Back faces are rendered dark in GPU mode

[Micha]

Hi,

is there a way to avoid that back sides are rendered much to dark in GPU mode?

-Micha

[Micha]

I got an idea and checked it. I found, if I export the material and edit it, that there is the option "use_double_sided_mode" and it was set 0. In CPU mode it doesn't show any effect, but in GPU mode it cause problems.

Test: I create a fresh material at VfR2 and set a texture. I export the material and found the same problem. So, it's a problem of all VfR2 materials and not caused by a wrong user setup. Please find a way to avoid this problem if VfR2 scene are rendered at VfR3x.

[palosanto]

Micha,
I noticed this problem a while ago and I got this response from Chaos support via email:
"In respect to the normals issue, kindly note that the Double-sided parameter is only partially supported by the GPU render engine. Additionally, please note that the Double-sided option is available for V-Ray BRDF materials (Advanced options). In respect to the legacy materials, the parameter is not exposed but enabled (in your case) and the reason CPU renders it as such."

[Micha]

Right, if I create a new material or diffuse layer, than this problem doesn't appear. But often I need to open old projects and to work on it again. I wished there would be a solution to fix this issue, maybe by a little script that set all

    <parameter handler="default" listType="none" type="bool" name="use_double_sided_mode" label="Enable double-sided mode">
     <value>0</value>

at 1.

Thank you Palosanto for your quote.

[palosanto]

Right, if I create a new material or diffuse layer, than this problem doesn't appear. But often I need to open old projects and to work on it again. I wished there would be a solution to fix this issue, maybe by a little script that set all

 <parameter handler="default" listType="none" type="bool" name="use_double_sided_mode" label="Enable double-sided mode">
<value>0</value>

at 1.

[Thank you Palosanto for your quote.

From Chaos response:

In respect to the legacy materials, the parameter is not exposed but enabled (in your case) and the reason CPU renders it as such.

For what I understand the v2 scenes when imported into v3 have the double sided parameter always enabled although hidden. The reason for the dark faces is not the parameter but the limitation of GPU renderer. That's why they render fine with CPU.
What would be ideal is an automatic conversion from layered material to BRDF in v2 so that it would read in v3 already as BRDF.

[Micha]

For what I understand the v2 scenes when imported into v3 have the double sided parameter always enabled although hidden. The reason for the dark faces is not the parameter but the limitation of GPU renderer.

This isn't so and you can test it. Take the simple standard material from my first post and the back faces are not right rendered. Now, edit the material and change the double side option and import this material and it works. So, the material isn't changed during the import and the GPU can render back sides, only it's a question to enable it at the material. So, the problem is quite easy and could be fixed - double sided isn't enabled per v2 default and will not be rendered until it is enabled.

[Micha]

Seems to be solved at VfR next.