Physical Sky renders through ai glass only

[Brandon_Curless]

Hello, I am trying to use the Physical Sun/Sky as my lighting, but render background as transparent, so to achieve this I just put the aiSkyDomeLightShape1 > Visibility > Camera to value 0.00. This mainly works but the background behind all materials that are 'glass' still render the Physical Sun/Sky. How can I make make this area transparent? Pics attached. Thanks for any suggestions.

Brandon C.

[daunish]

So one option would be to turn down the transmission value on the skydome. But this is essentially going turn your glass into a solid and the alpha will still not be transparent.

The other option is, on your glass material, under transmission check the box “transmit AOV” this will push the transparently into your alpha. Probably more what you are looking for.

I hope this helps, let me know!

[Brandon_Curless]

Thanks for your reply. I tried both options. Turning down 'transmission' on sky dome makes sky disappear, but does make the glass a solid object being opaque.  Checking 'transmit AOV' didn't have any effect on the render. Maya, Arnold, and GPU driver is all up to date. Hmm, strange. If you have anymore ideas please let me know. I'll keep experimenting. Thanks!!

Brandon C.

[daunish]

So turning down transmission on the skydome doesn’t make you glass opaque. It makes it look opaque because you have nothing behind it.

Two questions:

1 - Checking the transmit aov box on the glass. What does your alpha for the glass look like? It should be grey or black now so you can comp it.

2 - What result are you looking for? Do you want to comp the final image or do you plan on adding a 3D env to your render

If your alpha is still full white after transmit aov then thats the wrong result and you got a problem. Maybe up a version of your scene? Let me know.

[Brandon_Curless]

I am not sure where you control the alpha for the glass material. Under 'geometry' I drag the opaque slider to all black but that makes the glass just disappear in the render. Is there another slider?

I want to comp the final image over another image using After Effects. The 2 pics below I am using the 2 different settings. I comped the car over a bright solid in After Effects. I also tried unchecking 'opaque' in the Glass Shape > arnold node

1. SkydomeTransmission Zero

2. Glass > Transmission > AOVs checked

I can get the glass to render showing a Maya object (the cube) behind it, but the area behind the glass where there 

is no cube and it should reveal transparency, it's just opaque when comps over a solid in After Effects. I rendered a Tiff with transparency in Maya

I also attached a zip file of the scene. Thanks for help. I have been trying to read the help docs also. This has been a real brain buster 

Brandon C.

[daunish]

Okay, two quick notes.

1 - Lowering opacity in the geo section of your material won't help you pull off the glass. It's really better as an "opacity cut-out" for leaves and such. The transmission which you have in your scene is correct.

2 - You don't actually have to turn off the aiOpaque flag on your shape nodes anymore. The newest versions of Arnold will automatically turn off that flag when you turn on material transparency.

So on to your scene. If you check the "transmit AOV" on the material, and turn off the skydome transmission. You will get the image I shared (it's in a zip cuse these forums suck butt). That said, now the light isn't passing through the windows from the skydome and you will have to compensate for that. It's a give and take.

My last note and this is on a personal level. I recommend rendering to exr's. Tiff is totally fine but exr's are for sure better (they have really good compression algorithms and multi exr's are a godsend). I end up using them most in productions. This is just my opinion and definitely changes from person to person.

I think this is the result closer to what you are looking for. Let me know, if I'm off base id love to get to the bottom of this!

[Brandon_Curless]

Hmmm, not sure why I am getting a different result. With the scene I sent you, I turn transmission to 0, Transmit AOVs on Glass is already selected, and then I rendered an exr. Rendered pic attached is my result (I uploaded a Tiff, but the EXR has same result). From the scene I sent you, did all you do is turn down transmission on skydome and render an exr? 

Brandon C

[daunish · Accepted solution]

Hmmmm, you may have something else going wrong!

In your scene, all I did was turn down skydome transmission. You can hit render on the scene I sent you (it's yours).

I'm a bit out of it with my personal life a little crazy. But let me give this some thought and see if I can figure out what else may be causing this issue. 

In the meantime, if the file I sent you still isn't working. Perhaps try creating a simple scene, follow these rules, and see if you are still getting this issue. I'm on Maya 2018 and MTOA 3.0.0.2 maybe there is a bug in MTOA for 2020?

Also as a final totally unrelated note, I suggest uploading ma files in the future. It'll just allow people to read your scene and not open them. It's totally not applicable in this instance but it makes troubleshooting and batch changes easier in production.

Perhaps someone else can hop in here and let us know what we're missing! Let me know

[Brandon_Curless]

Problem solved! Your version of maya/arnold comment got me thinking about compatibility issues which led me to question rendering with the GPU. When I switched to CPU render, I got your result. Not sure why my high end graphics card, Quadro RTX 4000, can't render the scene, but that was the issue. Thanks Duanish for all your help/time on this problem! 

Brandon

[daunish]

OH!! That’s facinating.

ive been trying your scene on my laptop so it probably defaulted to CPU. I’ll have to try on my RTX when I get home.

You gotta be careful with GPU in Arnold. It’s not there yet. Typically I’ll do look dev in gpu but final renders in cpu. Complex scenes seem to really struggle on GPU

Thrilled you got it!

[Brandon_Curless]

Yeah it's really too bad. It takes 5x longer to render. And I have a 20 core cpu. I'll have to render overnight 😕

But at least it works!

Brandon