Grid rendering over splats - depth test issue

[d0rianb]

Hi, I'm trying to implement a grid similar to SuperSplat's infinite grid, but my grid renders on top of the splats instead of behind them.
How does SuperSplat handle the depth ordering between UI elements (grid, bounding boxes, etc.) and the splat rendering? Are there specific depthTest/depthWrite settings or layer configurations I should use?
Thanks!

[slimbuck]

Hi @d0rianb ,

The grid in supersplat editor renders before GS models using normal alpha blending.

However, the grid shader performs a test using the fragment alpha against a blue noise texture to decide whether to write a correct depth value for the fragment or 1.0 (/far).

This way you get a perfect looking grid where there is no GS and dithered (but correct) grid where there is.

Thanks

[d0rianb]

Hi @slimbuck, and thanks for your quick answer.

I understand that the grid is rendered before the GS by using the layer:prerender event. However, I do not understand how the grid appears above the GS when the camera moves below the model. I may not fully understand when the GS is actually rendered, although I assume it belongs to the World layer.

In addition, the GS bounding box does not appear to use a custom shader, yet it still renders correctly both above and below the GS. I would like to understand how this behavior is achieved.

Thank you

[slimbuck]

During GS rendering, every pixel is tested against the z-buffer. Anything part of the scene rendered to the z-buffer before GS will composite correctly.

The wireframe bounding box just renders solid lines with z-buffer writes enabled, before GS.

A good way to see what's happening is using the spector.js chrome extension. This tool lets you to capture a webgl frame and inspect the individual draw calls used.

[d0rianb]

Thanks, this extension is fantastic.
However, even if I have the same draw calls as SuperSplat, the GS rendering seems to ignore the global depthMap (even if the blending is enabled). Is there any differences between the engine gsplat shaders and the SuperSplat one ?

[slimbuck]

Sounds like perhaps your depth buffer isn't correctly configured?

Is this editor project? If you want to add me to it (slimbuck) I can take a quick look.

[d0rianb]

Unfortunately, it is a local project that uses the engine API.
However, I was able to find a solution : render to a custom RenderTarget instead of rendering directly into the backbuffer.
Thank you for your help, and thank you as well for introducing me to the SpectorJS extension. It's super useful.