Fix M166 Gradient Mix on delta printers

[Kadah]

Description

The updates for M166 gradient mix on delta printers use the z tower stepper position instead of the toolhead cartesian z position. This leads to current gradient mix being constantly changing during a single layer as seen here and results in the gradient being rotated and offset.

Example:

I am not sure if the fix I have made is the correct way to do it. I have been running with this patch and it does fix the issue. This likely creates additional cycles with having to call for a forward kinematics update more often, though a delta+mixing setup should already preclude 8-bit controllers.

Benefits

Allows M166 to work as intended on delta printers.

Configurations

RGB_Delta.zip

Related Issues

#18917

[Kadah]

Workflow failed due to error when trying to comment and close this for release target. Closing.

[thisiskeithb]

delta+mixing setup should already preclude 8-bit controllers.

If you wanted to be extra cautious, you could add a sanity check to warn AVR users that a delta + mixing is ill-advised.

[Kadah]

Corrected RP #19285