Struct Placement 

#[non_exhaustive]
pub struct Placement {
    pub parent: Option<ItemId>,
    pub z: f32,
    pub local_pos: Point,
    pub transform: Transform2D,
}

Where an item sits, as one property: logical parent, paint z, position in the parent frame, and local to parent transform.

Why these four together

Scene::set_item_parent deliberately does not rebase local_pos — a child’s position is stated in its parent’s frame, so adopting a new parent moves the item unless the caller compensates. A visually-stable reparent is therefore set_item_parent + set_local_pos + set_transform: three events, three things for a history to undo separately, and two intermediate states in which the item is visibly somewhere it never was.

Writing all four at once removes all three, and it is the half of Figma’s “parent + fractional index as one property” that Teksilo was missing. The other half — O(1) reorder with no sibling rewrite — is already here: z is an f32 and Scene::set_z writes one field, so Scene::z_between is a fractional insert.

#[non_exhaustive]: the crate hands this to consumer code and takes it back — and it is the one place a caller states a whole placement, so a fifth property joining the set is exactly the growth this guards. Build one with new.

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

parent: Option<ItemId>

Logical parent, or None for scene-rooted.

z: f32

Paint z-order within the band.

local_pos: Point

Origin of the item’s local frame, in the parent’s coordinates.

transform: Transform2D

Rotation / scale applied around the local origin.

Implementations

impl Placement

pub fn new( parent: Option<ItemId>, z: f32, local_pos: Point, transform: Transform2D, ) -> Self

A placement stated field by field — the constructor #[non_exhaustive] takes the place of a struct literal for.

Trait Implementations

impl Clone for Placement

fn clone(&self) -> Placement

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Placement

impl Debug for Placement

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for Placement

fn eq(&self, other: &Placement) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Placement