Objects and the Operator Stack
This page explains the two ideas at the center of every groom: the object that hair belongs to, and the operator stack that produces it.
Objects
When you import a mesh, it becomes an object in the scene. Hair is attached to an object and grows from its surface, so as the object moves or deforms, its hair follows. A scene can contain more than one object, each with its own hair.
Each object also has display settings of its own, apart from any material assigned to it: a colour, shown by the swatch next to its name in the Scene panel, and a transparency. Click the swatch to open the colour picker, which has a Transparency slider under it; the Select Scene Geometry tool shows the same transparency in its Display rollup and applies it to every selected object at once. Transparency fades the object on top of its material: with no material the object's colour is faded, with one the material's own opacity is scaled. A see-through object does not hide the guides and strands behind it, which helps when grooming under a hair mesh or a helmet.
Operators
An operator is a single step in building or styling hair. Some operators create strands - for example Guides from Mesh Operator grows guides on a surface, and Hair from Guides Operator interpolates dense hair from those guides. Others modify the strands they receive - Frizz Operator adds randomness, Clump Operator gathers strands together, Curl Operator adds waves. Each operator has its own parameters, edited in the Editing Operator Properties panel.
Throughout Ornatrix the words operator and modifier refer to the same thing. The App uses operator.
The stack
The operators applied to an object form an ordered list, the operator stack, evaluated from the bottom up. The bottom operator produces the first strands; each operator above receives the result of those below it and transforms it further. The order matters: moving an operator up or down the stack changes the result, because it then acts on different input. You build a groom by stacking operators in a deliberate order, and you refine it by editing, reordering, enabling, disabling, or removing them. See The Operator Stack for the panel and its controls.
Non-destructive by design
Nothing in the stack is baked until you choose to bake it. Every operator stays live and editable, so you can return to an early step - say, the guide length - long after adding later styling, and everything downstream recomputes. This is what makes procedural grooming flexible: experiments are cheap and reversible.
Stacks and graphs
A stack is a single straight line of operators, which suits most grooms. When a groom needs to branch, merge, or reuse a result in several places, the same operators can be viewed and edited as a network in the The Node Graph. The stack and the graph are two presentations of the same underlying object.
Guides and hair in the stack
A key reason the order matters is that operators expect a particular kind of strand. Some operate on sparse guides, some on dense hair, and some on either. Understanding the difference helps you place operators correctly. See Hair and Guides.