Opacity map causing object to look hollow

[Tom Bussey]

Hi, I'm a fairly novice user of Vray, so the answer to this is probablly blindingly easy, or I'm doing this all wrong. As you can see, on the test render below, I've used an opacity map to create holes in the object.

 

test by busseynova, on Flickr

 

The thing is it means you can see both sides separately, causing this 'phasing effect'. Is it possible to use the map in such a way as it appears to cut through a solid object, rather than a hollow one? The map and a photo of the real chair are below. I've tried ticking 'double sided' under material options but it seems to have no effect:

 

HMI_Sayl_Work_Back_Opacity_3D by busseynova, on Flickr

 

[Chris MacDonald]

I see what you're saying, and the way to do it would be either to use displacement, or model it.

 

I just thought of a great way to do it, but am not at a pc, and trying to type it would take a lifetime.

[matthewspencer]

I vote for "model it"

[Tom Bussey]

Yeah, I thought about that, I'll have to do it at home sometime, as I don't have Illustrator or photoshop to trace out the holes at work. I was hoping there was some clever way!

[Chris MacDonald]

I just did a test for proof of concept, and you can use displacement to create a 3D surface if you get clever about it. Will post results soon.

[Chris MacDonald]

here;

 

Standard opacity map & bump map:

 

Same but with displacement applied:

 

And the "solid" version I propose:

 

Here it is, exaggerated:

Edited May 3, 2013 by Macker

[cg_Butler]

Excellent example Chris. Kudos to you. :-)

[Chris MacDonald]

Cheers fella, quick explanation here; http://macviz.blogspot.co.uk/2013/05/3d-surfaces-using-displacement.html

[Tom Bussey]

That looks great, and I'm pretty sure I understand how that works, but can you explain what you meant by this bit: "It will require quite a lot of tweaking and so on to make sure the "middle" parts meet up" .

 

I guess you mean getting the cutouts to meet in the centre of the two planes? Bear in mind that I have never used displacement maps so I'm pretty ignorant in that department! Are the two objects actually sitting in the centre or on the outside face of that shape?

 

Thanks! Tom.

[Chris MacDonald]

They are both sat in the centre, facing in opposite directions - the displacement then pushes out the white parts of the map, leaving the black parts in their original positions.

 

To make the holes see-through you have two options; opacity map, or use the "water level" control on the vraydisplacementmod which will "clip" the geometry for you. The clip method will probably give you more flexibility in the long run.

[beestee]

Seeing this makes me wonder why something as seemingly simple as a "2-sided" or "mirror" option for displacement does not already exist.

 

That is a nice result Chris.

[Chris MacDonald]

I'm guessing because to do so Vray would have to create new geometry as opposed to what it does with displacement, which is subdivide existing geometry and move it around a bit.