DropInViewer seems to render but is invisible in three.js scene

[hybridherbst]

This project uses Needle Engine (a component system for three.js).
I attempted to add the gaussian splat viewer, however, something seems to be missing - the splats are rendered (I can see the corresponding draw call, but no visuals, in spector.js) but nothing shows up.

Reproduction: https://stackblitz.com/edit/three-dev-n6xvbd?file=main2.js

1. Load the page
2. Wait for installation
3. On the right side, a 3D scene appears
4. This repo's built-in progress bar correctly shows up
5. The draw call seems to be sent, but nothing is rendered

[seppestaes]

I'm not familiar with the product, from what i see in your example the grid and axisHelper are Needle's? Is there a way to access/pass Needle's camera, renderer to the viewer?

[hybridherbst]

Yes, but since Needle is using three.js under the hood camera and renderer are already accessible to GaussianSplats3D in the onBeforeRender callback that DropInViewer uses. There should be no difference to three.js in this regard.

If need be they can be accessed with this.context.mainCamera and this.context.renderer but I don't believe that should be necessary since they're already available in the callback.

[seppestaes]

Can you pass them to the DropInViewer?
const viewer = new DropInViewer({ selfDrivenMode: false, threeScene: scene, renderer: gl, camera: camera, ...

[hybridherbst]

I tried that and it does not change the behaviour.
DropInViewer ignores those parameters since they are passed into onBeforeRender:

GaussianSplats3D/src/DropInViewer.js

Lines 13 to 19 in f6f4ade

	options.selfDrivenMode = false;
	options.useBuiltInControls = false;
	options.rootElement = null;
	options.ignoreDevicePixelRatio = false;
	options.dropInMode = true;
	options.camera = undefined;
	options.renderer = undefined;

GaussianSplats3D/src/DropInViewer.js

Lines 123 to 125 in f6f4ade

	static onBeforeRender(viewer, renderer, threeScene, camera) {
	viewer.update(renderer, camera);
	}

[seppestaes]

As far as i understand: if you use the DropInViewer, the Viewer won't create new ones (camera, renderer) and they need to be passed in the options.

https://github.com/mkkellogg/GaussianSplats3D/blob/f6f4adea2e0a5745f942767214c7d3b335a10751/src/Viewer.js#L1607C5-L1608C73

Can you check the update in Viewer?

[hybridherbst]

As mentioned, they do get passed in by three.js in the onBeforeRender callback:

GaussianSplats3D/src/DropInViewer.js

Lines 123 to 125 in f6f4ade

	static onBeforeRender(viewer, renderer, threeScene, camera) {
	viewer.update(renderer, camera);
	}

I verified that the correct camera and renderer are passed into the update() call through the onBeforeRender callback. That's how DropInViewer works. I believe the issue here must be something else.

Can you check the update in Viewer?

As expected, passing in those options does not change the behaviour. I updated the StackBlitz repro:
https://stackblitz.com/edit/three-dev-n6xvbd?file=main2.js%3AL21

[seppestaes]

You're right, they are present. Camera settings? Frustum culling?

[hybridherbst]

If I knew I probably wouldn't have needed to open an issue :)

@mkkellogg wanted to take a look directly:

• Black Screen on Integrating the Advanced Viewer with Threejs Code #345 (comment)

[mkkellogg]

Sorry for the lack of movement on this one, I've been terribly busy with other things. I hope I can devote some time to it soon.

[mkkellogg]

After looking at your sample for a while, there's no obvious reason why it should not be working. There must be something happening under the hood with your engine that is affecting the rendering of the splats, and there's no way for me to debug that.

[hybridherbst]

Thanks for investigating. Needle is not doing anything special to the three.js renderer – it just adds objects to the scene graph. I'll see if I can find anything else.

---

EDIT: I found the issue! 🎉 Carefully comparing the uniforms passed to the drawcall, this zero was suspicious:

Turns out that Viewer/DropInViewer make a few assumptions that are not necessarily true:

1. the rootElement can never be passed into DropInViewer, it's overwritten
2. the rootElement is always the direct parent of the renderer.domElement
3. the rootElement has the same size (!) as the renderer.domElement 🐛

I believe the latter is what breaks rendering here. The rootElement might have a different size, e.g. height = 0, and then no splats are visible because while the renderer has a specific size, the size of the parent element is used.

If I replace this line with this.renderer.domElement then rendering works correctly:

GaussianSplats3D/src/Viewer.js

Line 306 in f6f4ade

this.rootElement = this.renderer.domElement.parentElement || document.body;

Couple questions @mkkellogg:

1. What's the reason why here the parentElement is used instead of the renderer.domElement?
2. What would be a good fix? For example, if DropInViewer didn't overwrite rootElement, I could pass the renderer.domElement as rootElement to fix the issue.

I updated the StackBlitz page with vanilla three.js and DropInViewer and the broken case –
https://stackblitz.com/edit/three-dev-n6xvbd?file=main.js
This is enough to break rendering:

  // This breaks it, because then the assumptions made by Viewer about the rendered size are wrong
  const div = document.createElement('div');
  div.style.height = 1000000; // stretchy lines
  div.style.height = 1; // giant vertical lines, very slow
  div.style.height = 0; // nothing renders at all (as described in this issue)

  document.body.appendChild(div);
  div.appendChild(renderer.domElement);

[mkkellogg]

To be completely honest, I think I somewhat arbitrarily added the .parentElement at some point during the early days of development, and then never thought about it again 😄 (It possibly was for testing purposes, but I can't remember what I would have been testing) I actually have no specific reason for attaching the render to the DOM in that manner, so I think it could probably just go away?

I'll remove it and do some quick testing. Thank you for digging into this!

[mkkellogg]

I have a branch with what I think should fix the issue (along with some other updates) here: https://github.com/mkkellogg/GaussianSplats3D/compare/minor-updates

Want to try it out to see if it works for you?

[hybridherbst]

Tested & looking good! Thank you!
Will you make a new (minor?) release with these changes?

[mkkellogg]

Yeah that's the plan!