VRay2sidedmtl strangeness

[peterguthrie]

As Mats pointed out on my blog, the VRay2sidedmtl doesn't seem to work as one would expect. In the image above (same one attached as well) I don't understand why the back side shows through even though there is no illumination on the back. (I tried with secondary bounces off too - same result). It seems you need to keep the rgb values for the translucency map under about 100 for it to work as (i think) it should.

Any ideas?

[vlado]

What is the setup for your material?

Best regards,
Vlado

[peterguthrie]

Can post a screengrab (and scene) tomorrow, but its just a vray2sidedmtl with no opacity or refraction in the front & back materials.

[vlado]

Here are my tests; everything seems to be ok. In the first two images, the light is above the plane; in the third and fourth image, it is below. The front material is green, the back is red, both with a circle for opacity map. A Noise map in turbulence mode is used for the translucency slot.

Best regards,
Vlado

[peterguthrie]

thanks for taking the time to look into it Vlado, I misunderstood how vray2sidedmtl works i think. I assumed it there wouldn't be any translucent effect if there was no light hitting the back side of the material.

[Drawehn]

I have to admit that I am having problems with the 2-sided material too. I find it behaves strange if you have 2 different materials for front and back. I am trying to use it for a lamp shade that has 2 different materials on front and back but the back material shines through even if the light inside the lamp isnt switched on. If you turn translucency fully on (white), then the back material becomes the front material and vica versa. When would that ever happen in reality?

[vlado]

When would that ever happen in reality?

It would probably be something like frosted glass, where most of the light still goes through the material, but comes out scattered on the other side.

Best regards,
Vlado

[peterguthrie]

So is it just a case of being careful with the translucency values? In my test above I found that rgb values of approx 0-100 work OK for things like leaves and paper.

[vlado]

Yep, I suppose such values make sense.

Best regards,
Vlado