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davo

isolating surface behind a surface of object

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does anybody know a way to isolate a front facing surface behind another front facing surface of an object in vex or vops? i need to have only front facing surfaces which are visible to the camera render with transparency but the front facing surfaces of surfaces behind the ones visible to the camera are being seen and i need to get rid of those.

thanks,

davo

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Perhaps this thread belongs in rendering?

Can you just cull out t he backfacing geometry when rendering? Append Delete SOP. Turn on Normal and Enable. Selecting your camera in the Backface From parameter. Set your render flag on the delete sop.

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That is a cool idea and it i will use it...but it doesn't remove front faces that are behind my transparent faces....for example i have eye geometry within a head, ears and mouth that shows up behind the transparent faces that i don't want to showup.

More importantly there are front faces that will show up that are not inside my body object but are actually parts of the body itself, this of course depends on the camera view of the animation as to which frontfaces will be behind other front faces that I wish to keep.

Thanks,

Davo

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Sounds like a job for COPs. All you have to do is take the Alpha channel of the leading surface, invert it, and use it as a mask for the back surface... Or am I misunderstanding something?

Maybe a pic will help explain things a bit?

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I think you are misunderstanding the problem....

If i did use cops it would still show the surface behind the surface.

I've attached a picture with an example. if you notice the right breast of the subject you will see that the arm is showing through it....

i want to be able to remove that so that the entire thing renders like the stomach area....i cannot predict where a surface will show up behind another as the animation will be done later.

Thanks,

Davo

post-28-1086496296.jpg

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Ahhh. I see, I thought you were talking about seperate objects.

It doesn't look like the surface is refracting; it's just transparent, so you can use COPs easily.

You can render multiple passes and composite them together. Render the backgroud. Render one pass of her with her diffuse color (completely opaque) and an alpha channel for masking. Composite her color layer over the background using the alpha as a mask so she appears in front of the background. If the transparency varies over the surface, you render another pass with the transparency map or shader, and use it as a transparency for the girl's color layer; if the transparency is unform, you can skip this and just set the transparency for the diffuse layer in COPs.

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I'm pretty lame with cops i've found....

can you be a bit more explicit...

if i use a composite cop, i'm not sure how to actually control the transparency other than setting it on something like average.

i ended up piping a render with the opaque body and the background into a blend cop with a render of just the background in the other , so i am not really even using either of the alphas...

this seems to the job but i'd like to know if this was what you had in mind or if you had a better way.

Thanks,

Davo :rolleyes:

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Yea that little vop works out very nice!... alittle easer then doing all the rendering...

... thanks all for all the help!

Davo

:D

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