Beer glass scene creation
This course contains a little bit of everything with modeling, UVing, texturing and dynamics in Maya, as well as compositing multilayered EXR's in Photoshop.
# 1 14-11-2013 , 08:14 PM
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shader acting up

So I'm following the Realistic Outdoor Environments tutorial, and I'm at the part where you use the path edge grass. However, when I render it the two grasses show up different. The thing I do not understand is that they are using the same shader network.

I've checked their UVs and there's nothing wrong with them either. Please help!

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# 2 15-11-2013 , 09:29 PM
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I'm confused. Could you circle the problem areas?


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# 3 15-11-2013 , 10:42 PM
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Certainly. So in this image, you can see the grass circled in blue is whiter, while the grass circled in red doesn't have any white on it. However it's the same shader, so I don't understand why that would be.

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# 4 15-11-2013 , 11:41 PM
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Ah, now I see. It's mostly like the normals for the geometry are facing inwards. The mia_material is set to ignore calculating reflections for internal faces. So either reverse the normals on the surface or uncheck "Skip reflection on inside" under the advanced reflection section of the mia_material's attributes. I'd probably chose the former route since backwards normals can cause other issues down the road.


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# 5 19-11-2013 , 11:09 PM
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Sorry I was away all weekend so I just tried this. I tried a combination of reversing the normals and unchecking that box and it didn't seem to have any effect.

# 6 20-11-2013 , 11:15 PM
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Just to reiterate and clarify, if you reverse geometry normals and uncheck skip reflections on inside, you'll be back at square one, so do one or the other. If it's still having problems, you could upload the scene here or email me a link to the upload.


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# 7 26-11-2013 , 12:33 AM
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Yeah I just did one or the other, it didn't seem to effect anything.

Gen, that would be awesome. I would greatly appreciate that. I can upload it here, it's not very large. Let me know if you need anything and thank you again!

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# 8 26-11-2013 , 01:46 AM
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Ok wait, I think I figured it out. Apparently I missed a step and never added random rotation to my shorter grass, and that seemed to solve the problem.


What I'm still curious about though, is why does my grass have so many highlights?


Last edited by bar_of_soap; 26-11-2013 at 01:57 AM.
# 9 26-11-2013 , 03:10 AM
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So I took a look and I noticed a couple things.

The grass was reflective but because the diffuse texture was missing on the ground plane, it turned it into a kind of black hole. Your grass is set to have very rough, blurry reflections, this coupled with the black hole made the grass appear like it wasn't reflecting anything.

Also, the raytrace reflection trace render settings were low so the reflections stopped being calculated too soon for the grass to look good.


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# 10 26-11-2013 , 11:44 PM
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Okay so, I bumped the raytracing reflection trace render setting up to 10, and I gave the ground it's texture back. However I don't see a change in the grass highlights.

Now when I take the reflectivity down to 0.4, it looks fine. But I guess I'm just not sure why in the tutorial his looks fine with reflectivity at 1.

# 11 27-11-2013 , 12:37 AM
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"Skip reflection on inside" was still activated on the shader. Since the grass has no thickness(in post #6 I assumed it had), unchecking that attribute should suffice, so nevermind about the normals.

I tested for reflections and did a comparison:

Turned off Final Gathering
Turned off primary visibility in the plane's render stats
Assigned a red lambert to plane

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