Hello Houdini Community,

I am setting up Tech Tests for the student project we are running at university. We are studying Film VFX so our pipeline mainly consist of tools used in that pipeline. Maya for modelling and animation, Mari for texturing, Nuke for compositing, Houdini for simulations and Solaris for lookdev and rendering.
Since we had trouble with color spaces in the past, I made a clean scene just for this purpose. It has a card, with an unlit material (only emission enabled) and the color checker from Nuke used as the texture.

My export from Nuke:
- sRGB color space PNG
- linear/raw EXR

When I import these images back to Nuke, they match color nearly perfectly (minimal clamping due to sRGB).

I made two setup for the material, one using the PNG with color space set to sRGB and the one with the EXR using raw as color space.

When I'm using PNG as the texture and in my karmarendersettings I am exporting the rendered frame as PNG it matches up in Nuke. Same applies for using EXR texture and rendering out an EXR (set to Raw in export).

The issue comes when I am saving my render as EXR and I am using the PNG material. Also reversed, so EXR texture and exporting to PNG. From my understanding setting the input color space properly is there to make sure colors are correct so I am not sure why my exports differ.

PNG texture (sRGB) - Render saved as EXR (Raw)


EXR texture (Raw) - Render saved as PNG (sRGB)


If my setup would be correct/would work correctly the two images look identical with colors. This is what I am looking for help with.

Renders:





If I can help with some other information for the project or settings I did not send, please don't hesitate to reach out.
Thank you for your guidance in advance!

Máté Dömötör

Hi everyone,

I recently created an HDA based on a Karma Material Builder, which I wanted to use as a preset in Solaris. However, the HDA never appeared in the Material Library LOP’s Tab menu, even though the asset was installed correctly.

The actual requirement for the Material Library to pick up a custom Material Builder is very simple:
The Material Library will only list HDAs whose names match the pattern defined in its Tab Menu Mask. By default this includes *builder, but you’re not limited to that. You can use any custom naming convention for your HDA and simply add that keyword to the Material Library’s Tab Menu Mask. If you want to keep this setup permanently, you can also save your customized Material Library node as the new permanent default, so it always uses your preferred mask and automatically recognizes your custom material assets.

In my case, I also wanted two additional behaviors for convenience:

the node should automatically be editable when created

the Material flag should be enabled

These are not required by Solaris, but they improve the usability of the asset. To achieve this, I added the following OnCreated Python script inside the HDA:

lop_node = hou.pwd()
node = kwargs
node.allowEditingOfContents()
node.setGenericFlag(hou.nodeFlag.Material, True)

With the correct naming and the optional setup script in place, the HDA finally appeared inside the Material Library and behaved exactly the way I wanted. I’m sharing this in case anyone else runs into the same issue or wants similar behavior for custom Material Builder HDAs.

Added a skylight to my scene and now my viewport and MPlay look like this



Smoke seems to stop rendering properly if I add any light to the scene

I have an rx 7900xtx, anyone else have this issue/know of a fix?

I can not see a volume in the viewport at the Dynamics level when using v.20.5.684 on Mac OSX, only at the Geometry level. When I use the Gas Axis Force node micro solver, only the widget shows at Dynamics level, although it does affect the simulation.

Would this be a bug or a limitation of the MAC OSX or some setting I need to change. It does show in v18.5 on a Mac, so it does not seem to be related to a Mac.

I had to upgrade from an earlier version to fix another viewport bug that was not recognising a light when using volumes. This version fixed that issue.

Hi guys,
When could we expect to get copernicus shader preset?

Thank you.

I created a uvrange handle using Type Properties. It works fine in Scene View but I would like to display it in UV View. Is this even possible?

Hello to whoever is reading this post.

I have ran into an issue.

Whenever I want to import groom cache (alembic file) from Houdini hair gen node to Unreal 5 I only get the first frame, static mesh and no groom cache, but if I cache it out from the guide groom node, everything suddenly is alright, Unreal 5 reads it fine and imports the groom cache (strand cache).

I don't use skin for this groom simulation in Houdini, since it's a vellum simulation out of lines (you can see it in the screenshot I attached), I use this simulation as my guides in guide groom and then I use the guide groom for my hair generation in hair gen node?

Am I missing something?

