Hello fellows.

I am new to rendering in Mantra and noticed an issue with the “mantra surface” shader:

When I render with a default mantra surface shader, the reflections are very defined or specular. the reflection “roughness” is set to .3 by default. (see attached image).

The problem is, when I try to make a slightly more diffuse reflection, even by increasing the “roughness” to .3000001, the result is a muuuch more difusse reflection (see other attached image).

So my question is: Is there a way of achieving a middle ground? maybe I am missing something obvious.

Hopefully someone can help me with this issue.

Thanks in advanced!

Sorry I haven't got a solution to what you've posted (which is odd indeed), but have you tried using the Principled Shader? I find it much more controllable 90% of the time

Hi, what build of Houdini are you using? There was a bug with the mantra surface shader's roughness (when set to exactly 0.3) but it's been fixed in the latest build. (15.0.393)

I agree with Carlo_C above, the Principled Shader is good option but as I use a metal/roughness workflow, I have some issues with them both…

The Mantra Surface Shader doesn't really work with a Metal/Roughness texturing workflow.
The Principled Shader doesn't display metallic materials properly in the OpenGL Viewport.

Both of these issues relate to the Metallic (mantra setting or Principled preview) using specular colour/maps instead of diffuse maps.

To answer your initial question, if you are using an older build, ignore the bugged 0.3 roughness results and work with any other values. ie. Bugged 0.3 is the same as 0 roughness. Your 0.300001 result is correct so in-between the two is 0.15 roughness.

Hope that helps
Rob

@Carlo_C: I haven't tried the Principled shader, I will give it a try, thanks.

@robsdesign: I am currently using build 15.02.244.16, I will update and hope to have more luck.

Thanks for the replies guys.