SMPL model visualizerΒΆ

Visualizer for SMPL human body models. Requires a .npz model file.

See here for download instructions:

https://github.com/vchoutas/smplx?tab=readme-ov-file#downloading-the-model

  1from __future__ import annotations
  2
  3import time
  4from dataclasses import dataclass
  5from pathlib import Path
  6
  7import numpy as np
  8import tyro
  9import viser
 10import viser.transforms as tf
 11
 12
 13@dataclass(frozen=True)
 14class SmplOutputs:
 15    vertices: np.ndarray
 16    faces: np.ndarray
 17    T_world_joint: np.ndarray  # (num_joints, 4, 4)
 18    T_parent_joint: np.ndarray  # (num_joints, 4, 4)
 19
 20
 21class SmplHelper:
 22    """Helper for models in the SMPL family, implemented in numpy."""
 23
 24    def __init__(self, model_path: Path) -> None:
 25        assert model_path.suffix.lower() == ".npz", "Model should be an .npz file!"
 26        body_dict = dict(**np.load(model_path, allow_pickle=True))
 27
 28        self.J_regressor = body_dict["J_regressor"]
 29        self.weights = body_dict["weights"]
 30        self.v_template = body_dict["v_template"]
 31        self.posedirs = body_dict["posedirs"]
 32        self.shapedirs = body_dict["shapedirs"]
 33        self.faces = body_dict["f"]
 34
 35        self.num_joints: int = self.weights.shape[-1]
 36        self.num_betas: int = self.shapedirs.shape[-1]
 37        self.parent_idx: np.ndarray = body_dict["kintree_table"][0]
 38
 39    def get_outputs(self, betas: np.ndarray, joint_rotmats: np.ndarray) -> SmplOutputs:
 40        # Get shaped vertices + joint positions, when all local poses are identity.
 41        v_tpose = self.v_template + np.einsum("vxb,b->vx", self.shapedirs, betas)
 42        j_tpose = np.einsum("jv,vx->jx", self.J_regressor, v_tpose)
 43
 44        # Local SE(3) transforms.
 45        T_parent_joint = np.zeros((self.num_joints, 4, 4)) + np.eye(4)
 46        T_parent_joint[:, :3, :3] = joint_rotmats
 47        T_parent_joint[0, :3, 3] = j_tpose[0]
 48        T_parent_joint[1:, :3, 3] = j_tpose[1:] - j_tpose[self.parent_idx[1:]]
 49
 50        # Forward kinematics.
 51        T_world_joint = T_parent_joint.copy()
 52        for i in range(1, self.num_joints):
 53            T_world_joint[i] = T_world_joint[self.parent_idx[i]] @ T_parent_joint[i]
 54
 55        # Linear blend skinning.
 56        pose_delta = (joint_rotmats[1:, ...] - np.eye(3)).flatten()
 57        v_blend = v_tpose + np.einsum("byn,n->by", self.posedirs, pose_delta)
 58        v_delta = np.ones((v_blend.shape[0], self.num_joints, 4))
 59        v_delta[:, :, :3] = v_blend[:, None, :] - j_tpose[None, :, :]
 60        v_posed = np.einsum(
 61            "jxy,vj,vjy->vx", T_world_joint[:, :3, :], self.weights, v_delta
 62        )
 63        return SmplOutputs(v_posed, self.faces, T_world_joint, T_parent_joint)
 64
 65
 66def main(model_path: Path) -> None:
 67    server = viser.ViserServer()
 68    server.scene.set_up_direction("+y")
 69    server.gui.configure_theme(control_layout="collapsible")
 70
 71    # Main loop. We'll read pose/shape from the GUI elements, compute the mesh,
 72    # and then send the updated mesh in a loop.
 73    model = SmplHelper(model_path)
 74    gui_elements = make_gui_elements(
 75        server,
 76        num_betas=model.num_betas,
 77        num_joints=model.num_joints,
 78        parent_idx=model.parent_idx,
 79    )
 80    body_handle = server.scene.add_mesh_simple(
 81        "/human",
 82        model.v_template,
 83        model.faces,
 84        wireframe=gui_elements.gui_wireframe.value,
 85        color=gui_elements.gui_rgb.value,
 86    )
 87    while True:
 88        # Do nothing if no change.
 89        time.sleep(0.02)
 90        if not gui_elements.changed:
 91            continue
 92
 93        gui_elements.changed = False
 94
 95        # If anything has changed, re-compute SMPL outputs.
 96        smpl_outputs = model.get_outputs(
 97            betas=np.array([x.value for x in gui_elements.gui_betas]),
 98            joint_rotmats=tf.SO3.exp(
 99                # (num_joints, 3)
100                np.array([x.value for x in gui_elements.gui_joints])
101            ).as_matrix(),
102        )
103
104        # Update the mesh properties based on the SMPL model output + GUI
105        # elements.
106        body_handle.vertices = smpl_outputs.vertices
107        body_handle.wireframe = gui_elements.gui_wireframe.value
108        body_handle.color = gui_elements.gui_rgb.value
109
110        # Match transform control gizmos to joint positions.
111        for i, control in enumerate(gui_elements.transform_controls):
112            control.position = smpl_outputs.T_parent_joint[i, :3, 3]
113
114
115@dataclass
116class GuiElements:
117    """Structure containing handles for reading from GUI elements."""
118
119    gui_rgb: viser.GuiInputHandle[tuple[int, int, int]]
120    gui_wireframe: viser.GuiInputHandle[bool]
121    gui_betas: list[viser.GuiInputHandle[float]]
