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Ibeechu
11-18-2009, 07:11 PM
Hey guys, I have a question for you experts. Last night I spent a good 3 hours or so finally figuring out how to do good fog in mental ray (ended up using a pati_volume shader linked to a material) and the results were better than I could have hoped for. I needed to learn this technique for a class I'm in where I'm planning to submit, as a project, a render in a foggy forest. However, I have another project that I'd love to apply this shader to, but I am stumped how to do it.

OK, so the shader, as I understand it, fills up an object with dust particles and such, and that's how the effect is created. WHat I'm trying to do is make an object essentially look like it's made up of light (like holograms you would see in a movie, or something). I guess this is analogous to filling the object with dust particles and making it transparent, so that when light hits it, the dust scatters it in the shape of the object. Trouble is I can't seem to get it to work. I'm very very new to this "parti_volume" shader and have been playing around with it all night, but I didn't get the idea to try to make a holographic thing until about an hour ago. After much toying, I'm getting nowhere. Can anyone help?

I'd post pictures, but I don't know what good they'd do, since the effect I want isn't happening at all.

Thanks a bunch!

InfernalDarkness
11-19-2009, 05:38 PM
The parti_volume shader doesn't actually fill your space with anything. You won't be able to dynamically affect the "dust" you see, as it's just a rendering trick really. (ray marching)

You could possibly use actual particles in conjunction with parti_volume?

But I don't know what you mean by "holographic". Do you mean like this...?

http://static.howstuffworks.com/gif/holographic-environment.jpg

Ibeechu
11-19-2009, 07:33 PM
Sort of. I'll try to better explain the effect I'm imagining. If you have a room full of smoke, and you shine a flashlight through it, you can see a visible conic that looks like it's made up of swirling smoke. Now, imagine that, instead of a cone shape, it's any other shape. In my case, it's 3D text. Essentially, I want the letters to look like it's made up only of light. Eventually, what would be really frakking cool, is to have some sort of a volume shader, I guess, to give the impression of swirling dust particles. Not necessarily in any specific pattern, just so that the text's brightness changes subtlely within it. To try to explain that in a different way, I don't want it to look like just letters made up of light. I want it to look like smoke or dust, exactly how it would look if you shined a laser through some smoke. Except instead of being in a narrow beam, I want it to be in the shape of the letters.

I hope that makes sense, but it probably doesn't. I'll try to see if I can get a reference photo of the effect having been done somewhere else. It might have been done in Wall-E or The Incredibles somewhere, I'll look.

EDIT: Duh, Star Wars! I considered referencing that in my original post, but decided against it because it wasn't exactly what I was looking for, but it's close enough for me to at least add on the additional effects I want:

http://www.technomoz.com/wp-content/uploads/2009/01/hologram.jpg

OK, the main reason I didn't mention the Star Wars holograms was because they all tend to have this scanline look to them. Like an interlaced video that isn't timed right or something. That never made sense to me and it's not the look I'm going for. So replace the scanlines with dust and smoke and that's pretty much exactly what I want. :D

InfernalDarkness
11-19-2009, 09:54 PM
I think that should be very possible. One way to do it would be to use a simple image, but that would be flat, and you mentioned you wanted to animate it? Another way would be to model your text and use texturing to achieve the desired effect, along with the parti_volume which you're already working with.

For example, if you modeled your text and set Primary Visibility to Off, but left shadow-casting on and such, it might work how you'd like it to. Just an idea!

Ibeechu
11-19-2009, 10:10 PM
Yeah, it's going to be animated. Interesting idea, though.

I think what I might have to end up doing is a 3D texture. I tried that, using procedural clouds whose values were driven by, say, the text's position (so that as the text moved, the clouds would change) and applied those to an alpha channel so that in some areas, the text would appear "thicker" than others. It wasn't working how I wanted it to so I gave up until i found this neat parti_volume shader and thought it might work with what I wanted to do. From what you're saying though, it appears not.

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