assimp-py

Minimal Python Bindings for ASSIMP Library using C-API

Installation

pip install assimp-py

from source

git clone https://github.com/ranjian0/assimp_py.git
cd assimp_py
python -m pip install .

cmake>=4.0 is required for building from source

Building from source downloads the pinned ASSIMP release (v6.0.5) via CMake FetchContent, so network access is required. For offline builds, point FETCHCONTENT_SOURCE_DIR_ASSIMP at a local assimp source checkout.

[Optional] Run tests to make sure everything works fine

pip install pytest
pytest tests

Example Program

import assimp_py

# -- loading the scene
process_flags = (
    assimp_py.Process_Triangulate | assimp_py.Process_CalcTangentSpace
)
scene = assimp_py.import_file("tests/models/cyborg/cyborg.obj", process_flags)

# -- getting data
for m in scene.meshes:
    # IMPORTANT 
    # All vertex data is stored as memoryviews


    # -- getting vertex data
    # vertices are guaranteed to exist
    verts = m.vertices
    # as a list
    verts_list = verts.tolist()
    # as bytes
    verts_bytes = verts.tobytes()
    # (Optional) as numpy array
    # np.asarray(verts)

    # other components must be checked for None
    normals = m.normals if m.normals else []
    tangents = m.tangents if m.tangents else []
    bitangents = m.bitangents if m.bitangents else []

    # texcoords come in sets, 'm.texcoords' is a list of memoryviews or None
    if m.texcoords:
      num_texcoords_sets = len(m.texcoords)

      texcoords1 = m.texcoords[0]
      # texcoords2 = m.texcoords[1]
      # texcoords3 = m.texcoords[2]
      print(texcoords1)


    # colors also come in sets, 'm.colors' is a list of memoryviews or None
    if m.colors:
      num_color_sets = len([] or m.colors)

      colors1 = m.colors[0]
      # colors2 = m.colors[1]
      # colors3 = m.colors[2]
      print(colors1)


    # -- getting materials
    # mat is a dict consisting of assimp material properties
    mat = scene.materials[m.material_index]

    # -- getting color
    diffuse_color = mat["COLOR_DIFFUSE"]
    print(diffuse_color)

    # -- getting textures
    diffuse_tex = mat["TEXTURES"][assimp_py.TextureType_DIFFUSE]
    print(diffuse_tex)

# Nodes are also available
root = scene.root_node

def traverse(root, indent=0):
   print(' '*indent + root.name)
   # print(root.transformation) -- transform matrix for the node
   for child in root.children:
      traverse(child, indent=indent+2)

print("Traversing nodes ...")
traverse(root)

Skeletal Animation

Bones are exposed per mesh; animations are exposed on the scene. Bone weights and animation keys are parallel read-only memoryviews (weights/weight_vertex_ids, *_key_times as float64 + *_key_values as float32), numpy-friendly via np.frombuffer(...).

import assimp_py
import numpy as np

scene = assimp_py.import_file(
    "model.glb",
    assimp_py.Process_Triangulate | assimp_py.Process_LimitBoneWeights,
)

# -- per mesh bones
for mesh in scene.meshes:
    for bone in mesh.bones:
        # 4x4 tuple-of-tuples transforming mesh space -> bone space (bind pose)
        bone.offset_matrix

        ids = np.frombuffer(bone.weight_vertex_ids, dtype=np.uint32)
        weights = np.frombuffer(bone.weights, dtype=np.float32)

        # match the bone to its joint node in scene.root_node by name;
        # or pass Process_PopulateArmatureData to get bone.node_name /
        # bone.armature_name resolved for you

# -- animations
for anim in scene.animations:
    duration_seconds = anim.duration / (anim.ticks_per_second or anim.duration)

    for channel in anim.channels:
        times = np.frombuffer(channel.rotation_key_times, dtype=np.float64)
        quats = np.frombuffer(channel.rotation_key_values, dtype=np.float32).reshape(-1, 4)

        # channel.pre_state / channel.post_state describe the behaviour
        # outside the key range (AnimBehaviour_DEFAULT/CONSTANT/LINEAR/REPEAT)

ticks_per_second is 0.0 when the file does not specify it — treat the duration as seconds in that case.

Demo

An interactive demo renders the textured cyborg next to the GPU-skinned, animated fox (orbit camera, wireframe and skeleton overlays):

pip install assimp-py[demo]
python examples/demo.py

Controls: 1/2/3 switch fox animations, Space pause, F wireframe, B skeleton overlay, mouse drag/wheel for the camera, Esc quit. Headless smoke run: python examples/demo.py --screenshot demo.png.

Supported Mesh Formats

AMF 3DS AC ASE ASSBIN B3D BVH COLLADA DXF CSM HMP IRRMESH IRR LWO LWS M3D MD2 MD3 MD5 MDC MDL NFF NDO OFF OGRE OPENGEX PLY MS3D COB BLEND IFC XGL FBX Q3D Q3BSP RAW SIB SMD STL TERRAGEN 3D X X3D GLTF 3MF MMD OBJ

ASSIMP Version 6.0.5