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Rendering realistic snow(not taking into account accumulation)

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Hi I am trying to find out how to render realstic looking snow, and I'm talking falling and fallen snow. I'm not considering realistic snow accumulation at the moment. So get a grip on where to go I have to ask, What are the state-of-the-art methods when it come down to rendering the snow, I'm looking to see what the difference are between rendering snow real-time and non-real-time. I have been looking at a lot of papers so far, but some are old and I haven't got a clue what methods are actually being used. What I would think of was that, the first thing was create realistic lighting, for this I would do some kind of environment mapping, then I would use a lighting model for the snow reflection(but which one, I am thinking Cook-Torrance), and then there would also have to be some kind of scattering method to take into account. Post effects could then be added, some Bloom effect maybe? And for the falling snow I could have a cone of particles around the camera, a texture scrolling further away, and then some fog to decrease view distance. But as this is some research for a report at the university I can't just come up with stuff, but have to make references to other techniques and evaluate them side by side, so what techniques are out there? EDIT: If anybody know of a reference in which snow is done nicely a tell would be appreciated too;-) regards Thx [Edited by - thallish on September 28, 2006 9:54:20 AM]

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And for the falling snow I could have a cone of particles around the camera, a texture scrolling further away, and then some fog to decrease view distance.


In addition to that, you might want to throw in some realistic lighting for the snow. From waht I've observed, if you did say, just (L dot V) to do scattered lighting and use that value to look up a 1D texture like for specular lighting (or, for a simpler solution, (L dot V)^n), then the snow would probably look really good.

For fallen, untouched, snow you could do Lambertian lighting for the majority of it, but the sparkles I'm not sure how you could do it on a practical level since it's so random and sharp. A big key, imo, would be to barely have the sparkle repeat, or not at all; a repeated sparkle pattern would be quickly and easily apparent. The only thing that comes to mind would be a very high resolution and extremely noisy normal map that a high power specular reflection could use. If not a high res normal map, then maybe you could do some kind of pseudo-randomized normal generation with some lookup tables inside the pixel shader using a stable input like the texture coordinate of the snow.

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Original post by Cypher19
In addition to that, you might want to throw in some realistic lighting for the snow. From waht I've observed, if you did say, just (L dot V) to do scattered lighting and use that value to look up a 1D texture like for specular lighting (or, for a simpler solution, (L dot V)^n), then the snow would probably look really good.


Could you elaborate on this, or throw a reference, would be appreciated ;-)

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A big key, imo, would be to barely have the sparkle repeat, or not at all; a repeated sparkle pattern would be quickly and easily apparent.


Ill keep that in mind. Thx for the input

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Original post by thallish
Quote:
Original post by Cypher19
In addition to that, you might want to throw in some realistic lighting for the snow. From waht I've observed, if you did say, just (L dot V) to do scattered lighting and use that value to look up a 1D texture like for specular lighting (or, for a simpler solution, (L dot V)^n), then the snow would probably look really good.


Could you elaborate on this, or throw a reference, would be appreciated ;-)


Elaborate on what? What I suggested is to basically use your standard Phong specular reflection (you should be able to find some papers on the math behind that) but instead of calculating R dot V, you just use L dot V.

Fwiw, the usage of L dot V was my own idea based on observations of reality. It's possible that if you looked up, say, scattered lighting, you'd see that idea pop up.

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Original post by Enrico
ShaderX3 has two articles about rendering snow. NVidia's developer section has the accompanying sample program. You can download the complete program (source and executable) and maybe some documentation there for free :)


It is ShaderX4 that got it;-) and it just arrived. It most certainly be a goal of mine to make prettier snow than that, so nice reference to have.

Thx

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Original post by Cypher19
What I suggested is to basically use your standard Phong specular reflection (you should be able to find some papers on the math behind that) but instead of calculating R dot V, you just use L dot V.

Fwiw, the usage of L dot V was my own idea based on observations of reality. It's possible that if you looked up, say, scattered lighting, you'd see that idea pop up.


And it is elaborated;-) You didn't state that it was Phong you meant, but now that is all cleared up.

Thx.

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Here are 3 citeseer articles about rendering snow:
* A Modeling and Rendering Method for Snow by Using Metaballs, Nishita & al.
* Computer Modelling Of Fallen Snow, Paul Fearing
* Animating Sand, Mud, and Snow, Summer & al.

citeseer can help you to find more articles (I found those by doing a "rendering snow" search, but I guess that you can also try some other queries).

HTH,

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