threejs-viewer

Lightweight Three.js viewer controlled from Python via WebSocket.

A Python client runs a WebSocket server that a browser-based Three.js viewer connects to. Designed for robotics visualization, scientific computing, and interactive 3D exploration.

Features

• Simple API: Add primitives, load models, update transforms
• PBR materials: Roughness, metalness, transparency and environment reflections on all objects
• GLB/PBR support: Load GLB models with PBR materials, embedded skeletal/morph animations
• Animation support: Pre-compute animations, scrub timeline, adjust playback speed
• Binary channels: Efficient transfer of large animations (100k+ objects × frames)
• Toolpath visualization: Extruded bead tubes with per-point colors, draw_range animation, and automatic LOD — handles 1M+ point toolpaths at 60 fps with smooth camera-distance-adaptive simplification via Web Worker
• 5-axis swept tool body: add_swept_tool lofts an oriented shank/holder profile about the per-station tool axis (decoupled from the path tangent) into a swept surface — visualizes 5-axis reorientation rate and tool-body collisions, with per-station heatmap colours and draw_range reveal
• GPU point clouds: add_points renders millions of unconnected points (voxel fields, metrology/deviation clouds, LiDAR scans) in a single THREE.Points draw call, with per-point colormap colours, distance size-attenuation, and draw_range reveal
• Per-point time windows: give each point a [birth, removal) lifetime and scrub a global time — points appear/disappear out of buffer order in the vertex shader (material-removal animations that a prefix reveal can't express), driven live or from the animation slider
• Octree LOD streaming: add_points(lod=True) builds a Potree-style sampled octree in Python and streams node payloads on demand — draw a ~1.5M-point budget of the biggest-on-screen nodes out of clouds far larger than one draw call, refining as you zoom; composes with the time windows at every LOD
• Auto-reconnect: Browser reconnects automatically, animations persist
• Z-up coordinates: Robotics convention (matches ROS, URDF)
• No build step: Self-contained HTML viewer, just open in browser

Installation

pip install threejs-viewer

Quick Start

from threejs_viewer import viewer

# Start server and wait for browser to connect
v = viewer()

# Add objects
v.add_sphere("ball", radius=0.3, color=0xFF0000, position=[0, 0, 0.5])
v.add_box("ground", width=5, height=5, depth=0.1, color=0x444444)

# Keep running
input("Press Enter to exit")

The viewer opens automatically in your default browser. To open it manually:

threejs-viewer open
# Or: threejs-viewer path  (prints path to viewer.html)

Usage

Objects

from threejs_viewer import Toolpath, viewer

# Primitives with PBR materials
v.add_box("box1", width=1, height=2, depth=0.5, color=0x4A90D9, roughness=0.5, metalness=0.1)
v.add_sphere("ball", radius=0.5, position=[2, 0, 0], roughness=0.3, metalness=0.7)
v.add_cylinder("cyl1", radius_top=0.3, radius_bottom=0.5, height=1)

# 3D models (binary transfer)
v.add_model_binary("robot", "robot.stl", format="stl")

# Polylines with colormaps
v.add_polyline("path", points, colors=z_values, colormap="viridis", line_width=3)

# Bead toolpath (parametric tube, built client-side)
tp = Toolpath.from_points(points, bead_width=0.3, bead_height=0.08)
tp.colorize(per_point_rgb)
v.add_toolpath("bead", tp)

# Transparency
v.set_opacity("box1", 0.5)
v.set_color("ball", 0xFF0000, opacity=0.3)

Transforms

# Single object
v.set_matrix("box1", matrix_4x4.flatten().tolist())

# Batch update (efficient for 60fps)
v.batch_update({
    "link1": {"position": [1, 2, 0.5]},
    "link2": {"position": [3, 0, 1], "rotation": [0, 0, 1.57]},
})

