SMPL human model

Visualize SMPL human body models with pose and shape parameter controls.

Requires a .npz model file. See here for download instructions:

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

Features:

• SMPL model loading and mesh generation

• Interactive pose parameter sliders

• Real-time body shape and pose updates

• 3D mesh visualization with viser.SceneApi.add_mesh_simple()

Note

This example requires external assets. To download them, run:

cd /path/to/viser/examples/assets
./download_assets.sh

Source: examples/04_demos/03_smpl_visualizer.py

Code

from __future__ import annotations

import time
from dataclasses import dataclass
from pathlib import Path

import numpy as np
import trimesh
import tyro

import viser
import viser.transforms as tf


@dataclass(frozen=True)
class SmplOutputs:
    vertices: np.ndarray
    faces: np.ndarray
    T_world_joint: np.ndarray  # (num_joints, 4, 4)
    T_parent_joint: np.ndarray  # (num_joints, 4, 4)


class SmplHelper:

    def __init__(self, model_path: Path) -> None:
        assert model_path.suffix.lower() == ".npz", "Model should be an .npz file!"
        body_dict = dict(**np.load(model_path, allow_pickle=True))

        self.J_regressor = body_dict["J_regressor"]
        self.weights = body_dict["weights"]
        self.v_template = body_dict["v_template"]
        self.posedirs = body_dict["posedirs"]
        self.shapedirs = body_dict["shapedirs"]
        self.faces = body_dict["f"]

        self.num_joints: int = self.weights.shape[-1]
        self.num_betas: int = self.shapedirs.shape[-1]
        self.parent_idx: np.ndarray = body_dict["kintree_table"][0]

    def get_outputs(self, betas: np.ndarray, joint_rotmats: np.ndarray) -> SmplOutputs:
        # Get shaped vertices + joint positions, when all local poses are identity.
        v_tpose = self.v_template + np.einsum("vxb,b->vx", self.shapedirs, betas)
        j_tpose = np.einsum("jv,vx->jx", self.J_regressor, v_tpose)

        # Local SE(3) transforms.
        T_parent_joint = np.zeros((self.num_joints, 4, 4)) + np.eye(4)
        T_parent_joint[:, :3, :3] = joint_rotmats
        T_parent_joint[0, :3, 3] = j_tpose[0]
        T_parent_joint[1:, :3, 3] = j_tpose[1:] - j_tpose[self.parent_idx[1:]]

        # Forward kinematics.
        T_world_joint = T_parent_joint.copy()
        for i in range(1, self.num_joints):
            T_world_joint[i] = T_world_joint[self.parent_idx[i]] @ T_parent_joint[i]

        # Linear blend skinning.
        pose_delta = (joint_rotmats[1:, ...] - np.eye(3)).flatten()
        v_blend = v_tpose + np.einsum("byn,n->by", self.posedirs, pose_delta)
        v_delta = np.ones((v_blend.shape[0], self.num_joints, 4))
        v_delta[:, :, :3] = v_blend[:, None, :] - j_tpose[None, :, :]
        v_posed = np.einsum(
            "jxy,vj,vjy->vx", T_world_joint[:, :3, :], self.weights, v_delta
        )
        return SmplOutputs(v_posed, self.faces, T_world_joint, T_parent_joint)


def main(
    model_path: Path = Path(__file__).parent / "../assets/SMPLH_NEUTRAL.npz",
) -> None:
    server = viser.ViserServer()
    server.scene.set_up_direction("+y")
    server.scene.add_grid("/grid", position=(0.0, -1.3, 0.0), plane="xz")

    # Main loop. We'll read pose/shape from the GUI elements, compute the mesh,
    # and then send the updated mesh in a loop.
    model = SmplHelper(model_path)
    gui_elements = make_gui_elements(
        server,
        num_betas=model.num_betas,
        num_joints=model.num_joints,
        parent_idx=model.parent_idx,
    )
    body_handle = server.scene.add_mesh_simple(
        "/human",
        model.v_template,
        model.faces,
        wireframe=gui_elements.gui_wireframe.value,
        color=gui_elements.gui_rgb.value,
    )

    # Add a vertex selector to the mesh. This will allow us to click on
    # vertices to get indices.
    red_sphere = trimesh.creation.icosphere(radius=0.001, subdivisions=1)
    red_sphere.visual.vertex_colors = (255, 0, 0, 255)  # type: ignore
    vertex_selector = server.scene.add_batched_meshes_trimesh(
        "/selector",
        red_sphere,
        batched_positions=model.v_template,
        batched_wxyzs=((1.0, 0.0, 0.0, 0.0),) * model.v_template.shape[0],
    )

    @vertex_selector.on_click
    def _(event: viser.SceneNodePointerEvent) -> None:
        event.client.add_notification(
            f"Clicked on vertex {event.instance_index}",
            body="",
            auto_close=3000,
        )

    while True:
        # Do nothing if no change.
        time.sleep(0.02)
        if not gui_elements.changed:
            continue

        gui_elements.changed = False

        # If anything has changed, re-compute SMPL outputs.
        smpl_outputs = model.get_outputs(
            betas=np.array([x.value for x in gui_elements.gui_betas]),
            joint_rotmats=tf.SO3.exp(
                # (num_joints, 3)
                np.array([x.value for x in gui_elements.gui_joints])
            ).as_matrix(),
        )

