3D Gaussian splatting for Three.js

Three.js-based implemetation of a renderer for 3D Gaussian Splatting for Real-Time Radiance Field Rendering, a technique for generating 3D scenes from 2D images. Their project is CUDA-based and needs to run natively on your machine, but I wanted to build a viewer that was accessible via the web.

The 3D scenes are stored in a format similar to point clouds and can be viewed, navigated, and interacted with in real-time. This renderer will work with the .ply files generated by the INRIA project, standard .splat files, or my own custom .ksplat files, which are a trimmed-down and compressed version of the original .ply files.

When I started, web-based viewers were already available -- A WebGL-based viewer from antimatter15 and a WebGPU viewer from cvlab-epfl -- However no Three.js version existed. I used those versions as a starting point for my initial implementation, but as of now this project contains all my own code.

Highlights

• Rendering is done entirely through Three.js
• Code is organized into modern ES modules
• Built-in viewer is self-contained so very little code is necessary to load and view a scene
• Viewer can import .ply files, .splat files, or my custom compressed .ksplat files
• Users can convert .ply or .splat files to the .ksplat file format
• Allows a Three.js scene or object group to be rendered along with the splats
• Built-in WebXR support
• Supports 1st and 2nd degree spherical harmonics for view-dependent effects
• Focus on optimization:
  • Splats culled prior to sorting & rendering using a custom octree
  • WASM splat sort: Implemented in C++ using WASM SIMD instructions
  • Partially GPU accelerated splat sort: Uses transform feedback to pre-calculate splat distances

Tips

• Progressively loaded .ply and .splat files will not have certain optimizations such as cache-optimized splat ordering applied to them. For optimial performance, convert these file types to .ksplat or load them non-progressively.
• Converting your scenes to .ksplat will result in the fastest loading times since its format matches the internal format for splat data.
• Scenes with large dimensions or high splat density will cause issues with the default settings. For those scenes, you can try a couple of things:
  • Set the viewer parameter integerBasedSort to false to force a slower, floating-point based splat sort.
  • Experiment with a larger value for viewer parameter splatSortDistanceMapPrecision, to adjust the precision for the distance map in the splat sort. Larger precision values will result in reduced performance, but often can alleviate visual artifacts that arise when the precision is too low.

Known issues

• Splat sort runs on the CPU – would be great to figure out a GPU-based approach
• Artifacts are visible when you move or rotate too fast (due to CPU-based splat sort)
• Sub-optimal performance on mobile devices
• Custom .ksplat file format still needs work, especially around compression
• Scenes with very large dimensions will probably crash (often with an Index out of bounds error from the splat sort). Changing splatSortDistanceMapPrecision or integerBasedSort will probably not help in those cases.

Limitations

Currently there are limits on the number of splats that can be rendered, and those limits depend mainly on the degree of spherical harmonics desired. Those limits are:

Future work will include optimizing how splat data is packed into data textures, which will help increase these limits.

Future work

This is still very much a work in progress! There are several things that still need to be done:

• Improve the way splat data is packed into data textures
• Continue optimizing CPU-based splat sort - maybe try an incremental sort of some kind?
• Support very large scenes (streaming sections & LOD)

Online demo

https://projects.markkellogg.org/threejs/demo_gaussian_splats_3d.php

Controls

Mouse

• Left click to set the focal point
• Left click and drag to orbit around the focal point
• Right click and drag to pan the camera and focal point

Keyboard

• C Toggles the mesh cursor, showing the intersection point of a mouse-projected ray and the splat mesh

• I Toggles an info panel that displays debugging info:

  • Camera position
  • Camera focal point/look-at point
  • Camera up vector
  • Mesh cursor position
  • Current FPS
  • Renderer window size
  • Ratio of rendered splats to total splats
  • Last splat sort duration

• U Toggles a debug object that shows the orientation of the camera controls. It includes a green arrow representing the camera's orbital axis and a white square representing the plane at which the camera's elevation angle is 0.

• Left arrow Rotate the camera's up vector counter-clockwise

• Right arrow Rotate the camera's up vector clockwise

• P Toggle point-cloud mode, where each splat is rendered as a filled circle

• = Increase splat scale

• - Decrease splat scale

• O Toggle orthographic mode

Building from source and running locally

Navigate to the code directory and run

npm install

Next run the build. For Linux & Mac OS systems run:

npm run build

For Windows I have added a Windows-compatible version of the build command:

npm run build-windows

To view the demo scenes locally run

npm run demo

The demo will be accessible locally at http://127.0.0.1:8080/index.html. You will need to download the data for the demo scenes and extract them into

<code directory>/build/demo/assets/data

The demo scene data is available here: https://projects.markkellogg.org/downloads/gaussian_splat_data.zip

