2sided Mtl - Gradient Ramp as Translucency Channel via MultiSubTex

[matthias_turbanisch]

Hello,

i found a very strange thing, I can't explain to myself.

I want to create a fabric material (VRay2SidedMtl) with stripes.

The stripes are generatet with a Gradient Ramp map.
The selection of the color of the stripes should be switchable by Material ID - so different Gradient Ramps are put in a MultiSubTex
The brighter the color of a stripe, the more translucent it should be.

I don't just want to use "Muliply by front diffuse" because I want to have a little more control over its behavior.

So I built a material like this

-> Image 1




You can see the detour, the stripe maps go, through an Output Map - leading to the translucency channel of the 2SidedMtl.

As long as the Output curve is straight 0-1 everything is fine.
100% white means, 100% of the backside ist visible.. and 0% of the front side.

-> Image 2




Now when I set the Output curve to exaggerated 0-0, the whole map gets black, and therefore there will be no translucency.
100% black means, 0% of the backside is visible.. and 100% of the front side.

This works for the map in Channel ID 1 of the MultiSubTex.

All following Channel IDs ignore this Output change.

This only happens with Gradient Ramps.
When the origin map is a Bitmap or Checker or something else, everything works fine.

-> Image 3

[hermit.crab]

I am not sure if understand the issue correctly. Could you attach the scene here so I can take a look?

[Joelaff]

It looks like perhaps the VRay2SidedMtl Translucency texture is not evaluating the Material IDs for the MultiSubTex.

[hermit.crab]

Everything seems to work as expected from what I tested. Best matthias_turbanisch sends the scene in question.

[matthias_turbanisch]

The MatIDs itself do work properly within the translucency channel.
As i wrote: with any other map, than a gradient map, everyything works fine.

I attached the file here in the post. I hope, i make this correctly since I'm not really experienced in this forum
(this is my first topic)

[hermit.crab]

Thank you for the report. It seems the issue occurs on V-Ray GPU only; the Gradient Ramp has wrong mapping when used in any slot other than 1 in the VRayMultiSubTex. We already have the issue logged (internal bug-tracker id: VGPU-3179) for developer investigation. As a workaround, you may bake the Gradient Ramp maps.