Camera projection shader does not work

[xsisupport]

Describe the bug
In the Solaris viewport, the camera projection shader always uses the render camera. An exported USD file has the wrong camera name for the projection shader ("/stage/projection_camera" instead of "/cameras/projection_camera"). An HDARNOLD_DEBUG_SCENE ass file has no an empty camera_projection.camera parameter.

To Reproduce
Steps to reproduce the behavior:

1. You can load the attached Houdini scene. Or kick the attached usd file.

camera_projection_test.zip

Used Software Versions

• Houdini 20.0.688 with latest HtoA

[BigRoy]

Is this a regression recently?

I recall in Houdini 20.0.590 with HtoA 6.2.5.2 to be able to do camera shader projections - however one had to manually disable some of the default expressions the materials would make in LOP material networks because it'd always assume you want geometry level objects but I believe specifying actually USD prim paths did work fine in our renders at the time?

[autodesk-oss-arnold-bot]

Issue synced internally to ARNOLD-15174

[cpichard]

Hi, it looks like the projection is working fine, however the Arnold Camera Projection houdini node is taking an operator for its camera value instead of a stage path. The aspect ratio also seems wrong at a first glance.

[cpichard]

[cpichard]

It is using the classic htoa way of selecting cameras, we need to translate somehow the operator path to the stage path.
I moved this ticket to HTOA: HTOA-2635

[BigRoy]

The aspect ratio also seems wrong at a first glance.

Ah yes, that's correct - we removed the expression and just entered the valid USD path.
So it's mostly "cosmetic" on the Houdini side - the actual render translation logic does work.

Basically:

• Allow the Houdini parm's picker to pick the USD stage Prim instead of Houdini Operator
• Update the Aspect Ratio expression to not rely on Houdini nodes/operators but on the camera prims inside the USD stage.