Installing as an NPM package

If you don't want to build the library from source, it is also available as an NPM package. The NPM package does not come with the source code or demos that are available in the source repository. To install, run the following command:

npm install @mkkellogg/gaussian-splats-3d

Basic Usage

To run the built-in viewer:

import * as GaussianSplats3D from '@mkkellogg/gaussian-splats-3d';

const viewer = new GaussianSplats3D.Viewer({
    'cameraUp': [0, -1, -0.6],
    'initialCameraPosition': [-1, -4, 6],
    'initialCameraLookAt': [0, 4, 0]
});
viewer.addSplatScene('<path to .ply, .ksplat, or .splat file>', {
    'splatAlphaRemovalThreshold': 5,
    'showLoadingUI': true,
    'position': [0, 1, 0],
    'rotation': [0, 0, 0, 1],
    'scale': [1.5, 1.5, 1.5]
})
.then(() => {
    viewer.start();
});

Viewer parameters

Parameters for addSplatScene()

Viewer can also load multiple scenes simultaneously with the addSplatScenes() function:

import * as GaussianSplats3D from '@mkkellogg/gaussian-splats-3d';

viewer.addSplatScenes([{
        'path': '<path to first .ply, .ksplat, or .splat file>',
        'splatAlphaRemovalThreshold': 20
    },
    {
        'path': '<path to second .ply, .ksplat, or .splat file>',
        'rotation': [-0.14724434, -0.0761755, 0.1410657, 0.976020],
        'scale': [1.5, 1.5, 1.5],
        'position': [-3, -2, -3.2]
    }
])
.then(() => {
    viewer.start();
});

The addSplatScene() and addSplatScenes() methods will accept the original .ply files, standard .splat files, and my custom .ksplat files.

Integrating THREE.js scenes

You can integrate your own Three.js scene into the viewer if you want rendering to be handled for you. Just pass a Three.js scene object as the threeScene parameter to the constructor:

import * as GaussianSplats3D from '@mkkellogg/gaussian-splats-3d';
import * as THREE from 'three';

const threeScene = new THREE.Scene();
const boxColor = 0xBBBBBB;
const boxGeometry = new THREE.BoxGeometry(2, 2, 2);
const boxMesh = new THREE.Mesh(boxGeometry, new THREE.MeshBasicMaterial({'color': boxColor}));
boxMesh.position.set(3, 2, 2);
threeScene.add(boxMesh);

const viewer = new GaussianSplats3D.Viewer({
    'threeScene': threeScene,
});
viewer.addSplatScene('<path to .ply, .ksplat, or .splat file>')
.then(() => {
    viewer.start();
});

Currently this will only work for objects that write to the depth buffer (e.g. standard opaque objects). Supporting transparent objects will be more challenging :)

A "drop-in" mode for the viewer is also supported. The DropInViewer class encapsulates Viewer and can be added to a Three.js scene like any other renderable:

import * as GaussianSplats3D from '@mkkellogg/gaussian-splats-3d';
import * as THREE from 'three';

const threeScene = new THREE.Scene();
const viewer = new GaussianSplats3D.DropInViewer({
    'gpuAcceleratedSort': true
});
viewer.addSplatScenes([{
        'path': '<path to .ply, .ksplat, or .splat file>'
        'splatAlphaRemovalThreshold': 5
    },
    {
        'path': '<path to .ply, .ksplat, or .splat file>',
        'rotation': [0, -0.857, -0.514495, 6.123233995736766e-17],
        'scale': [1.5, 1.5, 1.5],
        'position': [0, -2, -1.2]
    }
]);
threeScene.add(viewer);

Advanced options

The viewer allows for various levels of customization via constructor parameters. You can control when its update() and render() methods are called by passing false for the selfDrivenMode parameter and then calling those methods whenever/wherever you decide is appropriate. You can also use your own camera controls, as well as an your own instance of a Three.js Renderer or Camera The sample below shows all of these options:

import * as GaussianSplats3D from '@mkkellogg/gaussian-splats-3d';
import * as THREE from 'three';

const renderWidth = 800;
const renderHeight = 600;

const rootElement = document.createElement('div');
rootElement.style.width = renderWidth + 'px';
rootElement.style.height = renderHeight + 'px';
document.body.appendChild(rootElement);

const renderer = new THREE.WebGLRenderer({
    antialias: false
});
renderer.setSize(renderWidth, renderHeight);
rootElement.appendChild(renderer.domElement);

const camera = new THREE.PerspectiveCamera(65, renderWidth / renderHeight, 0.1, 500);
camera.position.copy(new THREE.Vector3().fromArray([-1, -4, 6]));
camera.up = new THREE.Vector3().fromArray([0, -1, -0.6]).normalize();
camera.lookAt(new THREE.Vector3().fromArray([0, 4, -0]));

