+    mesh : trimesh.Trimesh
+      Mesh, will not be altered by this function
+
+    Returns
+    ----------
+    permutated : trimesh.Trimesh
+      Mesh with same faces as input mesh but reordered
+      and rigidly transformed in space.
+    """
+    # rotate and translate randomly
+    matrix = transformations.random_rotation_matrix(translate=translation_scale)
+
+    # randomly re-order triangles
+    triangles = np.random.permutation(mesh.triangles).reshape((-1, 3))
+    # apply rigid transform
+    triangles = transformations.transform_points(triangles, matrix)
+
+    # extract the class from the input object
+    mesh_type = util.type_named(mesh, "Trimesh")
+    # generate a new mesh from the permutated data
+    permutated = mesh_type(**triangles_module.to_kwargs(triangles.reshape((-1, 3, 3))))
+
+    return permutated
+
+
+def noise(mesh, magnitude=None):
+    """
+    Add gaussian noise to every vertex of a mesh, making
+    no effort to maintain topology or sanity.
+
+    Parameters
+    ----------
+    mesh : trimesh.Trimesh
+      Input geometry, will not be altered
+    magnitude : float
+      What is the maximum distance per axis we can displace a vertex.
+      If None, value defaults to (mesh.scale / 100.0)
+
+    Returns
+    ----------
+    permutated : trimesh.Trimesh
+      Input mesh with noise applied
+    """
+    if magnitude is None:
+        magnitude = mesh.scale / 100.0
+
+    random = (np.random.random(mesh.vertices.shape) - 0.5) * magnitude
+    vertices_noise = mesh.vertices.copy() + random
+
+    # make sure we've re- ordered faces randomly
+    triangles = np.random.permutation(vertices_noise[mesh.faces])
+
+    mesh_type = util.type_named(mesh, "Trimesh")
+    permutated = mesh_type(**triangles_module.to_kwargs(triangles))
+
+    return permutated
+
+
+def tessellation(mesh):
+    """
+    Subdivide each face of a mesh into three faces with the new vertex
+    randomly placed inside the old face.
+
+    This produces a mesh with exactly the same surface area and volume
+    but with different tessellation.
+
+    Parameters
+    ------------
+    mesh : trimesh.Trimesh
+      Input geometry
+
+    Returns
+    ----------
+    permutated : trimesh.Trimesh
+      Mesh with remeshed facets
+    """
+    # create random barycentric coordinates for each face
+    # pad all coordinates by a small amount to bias new vertex towards center
+    barycentric = np.random.random(mesh.faces.shape) + 0.05
+    barycentric /= barycentric.sum(axis=1).reshape((-1, 1))
+
+    # create one new vertex somewhere in a face
+    vertex_face = (barycentric.reshape((-1, 3, 1)) * mesh.triangles).sum(axis=1)
+    vertex_face_id = np.arange(len(vertex_face)) + len(mesh.vertices)
+
+    # new vertices are the old vertices stacked on the vertices in the faces
+    vertices = np.vstack((mesh.vertices, vertex_face))
+    # there are three new faces per old face, and we maintain correct winding
+    faces = np.vstack(
+        (
+            np.column_stack((mesh.faces[:, [0, 1]], vertex_face_id)),
+            np.column_stack((mesh.faces[:, [1, 2]], vertex_face_id)),
+            np.column_stack((mesh.faces[:, [2, 0]], vertex_face_id)),
+        )
+    )
+    # make sure the order of the faces is permutated
+    faces = np.random.permutation(faces)
+
+    mesh_type = util.type_named(mesh, "Trimesh")
+    permutated = mesh_type(vertices=vertices, faces=faces)
+    return permutated
+
+
+class Permutator:
+    def __init__(self, mesh):
+        """
+        A convenience object to get permutated versions of a mesh.
+        """
+        self._mesh = mesh
+
+    def transform(self, translation_scale=1000):
+        return transform(self._mesh, translation_scale=translation_scale)
+
+    def noise(self, magnitude=None):
+        return noise(self._mesh, magnitude)
+
+    def tessellation(self):
+        return tessellation(self._mesh)
+
+
+try:
+    # copy the function docstrings to the helper object
+    Permutator.noise.__doc__ = noise.__doc__
+    Permutator.transform.__doc__ = transform.__doc__
+    Permutator.tessellation.__doc__ = tessellation.__doc__
+except AttributeError:
+    # no docstrings in Python2
+    pass