diff --git a/Dockerfile b/Dockerfile
index f134a1bfd..f864e423c 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -61,9 +61,11 @@ COPY --chown=499 pyproject.toml .
 COPY --chown=499 ./.git ./.git/
 
 USER root
-RUN trimesh-setup --install=test,gmsh,gltf_validator,llvmpipe,binvox
+RUN trimesh-setup --install=test,gmsh,gltf_validator,llvmpipe,binvox,blender
 USER user
 
+RUN blender --version
+
 # install things like pytest and make sure we're on Numpy 2.X
 RUN pip install .[all] && \
     python -c "import numpy as n; assert(n.__version__.startswith('2'))"
diff --git a/docker/trimesh-setup b/docker/trimesh-setup
index ba614dd18..f66977d7c 100755
--- a/docker/trimesh-setup
+++ b/docker/trimesh-setup
@@ -6,15 +6,14 @@ environment for `trimesh` in a Debian Docker image.
 It probably isn't useful for most people unless you are running
 this exact configuration.
 """
+
 import argparse
 import json
 import logging
 import os
-import shutil
 import subprocess
 import sys
 import tarfile
-import tempfile
 from fnmatch import fnmatch
 from io import BytesIO
 
@@ -43,8 +42,9 @@ config_json = """
     ],
     "test": [
       "curl",
-      "git"
-    ],
+      "git",
+      "libxkbcommon0"
+],
    "gmsh": ["libxft2", "libxinerama-dev", "libxcursor1","libgomp1"]
   },
   "fetch": {
@@ -52,21 +52,30 @@ config_json = """
       "url": "https://github.com/KhronosGroup/glTF-Validator/releases/download/2.0.0-dev.3.8/gltf_validator-2.0.0-dev.3.8-linux64.tar.xz",
       "sha256": "374c7807e28fe481b5075f3bb271f580ddfc0af3e930a0449be94ec2c1f6f49a",
       "target": "$PATH",
-      "chmod": 755,
+      "chmod": {"gltf_validator": 755},
       "extract_only": "gltf_validator"
     },
     "pandoc": {
       "url": "https://github.com/jgm/pandoc/releases/download/3.1.1/pandoc-3.1.1-linux-amd64.tar.gz",
       "sha256": "52b25f0115517e32047a06d821e63729108027bd06d9605fe8eac0fa83e0bf81",
       "target": "$PATH",
-      "chmod": 755,
+      "chmod": {"pandoc": 755},
       "extract_only": "pandoc"
     },
+
     "binvox": {
       "url": "https://trimesh.s3-us-west-1.amazonaws.com/binvox",
       "sha256": "82ee314a75986f67f1d2b5b3ccdfb3661fe57a6b428aa0e0f798fdb3e1734fe0",
       "target": "$PATH",
-      "chmod": 755
+      "chmod": {"binvox": 755}
+    },
+
+    "blender": {
+      "url": "https://mirrors.ocf.berkeley.edu/blender/release/Blender4.2/blender-4.2.3-linux-x64.tar.xz",
+      "sha256": "3a64efd1982465395abab4259b4091d5c8c56054c7267e9633e4f702a71ea3f4",
+      "target": "$PATH",
+      "chmod": {"blender": 755},
+      "strip_components": 1
     }
   }
 }
@@ -154,7 +163,22 @@ def fetch(url, sha256):
     return data
 
