Is there a way in Karma to do cameraprojection in shader (or for that matter any kind of projection)?

Yes, use a USDCoordsys to create a reference coordinate system, then in the shader use that coordsys' name in a space parameter on one of the mtlx transform nodes or on the mtlx position directly.

Thanks for the pointer. I also found an example in the docs but boy do I not understand how that works and why it needs to be setup in that way. For example why does it only work if the material is parented under the "World" primitive?

ronald_a
For example why does it only work if the material is parented under the "World" primitive?

yeah, it's kind of annoying that the hierarchy is restricted this way due to some USD reasons. The material, camera, and target need to be able to find the coordsys, and they can't find it if they don't share a common ancestor. USD is 'rootless' so without creating a true root, for example the 'world' primitive, the prims won't share a common ancestor.

jsmack
USD is 'rootless'

I believe it's spelled ruthless, at least from my experience

jsmack
The material, camera, and target need to be able to find the coordsys, and they can't find it if they don't share a common ancestor

The camera doesn't need to live in the same hierarchy. As for the rest of that, we're looking into a possible implementation issue in Karma. For *now*, yes, the coordsys binding should be applied on a parent prim common to the geometry & material.

jsmack
Yes, use a USDCoordsys to create a reference coordinate system, then in the shader use that coordsys' name in a space parameter on one of the mtlx transform nodes or on the mtlx position directly.

May I ask how to assemble this USDCoordsys in materialx shader builder?
I need to project a displacement map on geo.

I can't get this to work, and I even thing I've done exactly as the sample scene in the docs.

I've attached a screenshot which I hope describes it well. I'm using a single image which I'm trying to project from the camera shown in the viewport. But I must be doing something wrong as all attempts as failed

I'm using Houdini 20.0.724 ( linux )

We have hoped to put Karma in production soon, but this is a big stopper for us as we do a lot of camera projections. But I'm sure I'm doing something wrong.

regadrs
stefan

Solved, I just needed it to part of the root of the asset. Took me a while to understand the whole "rootless" comments. And attached a screenshot where it's illustrated.

The main issue now is that it's projecting also to the backfaces, and that it doesn't match the aspect of the camera. I've set the aspect to 1:1 but it seems to use something else and doesn't really react to change any of the paramters.
It only matches if the projection is 16:9

I hope the camera projection tools will be updated in the near future. It's really a must for DMP/environment and shot refinements.

regards
stefan

Hi Stefan, can you share your problematic scene? Have a look at the attached and scrub the timeline (I've linked the camera aspect ratio to the frame).

With the swift help from support I found that the issue is solved in a later production build. The problem I had is that we are locked to and earlier build due to some plugins. So in the latest build it’s not a problem.

Thanks for the example scene though!

Regards
Stefan

robp_sidefx
Hi Stefan, can you share your problematic scene? Have a look at the attached and scrub the timeline (I've linked the camera aspect ratio to the frame).

hey rob,

i set up a projection scene too with some old aproach via script. now i see this, which is a little nicer but does the same via ndc. my question is, how to get UVs from this, to be able to view the projection shader in Vulkan. because only working in karma has downsides. in vulkan you can see edges of geometry, no loading times and its way faster.

thx