When you generate an object from other objects, a modeling relation is established. For example, if you create a surface by extruding one curve along another curve, the resulting surface is linked to its generator curves. If you modify the curves, the surface updates automatically. The modeling relation is sometimes called construction history in other software.
Modeling Relation: The road was created by extruding a cross-section along a guide. When the original guide was deformed into a loop, the road was updated automatically.
You can modify the generated object in any way you like, for example, by moving points or applying a deformation. When you modify the generators, the generated object is updated and your modifications to it are preserved — the object does not "snap" back to its generated shape.
If you delete the input objects, the generated object is removed as well. To avoid this, freeze the generated object (see ) before deleting the inputs. If you use the Delete button in the Inputs section of the generator's property editor, the generator is automatically frozen first.
The original curve
Surface created by revolution
Revolved surface modified by moving points
MoveComponent operators are added to the stack after the Revolution.
The original curve is modified.
The revolved surface automatically updates to reflect the new curve shape. The modifications you made to the surface after revolving are preserved.
When an object is generated from others, you can choose the connection point from which the geometry and other attributes are read in the inputs' construction histories. Under Inputs' construction mode in the generator's property editor, select an option to read from the top of the corresponding region in the inputs' operator stack.
For example, suppose that WholeObject is the Boolean union of two shape-animated objects, LeftHalf and RightHalf. If you choose Modeling, then WholeObject is the union of the base shapes of LeftHalf and RightHalf. If you choose Secondary Shape (Result), WholeObject is the union of the animated shapes of LeftHalf and RightHalf. In both cases, the input transformations at the current frame are used.
The Generator Inputs option in the Modeling preferences determine whether the generator input objects are kept, hidden, or deleted automatically. This preference applies only when an object is generated without opening its property editor — that is, if Popup Property Editors on Node Creation is off in your Interaction preferences, or if it is on and you press Ctrl while choosing a menu item.
Hide turns off the view and render visibility of the inputs, but keeps the modeling relation. This simplifies the display of your scene, but still allows you to unhide and modify the inputs if you need to later.
Many modeling operations allow you to substitute one input object for a different one. For example, you can change the profile or guide curve of an extrusion. This works best when the object is an input to only one operator.
If the selected object has a modeling relation, it is linked to its input objects by lines. A label on the line identifies the type of relation (such as wave or revolution) and the name of the input object.
When a modeling relation exists, a large amount of data may need to be updated if the input objects are transformed or deformed. If you need to maintain the modeling relation, you can improve performance by turning off geometry updates for playback.