Pivot and Anchoring
Pivot modes (Absolute / Anchor / Percent), anchoring children to the parent bounds, and ratio-based size parameters.
A parametric shape manages its pivot as a parameter. And when the parent is a parametric shape or a Layout, a child's position and size can be tied to the parent's bounds — resize the parent and the child follows and scales with it.
The Pivot section
Pick an Anchor Mode in the Inspector's Pivot section.
| Mode | Meaning |
|---|---|
| Absolute | Use an absolute coordinate in source space as the pivot. Independent of the parent. |
| Anchor | Snap to a reference point on the parent bounds (min / center / max per axis). |
| Percent | Snap to a relative position inside the parent bounds (0 – 1 per axis). |
- Absolute shows a Position field. The mesh is offset by the inverse of this value so the transform pivot is preserved.
- Anchor and Percent show an Offset field — the local offset from the anchor point.
How anchoring behaves
In Anchor and Percent modes the child's local position is constrained to the anchor point plus Offset.
Moving the child in the Scene view is absorbed back into Offset. The anchor stays where it is, and only the distance from the anchor point changes.
When the parent's size changes, the anchor point is recalculated and the child moves to it. A light anchored to the top of a wall, for example, stays at the top as the wall gets taller.
Ratio (%) size parameters
Switching a size parameter's m ↔ % toggle to % makes that field's value a ratio of the parent's axis length.
With height = 0.5 in % mode, the effective height is half the parent's height.
Each parameter maps to a parent axis as follows.
| Parameter | Parent axis used |
|---|---|
width, stepWidth | X size |
height, stepHeight, thickness | Y size |
depth | Z size |
radius, radius1, radius2 | min(X, Z) × 0.5 |
Radius-like parameters use min(X, Z) × 0.5 because that is the largest radius whose circular section still fits inside the parent's footprint.
The All % / All m buttons switch every size parameter at once.
Blocking out space with the Layout shape
Layout is a mesh-less AABB box. It is never rendered and only appears as a wire box in the Scene view.
Use it whenever you only need a reference volume — one floor of a building, a single room, a UI panel area — that says "lay things out inside here." Parent children to a Layout with anchors and ratios, and resizing the Layout alone resizes the whole composition.
Layout "Floor" (width 8, depth 6, height 3)
├─ Box "WallNorth" pivot=top-back, width 100% ← stretches with the Layout width
├─ Box "WallSouth" pivot=top-front, width 100%
└─ Cylinder "Pillar" pivot=bottom-center
Setting it from a script
In the script DSL the same settings are expressed with pivot=, offset= and ratio=.
layout "Floor" w=8 d=6 h=3 @0,0,0
box "WallNorth" pivot=top-back ratio=width,height w=1 h=0.9 d=0.2
The syntax is covered in Scene Script Syntax (umx_parametric_shape).