Support importing EXT_meshopt_compression?

[donmccurdy]

Would we be interested in support for importing models with EXT_meshopt_compression? I'm asking because this came up in a user report recently (donmccurdy/glTF-Transform#347), but some recent work by @zeux and Jasper St. Pierre would make this potentially much easier — we don't need to bring any native code into Blender itself, we can create a small Python implementation similar to the reference here: zeux/meshoptimizer#331.

[scurest]

I think it'd be much easier to bring in native code. It's fast and has already been debugged. Here's a small prototype, it's only about 200 lines.

Patch

diff --git a/addons/io_scene_gltf2/io/imp/gltf2_io_binary.py b/addons/io_scene_gltf2/io/imp/gltf2_io_binary.py
index 800614ea..6fb38a58 100644
--- a/addons/io_scene_gltf2/io/imp/gltf2_io_binary.py
+++ b/addons/io_scene_gltf2/io/imp/gltf2_io_binary.py
@@ -17,6 +17,7 @@ import numpy as np
 
 from ..com.gltf2_io import Accessor
 from ..com.gltf2_io_constants import ComponentType, DataType
+from .gltf2_io_binary_meshopt import MeshoptDecompressor
 
 
 class BinaryData():
@@ -46,6 +47,9 @@ class BinaryData():
         """Get binary data for buffer view."""
         buffer_view = gltf.data.buffer_views[buffer_view_idx]
 