 
-def copy_to_path(file_path, prefix="~"):
+def is_writable(path: str) -> bool:
+    if not os.path.isdir(path):
+        return False
+
+    test_fn = os.path.join(path, ".test_writeable_file")
+    try:
+        with open(test_fn, "w") as f:
+            f.write("can we write here?")
+        os.remove(test_fn)
+        return True
+    except BaseException as E:
+        print(path, E)
+        return False
+
+
+def choose_in_path(prefix="~") -> str:
     """
     Copy an executable file onto `PATH`, typically one of
     the options in the current user's home directory.
@@ -167,18 +191,6 @@ def copy_to_path(file_path, prefix="~"):
       The path prefix it is acceptable to copy into,
       typically `~` for `/home/{current_user}`.
     """
-    # get the full path of the requested file
-    source = os.path.abspath(os.path.expanduser(file_path))
-
-    # get the file name
-    file_name = os.path.split(source)[-1]
-
-    # make sure the source file is readable and not empty
-    with open(source, "rb") as f:
-        file_data = f.read()
-    # check for empty files
-    if len(file_data) == 0:
-        raise ValueError(f"empty file: {file_path}")
 
     # get all locations in PATH
     candidates = [
@@ -202,13 +214,9 @@ def copy_to_path(file_path, prefix="~"):
 
     # try writing to the shortest paths first
     for index in argsort(scores):
-        path = os.path.join(candidates[index], file_name)
-        try:
-            shutil.copy(source, path)
-            print(f"wrote `{path}`")
+        path = candidates[index]
+        if is_writable(path):
             return path
-        except BaseException:
-            pass
 
     # none of our candidates worked
     raise ValueError("unable to write to file")
@@ -259,17 +267,31 @@ def handle_fetch(
       A hex string for the hash of the remote resource.
     target : str
       Target location on the local file system.
-    chmod : None or int.
+    chmod : None or dict
       Change permissions for extracted files.
     extract_skip : None or iterable
-      Skip a certain member of the archive.
-    extract_only : None or str
-      Extract *only* a single file from the archive,
-      overrides `extract_skip`.
+      Skip a certain member of the archive using
+      an `fnmatch` pattern, i.e. "lib/*"
+    extract_only : None or iterable
+      Extract only whitelisted files from the archive
+      using an `fnmatch` pattern, i.e. "lib/*"
     strip_components : int
       Strip off this many components from the file path
       in the archive, i.e. at `1`, `a/b/c` is extracted to `target/b/c`
     """
+    if target.lower().strip() == "$path":
+        target = choose_in_path()
+        log.debug(f"identified destination as `{target}`")
+
+    if chmod is None:
+        chmod = {}
+        
+    if extract_skip is None:
+        extract_skip = []
+    # if passed a single string
+    if isinstance(extract_only, str):
+        extract_only = [extract_only]
+
     # get the raw bytes
     log.debug(f"fetching: `{url}`")
     raw = fetch(url=url, sha256=sha256)
@@ -284,10 +306,10 @@ def handle_fetch(
         # get the archive
         tar = tarfile.open(fileobj=BytesIO(raw), mode=mode)
 
-        if extract_skip is None:
-            extract_skip = []
-
         for member in tar.getmembers():
+            if member.isdir():
+                continue
+
             # final name after stripping components
             name = "/".join(member.name.split("/")[strip_components:])
 
@@ -296,44 +318,28 @@ def handle_fetch(
                 log.debug(f"skipping: `{name}`")
                 continue
 
-            if extract_only is None:
-                path = os.path.join(target, name)
-                log.debug(f"extracting: `{path}`")
-                extract(tar=tar, member=member, path=path, chmod=chmod)
-            else:
-                name = name.split("/")[-1]
-                if name == extract_only:
-                    if target.lower() == "$path":
-                        with tempfile.TemporaryDirectory() as D:
-                            path = os.path.join(D, name)
-                            log.debug(f"extracting `{path}`")
-                            extract(tar=tar, member=member, path=path, chmod=chmod)
-                            copy_to_path(path)
-                            return
-
-                    path = os.path.join(target, name)
-                    log.debug(f"extracting `{path}`")
-                    extract(tar=tar, member=member, path=path, chmod=chmod)
-                    return
+            if extract_only is not None and not any(
+                fnmatch(name, p) for p in extract_only
+            ):
+                log.debug(f"skipping: `{name}`")
+                continue
+
+            path = os.path.join(target, name)
+            log.debug(f"extracting: `{path}`")
+            extract(tar=tar, member=member, path=path, chmod=chmod.get(name, None))
+
     else:
         # a single file
         name = url.split("/")[-1].strip()
-        if target.lower() == "$path":
-            with tempfile.TemporaryDirectory() as D:
-                temp_path = os.path.join(D, name)
-                with open(temp_path, "wb") as f:
-                    f.write(raw)
-                # move the file somewhere on the path
-                path = copy_to_path(temp_path)
-        else:
-            path = target
-            with open(path, "wb") as f:
-                f.write(raw)
+        path = os.path.join(target, name)
+        with open(path, "wb") as f:
+            f.write(raw)
 