        # Update the mesh properties based on the SMPL model output + GUI
        # elements.
        body_handle.vertices = smpl_outputs.vertices
        body_handle.wireframe = gui_elements.gui_wireframe.value
        body_handle.color = gui_elements.gui_rgb.value
        vertex_selector.batched_positions = smpl_outputs.vertices

        # Match transform control gizmos to joint positions.
        for i, control in enumerate(gui_elements.transform_controls):
            control.position = smpl_outputs.T_parent_joint[i, :3, 3]


@dataclass
class GuiElements:

    gui_rgb: viser.GuiInputHandle[tuple[int, int, int]]
    gui_wireframe: viser.GuiInputHandle[bool]
    gui_betas: list[viser.GuiInputHandle[float]]
    gui_joints: list[viser.GuiInputHandle[tuple[float, float, float]]]
    transform_controls: list[viser.TransformControlsHandle]

    changed: bool


def make_gui_elements(
    server: viser.ViserServer,
    num_betas: int,
    num_joints: int,
    parent_idx: np.ndarray,
) -> GuiElements:

    tab_group = server.gui.add_tab_group()

    def set_changed(_) -> None:
        out.changed = True  # out is define later!

    # GUI elements: mesh settings + visibility.
    with tab_group.add_tab("View", viser.Icon.VIEWFINDER):
        gui_rgb = server.gui.add_rgb("Color", initial_value=(90, 200, 255))
        gui_wireframe = server.gui.add_checkbox("Wireframe", initial_value=False)
        gui_show_controls = server.gui.add_checkbox("Handles", initial_value=True)

        gui_rgb.on_update(set_changed)
        gui_wireframe.on_update(set_changed)

        @gui_show_controls.on_update
        def _(_):
            for control in transform_controls:
                control.visible = gui_show_controls.value

    # GUI elements: shape parameters.
    with tab_group.add_tab("Shape", viser.Icon.BOX):
        gui_reset_shape = server.gui.add_button("Reset Shape")
        gui_random_shape = server.gui.add_button("Random Shape")

        @gui_reset_shape.on_click
        def _(_):
            for beta in gui_betas:
                beta.value = 0.0

        @gui_random_shape.on_click
        def _(_):
            for beta in gui_betas:
                beta.value = np.random.normal(loc=0.0, scale=1.0)

        gui_betas = []
        for i in range(num_betas):
            beta = server.gui.add_slider(
                f"beta{i}", min=-5.0, max=5.0, step=0.01, initial_value=0.0
            )
            gui_betas.append(beta)
            beta.on_update(set_changed)

    # GUI elements: joint angles.
    with tab_group.add_tab("Joints", viser.Icon.ANGLE):
        gui_reset_joints = server.gui.add_button("Reset Joints")
        gui_random_joints = server.gui.add_button("Random Joints")

        @gui_reset_joints.on_click
        def _(_):
            for joint in gui_joints:
                joint.value = (0.0, 0.0, 0.0)

        @gui_random_joints.on_click
        def _(_):
            rng = np.random.default_rng()
            for joint in gui_joints:
                joint.value = tf.SO3.sample_uniform(rng).log()

        gui_joints: list[viser.GuiInputHandle[tuple[float, float, float]]] = []
        for i in range(num_joints):
            gui_joint = server.gui.add_vector3(
                label=f"Joint {i}",
                initial_value=(0.0, 0.0, 0.0),
                step=0.05,
            )
            gui_joints.append(gui_joint)

            def set_callback_in_closure(i: int) -> None:
                @gui_joint.on_update
                def _(_):
                    transform_controls[i].wxyz = tf.SO3.exp(
                        np.array(gui_joints[i].value)
                    ).wxyz
                    out.changed = True

            set_callback_in_closure(i)

    # Transform control gizmos on joints.
    transform_controls: list[viser.TransformControlsHandle] = []
    prefixed_joint_names = []  # Joint names, but prefixed with parents.
    for i in range(num_joints):
        prefixed_joint_name = f"joint_{i}"
        if i > 0:
            prefixed_joint_name = (
                prefixed_joint_names[parent_idx[i]] + "/" + prefixed_joint_name
            )
        prefixed_joint_names.append(prefixed_joint_name)
        controls = server.scene.add_transform_controls(
            f"/smpl/{prefixed_joint_name}",
            depth_test=False,
            scale=0.2 * (0.75 ** prefixed_joint_name.count("/")),
            disable_axes=True,
            disable_sliders=True,
            visible=gui_show_controls.value,
        )
        transform_controls.append(controls)

        def set_callback_in_closure(i: int) -> None:
            @controls.on_update
            def _(_) -> None:
                axisangle = tf.SO3(transform_controls[i].wxyz).log()
                gui_joints[i].value = (axisangle[0], axisangle[1], axisangle[2])

        set_callback_in_closure(i)

    out = GuiElements(
        gui_rgb,
        gui_wireframe,
        gui_betas,
        gui_joints,
        transform_controls=transform_controls,
        changed=True,
    )
    return out


if __name__ == "__main__":
    tyro.cli(main, description=__doc__)