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# 1 25-11-2012 , 01:01 AM
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Glass Refractions

This may be very basic as I don't know much about raytracing, its a fairly new topic for me. But I've started texturing/lighting a scene this evening and having problems getting good refraction's. The first image posted is the scene how it is at the moment with refraction's turned off on the glass Blinn shader. However in the second image you can see that when I turn refraction's on (currently set to 1.5) all I get is the light being bent from way over at the side and completely loose sight of the contents in the jars. I would of expected the ray to enter the glass and bend then enter the darker material inside and change before coming back out, but it appears to be completely bypassing the contents of both the pepper shaker and vinegar jar. Anyone know what I'm doing wrong?

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# 2 25-11-2012 , 02:27 AM
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You'll need to increase the number of times mental ray calculates light passing through an object. In render settings, under raytracing, increase Reflections and Refractions and set the Max Trace Depth equal to the sum of these.

# 3 25-11-2012 , 03:03 AM
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I would seriously suggest you watch Miss_Nova's tutorial on making a glass. It is not as simple or easy as it looks to get the real looking thing.


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# 4 25-11-2012 , 06:21 AM
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# 5 25-11-2012 , 09:04 AM
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Change your raytrace settings like stwert said and also don't use blinn, with the best will in the world you're not going to get that material looking right. What you need to do with blinn is create fresnel reflections by connecting in two ramps with sampler info nodes to the reflectivity and transparency which is sort of overcomplicating it when you could just render with the mia_material_x in mental ray, fresnel's built in and it looks better.

Look up the fresnel effect, it basically states that reflection changes with the viewing angle so if you fly over the sea you'll be able to look through the water whereas if you stand at the beach light reflects off and it's no longer transparent.

https://www.youtube.com/watch?v=F-2cUWUe0fY

If you look in the manual you'll find some tips on how to set it up;

https://docs.autodesk.com/MENTALRAY/2...ntal-ray-help/
mental ray architectural shader library > quick guide to some common materials

I think your lighting looks quite nice but I'd change all my materials to this one instead, there's a preset for thick glass which would work in your scene. Also check out master zap's blog https://mentalraytips.blogspot.cz/

# 6 25-11-2012 , 12:57 PM
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Had another play but still getting similar problems the glass material is now the mia_material_x Thick glass preset with the exception of the black on on the right that is the dielectric material. As you can see neither are giving me good results. I have my refractive and reflective index's set VERY high to make sure light can get all the way through and my max trace depth set at the sum of the two.

EDIT: Also forgot to say thanks for all the help people, really appreciate it. user added image


Last edited by ckyuk; 25-11-2012 at 07:02 PM.
# 7 25-11-2012 , 01:30 PM
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It's in your render settings you need to change it, not the material. If you look at your glass with liquid, the light needs to pass through 6 surfaces (outside glass, inside glass, liquid x2), so that would be the minimum amount of refractions you need. I just set it to 10, 10, 20 as in the screen to prevent problems, it will give you the same result as counting surfaces.

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# 8 25-11-2012 , 01:39 PM
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Hi Ckyuk

I'm no expert but try this and let us know if it works:-

1> Give some thickness to the object if it doesn't already have one and make sure the normals are facing outwards.

2> Give the objects mia_material and from the attribute editor select preset>glassthick>replace

3> In your render settings, keep reflection & refraction at 5 and a max trace depth of 10.

4> Increase your ray depth limit for all of your lights under raytracing shadows to 5 as well.

Render and post the results.


Last edited by zestken; 25-11-2012 at 01:48 PM. Reason: Mispelled user name
# 9 25-11-2012 , 03:05 PM
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Your all going to have a good laugh now when I tell you what fixed it user added image We were all looking far to deep into it and missed out one very important aspect. I had visible in refraction's turned off on almost all the objects in the scene. Works much better now user added image


Last edited by ckyuk; 02-12-2012 at 11:02 PM.
# 10 25-11-2012 , 04:01 PM
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Wow, I couldn't guess that user added image.

# 11 26-11-2012 , 05:53 AM
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That would do it! Glad it worked out.

Also... Is there water in the salt shaker?


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# 12 01-12-2012 , 11:15 AM
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Sorry I didn't reply for so long, had the week without access to the internet. No there is not supposed to be water in any of the shakers, can you point out exactly where and what you think is wrong?


Last edited by ckyuk; 02-12-2012 at 11:02 PM.
# 13 01-12-2012 , 04:34 PM
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I think you may have some artifacting going on inside the pepper shaker with that blockiness happening. And the shadow depth might need increasing as the shadows aren't persisting through the glass.

Sidenote: The shader on the sugar dispenser is getting blown out, it does seem less like glass now and the rough super bright highlight makes it look really vague and almost like it doesn't fit in the scene. The coffee stains are a nice touch, but the darker rim on them is a bit harsh and uniformed I think.


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# 14 02-12-2012 , 11:06 PM
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Thanks GecT it was the shadow depth that was causing the issue with the shadows through the pepper shaker, seemed to of fixed that. Also stopped the sugar dispenser looking so blown out but want to add some depth to the material as the walls look far to thin. Going for a semi-transparent plastic on this opposed to the glass of the other objects.

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