+        current = chmod.get(name, None)
         # apply chmod if requested
-        if chmod is not None:
+        if current is not None:
             # python os.chmod takes an octal value
-            os.chmod(path, int(str(chmod), base=8))
+            os.chmod(path, int(str(current), base=8))
 
 
 def load_config():
@@ -357,8 +363,8 @@ if __name__ == "__main__":
     # collect `apt-get install`-able package
     apt_select = []
     handlers = {
-        "fetch": lambda x: handle_fetch(**x),
         "apt": lambda x: apt_select.extend(x),
+        "fetch": lambda x: handle_fetch(**x),
     }
 
     # allow comma delimiters and de-duplicate
@@ -366,7 +372,7 @@ if __name__ == "__main__":
         parser.print_help()
         exit()
     else:
-        select = set(" ".join(args.install).replace(",", " ").split())
+        select = " ".join(args.install).replace(",", " ").split()
 
     log.debug(f'installing metapackages: `{", ".join(select)}`')
 
diff --git a/pyproject.toml b/pyproject.toml
index 6a906c4e5..b385a4929 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -5,7 +5,7 @@ requires = ["setuptools >= 61.0", "wheel"]
 [project]
 name = "trimesh"
 requires-python = ">=3.8"
-version = "4.5.1"
+version = "4.5.2"
 authors = [{name = "Michael Dawson-Haggerty", email = "mikedh@kerfed.com"}]
 license = {file = "LICENSE.md"}
 description = "Import, export, process, analyze and view triangular meshes."
@@ -24,10 +24,12 @@ classifiers = [
     "Topic :: Multimedia :: Graphics",
     "Topic :: Multimedia :: Graphics :: 3D Modeling"
 ]
-urls = {Homepage = "https://github.com/mikedh/trimesh"}
-
 dependencies = ["numpy>=1.20"]
 
+[project.urls]
+homepage = "https://github.com/mikedh/trimesh"
+documentation = "https://trimesh.org"
+
 [project.readme]
 file = "README.md"
 content-type = "text/markdown"
diff --git a/tests/test_boolean.py b/tests/test_boolean.py
index 9e842fa54..d6439d208 100644
--- a/tests/test_boolean.py
+++ b/tests/test_boolean.py
@@ -5,16 +5,11 @@
 
 import numpy as np
 
-try:
-    import manifold3d
-except BaseException:
-    manifold3d = None
-
-
-engines = [
-    ("blender", g.trimesh.interfaces.blender.exists),
-    ("manifold", manifold3d is not None),
-]
+# test only available engines by default
+engines = g.trimesh.boolean.engines_available
+# test all engines if all_dep is set
+if g.all_dependencies:
+    engines = g.trimesh.boolean._engines.keys()
 
 
 def test_boolean():
@@ -23,13 +18,7 @@ def test_boolean():
     truth = g.data["boolean"]
 
     times = {}
-    for engine, exists in engines:
-        # if we have all_dep set it means we should fail if
-        # engine is not installed so don't continue
-        if not exists:
-            g.log.warning("skipping boolean engine %s", engine)
-            continue
-
+    for engine in engines:
         g.log.info("Testing boolean ops with engine %s", engine)
 
