2.9.0-alpha1 incorrect calculation of volumetric flow rate

[h4lf]

Description of the bug

Incorrect calculation of volumetric flow rate for some combination of settings.

Project file & How to reproduce

bug36mm118.zip

Checklist of files included above

• Project file
• Screenshot

Version of PrusaSlicer

Version 2.9.0-alpha1

Operating system

Windows 10 Home 22H2 Build 19045.5131

Printer model

Ender 3

I was going to report under-extrusion, and other bugs, but they may all be related. Infill doesn't contact the walls, and I could see that there is a significant reduction in extrusion as the infill gets closer to the wall. This is all visible during printing, so it should be easy to diagnose.

[jmd73]

@h4lf It seems to be related to the printer parameters "Use relative E distances" and "Retract on layer change".

If the checkbox "Retract on layer change" is checked, then you get a little bit more sane values, but they still seem to be off.
If "Use relative E distances" is checked the values are good.
If "Use relative E distances" is checked, the "Retract on layer change" parameter makes no difference to the result.

So the main culprit seems to be the checkbox for "Use relative E distances".

That is hopefully to some help for others to get them started on the investigation.

[SachCZ]

Hello @h4lf, sorry for bothering you, but can you please clarify if it is just a visual bug or are there printing issues? What @Kaelum is suggesting is way more serious. @Kaelum, if you are seeing printing issues you did not see with the previous version (2.8.1) please create a new issue. For now we are treating this as a visual bug.

Also thank you @jmd73, your investigation is indeed of great use to us.

[Jan-Soustruznik]

Hello, @h4lf , thank you for your report. We created internal issue, no. SPE-2577. We will try to fix in some next release. Have a nice day

[h4lf]

Hello @h4lf, sorry for bothering you, but can you please clarify if it is just a visual bug or are there printing issues? What @Kaelum is suggesting is way more serious. @Kaelum, if you are seeing printing issues you did not see with the previous version (2.8.1) please create a new issue. For now we are treating this as a visual bug.

Also thank you @jmd73, your investigation is indeed of great use to us.

I don't see any issues with printing.

[FidelCapo]

This issue should be fixed in version 2.9.0-beta1.
Closing.