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Question about froxel volume rendering tech used by Frostbite

Started by grunt123 Oct 28, 2016 at 1:15 AM 3 replies 13.2k views

Original Post

Oct 28, 2016 at 1:15 AM

http://www.frostbite.com/2015/08/physically-based-unified-volumetric-rendering-in-frostbite/

i'm specifically looking at the above paper. In there, it's using so called 'froxel' technique to do volumetric rendering. i think i understand the overall idea, but i just can't figure out how to voxelize participating media. They are using 'VBuffer', and is this 3D texture that has the same dimension as main froxel buffer? If so, it seems way too low resolution for rendering density media?

i'd appreciate any help on this.

$multifractal$

multifractal

Nov 3, 2016 at 6:37 PM

You really don't need a very high resolution 3D texture for the rendering of fog. Fog in nature isn't very sharply defined so a low resolution texture with interpolation works quite satisfactory. I'm sure you've seen it already but if not this may give you a better understanding of the topic: http://advances.realtimerendering.com/s2014/wronski/bwronski_volumetric_fog_siggraph2014.pdf

ErnieDingo

Nov 3, 2016 at 7:15 PM

You really don't need a very high resolution 3D texture for the rendering of fog. Fog in nature isn't very sharply defined so a low resolution texture with interpolation works quite satisfactory. I'm sure you've seen it already but if not this may give you a better understanding of the topic: http://advances.realtimerendering.com/s2014/wronski/bwronski_volumetric_fog_siggraph2014.pdf

Doing this in my own smoke animation. But instead of lerping between frames you are lerping between layers depending on your position with in or outside the froxel?.

grunt123

Nov 4, 2016 at 12:06 AM

You really don't need a very high resolution 3D texture for the rendering of fog. Fog in nature isn't very sharply defined so a low resolution texture with interpolation works quite satisfactory. I'm sure you've seen it already but if not this may give you a better understanding of the topic: http://advances.realtimerendering.com/s2014/wronski/bwronski_volumetric_fog_siggraph2014.pdf

thx for the reply. But, that pdf is about global fog effects, which is different from what frostbite volume tech is doing. Frostbite volume is rendering a local/individual fog volume, so it can render multiple number of fog volumes that are differently authored by artist. (and each fog volume can have its own noise texture too). If this is global fog effect (that is used in AC4 in that pdf), i would agree that low res texture would suffice ... But, for localized volume rendering? i'm not quite sure. Frostbite volume tech is using temporal reprojection trick, but does this help much ? i implemented simple version of frostbite tech just to render local volumes, and rendering into low res (froxel size buffer) produced really low quality volume.

Hodgman

Nov 4, 2016 at 12:25 AM

The link from multifractal does have a lot in common with the Frostbite one. Yes, the frostbite one better allows level creators to make different fog volumes in different locations, but the froxel idea is basically the same in both.

Yes, the low resolution limits the amount of detail that's possible to see in the shape of a fog volume.

Reprojection helps a lot with solving the aliasing problems of the low resolution, but does not enhance detail.

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