         tic = g.time.time()
@@ -67,9 +56,9 @@ def test_multiple():
     """
     Make sure boolean operations work on multiple meshes.
     """
-    for engine, exists in engines:
-        if not exists:
-            continue
+    for engine in engines:
+        g.log.info("Testing multiple union with engine %s", engine)
+
         a = g.trimesh.primitives.Sphere(center=[0, 0, 0])
         b = g.trimesh.primitives.Sphere(center=[0, 0, 0.75])
         c = g.trimesh.primitives.Sphere(center=[0, 0, 1.5])
@@ -82,9 +71,8 @@ def test_multiple():
 
 
 def test_empty():
-    for engine, exists in engines:
-        if not exists:
-            continue
+    for engine in engines:
+        g.log.info("Testing empty intersection with engine %s", engine)
 
         a = g.trimesh.primitives.Sphere(center=[0, 0, 0])
         b = g.trimesh.primitives.Sphere(center=[5, 0, 0])
@@ -95,72 +83,74 @@ def test_empty():
 
 
 def test_boolean_manifold():
-    if manifold3d is None:
-        return
+    from trimesh.boolean import _engines, boolean_manifold
 
     times = {}
-    for operation in ["union", "intersection"]:
-        if operation == "union":
-            # chain of icospheres
-            meshes = [
-                g.trimesh.primitives.Sphere(center=[x / 2, 0, 0], subdivisions=0)
-                for x in range(100)
-            ]
-        else:
-            # closer icospheres for non-empty-intersection
-            meshes = [
-                g.trimesh.primitives.Sphere(center=[x, x, x], subdivisions=0)
-                for x in np.linspace(0, 0.5, 101)
-            ]
+    exists = not isinstance(_engines["manifold"], g.trimesh.exceptions.ExceptionWrapper)
 
-        # the old 'serial' manifold method
-        tic = g.time.time()
-        manifolds = [
-            manifold3d.Manifold(
-                mesh=manifold3d.Mesh(
-                    vert_properties=np.array(mesh.vertices, dtype=np.float32),
-                    tri_verts=np.array(mesh.faces, dtype=np.uint32),
+    # run this test only when manifold3d is available or `all_dep` is enabled
+    if exists or g.all_dependencies:
+        import manifold3d
+
+        for operation in ["union", "intersection"]:
+            if operation == "union":
+                # chain of icospheres
+                meshes = [
+                    g.trimesh.primitives.Sphere(center=[x / 2, 0, 0], subdivisions=0)
+                    for x in range(100)
+                ]
+            else:
+                # closer icospheres for non-empty-intersection
+                meshes = [
+                    g.trimesh.primitives.Sphere(center=[x, x, x], subdivisions=0)
+                    for x in np.linspace(0, 0.5, 101)
+                ]
+
+            # the old 'serial' manifold method
+            tic = g.time.time()
+            manifolds = [
+                manifold3d.Manifold(
+                    mesh=manifold3d.Mesh(
+                        vert_properties=np.array(mesh.vertices, dtype=np.float32),
+                        tri_verts=np.array(mesh.faces, dtype=np.uint32),
+                    )
                 )
+                for mesh in meshes
+            ]
+            result_manifold = manifolds[0]
+            for manifold in manifolds[1:]:
+                if operation == "union":
+                    result_manifold = result_manifold + manifold
+                else:  # operation == "intersection":
+                    result_manifold = result_manifold ^ manifold
+            result_mesh = result_manifold.to_mesh()
+            old_mesh = g.trimesh.Trimesh(
+                vertices=result_mesh.vert_properties, faces=result_mesh.tri_verts
             )
-            for mesh in meshes
-        ]
-        result_manifold = manifolds[0]
-        for manifold in manifolds[1:]:
-            if operation == "union":
-                result_manifold = result_manifold + manifold
-            else:  # operation == "intersection":
-                result_manifold = result_manifold ^ manifold
-        result_mesh = result_manifold.to_mesh()
-        old_mesh = g.trimesh.Trimesh(
-            vertices=result_mesh.vert_properties, faces=result_mesh.tri_verts
-        )
-        times["serial " + operation] = g.time.time() - tic
+            times["serial " + operation] = g.time.time() - tic
 
