🖼️ GLB Preview

Image-to-3D is a lottery, and the honest state of the field is that you get a decent silhouette bolted to garbage topology - the model's own author admitted as much about the flagship. So the useful question after a generation isn't "is the file valid", it's "does this thing look like the prompt". GLBPreview answers that in the graph, at any point, with a rotatable viewer. You can check the mesh before you spend ten minutes rigging it.

Why it exists

The ComfyUI-3D-Pack viewer is a nice piece of work - it hooks into a node's output UI data under the key three_model and renders it with Three.js in an iframe. The problem is that most mesh-producing nodes aren't output nodes, and the ones that are write their GLB somewhere the browser can't fetch it. GLBPreview is the bridge: point it at any GLB path and it makes the viewer work.

That includes files nowhere near ComfyUI. A mesh sitting in /tmp, or on a mounted scratch disk, gets symlinked into output/ so ComfyUI's /view endpoint can serve it to the browser. Zero copy, zero disk cost.

How it works

You feed it a path. It resolves your input in this order: as an absolute path, then relative to input/, then relative to output/. Not found in any of those, and it errors rather than passing a dead string downstream.

If the file is already inside output/, it just reports the relative filename and subfolder. If it's anywhere else, it creates a symlink in output/ named preview_<original_filename>. If symlinking fails - cross-device, or a filesystem that won't do it - it falls back to a real copy, but only under 500 MB. Larger than that and you get a clear error telling you to move the file into output/ yourself. That cap is a good decision; silently copying a 3 GB splat-adjacent asset into your output folder is the kind of thing you only notice when your drive is full.

The actual preview is rendered by a small frontend extension in the pack (web/js/glb_preview.js), which loads ComfyUI-3D-Pack's threeVisualizer.html in an iframe on the node and feeds it the filename the Python side returned. Orbit, zoom, pan - it's the 3D-Pack viewer, not a reimplementation.

Inputs and output

glb_path - a STRING. The source marks it a forced input, so in practice you wire it (from GLBLoader, from a generation node's string output, from a primitive) rather than typing it. It also means a typo can't creep in, which is the point.

glb_path (output) - the same string, unchanged. Passthrough, so you can slot the preview in the middle of a chain without breaking it: generate → preview → rig. It's an output node, so it always executes.

Installing it

cd /path/to/ComfyUI/custom_nodes
git clone https://github.com/JayDataEngineer/melite-utility-nodes.git

Restart ComfyUI. In ComfyUI Manager, search Melite Utility Nodes, or install by Git URL. The pack's requirements.txt (and the matching pyproject.toml) pulls matplotlib and av; neither is needed for this node, they're for the plot and decode nodes elsewhere in the pack.

The viewer itself needs ComfyUI-3D-Pack installed - that's where the Three.js bundle and the iframe page come from. And this is the real cost of the whole affair, so don't let anyone undersell it: 3D-Pack builds a stack of compiled CUDA extensions (pointnet2_ops, simple-knn, diff-gaussian-rasterization and friends) against your exact torch and CUDA versions, ships prebuilt wheels for one pinned target, and its issue tracker reads like a support group. If you only want the preview and not the models, that's a lot of build pain for a viewport.

Where it bites

• No 3D-Pack, no inline viewer. The node doesn't fail - it renders an overlay saying the pack is required, and the passthrough still works. The GLB is still symlinked into output/, so you can click it in the output list and get your OS's default viewer instead. Just don't file a bug about the black rectangle.
• Same-named meshes fight. The symlink is named from the file's basename with a preview_ prefix. Two previews of two different mesh.glb files in different folders are two writers to one destination, and the second one deletes the first's link to install its own. Rename one.
• Empty input is an error, not a blank viewer. You'll get a ValueError for an empty path; check the wire before you blame the renderer.
• It re-previews on file mtime, which is the behaviour you want for a file that a node upstream just rewrote - and also means a mesh regenerated with identical content will still re-render the viewer.