const viewer = new GaussianSplats3D.Viewer({
    'selfDrivenMode': false,
    'renderer': renderer,
    'camera': camera,
    'useBuiltInControls': false,
    'ignoreDevicePixelRatio': false,
    'gpuAcceleratedSort': true,
    `enableSIMDInSort`: true,
    'sharedMemoryForWorkers': true,
    'integerBasedSort': true,
    'halfPrecisionCovariancesOnGPU': true,
    'dynamicScene': false,
    'webXRMode': GaussianSplats3D.WebXRMode.None,
    'renderMode': GaussianSplats3D.RenderMode.OnChange,
    'sceneRevealMode': GaussianSplats3D.SceneRevealMode.Instant,
    'antialiased': false,
    'focalAdjustment': 1.0,
    'logLevel': GaussianSplats3D.LogLevel.None,
    'sphericalHarmonicsDegree': 0,
    `enableOptionalEffects`: false,
    `inMemoryCompressionLevel`: 2
    `freeIntermediateSplatData`: false
});
viewer.addSplatScene('<path to .ply, .ksplat, or .splat file>')
.then(() => {
    requestAnimationFrame(update);
});

Since selfDrivenMode is false, it is up to the developer to call the update() and render() methods on the Viewer class:

function update() {
    requestAnimationFrame(update);
    viewer.update();
    viewer.render();
}

Creating KSPLAT files

To convert a .ply or .splat file into the stripped-down and compressed .ksplat format, there are several options. The easiest method is to use the UI in the main demo page at http://127.0.0.1:8080/index.html. If you want to run the conversion programatically, run the following in a browser:

import * as GaussianSplats3D from '@mkkellogg/gaussian-splats-3d';

const compressionLevel = 1;
const splatAlphaRemovalThreshold = 5; // out of 255
const sphericalHarmonicsDegree = 1;
GaussianSplats3D.PlyLoader.loadFromURL('<path to .ply or .splat file>',
                                        onProgress,
                                        progressiveLoad,
                                        onProgressiveLoadSectionProgress,
                                        minimumAlpha,
                                        compressionLevel,
                                        optimizeSplatData,
                                        sphericalHarmonicsDegree)
.then((splatBuffer) => {
    GaussianSplats3D.KSplatLoader.downloadFile(splatBuffer, 'converted_file.ksplat');
});

Both of the above methods will prompt your browser to automatically start downloading the converted .ksplat file.

The third option is to use the included nodejs script:

node util/create-ksplat.js [path to .PLY or .SPLAT] [output file] [compression level = 0] [alpha removal threshold = 1] [scene center = "0,0,0"] [block size = 5.0] [bucket size = 256] [spherical harmonics level = 0]

For the nodejs script, it may be necessary to increase the heap size for larger scenes. Use the parameter --max-old-space-size=[heap size in MB] to do so:

node util/create-ksplat.js --max-old-space-size=8192 [... remaining arguments]

Currently supported values for compressionLevel are 0, 1, or 2. 0 means no compression and 1 means compression of scale, rotation, position, and spherical harmonics coefficient values from 32-bit to 16-bit. 2 is similar to 1 except spherical harmonics coefficients are compressed to 8-bit.

CORS issues and SharedArrayBuffer

By default, the Viewer class uses shared memory (via a typed array backed by a SharedArrayBufffer) to communicate with the web worker that sorts the splats. This mechanism presents a potential security issue that is outlined here: https://web.dev/articles/cross-origin-isolation-guide. Shared memory can be disabled by passing false for the sharedMemoryForWorkers parameter to the constructor for Viewer, but if you want to leave it enabled, a couple of extra CORS HTTP headers need to be present in the response from the server that is sent when loading the application. Without those headers set, you might see an error like the following in the debug console:

"DOMException: Failed to execute 'postMessage' on 'DedicatedWorkerGlobalScope': SharedArrayBuffer transfer requires self.crossOriginIsolated."

For the local demo I created a simple HTTP server (util/server.js) that sets those headers:

response.setHeader("Cross-Origin-Opener-Policy", "same-origin");
response.setHeader("Cross-Origin-Embedder-Policy", "require-corp");

CORS with Apache

For Apache, you can edit the .htaccess file to allow CORS by adding the lines:

Header add Cross-Origin-Opener-Policy "same-origin"
Header add Cross-Origin-Embedder-Policy "require-corp"

Additionally you may need to require a secure connection to your server by redirecting all access via http:// to https://. In Apache this can be done by updating the .htaccess file with the following lines:

RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R,L]

CORS with Vite

For Vite, one popular option is to install the vite-plugin-cross-origin-isolation plugin via npm and then add the following to your vite.config.js file.

import { defineConfig } from "vite";

export default defineConfig({
  plugins: [
    {
      name: "configure-response-headers",
      configureServer: (server) => {
        server.middlewares.use((_req, res, next) => {
          res.setHeader("Cross-Origin-Embedder-Policy", "require-corp");
          res.setHeader("Cross-Origin-Opener-Policy", "same-origin");
          next();
        });
      },
    },
  ],
});

There are other ways to configure Vite to handle this referenced in issue #41.