-        # new 'binary' method
-        tic = g.time.time()
-        new_mesh = g.trimesh.boolean.boolean_manifold(meshes, operation)
-        times["binary " + operation] = g.time.time() - tic
+            # new 'binary' method
+            tic = g.time.time()
+            new_mesh = boolean_manifold(meshes, operation)
+            times["binary " + operation] = g.time.time() - tic
 
-        assert old_mesh.is_volume == new_mesh.is_volume
-        assert old_mesh.body_count == new_mesh.body_count
-        assert np.isclose(old_mesh.volume, new_mesh.volume)
+            assert old_mesh.is_volume == new_mesh.is_volume
+            assert old_mesh.body_count == new_mesh.body_count
+            assert np.isclose(old_mesh.volume, new_mesh.volume)
 
-    g.log.info(times)
+        g.log.info(times)
 
 
 def test_reduce_cascade():
     # the multiply will explode quickly past the integer maximum
-
     from functools import reduce
 
-    from trimesh.boolean import reduce_cascade
-
     def both(operation, items):
         """
         Run our cascaded reduce and regular reduce.
         """
 
-        b = reduce_cascade(operation, items)
+        b = g.trimesh.iteration.reduce_cascade(operation, items)
 
         if len(items) > 0:
             assert b == reduce(operation, items)
@@ -219,11 +209,7 @@ def test_multiple_difference():
     spheres = [g.trimesh.creation.icosphere()]
     spheres.extend(g.trimesh.creation.icosphere().apply_translation(c) for c in center)
 
-    for engine, exists in engines:
-        if not exists:
-            g.log.warning("skipping boolean engine %s", engine)
-            continue
-
+    for engine in engines:
         g.log.info("Testing multiple difference with engine %s", engine)
 
         # compute using meshes method
diff --git a/trimesh/__init__.py b/trimesh/__init__.py
index 00ebec5d2..0742d68f5 100644
--- a/trimesh/__init__.py
+++ b/trimesh/__init__.py
@@ -25,6 +25,7 @@
     grouping,
     inertia,
     intersections,
+    iteration,
     nsphere,
     permutate,
     poses,
@@ -102,6 +103,7 @@
     "graph",
     "grouping",
     "inertia",
+    "iteration",
     "intersections",
     "load",
     "load_mesh",
diff --git a/trimesh/boolean.py b/trimesh/boolean.py
index 009d767d3..4c113f577 100644
--- a/trimesh/boolean.py
+++ b/trimesh/boolean.py
@@ -7,14 +7,16 @@
 
 import numpy as np
 
-from . import exceptions, interfaces
-from .typed import Callable, NDArray, Optional, Sequence, Union
+from . import interfaces
+from .exceptions import ExceptionWrapper
+from .iteration import reduce_cascade
+from .typed import Callable, Dict, Optional, Sequence
 
 try:
     from manifold3d import Manifold, Mesh
 except BaseException as E:
-    Mesh = exceptions.ExceptionWrapper(E)
-    Manifold = exceptions.ExceptionWrapper(E)
+    Mesh = ExceptionWrapper(E)
+    Manifold = ExceptionWrapper(E)
 
 
 def difference(
@@ -168,76 +170,32 @@ def boolean_manifold(
     return Trimesh(vertices=result_mesh.vert_properties, faces=result_mesh.tri_verts)
 
