Enhancement: ERS - Option to limit ERS to external perimeters and overhangs only

[igiannakas]

Description

Extrusion rate smoothing can materially help smooth out speed transitions during overhangs, leading to better external finish. This is similar to the latest bambu slicer release where speed transition smoothing has been introduced.

However current implementation applies smoothing to all features which will increase print time with marginal benefit visually.

Therefore, this PR introduces an option to limit ERS to the areas that are visible to the user, reducing print time impact.

Debating whether to enable this option by default when ERS is enabled, as internal features do not benefit much from extrusion rate smoothing compared to slowdown for overhangs that does materially benefit especially for printers with high accelerations, where PA cannot keep up with the requested speed changes over time.

Screenshots/Recordings/Graphs

Tests

Basic regression tests done-no adverse impact with it disabled to the existing feature. Enabled limits only to external perimeters & overhangs.

[lookypanda]

Hi, sounds as really cool feature!
Is there any way to somehow download the orca build with all three of your ERS improvements at once?
I would like to test it.

[igiannakas]

Yes I have them all on my dev branch here: https://github.com/igiannakas/OrcaSlicer/actions/runs/11783977166

[lookypanda]

Hi, @igiannakas . I tested a bit the build with your modifications.
Should ERS be applied on the top surface?
Because when the external perimeters option are ticked, ERS is not applied on the top surface, but maybe it could be useful there. (But I haven't tested how much the ERS is really needed on the top surface).

[igiannakas]

Nope it should only be applied to external perimeters specifically for overhang regions. To avoid artefacts from rapid acceleration and deceleration when moving in and away from sharp overhangs.

[lookypanda]

Over the past few days I have tested the build with all 3 new ERS improvements on about 5 prints.
No problems have been detected. ERS works as it should, slowing down before and after overhangs.
printer Ender 3 S1 on klipper
Thanks for a great work and a great feature!

[igiannakas]

These look perfect! Well done on taming the S1!!