Wasn’t this about how to use the background plate lop? Usually this is used to do exactly that - integrate cg onto a plate (still or video). Not sure why you would want to comp onto an environment hdr (I am sure you have good reasons).Also this setup is still valid for that. Use the setup to render your beauty/shadow aov and comp onto a background (which can be an hdr on a domelight you render in a separate go). For preview purposes just disable the backgroundplate lop & shadow catcher geo and you are good to go

No, the OP was asking about a Karma Shadow Matte and how to replicate the same effect that all other renderers are able to do quite easily, the background plate is some sort of convoluted way Houdini has created to tackle this issue, but it is not the same, if Houdini had a Shadow Matte material in the same context as other renderers like Arnold and Pixar's, the creation of shadows on a plane which on render causes the plane to become transparent but leaving the shadows on it visible, then the issue would be solved in a simple and easy way. I really don't understand why it's taking so long to achieve this material. Forget this background plate and just make the Shadow Matte Material which we can assign to a plane under the geometry so that it can catch the required shadows and display them in the beauty pass.
T.

This!
Keep it stupid simple.

Tser
No, the OP was asking about a Karma Shadow Matte and how to replicate the same effect that all other renderers are able to do quite easily, the background plate is some sort of convoluted way Houdini has created to tackle this issue, but it is not the same, if Houdini had a Shadow Matte material in the same context as other renderers like Arnold and Pixar's, the creation of shadows on a plane which on render causes the plane to become transparent but leaving the shadows on it visible, then the issue would be solved in a simple and easy way. I really don't understand why it's taking so long to achieve this material. Forget this background plate and just make the Shadow Matte Material which we can assign to a plane under the geometry so that it can catch the required shadows and display them in the beauty pass.
T.

While it did take me some time to understand how Houdini/Karma does this(coming from Vray) I have to say that i prefer this workflow (at least compared to vray). And then again, is it so much different than creating a shadowcatcher shader and assign it to a plane (or multiple object) and creating an aov for it? This is all the background plate lop does/is - pretty stupid simple

I don't think you understand what I/we need, you don't create a Shadow catcher Shader (Shadow Matte), you just assign it to the ground plane the same as you would any other available shader, you don't assign it to other objects in the scene, it does one thing and one thing only, that is capture the shadows which fall on the ground plane, extremely simple, you don't need to create AOV's and it's fast. If you use a Dome light with a 360 deg HDR image on it then the shadows captured by the ground plane simulates shadows superimposed on the Dome light's image, try doing that with the Background Plate. As you pan around, the 360 degree background image updates and you are submersed in a 3D environment where the shadows make the objects in the scene feel part of the 360 deg 3D background image. As said, the updating is very fast, even with my two rtx 2080ti's, not so much with the Houdini Background Plate.
T.

It seems I do not understand what you are after. Do you have any kind of example (video) that shows this working as you expect with another renderer (maybe even in another dcc).

Your text to link here... [www.sidefx.com]

So while this is not "simple stupid" I think it does what you want using cops/slapcomp. Be advised to look through the camera (and lock it) before hitting the slapcomp button or houdini will crash on you.

just figured out that this can be done without the slapcomp feature as well (still using cops).

Ron, thanks for the scene, it basically works, but as soon as you try to pan the scene Houdini 20.5.400 locks up and it has to be killed, also it is very slow, do you know why it crashes Houdini?

Tser
Ron, thanks for the scene, it basically works, but as soon as you try to pan the scene Houdini 20.5.400 locks up and it has to be killed, also it is very slow, do you know why it crashes Houdini?

If you are using XPU try to update driver. But yes, background plate node is slow when rendering high resolution in XPU.

Tser
Ron, thanks for the scene, it basically works, but as soon as you try to pan the scene Houdini 20.5.400 locks up and it has to be killed, also it is very slow, do you know why it crashes Houdini?

aleays make sure to look through the camera and have it lock so you don‘t step out of it. But saying I did find that this workflow is not very stable and especially camera moves are not fast as it has to run through a sops/cops setup to create the texture used on the background plate lop (not sure if did examine the setup, but it is not actually rendering the domelight but a texture on a sphere that is point constaint to the camera). So this is probe to be not as fast. Sure there is room for improvement improvment from sidefx (which might actually be a good idea for an rfe). Then again, we don‘t have the same requirement, and for the way we use the background plate it does work good. Just out of curiosity: are you rendering the domelight-background with the shadow and the rest of the scene in one go and this is your final result or is this just for preview purposes and better context?

