5.9alpha - Gcode file "Initial Layer" preview is odd

[GregValiant]

Cura Version

5.9.0-alpha.0+b514f5

Operating System

Windows 10 Pro

Printer

Ender 3 Pro

Reproduction steps

I was playing with the new StartUp Gcode and came across this bizarre behavior. It appears to be limited to the "Initial Layer". The static preview appears to be fine, but the dynamic preview is odd.

1. Sliced a model and saved the gcode
2. Cleared the build plate.
3. Opened the Gcode in Cura.
4. Watched the preview of LAYER:0

Actual results

The "Initial Layer" preview shows trace amounts of time travel. Lines are extruded before the move is made. It looks like a rubberband is pulling the virtual nozzle along. The preview looks OK when it's finished with the video portion, but it's odd.
I did not notice the same behavior on any upper layers, just the first one. No post processors were running.

Expected results

An Initial Layer preview that acts normally

Add your .zip and screenshots here ⬇️

Gcode Preview Oddity.zip
Gcode Preview Oddity Project.zip

I don't see any oddities in the log file so I won't include it at this time.

[HellAholic]

Hey @GregValiant , thanks for the report.
This one is a shortcoming of the preview system in general, you can replicated it in 5.8.1 as well without any special gcode or processing modifications.
Just a guesstimate on my part but I think some information about the model/print setting/etc are in use during the simulation view, and when loading a pure Gcode, those information nuggets are missing (since it's a gcode).
Have to look through the backlog to see if we have a ticket for it, and if not I'll add one (easy enough to do with project, recording, and the explanation). To be honest, I don't see a high chance of this being picked up, but I'll make sure it is noted. Thanks once again!
Let me know if you found anything else :P Happy hunting!
PS. The dreaded text overlay for the Start-End Gcode has been removed as well in the alpha build.

[GregValiant]

I can see this one generating some bug reports. It is an odd effect.
Should I close this?

[HellAholic]

Let us do a quick investigation first, if it's an easy fix we might be able to fit it in between. If it requires more work then at least the ticket can act as a base to see how many people experience it and how much weight it gets.

[HellAholic]

Internal reference: CURA-12144