Glow Surface Shader

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Does anyone know how to build a glow attribute for a surface shader in Vex? I have had the hardest time figuring out how to do this. I figured it would have something to do with the light shading nodes but I have no idea really how to go about it.

Cheers,
Nate Nesler

P.S. Thanks In Advance!
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What about fire node?
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I don't know if it can be done with shaders,
but a more practical way is to render the
items you want to glow with everything else
in the scene hidden or using a matte shader
and then glow in the compositor.

-cpb
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Completely out of curiosity, when you say compositor do you mean Halo or some 3rd party compositor? Just wondering how people think in these terms with Houdini..
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Yeah the fire node was the first thing I tried. I did not really get a glow out of it though. So … I was trying to use it on particles, and I tried it on metaballs with particles. I could try it on nurbs to see if it will glow on there. I need several things to glow so. I thought of using the light nodes tied together and make the surface an emition point for the light some way. I don't know I am just running ideas right now. lol There has got to be a way.

Cheers, 8)
Nate Nesler
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I also asked myself some questions about realizing glow fx. :shock:
The problem with creating the glow with the compositer is that you apply a
glow in “image space”, so it will make a big-object-far and a little-object-near glow the same manner, which is not correct. :evil:
Whatever you do that with a built-in glow function or a subnet of COPs (like expand-blur -color multiply), it will consist on expanding the matte“ in image space.
What you need is to ”expand the matte“ in object space. The way i would suggest you to do that is to apply a constant displacement shader to the geometry (it will ”offset" the geometry) and to apply then a constant white shader, or something
more elaborate).
it will create the zone you will glow.
Parallelly, just render the object with its normal shader .
And composite the two frames.

I hope it works for what you want to do. :?
I didn't do such a thing, but it's just an idea about how it can be done.

I saw that there's a glow function in fog shader VOP,
but i think it probably requires raytracing.

Hope it can help! :wink:
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What about rendering out the depth (Z) plane with your image as well? Then you can use the depth information to have glow that vary with the distance from the camera.
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Hey,

I don't mind raytracing at all. I am doing it right now on my images. The fog makes total since because for something to glow it has to charge the particles in the air around it. Didn't think about that. Thank You FrenchOP. Also thanks for the info on the image space verus object space. It may be possible though to set up a distance from camera and script that in to alter the glow attributes for the object in image space. That might take care of the problem you mentioned. I have to agree with edward on that. I might try that out too. I was really hoping for Object space because I don't want to have to use the compositor Halo. I will try the fog and I may even write a script or something to control fog around the object to control the glow better. The thing about the displacement is you would have to use a ramp between the two objects in order to make the fadeout. Otherwise it will have a halting effect.

Cheers, :idea: 8)
Nate Nesler
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could you give us a brief description on how you make your final glow effect when it's over?

( about the displacement: you're right, you must have a good fadeout => so you can blur the matte( but it means compositing), or apply a ramp with the “facingRatio” factor (i.e -N.I) )
good luck in your work!
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to glow in image space is usually correct if the
glow is a lens (natural or artificial) artefact. If
the glow is something volumetric like some plumes
of red fire venting from the eye sockets of an
evil poodle then a particle/geometry solution is best.
for image glow you can use halo by colour correct, blurring,
and then adding. 3rd party programs (like digital fusion, shake
etc.) will offer more interesting options but they are
mostly comfort features that can be replicated to some
extent in halo.

-cpb
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I perfer softglow node of Digital Fusion. It works well.
^_^
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Yeah no problem I will do a full write up on it. I will take screen shots of my node configurations etc. I will post in the odforce forum and then post here and make a link to it.

Cheers,
Nate Nesler
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wow!
thank you very much! * ( + ) + :wink: ^n

(i didn't ask so much!)
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If you only need a circular glow there's an easy render solution:

Copy sphere primitives to each point that needs a glow. Assign a shader with:

apara = .5
aperp = 0
alpha roll = .3

These numbers are approximations.

What this does is have the outer edges of the sphere fade off perpendicular to the line of sight. By playing with the roll value you can change the look of the glow. I've used this with point colors copied to the sphere primitive for multicolor glowing points.

Good Luck!
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Hey all,

Ok well the problem is harder than I thought. I did get some results but not what I wanted I ended up with a glow that went on and on and never really ended. I want a contained glow radius and well that is much more difficult as I have found out. I am going to buy several render man books probably at the siggraph conference. I don't know maybe before then. I plan on getting Advanced Renderman but does anyone else have suggestions on other render man books. I don't care how hard they are. I want indepth books. I sat through the renderman class last year at siggraph and understood everything that was said all 9 hours. lol Those light models are tough . This shader is essential to my piece so … I will post the tutorial when I get but expect it to be real soon. Its going to take me some time to wade through all of the reading material not mention I am learning Lightwave right now and I am also writing a plugin. Thats work. though. I am going to have to become very good with Vex before we can use houdini. Ouch. Its important though. If anyone has a suggestion for containing the radius of a fog effect code, Vex or both I am all ears.

Cheers,
Nate Nesler
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I just noticed that the Lighting COP has something that does atmospheric light with a fall off. It's written in VEX too so you can modify if it doesn't do what you want. Just make sure you render a point and normal plane out.
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Can we do glow in compositor nodes now?
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you always could, maybe not as a dedicated node, but it's very easy to make one
as mentioned above, just blur the image and add on top
you can add some lumakey to extract only bright regions before bluring, etc.

here is a quick example, the glow node is just a subnet for now, feel free to look inside

Attachments:
ts_cop_glow.hip (29.4 KB)

Tomas Slancik
FX Supervisor
Method Studios, NY
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