I’m trying to better understand how the History command works in Rhino and I ran into something that I can’t quite explain. Here’s the process I’m following:
I create a straight line.
I activate Record History, with Always Record History and Update Children enabled.
I extrude the line to create a surface.
When I move the original line, the surface updates correctly — so far, so good.
Then I extrude the surface to create a solid.
What confuses me is that I get no warning about history breaking, but when I move the original line, only the first surface updates. The solid generated from the second extrusion does not change.
Why does this happen?
Is there a way to make this “history chain” work so that the original line affects all the geometry derived from it, including the second extrusion?
When you extrude the original line, is the resulting object an Extrusion or a Surface? If you are using Extrusions, then you use ExtrudeSrf, the result is a Polysurface (replacing the extrusion with a surface). It looks like when you move the line, the history updates with a new extrusion object and causes the disconnect you are experiencing.
You could certainly try turning off the option to “Use extrusions when possible” in your Rhino Options > General settings. For me, this seemed to result in the desired history behavior.
Extruding the line creates the surface which is history-related. But, the rest will depend on how you extrude the surface. If you extrude the surface using the Gumball dot, the original surface is automatically deleted so you lose the history chain.
If you extrude the surface with the Solid tools command ExtrudeSrf and you use the option DeleteInput=No, then the surface remains, this history chain is unbroken, and both the surface plus the extruded solid will update when you move the line. If you set DeleteInput to Yes when extruding the surface, then it will behave like the Gumball extrusion and history will be lost.
Extrusions are, essentially, a “lighter weight” alternative to creating surfaces in some instances - saves on machine resources in more complex models.
