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Stepped F-Curve Modifier permanently changes Motion Path
Closed, ResolvedPublic


System Information
Operating system: macOS 10.14.2
Graphics card:
Radeon Pro 560 4096 MB
Intel HD Graphics 630 1536 MB

Blender Version
Broken: 2.80, 1b6b0fbd957f, blender2.8, 2019-01-08, built locally, no local changes

Worked: (optional): 2.79, 66c3eb369d274, blender2.29, 2019-01-04, 00:09)

Load the attached file
On the Object tab, enable and calculate the motion path - notice a smooth path
In the F-Curve modifiers (with the Z Channel Selected) add a Stepped Modifier, verify it is working in the graph view and in the 3D view.

On the Object tab, updated the motion path - it will become stepped

Remove the Stepped F-Curve Modifier - notice the curve in the graph window is smooth and the motion is smooth in 3D view.

On the Object tab, updated the motion path - it will stay stepped
On the Object tab, remove and re-calculate the motion path - it will stay stepped

Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).

Event Timeline

Jacques Lucke (JacquesLucke) triaged this task as Confirmed, Medium priority.

Looks like there is some update missing when a fcurve modifier is removed.

@Sergey Sharybin (sergey), I think I need your help to solve this correctly.
I'd think that I just need to add DEG_id_tag_update in delete_fmodifier_cb. However, I don't seem to have access to the id that needs to be updated..