Performance degraded for PointInstancer when using depth peeling mode

[csyshing]

Describe the bug

Hi,

Our production has reported a performance degrade when switching from default 'object sorting' to 'depth peeling'.
This happens for PointInstancer but seems better for non-instanced prims.

Example - non-instanced prims: all the tiny cubes in the viewport are just regular prims:

• 🆗Navigate the viewport on 'object sorting' in smooth shaded mode: performs reasonable;
• 🆗Navigate the viewport on 'object sorting' in wireframe mode: performs reasonable;
• 🆗Switch to 'depth peeling', without changing display mode: performs reasonable;
• 🆗Then switch to either smooth shaded or wireframe mode: becomes unresponsive at first and then becomes reasonable later, Maya might be doing something at the beginning but as long as the viewport responses normally, I think it's acceptable.

Example - PointInstancer prims: all the tiny cubes positions & numbers match exactly the non-instanced example:

• 🆗Navigate the viewport on 'object sorting' in smooth shaded mode: performs reasonable;
• 🆗Navigate the viewport on 'object sorting' in wireframe mode: performs reasonable;
• 🆗Switch to 'depth peeling', without changing display mode: performs reasonable;
• 🚫Then switch to either smooth shaded or wireframe mode: becomes unresponsive, needs to wait for much longer than non-instanced example until Maya UI responses, but then keep navigating the viewport, it's still unresponsive for a long time before coming back to user.

Example - Navite Maya geometries: imported (converted) from non-instanced example into Maya as native geometries, just for reference:

• No matter which transparency mode and/or shading mode combination, viewport runs quite good actually.

Steps to reproduce
Steps to reproduce the behavior:

1. Launch Maya and load either the example USD file example_non_instanced_prims.usda or example_point_instancer.usda
2. Change the transparency mode from default 'object sorting' to 'depth peeling'
3. Switch viewport shading mode to either smooth shaded or wireframe mode
4. Navigate in the viewport and observe the responsive time

Expected behavior
Improve the viewport performance for PointInstancer when using depth peeling mode.

Attachments
Example USD files:
performance_degrade_example_USD_files.zip

Specs (if applicable):

• OS & version: CentOS 7.8
• Compiler & version: gcc 6.3
• Maya version: Tested on Maya 2022 / 2023.3
• Maya USD commit SHA: Tested on official v0.23.0 / v0.26.0 / v0.30.0
• Pixar USD commit SHA: Tested on official USD-22.05/24.03

[wallworm]

Thank you for reporting.