Warping fails on driver version > 460.91, Blending still works

Hi,
I have a dome projection setup with 4 projectors connected with 4 dvi cables each to 4 identical Dell Precision workstations with Quadro P5000 cards running Ubuntu 20.04. I adapted the nv-control-warpblend code to read my own warp matrix and blend image to apply the corrections according to the camera based calibration. This worked very well until I updated the driver to 495.44 from the graphics-drivers ppa. Since then only the blending image is applied to the image but not warp matrix. To verify the behaviour I cloned nvidia-settings repository, compiled the code and tried the nv-control-warpblend executable but with no success: the blend image is applied but the image remains unwarped. Due to the hight resolution each projector is connected with 4 dvi cables to the graphics card and each projector appears as 4 screens with 1024x2400 pixel resolution. For debugging purpose only 3 screens of the projectors are connected while the 4th is output is connected to a normal monitor. Each of the screens is warped and blended separately and the warpmatrix and blend image must be split accordingly. As said, up to version 460.91.03 this works very well.
Unwarped Desktop (left), correctly warped (driver version 460.91.03, center), only blended (driver version 495.44, right):


I already posted an issue on the nvidia-settings github repository (GitHub - NVIDIA/nvidia-settings: NVIDIA driver control panel) where the XNVCtrl API and corresponding examples can be downloaded. Can anybody confirm this error and knows how to fix it or whom to contact?

Cheers,
HellG

Since the nvidia-settings github repo is maintained by aplattner, I guess the correct nvidia officials should know.
Furthermore, this
https://forums.developer.nvidia.com/t/does-warp-blend-work-on-quadro-k4000/190444
looks like it’s been an issue with the Windows drivers as well and is being addressed.

The issue on Windows with driver 466 has been verified and it should be fixed also in the linux driver 470.86 (see Problem with WarpBlendSample.exe on Quadro k4000). However it does not work for drivers 495.44 and the thread is closed.

Dear @HellGL

Thanks for tagging the relevant thread. I will go through your problem description and forward it to the correct team. Please give us some time for the internal investigation.

Thank you.
NVIDIA Forum Moderator