 
-def reduce_cascade(operation: Callable, items: Union[Sequence, NDArray]):
-    """
-    Call an operation function in a cascaded pairwise way against a
-    flat list of items.
-
-    This should produce the same result as `functools.reduce`
-    if `operation` is commutable like addition or multiplication.
-    This may be faster for an `operation` that runs with a speed
-    proportional to its largest input, which mesh booleans appear to.
-
-    The union of a large number of small meshes appears to be
-    "much faster" using this method.
-
-    This only differs from `functools.reduce` for commutative `operation`
-    in that it returns `None` on empty inputs rather than `functools.reduce`
-    which raises a `TypeError`.
-
-    For example on `a b c d e f g` this function would run and return:
-        a b
-        c d
-        e f
-        ab cd
-        ef g
-        abcd efg
-     -> abcdefg
-
-    Where `functools.reduce` would run and return:
-        a b
-        ab c
-        abc d
-        abcd e
-        abcde f
-        abcdef g
-     -> abcdefg
-
-    Parameters
-    ----------
-    operation
-      The function to call on pairs of items.
-    items
-      The flat list of items to apply operation against.
-    """
-    if len(items) == 0:
-        return None
-    elif len(items) == 1:
-        # skip the loop overhead for a single item
-        return items[0]
-    elif len(items) == 2:
-        # skip the loop overhead for a single pair
-        return operation(items[0], items[1])
-
-    for _ in range(int(1 + np.log2(len(items)))):
-        results = []
-        for i in np.arange(len(items) // 2) * 2:
-            results.append(operation(items[i], items[i + 1]))
-
-        if len(items) % 2:
-            results.append(items[-1])
+# which backend boolean engines do we have
+_engines: Dict[str, Callable] = {}
 
-        items = results
+if isinstance(Manifold, ExceptionWrapper):
+    # manifold isn't available so use the import error
+    _engines["manifold"] = Manifold
+else:
+    # manifold3d is the preferred option
+    _engines["manifold"] = boolean_manifold
 
-    # logic should have reduced to a single item
-    assert len(results) == 1
 
-    return results[0]
+if interfaces.blender.exists:
+    # we have `blender` in the path which  we can call with subprocess
+    _engines["blender"] = interfaces.blender.boolean
+else:
+    # failing that add a helpful error message
+    _engines["blender"] = ExceptionWrapper(ImportError("`blender` is not in `PATH`"))
 
+# pick the first value that isn't an ExceptionWrapper.
+_engines[None] = next(
+    (v for v in _engines.values() if not isinstance(v, ExceptionWrapper)),
+    ExceptionWrapper(
+        ImportError("No boolean backend: `pip install manifold3d` or install `blender`")
+    ),
+)
 
-# which backend boolean engines
-_engines = {
-    None: boolean_manifold,
-    "manifold": boolean_manifold,
-    "blender": interfaces.blender.boolean,
+engines_available = {
+    k for k, v in _engines.items() if not isinstance(v, ExceptionWrapper)
 }
diff --git a/trimesh/exchange/xaml.py b/trimesh/exchange/xaml.py
index 20a339267..a988a5188 100644
--- a/trimesh/exchange/xaml.py
+++ b/trimesh/exchange/xaml.py
@@ -136,7 +136,7 @@ def element_to_transform(element):
             normals.append(c_normals)
 
     # compile the results into clean numpy arrays
-    result = {}
+    result = {"units": "meters"}
     result["vertices"], result["faces"] = util.append_faces(vertices, faces)
     result["face_colors"] = np.vstack(colors)
     result["vertex_normals"] = np.vstack(normals)
diff --git a/trimesh/interfaces/__init__.py b/trimesh/interfaces/__init__.py
index 4f58ef4af..45416ec8b 100644
--- a/trimesh/interfaces/__init__.py
+++ b/trimesh/interfaces/__init__.py
@@ -1,4 +1,4 @@
 from . import blender, gmsh
 