Heileif

Tser
Ron, thanks for the scene, it basically works, but as soon as you try to pan the scene Houdini 20.5.400 locks up and it has to be killed, also it is very slow, do you know why it crashes Houdini?

If you are using XPU try to update driver. But yes, background plate node is slow when rendering high resolution in XPU.

I find that the background lop renderspeed has massively improved in 20.5 because of the adaptive sampling - so much so that we actually switched from 20 to 20.5 mid project (which would normally be a big no no). Concerning driver update: I have just been told by support to update to the latest (studio) version and it works great. There was a weird issue only a couple of weeks ago where the then latest studio driver would mess up color/shadow in the renders. This seems to be fixed now (with the driver, not workaround in houdini)

Hey Ron, the first scene background_plate_example_v02.hip doesn't crash Houdini only the last one.

"Just out of curiosity: are you rendering the domelight-background with the shadow and the rest of the scene in one go and this is your final result or is this just for preview purposes and better context? "

Yes, I am rendering the domelight background with the shadows and the rest of the scene, I use this in low rez for preview, then when happy I crank up the rez to 4k and render, it is very fast, I have created a .hda which uses 7xMask by feature nodes, a light emitting grid, an envlight, a shadow catcher grid and a material which takes the Masks and applies them to the shadow catcher grid to create its transparency.
This works very well and fast, but it's not a proper Shadow Matte material as what other renderers use.

Tser
Hey Ron, the first scene background_plate_example_v02.hip doesn't crash Houdini only the last one.

I just tested v3 in the latest production build and the latest daily build and they don't crash for me. Do you have the latest studio drivers installed? You might also wanna try and disable the cuda device (there are some variables for it I cant remember right now) to see if it is related to the gpu.

That being said, I found that using cops together with xpu is not the most stable (maybe because they both use the gpu). Let's see what the next major update brings...

I guess you already put in an RFE for a Shadow Matte material. If not, it might be a good idea to do so.

Hi Ron,I am running Houdini 20.5.400 in Rocky Linux 8.10 and it is extremely stable with everything I have thrown at it, but the back and forth stuff that is going on with the cop net seems to be too much, I haven't put in an RFE, but do it if you can.

Hi Guy's, I thought I would post a video I just made using the Arnold renderer in Solaris, the scene is very sparse and clean, only two objects, the sphere and the grid, the grid has the Shadow Matte material on it (from Arnold) and the Sphere has a chrome material, the Dome light has a hdri on it (blue_lagoon_8k.hdr) which you can get on line for free, there are no tricks or gimmicks here, the scene just works and it is fast on my two 2080ti's, I had to turn off the default denoiser in the render settings, that is all.
If Arnold can do this, why the hell can't Karma...
T.

Tser
I don't think you understand what I/we need, you don't create a Shadow catcher Shader (Shadow Matte), you just assign it to the ground plane the same as you would any other available shader, you don't assign it to other objects in the scene, it does one thing and one thing only, that is capture the shadows which fall on the ground plane, extremely simple, you don't need to create AOV's and it's fast. If you use a Dome light with a 360 deg HDR image on it then the shadows captured by the ground plane simulates shadows superimposed on the Dome light's image, try doing that with the Background Plate. As you pan around, the 360 degree background image updates and you are submersed in a 3D environment where the shadows make the objects in the scene feel part of the 360 deg 3D background image. As said, the updating is very fast, even with my two rtx 2080ti's, not so much with the Houdini Background Plate.
T.

+1 to this and previous post from Tser. I think the AOV workflow through "Background Plate [www.sidefx.com]" node has it's place when you are working with plates or footage and want to have finer adjustment, but if you just want simply to have a shadow on a transparent plane then the solution has to be simpler. Also, the above mentioned AOV workflow creates "holdout_shadows" pass but it doesn't have an alpha channel So you have to "Channel Copy" the alpha channel from the RGB to get the transparency, which although does the job is not 100% accurate I believe.

In Blender [www.youtube.com] (see video at 0:41) it's just one checkbox on a mesh to turn it into a "shadow catcher". Super simple and works right away. It would be amazing to have something similar in Houdini. Please SideFX!

I understand SideFX ide and Houdini is tool creator, here are parts make whatever you need alone. But having some tools right there helps users a ot. So keeping that freedom and option to create all fromunder the hud but also having ready made tools like this one check box is big step forward user friendliness