Rolling Back Through History
Drag the playhead handle up the timeline and the part reverts to how it looked at that step. Drop a new step while you are there and it lands in the middle of the history rather than at the end.
Moving the playhead
The playhead is the light-blue line down the left edge of the timeline strip, ending in a small triangular handle. Drag the handle up or down, and on release it snaps to the nearest pill.
Everything below it fades to almost nothing and drops out of the view. Fading is all that happens: each pill keeps its own colour, so a run of future steps still reads green, violet, red down the strip. None of them turns gray. Gray is what disabling does, and that is how you tell a step you have rolled past from a step you switched off.
The part in the viewport is the part as it stood after the step the playhead sits on.
Clicking a pill does not move the playhead. Clicking selects the step and opens its panel, which is a different operation with a different effect on the view. Only the handle moves the playhead.
Getting back
When the playhead is anywhere other than the last step, an amber Return to latest pill appears at the bottom-left of the viewport. Click it and the playhead jumps back to the end and the whole model returns.
That pill is also the answer to the most common scare in the editor. If half your part has disappeared and the timeline has gone faint below a certain point, nothing has been deleted: the playhead is parked mid-history. Click Return to latest.
Rolling back computes nothing
Moving the playhead is display-only. No step is re-evaluated, nothing is disabled, and the document does not change. The display walks back to the nearest stored snapshot of the body and shows you that.
That walk is worth understanding, because it can leave you looking at something older than the pill you dropped the playhead on. Not every step has a snapshot the display can use: a step that failed does not, and neither does one that has never been evaluated. So the display searches from where you landed back up the strip and shows the first step it finds that built successfully. A failed step is skipped even though it has geometry of its own.
The consequence is a viewport that does not always match the pill. Land on a red step and what you see is the part as it stood before it, with no sign that you are looking at older geometry than you asked for. Land above everything that has ever built, on the opening sketch of a part, and the viewport is empty because there is nothing earlier to fall back on. Neither is a lost model. Click Return to latest.
Two more consequences worth having. Rolling back is cheap, however long the history, so use it freely to work out which step did what. And rolling back is not a way to test whether a step still works: to take a step out of the calculation you disable it, which is a real change and does rebuild. Editing a Part You Have Built covers disabling.
Inserting a step in the middle
A new step is inserted just after the playhead, not at the end of the timeline, and the playhead then advances onto it.
So to add a chamfer that should have happened before the shell:
- Drag the playhead to the step the chamfer should follow.
- Build the chamfer as usual. It is inserted there.
- Click
Return to latest. Every step that was already below the insertion point rebuilds on top of the new one.
The rebuild is real, and it is where you find out whether the later steps survive the change. Watch the timeline rather than the part: if a pill turns red, the step you inserted moved or removed something a later step was pointing at.
Deleting a step that sits above the playhead moves the playhead back one, so the same steps stay applied.
One place to insert carefully is inside a group: the new step lands outside it and splits the group in two. Reading the Timeline covers what that looks like and how to put it back.
There is no way to reorder steps
You cannot drag a step to a different position in the timeline. There is no drag handle on the pills, no Move up in the context menu, and no other route to it. A step stays where it was created for as long as it exists.
To get a step into a different position, delete it and build it again at the point you want, which is exactly the rollback-and-insert loop above. When the step is expensive to recreate, note its settings before you delete it.
Two lists inside the app do reorder, and they are easy to mistake for timeline reordering because they look like stacks of steps: the positioning steps inside a single Transform, and the profile list inside a Loft. Both reorder within their own step, and neither moves anything in the timeline.
When it goes wrong
A pill has no right-click menu. It is below the playhead. Return to latest first; Reading the Timeline has the rest of the inert states.
The viewport is empty, or older than the step you landed on. The step has no snapshot the display can use, so it fell back to the nearest earlier step that built. Click Return to latest and nothing is lost.
A new step landed in the middle when you wanted it at the end. The playhead was not at the end. This is the same mechanism working as designed, and undo is the quickest fix.
A step you inserted turned later steps red. Rolling back and inserting does not protect downstream steps from the change. Open the red step and read its banner: When a Step Goes Red covers what the messages mean, and References That Survive an Edit covers the case where a face moved too far to be found again.
See also
- Reading the Timeline: the playhead, the pills, and what each state means
- Editing a Part You Have Built: opening a step, changing it, and disabling one
- When a Step Goes Red: what to do when an insertion breaks a later step