 # add to __all__ as per pep8
-__all__ = ["blender", "gmsh"]
+__all__ = ["gmsh", "blender"]
diff --git a/trimesh/iteration.py b/trimesh/iteration.py
new file mode 100644
index 000000000..5994341fe
--- /dev/null
+++ b/trimesh/iteration.py
@@ -0,0 +1,125 @@
+import numpy as np
+
+from .typed import Any, Callable, Iterable, List, NDArray, Sequence, Union
+
+
+def reduce_cascade(operation: Callable, items: Union[Sequence, NDArray]):
+    """
+    Call an operation function in a cascaded pairwise way against a
+    flat list of items.
+
+    This should produce the same result as `functools.reduce`
+    if `operation` is commutable like addition or multiplication.
+    This may be faster for an `operation` that runs with a speed
+    proportional to its largest input, which mesh booleans appear to.
+
+    The union of a large number of small meshes appears to be
+    "much faster" using this method.
+
+    This only differs from `functools.reduce` for commutative `operation`
+    in that it returns `None` on empty inputs rather than `functools.reduce`
+    which raises a `TypeError`.
+
+    For example on `a b c d e f g` this function would run and return:
+        a b
+        c d
+        e f
+        ab cd
+        ef g
+        abcd efg
+     -> abcdefg
+
+    Where `functools.reduce` would run and return:
+        a b
+        ab c
+        abc d
+        abcd e
+        abcde f
+        abcdef g
+     -> abcdefg
+
+    Parameters
+    ----------
+    operation
+      The function to call on pairs of items.
+    items
+      The flat list of items to apply operation against.
+    """
+    if len(items) == 0:
+        return None
+    elif len(items) == 1:
+        # skip the loop overhead for a single item
+        return items[0]
+    elif len(items) == 2:
+        # skip the loop overhead for a single pair
+        return operation(items[0], items[1])
+
+    for _ in range(int(1 + np.log2(len(items)))):
+        results = []
+        for i in np.arange(len(items) // 2) * 2:
+            results.append(operation(items[i], items[i + 1]))
+
+        if len(items) % 2:
+            results.append(items[-1])
+
+        items = results
+
+    # logic should have reduced to a single item
+    assert len(results) == 1
+
+    return results[0]
+
+
+def chain(*args: Union[Iterable[Any], Any, None]) -> List[Any]:
+    """
+    A less principled version of `list(itertools.chain(*args))` that
+    accepts non-iterable values, filters `None`, and returns a list
+    rather than yielding values.
+
+    If all passed values are iterables this will return identical
+    results to `list(itertools.chain(*args))`.
+
+
+    Examples
+    ----------
+
+    In [1]: list(itertools.chain([1,2], [3]))
+    Out[1]: [1, 2, 3]
+
+    In [2]: trimesh.util.chain([1,2], [3])
+    Out[2]: [1, 2, 3]
+
+    In [3]: trimesh.util.chain([1,2], [3], 4)
+    Out[3]: [1, 2, 3, 4]
+
+    In [4]: list(itertools.chain([1,2], [3], 4))
+      ----> 1 list(itertools.chain([1,2], [3], 4))
+      TypeError: 'int' object is not iterable
+
+    In [5]: trimesh.util.chain([1,2], None, 3, None, [4], [], [], 5, [])
+    Out[5]: [1, 2, 3, 4, 5]
+
+
+    Parameters
+    -----------
+    args
+      Will be individually checked to see if they're iterable
+      before either being appended or extended to a flat list.
+
+
+    Returns
+    ----------
+    chained
+      The values in a flat list.
+    """
+    # collect values to a flat list
+    chained = []
+    # extend if it's a sequence, otherwise append
+    [
+        chained.extend(a)
+        if (hasattr(a, "__iter__") and not isinstance(a, str))
+        else chained.append(a)
+        for a in args
+        if a is not None
+    ]
+    return chained
diff --git a/trimesh/path/polygons.py b/trimesh/path/polygons.py
index e481dd57b..7fa793dba 100644
--- a/trimesh/path/polygons.py
+++ b/trimesh/path/polygons.py
@@ -3,9 +3,9 @@
 from shapely.geometry import Polygon
 
