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Glass And Compositing Passes?!


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Hi,

I have serious problems with my logic behind comping different passes involving a glass (transparent) object...

I just could not find a way of having different passes for the parts that are behind the glass...

Actually I have rendered passes to use for the sections behind the glass... but it worked only for those that are totally behind the glass.

When some of the objects get half behind the glass and half in front of it... the "passes" thing gets confusing...

So after all my tries... I ended up using this logic:

1. Every thing that is not glass is rendered in passed and the object that is glass is in MATTE mode (in the Render tab.)

2. Everything that is not glass is in PHANTOM mode so it gets refracted.

3. The glass object is assigned just a normal shader (VEX Clay etc.) and everything else is in MATTE mode to mask portions of the glass object.

This is used as an ALPHA for the glass.

But this prevents me from having control on the renders that are behind the glass.

(1) Every thing that is not glass is rendered, glass is MATTE:

post-1724-1187217520_thumb.jpg

(2) Everything that is not glass is PHANTOM, the glass is just glass:

post-1724-1187217565_thumb.jpg

(3) The glass object is rendered and masked by the other object that are in MATTE mode:

post-1724-1187217680_thumb.jpg

//

The Comp. network:

post-1724-1187217713_thumb.jpg

The final result:

post-1724-1187217743_thumb.jpg

//

Any ideas? How should I approach this "passes" and "glasses" problem?

Thanks.

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it's hard to follow you (at least for me) quite esoteric issue. If you could post your layers here, (C+alpha, not just jpeg) it would be easier to help you.

sorry about that...

:(

but this is the problem... i do not know how to setup my Houdini workflow in order to get correct layers and passes...

...the thing is that if something is behind the glass... it is kind of ok... if something is in front of the glass it ok as well... but the problem

starts when you have objects that are partly behind the glass and partly in front of the glass...

I am not able to get proper ALPHA channels for the parts of the objects that are refracted (behind the glass)... I can just get the alpha for the glass object...

so this makes it impossible to render objects that are half behind the glass and half infront of the glass in different passes to be comped together later...

for example the frame around the glass in the posted images... it is both in front of the glass and then it goes behind it... I am not able to get the alpha of that part goes behind the glass...

:(

I am aware of the fact that this is a complex issue and it is really hard for me to build a proper question... :(

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It shouldn't be a problem unless you have multiple reflective/transmissive objects interlocking and which need to be separated -- then you might get into situations where some objects will need to be made both phantom *and* matte. But for a single glass bit surrounded by hard surfaces, it should be straight forward...

As a rule of thumb: making all these surfaces into a single object (like you did in the example glass on the other thread) with different SOP-level SHOP assignments, is not generally a good idea -- especially if they need to be split up later.

Again, as SYmek mentions, an example hip file here would be worth 1000 words.

P.S: The interior of most lamps are usually reflective (they have faceted, mirror-like reflectors behind the bulb).

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nothing to sorry about, it's just easier to find solution in shake/halo than writing it from imagination ;)

ow!... yes you are right...

since the passes do not work... there is no point to post their *.tif files... but I can post the *.hip file.

Here it is:

trans_test_v1r15_for_post.hip

so there i have the glass object in a separate GEO... and the rest in a separate GEO as well... so that I can make PHANTOM / MATTE combinations.

but I think the problem is with the glass shader... I am using an early version of glass from the SHADERs section...

As I said before... I can not isolate the objects rendered through the refracted glass... basically if I have a refracted diffuse pass, refracted light pass, refracted specular pass etc.

everything gets on top of each other and... yeah... thats it...

:(

thanks for your time and for your interest in this topic...

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