+        if 'EXT_meshopt_compression' in (buffer_view.extensions or {}):
+            return MeshoptDecompressor.get_buffer_view(gltf, buffer_view_idx)
+
         if buffer_view.buffer in gltf.buffers.keys():
             buffer = gltf.buffers[buffer_view.buffer]
         else:
diff --git a/addons/io_scene_gltf2/io/imp/gltf2_io_binary_meshopt.py b/addons/io_scene_gltf2/io/imp/gltf2_io_binary_meshopt.py
new file mode 100644
index 00000000..85c36261
--- /dev/null
+++ b/addons/io_scene_gltf2/io/imp/gltf2_io_binary_meshopt.py
@@ -0,0 +1,171 @@
+# Copyright 2022 The glTF-Blender-IO authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import ctypes
+import sys
+import os
+from .gltf2_io_gltf import ImportError
+
+
+class MeshoptDecompressor:
+    """Decompressor for """
+    def __new__(cls, *args, **kwargs):
+        raise RuntimeError("%s should not be instantiated" % cls)
+
+    @staticmethod
+    def find_library():
+        """Returns path to the meshoptimizer library."""
+        import site
+
+        lib_name = 'meshoptimizer'
+        lib_name = {
+            'win32':  f'{lib_name}.dll',
+            'linux':  f'lib{lib_name}.so',
+            'darwin': f'lib{lib_name}.dylib',
+        }.get(sys.platform)
+
+        locs = site.getsitepackages() + [site.getusersitepackages()]
+        locs = [os.path.join(loc, lib_name) for loc in locs]
+        for loc in locs:
+            if os.path.exists(loc):
+                return loc
+
+        print(f'Looked for {lib_name} in the following locations:')
+        for loc in locs:
+            print('  ', loc)
+        print()
+
+        raise ImportError(
+            "Can't load model using EXT_meshopt_compression. "
+            f"Couldn't find {lib_name}. "
+            "See console for where to install it."
+        )
+
+    @staticmethod
+    def load_library(gltf):
+        if hasattr(gltf, 'meshopt_lib'):
+            return
+
+        lib_path = MeshoptDecompressor.find_library()
+        try:
+            lib = ctypes.CDLL(lib_path)
+        except Exception as e:
+            raise RuntimeError('Error loading meshopt library:', e)
+
+        gltf.meshopt_lib = lib
+
+        # declare type signatures
+
+        decode_fns = [
+            lib.meshopt_decodeVertexBuffer,
+            lib.meshopt_decodeIndexBuffer,
+            lib.meshopt_decodeIndexSequence,
+        ]
+        for fn in decode_fns:
+            fn.restype = ctypes.c_int
+            fn.argtypes = [
+                ctypes.c_void_p,  # void* destination
+                ctypes.c_size_t,  # size_t count
+                ctypes.c_size_t,  # size_t stride
+                ctypes.POINTER(ctypes.c_ubyte),  # const unsigned char* buffer
+                ctypes.c_size_t,  # size_t buffer_size
+            ]
+
+        filter_fns = [
+            lib.meshopt_decodeFilterOct,
+            lib.meshopt_decodeFilterQuat,
+            lib.meshopt_decodeFilterExp,
+        ]
+        for fn in filter_fns:
+            fn.restype = None
+            fn.argtypes = [
+                ctypes.c_void_p,  # void* buffer
+                ctypes.c_size_t,  # size_t count
+                ctypes.c_size_t,  # size_t stride
+            ]
+
+    @staticmethod
+    def get_buffer_view(gltf, bufferview_idx):
+        """Decodes EXT_meshopt_compression-compressed buffer view."""
+        # check if already in cache
+        if not hasattr(gltf, 'meshopt_cache'):
+            gltf.meshopt_cache = {}
+        if bufferview_idx in gltf.meshopt_cache:
+            return gltf.meshopt_cache[bufferview_idx]
+
+        bufview = gltf.data.buffer_views[bufferview_idx]
+        ext = bufview.extensions['EXT_meshopt_compression']
+
+        buffer_idx = ext['buffer']
+        byte_length = ext['byteLength']
+        byte_offset = ext.get('byteOffset', 0)
+        byte_stride = ext['byteStride']
+        count = ext['count']
+        mode = ext['mode']
+        filter = ext.get('filter', 'NONE')
+
+        # load library
+        MeshoptDecompressor.load_library(gltf)
+        lib = gltf.meshopt_lib
+
+        # load buffer
+        if buffer_idx not in gltf.buffers:
+            gltf.load_buffer(buffer_idx)
+
+        buffer = gltf.buffers[buffer_idx]
+        buffer = buffer[byte_offset : byte_offset + byte_length]
+
+        # create output buffer
+        output = memoryview(bytearray(count * byte_stride))
+
+        dst_ptr = (ctypes.c_ubyte * len(output)).from_buffer(output)
+        # TODO: this creates an unnecessary copy, I don't know how to
+        #       pass it to C without one though
+        buf_ptr = (ctypes.c_ubyte * len(buffer)).from_buffer_copy(buffer)
+
+        decode_fn = {
+            'ATTRIBUTES': lib.meshopt_decodeVertexBuffer,
+            'TRIANGLES': lib.meshopt_decodeIndexBuffer,
+            'INDICES': lib.meshopt_decodeIndexSequence,
+        }[mode]
+
+        # decode
+        error_code = decode_fn(
+            dst_ptr,
+            count,
+            byte_stride,
+            buf_ptr,
+            len(buffer),
+        )
+
+        if error_code != 0:
+            raise RuntimeError(
+                'EXT_meshopt_compression: decoding error '
+                f'(buffer view: {bufferview_idx}, error code: {error_code})'
+            )
+
+        # apply filters
+        if mode == 'ATTRIBUTES' and filter != 'NONE':
+            filter_fn = {
+                'OCTAHEDRAL': lib.meshopt_decodeFilterOct,
+                'QUATERNION': lib.meshopt_decodeFilterQuat,
+                'EXPONENTIAL': lib.meshopt_decodeFilterExp,
+            }[filter]
+
+            filter_fn(dst_ptr, count, byte_stride)
+
+        # cache result
+        gltf.meshopt_cache[bufferview_idx] = output
+
+        return output
diff --git a/addons/io_scene_gltf2/io/imp/gltf2_io_gltf.py b/addons/io_scene_gltf2/io/imp/gltf2_io_gltf.py
index 407afccd..208218bb 100644
--- a/addons/io_scene_gltf2/io/imp/gltf2_io_gltf.py
+++ b/addons/io_scene_gltf2/io/imp/gltf2_io_gltf.py
@@ -55,7 +55,8 @@ class glTFImporter():
             'KHR_texture_transform',
             'KHR_materials_clearcoat',
             'KHR_mesh_quantization',
-            'KHR_draco_mesh_compression'
+            'KHR_draco_mesh_compression',
+            'EXT_meshopt_compression',
         ]
 
         # Add extensions required supported by custom import extensions

In order to work, it needs libmeshoptimizer.so (or equivalent on Windows/Mac), that you can get by building zeux/meshoptimizer, placed in the site-package directory. Just try importing and it will tell you where you should put it if it doesn't find it.

Here's a test file: CesiumMan_Meshopt.zip

[autonomobil]

Any updates in this regard?

[tollermine]

I would also be really interested in any updates in this regard.