 from .. import bounds, geometry, graph, grouping
-from ..boolean import reduce_cascade
 from ..constants import log
 from ..constants import tol_path as tol
+from ..iteration import reduce_cascade
 from ..transformations import transform_points
 from ..typed import Iterable, NDArray, Number, Optional, Union, float64, int64
 from .simplify import fit_circle_check
diff --git a/trimesh/util.py b/trimesh/util.py
index ab452e695..66ac4775d 100644
--- a/trimesh/util.py
+++ b/trimesh/util.py
@@ -22,8 +22,10 @@
 
 import numpy as np
 
+from .iteration import chain
+
 # use our wrapped types for wider version compatibility
-from .typed import Any, Iterable, List, Union
+from .typed import Union
 
 # create a default logger
 log = logging.getLogger("trimesh")
@@ -1384,59 +1386,6 @@ class : Optional[Callable]
     raise ValueError("Unable to extract class of name " + name)
 
 
-def chain(*args: Union[Iterable[Any], Any, None]) -> List[Any]:
-    """
-    A less principled version of `list(itertools.chain(*args))` that
-    accepts non-iterable values, filters `None`, and returns a list
-    rather than yielding values.
-
-    If all passed values are iterables this will return identical
-    results to `list(itertools.chain(*args))`.
-
-
-    Examples
-    ----------
-
-    In [1]: list(itertools.chain([1,2], [3]))
-    Out[1]: [1, 2, 3]
-
-    In [2]: trimesh.util.chain([1,2], [3])
-    Out[2]: [1, 2, 3]
-
-    In [3]: trimesh.util.chain([1,2], [3], 4)
-    Out[3]: [1, 2, 3, 4]
-
-    In [4]: list(itertools.chain([1,2], [3], 4))
-      ----> 1 list(itertools.chain([1,2], [3], 4))
-      TypeError: 'int' object is not iterable
-
-    In [5]: trimesh.util.chain([1,2], None, 3, None, [4], [], [], 5, [])
-    Out[5]: [1, 2, 3, 4, 5]
-
-
-    Parameters
-    -----------
-    args
-      Will be individually checked to see if they're iterable
-      before either being appended or extended to a flat list.
-
-
-    Returns
-    ----------
-    chained
-      The values in a flat list.
-    """
-    # collect values to a flat list
-    chained = []
-    # extend if it's a sequence, otherwise append
-    [
-        chained.extend(a) if is_sequence(a) else chained.append(a)
-        for a in args
-        if a is not None
-    ]
-    return chained
-
-
 def concatenate(
     a, b=None
 ) -> Union["trimesh.Trimesh", "trimesh.path.Path2D", "trimesh.path.Path3D"]:  # noqa: F821
diff --git a/trimesh/viewer/widget.py b/trimesh/viewer/widget.py
index a6e8c9093..3636a3da2 100644
--- a/trimesh/viewer/widget.py
+++ b/trimesh/viewer/widget.py
@@ -14,7 +14,7 @@
 
 from .. import rendering
 from .trackball import Trackball
-from .windowed import SceneViewer, geometry_hash
+from .windowed import SceneViewer, _geometry_hash
 
 
 class SceneGroup(pyglet.graphics.Group):
@@ -249,7 +249,7 @@ def on_mouse_scroll(self, x, y, dx, dy):
         self._draw()
 
     def _update_node(self, node_name, geometry_name, geometry, transform):
-        geometry_hash_new = geometry_hash(geometry)
+        geometry_hash_new = _geometry_hash(geometry)
         if self.vertex_list_hash.get(geometry_name) != geometry_hash_new:
             # if geometry has texture defined convert it to opengl form
             if hasattr(geometry, "visual") and hasattr(geometry.visual, "material"):