122    gui_joints: list[viser.GuiInputHandle[tuple[float, float, float]]]
123    transform_controls: list[viser.TransformControlsHandle]
124
125    changed: bool
126    """This flag will be flipped to True whenever the mesh needs to be re-generated."""
127
128
129def make_gui_elements(
130    server: viser.ViserServer,
131    num_betas: int,
132    num_joints: int,
133    parent_idx: np.ndarray,
134) -> GuiElements:
135    """Make GUI elements for interacting with the model."""
136
137    tab_group = server.gui.add_tab_group()
138
139    def set_changed(_) -> None:
140        out.changed = True  # out is define later!
141
142    # GUI elements: mesh settings + visibility.
143    with tab_group.add_tab("View", viser.Icon.VIEWFINDER):
144        gui_rgb = server.gui.add_rgb("Color", initial_value=(90, 200, 255))
145        gui_wireframe = server.gui.add_checkbox("Wireframe", initial_value=False)
146        gui_show_controls = server.gui.add_checkbox("Handles", initial_value=True)
147
148        gui_rgb.on_update(set_changed)
149        gui_wireframe.on_update(set_changed)
150
151        @gui_show_controls.on_update
152        def _(_):
153            for control in transform_controls:
154                control.visible = gui_show_controls.value
155
156    # GUI elements: shape parameters.
157    with tab_group.add_tab("Shape", viser.Icon.BOX):
158        gui_reset_shape = server.gui.add_button("Reset Shape")
159        gui_random_shape = server.gui.add_button("Random Shape")
160
161        @gui_reset_shape.on_click
162        def _(_):
163            for beta in gui_betas:
164                beta.value = 0.0
165
166        @gui_random_shape.on_click
167        def _(_):
168            for beta in gui_betas:
169                beta.value = np.random.normal(loc=0.0, scale=1.0)
170
171        gui_betas = []
172        for i in range(num_betas):
173            beta = server.gui.add_slider(
174                f"beta{i}", min=-5.0, max=5.0, step=0.01, initial_value=0.0
175            )
176            gui_betas.append(beta)
177            beta.on_update(set_changed)
178
179    # GUI elements: joint angles.
180    with tab_group.add_tab("Joints", viser.Icon.ANGLE):
181        gui_reset_joints = server.gui.add_button("Reset Joints")
182        gui_random_joints = server.gui.add_button("Random Joints")
183
184        @gui_reset_joints.on_click
185        def _(_):
186            for joint in gui_joints:
187                joint.value = (0.0, 0.0, 0.0)
188
189        @gui_random_joints.on_click
190        def _(_):
191            rng = np.random.default_rng()
192            for joint in gui_joints:
193                joint.value = tf.SO3.sample_uniform(rng).log()
194
195        gui_joints: list[viser.GuiInputHandle[tuple[float, float, float]]] = []
196        for i in range(num_joints):
197            gui_joint = server.gui.add_vector3(
198                label=f"Joint {i}",
199                initial_value=(0.0, 0.0, 0.0),
200                step=0.05,
201            )
202            gui_joints.append(gui_joint)
203
204            def set_callback_in_closure(i: int) -> None:
205                @gui_joint.on_update
206                def _(_):
207                    transform_controls[i].wxyz = tf.SO3.exp(
208                        np.array(gui_joints[i].value)
209                    ).wxyz
210                    out.changed = True
211
212            set_callback_in_closure(i)
213
214    # Transform control gizmos on joints.
215    transform_controls: list[viser.TransformControlsHandle] = []
216    prefixed_joint_names = []  # Joint names, but prefixed with parents.
217    for i in range(num_joints):
218        prefixed_joint_name = f"joint_{i}"
219        if i > 0:
220            prefixed_joint_name = (
221                prefixed_joint_names[parent_idx[i]] + "/" + prefixed_joint_name
222            )
223        prefixed_joint_names.append(prefixed_joint_name)
224        controls = server.scene.add_transform_controls(
225            f"/smpl/{prefixed_joint_name}",
226            depth_test=False,
227            scale=0.2 * (0.75 ** prefixed_joint_name.count("/")),
228            disable_axes=True,
229            disable_sliders=True,
230            visible=gui_show_controls.value,
231        )
232        transform_controls.append(controls)
233
234        def set_callback_in_closure(i: int) -> None:
235            @controls.on_update
236            def _(_) -> None:
237                axisangle = tf.SO3(transform_controls[i].wxyz).log()
238                gui_joints[i].value = (axisangle[0], axisangle[1], axisangle[2])
239
240        set_callback_in_closure(i)
241
242    out = GuiElements(
243        gui_rgb,
244        gui_wireframe,
245        gui_betas,
246        gui_joints,
247        transform_controls=transform_controls,
248        changed=True,
249    )
250    return out
251
252
253if __name__ == "__main__":
254    tyro.cli(main, description=__doc__)