Instancer Motion Blur not working on first render in interactive mode

[cpichard]

Describe the bug
When we render with the render delegate in interactive mode, the motion blur is not working. Changing frame will reenable it.

To Reproduce
Steps to reproduce the behavior:

1. In houdini 20.5 with htoa 5.3.7, use the attach scene and render with arnold render delegate.

Used Software Versions

• Arnold: [7.3.7.0 +]
• USD: [24.11]

[autodesk-oss-arnold-bot]

Issue synced internally to ARNOLD-16223

[cpichard]

After some debugging it looks like the instancer primvars are correctly sampled but the function HdArnoldUnboxResample used to resample the values uniformly in time is passed an incorrect shutter range. The shutter range is coming from the renderParams and at this stage of the scene evaluation is is not correctly set.

[cpichard]

Hi @marcantoinep, this should be fixed in the next bug release version (could be 7.4.1.1)