Additive VRayBlendMtl issues

[AJ Jefferies]

I've been using VRayBlend materials in additive mode to introduce a shellac like coat of reflection to some materials which works perfectly, however I've then tried to create a new material that blends between multiple VRayBlendMtls and have been getting some odd behaviour.

Even though the new VRayBlendMtl isn't set to additive, it always seems to additively blend the coat materials. What's stranger is that when using GI the secondary bounce looks to calculate the material 'correctly' (i.e. as I would expect).




I realise that using additive mode isn't physically correct but it seems strange that it should affect the end result of a 'separate' material. I've attached a Max file that hopefully demonstrates the problem.

http://mdi-digital.com/Offsite/AditiveBlend_2013.zip

[AJ Jefferies]

Here's a grab of the lightcache from the same file, which shows the blend acting as I would expect.

[Morbid Angel]

thought I don't have max2013, I suspect that your issue is that in your blend material your blend value is set below the 100% value. In my test the two blend materials one being shellac the other is not, works as expected, so I would check your map settings... Or if you can post a max 2012 scene...

[AJ Jefferies]

2012 file here : http://mdi-digital.com/Offsite/AditiveBlend_2012.zip

The blend is controlled by a map which is 100% white and 100% black, so I'm pretty sure it isn't that...

[Morbid Angel]

I can't seem to download that file...

[AJ Jefferies]

I am an idiot! http://mdi-digital.com/Offsite/AdditiveBlend_2012.zip

[Morbid Angel]

hmmm really odd, this one is for vlado for sure, it happens only on the diffuse element and only of the top material. The reflection component is fine however...It also happens in maya, as I just checked.

On another note, why do you need additive mode? you cant get a good result with just layering coat using fresnel map?

[AJ Jefferies]

On another note, why do you need additive mode? you cant get a good result with just layering coat using fresnel map?

I'm using it to add an extra coat of reflection to SSS2 materials, I'm then trying to blend between 3/4 of these to save rendering out multiple passes/masks.

I can work round it for now but it would be good to know why it behaves this way.

[Svetlozar Draganov]

Hello guys,

Thank you very much for your feedback.
I've tested your scene , and I got the same result.
I am going to post this into our bug-tracking system and I'll inform you when we have a solution for it.

Thank you again.