Transparent plastic material, how to?

[irongraft]

Hi guys,

I'm very brand new to this community and to this amazing software, other than being a newby in the 3D graphics field.

Some months ago, I started studying Blender, which seems to me to be a great software. For some reasons I approached to Houdini and wanted to make the very same model I've realized with Blender also with it. It is attached.

 

My model is a simple laboratory couple of vials with some liquid inside. As you can see, with Blender I've managed to do two great (for me) things, that I'm not able to replicate with Houdini:

 

1) thick surfaces (In blender it exists the "solidify" function that makes primitives thicker automatically);

2) the effect of curved plastic, darker and less refractive (!?)

3) the actual material effect that here looks not glass but plastic, that I'm not able to replicate.

 

Could you drive me on the right path, with suggestions on how to set parameters, shaders, and whatnot? (also readings)

 

Thanks and happy Easter,

Tom

 

[Atom]

You can emulate Blender's Solidify modifier by using a PolyExtrude node and setting the distance to a small number.

 

For the shader use the Mantra Surface. You could start with the Glass preset or start with the Plastic preset and add Opacity Falloff.

http://www.sidefx.com/docs/houdini15.0/nodes/shop/mantrasurface

 

Here is a shader building tutorial as well.

http://www.sidefx.com/docs/houdini15.0/shade/build

[irongraft]

thanks for the reply,

 

1) after using the PolyExtrude node, shoud I use the Boolean to make the intersection between the outer and inner surface?

 

2) If yes, can you help me understand the inside/outside IOR values?

In case I used the polyextrude and boolean, to the generated mesh I'd assign a mantra surface which would have only Refract and Opacity fallof enabled, without changing (for now) the standard values. In the Settings tab I'd assign Inside IOR = 1.4 (clean plastic) and Outside IOR = 1 (air). Is that correct? Or should I consider the outer surface as a mesh and assign to it Inside IOR = 1.4 (clean plastic) and Outside IOR = 1 (air) [normals pointing to outside], while the inner surface: Inside IOR = 1.4 (clean plastic) and Outside IOR = 1 (air) [normals poiting inside the cube]?

 

3) How to increase the refractive (?) distortion through the glass, to act like a lens?

 

my render here: https://www.dropbox.com/s/xcoi8dvdxvca0hq/test_plastic_cube.tif?dl=0

 

Sorry if this may seem confusing, but I am sure to be missing important concepts.

Thanks in advance

[jrockstad]

I'm not a hundred percent clear on what you mean by using a boolean after the PolyExtrude - can you explain how you've set up your PolyExtrude? Perform a negative extrude on the local Z axis, then tick the Output Back setting under Options and you should have a nice clean mesh ready to go. 

[irongraft]

Yes, maybe because I miss something.

I used the Boolean because I thought the cube was filled. But I'm realizing now that I confused the PolyExtrude with Scale tool...

 

OK, If I followed your suggestion and used the PolyExtrude tool, how to setup the IOR in order to take into account that the plastic has air inside? To be clearer, after extrusion, I'd set up IOR outside = 1 (air outside the object) and IOR = 1.4 (plastic inside). But the cube is not completely plastic filled. So how to deal with the case to have air inside?

 

Then, how to create distortion through the plastic, like a lens?

 

Thanks

[jrockstad]

In this context, inside means within the implicit volume defined by your thickened geometry, whereas outside is everything that surrounds that geometry, even if it is 'inside' the model... if that makes sense. You can visualize this by feeding your geometry into an IsoOffset SOP and converting to a volume - anything inside the volume is 'inside' for the purposes of IOR calculation. The short answer is that you should be just fine with a single material on the geometry set to 1 outside IOR and whatever you need for the inside IOR. 

 

As far the distortion goes, are you after a kind of magnifying glass effect? I've never really tried that myself, but I would think if you had an accurate model (i.e., accounting for the curvature in the glass), the correct IOR, and caustics enabled you could probably get close. My hunch is that most times you see this effect in 3D it's probably faked one way or another though. For caustics, you need an Indirect Light:

 

http://www.sidefx.com/docs/houdini15.0/nodes/obj/indirectlight

Edited March 29, 2016 by jrockstad

[irongraft]

Hi,

thank you, I've got your suggestions.

That attached is the best I could do.

 

1) No diffuse

2) Reflect base (intensity = 0.7, specular min = 0.1)

3) No reflect coat

4) Refract (Intensity = 1, min = 0.1)

 

IOR inside = 1.488

IOR outside = 1

 

Have you any other suggestion on hot to improve this and to get closer to the render I've made with Blender?

 

Thanks you

 

 

 

In this context, inside means within the implicit volume defined by your thickened geometry, whereas outside is everything that surrounds that geometry, even if it is 'inside' the model... if that makes sense. You can visualize this by feeding your geometry into an IsoOffset SOP and converting to a volume - anything inside the volume is 'inside' for the purposes of IOR calculation. The short answer is that you should be just fine with a single material on the geometry set to 1 outside IOR and whatever you need for the inside IOR. 

 

As far the distortion goes, are you after a kind of magnifying glass effect? I've never really tried that myself, but I would think if you had an accurate model (i.e., accounting for the curvature in the glass), the correct IOR, and caustics enabled you could probably get close. My hunch is that most times you see this effect in 3D it's probably faked one way or another though. For caustics, you need an Indirect Light:

 

http://www.sidefx.com/docs/houdini15.0/nodes/obj/indirectlight

 

Edited March 30, 2016 by irongraft