How to create a double-sided material in Karma?

Forums Solaris and Karma How to create a double-sided material in Karma?

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cheesetroyer: Member; 53 posts; Joined: Nov. 2016; Offline

Nov. 30, 2023 11:05 a.m.

Can someone explain to me how I can create and apply a double-sided material to in Karma?

I found a post on this forum, but it didn't make it understandable for me.


Enivob: Member; 2631 posts; Joined: June 2008; Offline

Nov. 30, 2023 1:05 p.m.

You'd think the kma_ray_import would offer some type of 0-1 output value you could use to drive the bias on a mtlxMix. Can't figure it out yet. Some way to fetch the sign of the magnitude of ray:direction then remap that into 0-1?

Using Houdini Indie 20.0
Windows 11 64GB Ryzen 16 core.
nVidia 3050RTX 8BG RAM.


jsmack: Member; 8045 posts; Joined: Sept. 2011; Offline

Nov. 30, 2023 2:04 p.m.

Enivob
You'd think the kma_ray_import would offer some type of 0-1 output value you could use to drive the bias on a mtlxMix. Can't figure it out yet. Some way to fetch the sign of the magnitude of ray:direction then remap that into 0-1?

N.I plugged into a greaterthan(0) should do it


cheesetroyer: Member; 53 posts; Joined: Nov. 2016; Offline

Dec. 1, 2023 3:14 a.m.

Would someone be willing to give a more detailed explanation on how to do this?


Enivob: Member; 2631 posts; Joined: June 2008; Offline

Dec. 1, 2023 5:12 p.m.

I tried this type of setup, but couldn't get it to work. N.I means reference the ray normal and export it using an integer signature, right?

Attachments:
Untitled-1.jpg (292.3 KB)
ap_kr_two_sided_grid_image_120123.hiplc (716.5 KB)

Using Houdini Indie 20.0
Windows 11 64GB Ryzen 16 core.
nVidia 3050RTX 8BG RAM.


jsmack: Member; 8045 posts; Joined: Sept. 2011; Offline

Dec. 1, 2023 10:28 p.m.

Enivob
N.I means reference the ray normal and export it using an integer

no, it means N dot I, as in dot product of the ray direction and the surface normal


Enivob: Member; 2631 posts; Joined: June 2008; Offline

Dec. 4, 2023 12:32 p.m.

Getting close with your suggestion. I see some purple, but I need red on one side and blue on the other.

Attachments:
ap_kr_two_sided_grid_image_120123.hiplc (737.3 KB)
Untitled-1.jpg (321.8 KB)

Using Houdini Indie 20.0
Windows 11 64GB Ryzen 16 core.
nVidia 3050RTX 8BG RAM.


jsmack: Member; 8045 posts; Joined: Sept. 2011; Offline

Dec. 4, 2023 1:34 p.m.

Enivob
Getting close with your suggestion. I see some purple, but I need red on one side and blue on the other.

What is the input range of the remap set to? it should be something like -0.000001, 0.000001 to 0, 1 and clamped to simulate a switch. The ifgreater would be a better choice.


jomaro: Member; 102 posts; Joined: April 2017; Offline

Dec. 4, 2023 3:55 p.m.

I don't know maybe this is the setup you are after?
I think this is not yet supported by XPU

Edited by jomaro - Dec. 4, 2023 16:10:36


jsmack: Member; 8045 posts; Joined: Sept. 2011; Offline

Dec. 4, 2023 4:27 p.m.

jomaro
I don't know maybe this is the setup you are after?
I think this is not yet supported by XPU

That node isn't supported in XPU, but it's trivial to emulate it using switches going into a standard material.


Enivob: Member; 2631 posts; Joined: June 2008; Offline

Dec. 4, 2023 5:13 p.m.

@jsmack I tried the very small range numbers and very large. The greaterif didn't seem to help either.

I just wonder if the ray_import is actually working?

@jamaro Your method certainly works for CPU only render.

Edited by Enivob - Dec. 4, 2023 17:17:35

Using Houdini Indie 20.0
Windows 11 64GB Ryzen 16 core.
nVidia 3050RTX 8BG RAM.


jsmack: Member; 8045 posts; Joined: Sept. 2011; Offline

Dec. 4, 2023 7:15 p.m.

Enivob
I just wonder if the ray_import is actually working?

hmm, it's possible that's the issue. There are presets in the menu that should work for getting the ray direction though. I recently used it for making a fresnel blend, since one is missing in the factory node set.


antc: Member; 339 posts; Joined: Nov. 2013; Online

Dec. 4, 2023 7:31 p.m.

rayimport seems to be working for me with xpu (on Mac OS tho)

Attachments:
rayimport.png (693.1 KB)


jsmack: Member; 8045 posts; Joined: Sept. 2011; Offline

Dec. 4, 2023 7:43 p.m.

Working fine here as well.

Attachments:
karma_twosided.hip (248.5 KB)
twoside.jpg (233.1 KB)


Enivob: Member; 2631 posts; Joined: June 2008; Offline

Dec. 5, 2023 8:37 a.m.

That was it. Thanks, everyone!

I was using ray:hitN instead of mtlxNormal node. I guess hitN is not the same as the geometry normal.

Using Houdini Indie 20.0
Windows 11 64GB Ryzen 16 core.
nVidia 3050RTX 8BG RAM.


cheesetroyer: Member; 53 posts; Joined: Nov. 2016; Offline

Dec. 6, 2023 12:24 p.m.

Thank you guys very much!


boning: Member; 19 posts; Joined: July 2018; Offline

Dec. 26, 2023 10:37 a.m.

There's a simpler way other then using 2 rayimport and dot product. You can directly using ray:backface to get a bool. This is listed in the documentation of the rayimport node, but don't know why it's not listed in the drop down menu probably is a bug.


CalvinJor: Member; 1 posts; Joined: April 2024; Offline

Nov. 4, 2024 11:54 p.m.

What should I do if I wanna put a roughness or normal texture on it??


alli13: Member; 7 posts; Joined: Sept. 2020; Offline

Nov. 12, 2024 4:48 p.m.

CalvinJor
What should I do if I wanna put a roughness or normal texture on it??

Just use it as a switch input instead of plugging it directly.


YuRock: Member; 2 posts; Joined: April 2019; Offline

Nov. 17, 2024 8:16 a.m.

Thanks for the advice, but what if I need 2 different shaders (materials) on different sides, and not just 2 different pictures, colors?

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