Combine infill feature only works if both infill extruder parameters are equal

[BaconFase]

Description of the bug

Usecase:

Any print where the top and bottom of a model is expected to use the same extruder(material/color) as the side perimeters (So bascially most prints) that would also like to leverage the infill combination feature.

Problem:

The combine infill feature does not work as expected if Infill extruder and Solid infill extruder are not set to the same extruder.

Fix:

Decouple the Solid infill extruder from the infill combination feature.

Solid infill is [usually] the top and bottom of a print which is expected to be the same as perimeters anyway. Infill combination feature is expected to only affect the inner-supporting structure, not anything outwardly visible.

Project file & How to reproduce

EXAMPLE Multi Diameter Height Material Print.zip

Set project to combine infill every 3 layers (.6mm layer height infill):

When the two infill parameters do not match each other, the infill stays printed with .2mm layer height:

When the two infill parameters do match each other, infill is printed with expected .6mm layer height:

Checklist of files included above

• Project file
• Screenshot

Version of PrusaSlicer

2.9.2

Operating system

Windows 10 Pro

Printer model

Prusa XL-5T

[BaconFase]

The secondary problem caused from this issue is the visible solid infill is "incorrect".

Not painted. All just default faces:

Result.The top of the model is different from the side perimeters which is unwanted but a result of having to equal both infill parameters.

The workaround is using the painter tool to paint the top and bottom faces to the same extruder as the side perimeters:

This is the wanted and expected:

Easy workaround for a cube. Not so easy the more complex/organic the model is.

[jimmysun2000]

It looks like the maximum height infill combination can do is limited by the smaller of the two extruders (infill & solid infill). Which means even if you have a 0.6mm nozzle for infill, it will only combine up to 0.2mm, which is your solid infill nozzle.

I have created a pull request #14566 that decouples solid infill from the infill combination feature, because solid infills are usually on the outside of the print as you described.