Mantra surface shader - mirror refl. with roughness <=0.3 | Forums

Forums Technical Discussion Mantra surface shader - mirror refl. with roughness <=0.3

Mantra surface shader - mirror refl. with roughness <=0.3

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ajz3d: Member; 654 posts; Joined: Aug. 2014; Offline

Nov. 26, 2015 4:21 p.m.

I'm experiencing a strange problem with Mantra Surface Shader. Whenever I bring roughness down to 0.3, the surface immediately becomes mirror-like. Tweaking it a little bit over 0.3, to something like 0.30000000000000004, results in correct shading.
Is this a bug or something? I'm using the latest production build (244.16)


ajz3d: Member; 654 posts; Joined: Aug. 2014; Offline

Nov. 26, 2015 5:01 p.m.

Roughness values lower or equal to 0.29999999999999993 don't cause any problems. It's just that 0.3. :shock:


mosssi: Member; 51 posts; Joined: Nov. 2015; Offline

Nov. 26, 2015 5:13 p.m.

0.3 is default value for roughness and its not a mirror roughness, so please upload your scene or a test scene so we can check if it has the same result on our systems.

2 x Xeon E5-2670 - 64 GB DDR3 RAM - Nvidia GTX 960 - Win 10 64x


ajz3d: Member; 654 posts; Joined: Aug. 2014; Offline

Nov. 26, 2015 5:41 p.m.

That's the problem. 0.3 as a mirror type of surface doesn't make any sense.
I temporarily moved my preferences directory, but the problem persists.
Anyway, I quickly assembled a test scene. The torus has 0.3 roughness but it renders as pure mirror. If I tweak it to ANYTHING else than 0.3, it renders fine. If I pipe in a roughness texture map, but keep roughness at 0.3, it renders as pure mirror too.
(Houdini Indie 15.244.16)

Attachments:
reflection_roughness_problem.hipnc (1.8 MB)


mosssi: Member; 51 posts; Joined: Nov. 2015; Offline

Nov. 26, 2015 5:49 p.m.

Your mantra surface metallic parameter is set to 1 and this the cause, (on reflect tab). maybe you saved this setting as default preset before, accidentally.

2 x Xeon E5-2670 - 64 GB DDR3 RAM - Nvidia GTX 960 - Win 10 64x


ajz3d: Member; 654 posts; Joined: Aug. 2014; Offline

Nov. 26, 2015 6 p.m.

I changed it to 1 on purpose in order to better visualize the problem with reflections. Lowering it down to 0 doesn't change anything if roughness is 0.3. It only makes the problem less visible, while the reflections are still super sharp.


mosssi: Member; 51 posts; Joined: Nov. 2015; Offline

Nov. 26, 2015 6:06 p.m.

In my system it renders ok. I don't know. maybe a bug then.

Attachments:
mirror.jpg (49.2 KB)

2 x Xeon E5-2670 - 64 GB DDR3 RAM - Nvidia GTX 960 - Win 10 64x


ajz3d: Member; 654 posts; Joined: Aug. 2014; Offline

Nov. 26, 2015 6:20 p.m.

mosssi
In my system it renders ok. I don't know. maybe a bug then.

Mossi, your screenshots show that it doesn't render ok.

Look how sharp are the reflections on both of your images. That's the same problem that I have. Try decreasing roughness to 0.29, render and then tweak it up to 0.31. You'll notice that in both cases the surface will get much rougher than when it was at 0.3.

Like on the images I'm attaching (with HDR envmap, to make it more visible).

Thanks for testing! This must be a bug.

Attachments:
mantra_surface_shader_roughness_problem.jpg (405.0 KB)


mosssi: Member; 51 posts; Joined: Nov. 2015; Offline

Nov. 26, 2015 6:29 p.m.

I didn't noticed that

Yes you are right, the 0.3 is exactly the 0 roughness. so this is probably a bug. let me dive inside to check why.
and I'm on Houdini 15.0.301 so that's strange if they didn't noticed that.

2 x Xeon E5-2670 - 64 GB DDR3 RAM - Nvidia GTX 960 - Win 10 64x


ajz3d: Member; 654 posts; Joined: Aug. 2014; Offline

Nov. 26, 2015 6:32 p.m.

mosssi
let me dive inside to check why.

Awesome!

I'm curious why it's 0.3. Why not 0.5, 0.2 or some other value.


mosssi: Member; 51 posts; Joined: Nov. 2015; Offline

Nov. 26, 2015 6:48 p.m.

I think the parameter that imports roughness from user is disabled by default. I replaced it with a new parameter and it works fine. that's maybe for the expression in disable when field. and also when you check use this node to set parameter its ok. but really why, I don't understand.

Attachments:
mirror.jpg (96.6 KB)

2 x Xeon E5-2670 - 64 GB DDR3 RAM - Nvidia GTX 960 - Win 10 64x


ajz3d: Member; 654 posts; Joined: Aug. 2014; Offline

Nov. 26, 2015 7:46 p.m.

Fantastic. Many thanks Mosssi for investigating this issue. Use This Node to Set Parameter Attributes seems to fix the roughness and I didn't even have to replace the parameter with a new one.


KaiStavginski: Staff; 664 posts; Joined: Aug. 2013; Offline

Nov. 27, 2015 1:58 a.m.

We got a report about this already and I'm looking into it. I can reproduce it as well.

Kai Stavginski
Senior Technical Director
SideFX


mosssi: Member; 51 posts; Joined: Nov. 2015; Offline

Nov. 27, 2015 4:57 a.m.

Thank you KaiStavginski

2 x Xeon E5-2670 - 64 GB DDR3 RAM - Nvidia GTX 960 - Win 10 64x


ajz3d: Member; 654 posts; Joined: Aug. 2014; Offline

Nov. 27, 2015 10:13 a.m.

KaiStavginski
We got a report about this already and I'm looking into it. I can reproduce it as well.

Thank you!

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