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Comment by thih9 | Hacker News Reader

About “can't display general occlusion”, wikipedia calls this a misconception. But it does later state that it requires sacrificing vertical parallax.

> It is often claimed that volumetric displays are incapable of reconstructing scenes with viewer-position-dependent effects, such as occlusion and opacity. This is a misconception; a display whose voxels have non-isotropic radiation profiles are indeed able to depict position-dependent effects.

> the ability to reconstruct scenes with occlusion and other position-dependent effects have been at the expense of vertical parallax, in that the 3D scene appears distorted if viewed from locations other than those the scene was generated for.

https://en.m.wikipedia.org/wiki/Volumetric_display

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"non-isotropic radiation profiles" is probably better expressed as the ability to produce light that can be modulated differently in different directions. That's what's required to show proper view dependent shading on a surface, and what's required to turn off a voxel that's behind another voxel from a particular view angle.

That's arguably a different class of display, and an extremely complex one.

To build it you'd likely want to sacrifice vertical parallax (to allow the use of a spinning lenticular sheet or something else, and to reduce the information capacity required), but there's no fundamental reason that prevents a full parallax display of this type (a spinning integral photograph).

From an engineering complexity point of view, it's the hardest of all worlds.

> This is a misconception; a display whose voxels have non-isotropic radiation profiles are indeed able to depict position-dependent effects.

Sure, if you replace each pixel with a tiny light field display pixel you can do occlusion.

Unfortunately, that's a big challenge for a volumetric display, particularly a spinning one. There's a mass problem (heavier spinny things are more difficult than lightweight spinny things). There's also a wire problem if the elements on the spinning element are active and need to be addressed, since the wires generally need to come through the hub. If a projector is used and the spinning element is passive, then there's a tricky alignment issue.

And in any case, there's a bandwidth issue, since every 3d point is now addressed by a 1D or 2D array. That's an enormous amount of the data that ultimately needs to be uncompressed by the time it hits the display hardware.

A hogel volume can be reduced into a 1bpp 2d plane representing the interference problem. Literally, a hologram. Probably the computational effort to do this in realtime is within reach of current GPUs.

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