Hello,
I'm trying to setup hqueue server/client.
I followed this steps to change the user account on which the client should starts: https://www.sidefx.com/docs/houdini/hqueue/faqs.html#change_client_user_account_windows [www.sidefx.com]
But the client always starts with user "hquser" (as shown in the server page), no matter the user I setup via task scheduler. The hqueue client service is not visible in services either. Am I missing something?.
Thank you
Jose

Hi peoples,

I'm currently trying to create a little tool that should be accessible from within MPlay. Therefore I created a new MainMenuMPlay.xml, added a sub menu and created a script item to call my little python script. Unfortunately MPlay doesn't seem to correctly inherit the main houdini session's environment anymore.
results in "untitled".
The only "HIP-related" env variable that seems to work is "HIP".
correctly prints the directory where my hipfile is located.

I'm using Houdini 21.0.440 (default python 3.11). I'm pretty sure this has worked in the past, does anybody have a clue if this is a bug or if there's some workaround for this?

Any help appreciated!

Cheers

Michael

Hello,
I am looking for a really simple example of a graph where two FK skeletons can control and blend each other’s transforms dynamically in animation. How can I copy the transformations from one to the other (and vice-versa)?

And how to implement the same functionality in my rig, as we see on the picture - the IK switch and match xform. Is it only graph setup on there is additional script somehow controlling the process

Hi everyone, my name is Alessandra.

I’m having an issue with a Karma render in Houdini 21.
I’m rendering a laser effect created with the new Pyro Thruster Exhaust, set up using two separate pyro nodes.

What I’d like to do is export two different passes (AOVs) for these two nodes, so I can adjust each one separately in compositing.
Ideally, I’d prefer to keep everything in a single render instead of rendering each pyro element separately.

Has anyone done something similar or found a good workflow for isolating multiple pyro sources in Karma?
Any tips or best practices would be greatly appreciated.

Thanks in advance for your help!

— Alessandra

I spent an entire day trying to import a character animation created in APEX into Solaris. Everything else works fine, but I just can’t find a way to export the blend shape data.

Is it possible to use kinefx to pose a mesh then export that mesh out as static geometry? Use case for this is being able to match the pose of some clothing assets from a marketplace to my reference character so I can easily align the cloth and transfer weights to the cloth.

Hi everyone,

I’m a Houdini enthusiast and have been exploring the new Shadow Catcher workflow in Karma (since Houdini 21). First of all, I appreciate the improvements; it seems largely based on the old background plate workflow, giving holdout geometry a matte material that allows shadows to appear while maintaining visibility in the viewport.

However, I’ve run into a problem with certain layered rendering workflows. Here’s the setup:

* I have a scene with a ground environment, debris, and an explosion.
* The scene requires layered rendering so that each element can be rendered separately, while still allowing other objects to contribute shadows for compositing.

My rendering workflow is as follows:

1. **Ground pass:** Render the clean ground only, using a prune node to disable other objects.
2. **Debris pass:** Disable the explosion via prune, set the ground as a holdout matte, and output the required AOVs: `beauty`, `holdout_shadow`, `holdout_reflect`, etc.
3. **Explosion pass:** Set both ground and debris as holdout matte, then output AOVs: `beauty`, `holdout_shadow`, `holdout_reflect`, etc.

Because volume rendering is extremely time-consuming, I only render the explosion once. This workflow allows me to get the beauty of each element and the corresponding `holdout_shadow` / `holdout_reflect` AOVs for compositing.

**The problem:**

* When the holdout is set to **Matte**, the `holdout_shadow` AOV **includes shadows cast by the holdout geometry onto itself**, which is undesirable for compositing.
* If the holdout is set to **Background**, the `holdout_shadow` AOV **no longer includes the holdout’s shadows at all**, meaning the holdout geometry does not cast shadows onto any other object — which is a critical issue for compositing layered elements correctly.

In short, with the current implementation, it’s difficult (or impossible) to achieve a workflow where:

1. The holdout remains a matte for visibility and indirect contribution (reflections, indirect lighting).
2. `holdout_shadow` includes **only shadows from other objects**, excluding self-shadow from the holdout itself.

This limitation makes compositing layered renders in Karma challenging, especially for complex scenes with debris, explosions, and volumetrics.

I would greatly appreciate any insights, workarounds, or guidance from the community or SideFX engineers on how to handle this scenario efficiently in Karma.

Thanks in advance!

Hey guys! Bit of a more technical problem I'm stuck on:

I used Hydro FX storm for my fluid simulation. I then exported out a surface vdb and alembic particles.