Picking points on lines & beads

# Click a point anywhere along any polyline or parametric tube; the pick
# travels back to Python. Hovering glides a marker to the closest point.
def on_pick(pick):
    print(f"{pick['kind']} {pick['id']}: {pick['fraction']:.1%} along  at {pick['point']}")

v.on_polyline_pick(on_pick)   # also enables picking

Each click sends {id, kind, fraction, point, local_point, segment, t} where kind is "line" or "tube". Movement is continuous — the marker never snaps to vertices. Picking is opt-out per object — pass pickable=False to add_polyline / add_parametric_tube to exclude one from picking (it stays rendered); adding objects costs nothing when picking is never enabled. For a tube, segment indexes the full-resolution spine 1:1 with the per-point arrays you built it from, so it doubles as a lookup key for other per-point data at the picked point. A browser embedder can subscribe in JS instead — viewer.onPolylinePick(cb) (click) / viewer.onPolylineHover(cb) (every hover move) — for a live readout with no Python round-trip. See examples/22_polyline_picking.py.

Point clouds: time windows & octree LOD

# Per-point lifetimes: a point is visible while birth_time <= t < removal_time.
# NaN = unbounded (never born-late / never removed).
v.add_points("stock", positions, colors=depth, colormap="turbo",
             birth_times=birth, removal_times=removal)
v.set_points_time("stock", 3.0)   # scrub the time directly...

# ...or map the animation slider onto it (drag to scrub points in/out):
anim = Animation(loop=True)
anim.set_frame_times(times)
anim.set_point_time_data(["stock"], times.reshape(-1, 1))
v.load_animation(anim)

# Octree LOD for clouds beyond one draw call (10M+ points): nodes stream
# on demand from Python under a point budget as the camera moves. Keep the
# Python process running — it serves node payloads.
v.add_points("big", positions, colors=scalars, lod=True)
# tunable: lod={"node_capacity": 15000, "point_budget": 1_500_000,
#               "refine_pixels": 12, "seed": 0}

Both compose: octree node samples are stratified over the time values, so scrubbing thins every LOD level uniformly. On LOD clouds use the time window instead of set_draw_range (buffer order is spatial there). See examples/27_points_octree_lod.py — point count tunable from the command line.

Animations

from threejs_viewer import Animation

animation = Animation(loop=True)
for t in times:
    animation.add_frame(
        time=t,
        transforms=compute_transforms(t),
        colors={"robot": 0xFF0000 if collision else 0x00FF00},
        clip_times={"glb_model": t},  # drive embedded GLTF animations
    )
animation.add_marker(3.5, "Collision detected")

client.load_animation(animation)

Viewer controls: Space (play/pause), Arrow keys (step frames), 1-5 (speed), L (loop)

Binary Channels (Large Animations)

For animations with many objects or frames, use binary channels instead of Frame dicts for much faster serialization and transfer:

import numpy as np
from threejs_viewer import Animation

animation = Animation(loop=True)
animation.set_frame_times(np.arange(n_frames) / 60.0)

# Transforms: (n_frames, n_objects, 16) float32
animation.set_transform_data(object_ids, transform_array)

# Draw ranges: (n_frames, n_objects) float32
animation.set_draw_range_data(object_ids, draw_range_array)

# Clip times for embedded GLTF animations: (n_frames, n_objects) float32
animation.set_clip_time_data(object_ids, clip_time_array)

# Colors with indexed colormap: (n_frames, n_objects) uint8
animation.add_channel("colors", object_ids, color_indices, dtype="uint8",
                       metadata={"colormap": [0x44AA44, 0xFF3333]})

# Visibility: (n_frames, n_objects) uint8 (0=hidden, 1=visible)
animation.add_channel("visibility", object_ids, vis_data, dtype="uint8")

client.load_animation(animation)

Binary channels and Frame-based JSON can be mixed. A binary channel supersedes the same-named Frame field.

GLB Models with Embedded Animations

# Load a GLB with embedded animations (skeletal, morph targets)
client.add_model_binary("fox", "fox.glb", format="glb")

# Seek embedded animation to a specific time (seconds)
client.set_clip_time("fox", 1.5)

Documentation

• DESIGN.md - Architecture and protocol details
• examples/ - Runnable demo scripts

CLI

threejs-viewer path    # Print path to viewer.html
threejs-viewer open    # Open in default browser
threejs-viewer code    # Open in VS Code (use "Show Preview" for docked view)

License

MIT