How do I get the surface VDB and the particles .ABC to feed into the Houdini whitewater source SOP? My goal is to then use it for the whitewater solver.

I'm trying to unpack the alembic particles, which seem to be working ok. added an attribute wrangle for pscale which I think whitewater source needs? Very confused about the VDB though, It has the information but when I tried using it in the whitewater source nothing happened.

Hi!

I've got about 100 cameras in my scene. I made a script that gives a list of all cameras that can see a specifique geo/asset. I wanted to know how to use my list in the Find Node window to find all cameras...

...As I was writing this post, I found it! You need to use | like this:

Camera_A | Camera_B | Camera_Z

-Olivier

I'm trying to render a ripple simulation in Mantra. I've created bgeos from the simulation, and I added an ocean shader. However, when I tried rendering it out in Mantra,I didn't see anything even in the alpha channel. How do I render out this simulation so I can actually see it in Mantra?

Hi everyone,

We built a page and tool that lets you copy and paste Houdini node recipes from the website directly into any Houdini context. So far we've compiled a small collection of recipes we use in our projects. Check it out here: https://codercat.xyz/cookbook/ [codercat.xyz]

Hello There,
I’ve been experimenting with animation on H21, and while the tool has quite matured since the last version of Houdini, I’m having trouble with my workflow involving animating cycles. Most of the tools currently available in the scene animation are either buggy or unfriendly for that kind of workflow.

I tried to report some of these bugs, but they haven’t been addressed in a while, as I have been told that the problem is how the feature I’m trying to use works and why they aren’t just bugs. So I’d like to discuss my problem here in the hope that these will be addressed in a future Houdini update.

My workflow involves doing a lot of small cycle animations, often very simple; each cycle usually lasts between 1 to 5 seconds, and often involves using a limited number of keys that form a sinusoidal shape, relying on the tangent handles to tweak it.

To demonstrate, here is a little gif showing the idea:
and the curve (for demonstration purposes, I’ll limit to showing the X axis only; notice that this is an extreme case demonstration, where every key has a very specific tangent defined, including the first and last key): .

If I want to mirror that motion to the mirror controller, I can use the mirror with plane tool and the bake feature. That’s where the problem starts:
To mirror this animation, I have to use the ‘bake’ tool, which forces me to: resample keys, break the tangents of the first and last frame, and worse: break the tangents of the first and last key of ALL my controllers.

Target Motion Curve:

Original Controller Curve (and any other controller that had a specific tangent defined):

The information of the animation is entirely lost.

Using the Mirror tool to bake the motion of one controller to another will break EVERY tangent information from the first and last key of all my controllers; that’s a very destructive process.

I understand that I can avoid this “every controller gets rebaked” by baking information into a new layer, but that’s not something I want to do. I wish to mirror my animation into the opposite side controller and keep working on both without the hassle of a layer.

When I mirror a controller, I want to keep all my keys as they are. My source controller has 4 keys with manually defined tangents; I would like my target controller to also end with 4 keys and their manually defined tangents, as I’d still wish to tweak the motion once mirrored. I do not want to resample my keys.

It would also be very convenient if, when the channel extrapolation is set to “Cycle”, the auto-tangent would automatically guess the slope based on the extrapolation information, as it’s currently something I have to manually set every time I tweak a key.




I’ve been trying to explore alternatives, for example by constraining each controller to a custom-made constraint where the motion is defined in terms of placing controls in key positions, as such:
.
However, there seem to be several limitations in what is possible with constraint currently :

- None of the SplineResample/Interpolate nodes in Apex feature ‘closed loop’ mode. Or lets you output the interpolated rotation information from the input matrix ( I want my constraint's controller rotation to describe the rotation of the driven controller, rather than follow the curve's own tangent)
- There is no way to sample an attribute using primuv (aside from using a vexsnippet in Apex, which is eww), so I can’t get the rotation information I actually want from the curve.
- There’s no way to output a visualizer shape in a custom constraint, making it difficult to accurately edit the motion curve during animation.

This is my two cents about a niche workflow. It’s more of a ‘video game’ focused workflow, but when it’s 80% of what you do, these few points would mean a lot if they could be addressed in the futur!

Thanks for reading

Hi!

I had a presentation on our Pax Dei world generation pipeline at the Everything Procedural Conference last April.

If you're interested in large scale game world generation, procedural techniques, Houdini and Unreal, take a look!

https://www.youtube.com/watch?v=Vlyt8lDx-Zk&t=5s [www.youtube.com]