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Documentation Index

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Modifier3D is Spatial’s immutable transform chain — analogous to Compose’s Modifier but designed for 3D space. It is annotated @Immutable, so every operation returns a new Modifier3D instance rather than mutating the existing one. Chaining is therefore safe and composable. Under the hood, the chain is resolved into a column-major 4×4 model matrix (T × Rz × Ry × Rx × S order) before each frame is submitted to the render host.

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Default

Modifier3D.Default is the zero-transform baseline — position at the world origin, no rotation, and a uniform scale of (1 m, 1 m, 1 m): 
val Default = Modifier3D(
    position = Vec3Distance(0.meters, 0.meters, 0.meters),
    rotation = Rotation3D(),           // no rotation on any axis
    scale    = Vec3Distance(1.meters, 1.meters, 1.meters),
    size     = null,                   // falls back to scale
)
Start every element modifier with Modifier3D.Default and chain operations onto it.

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Available Operations

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position

Sets the element’s world-space position. Two overloads are available: 
// Overload 1 — raw Float values (interpreted as meters)
fun position(x: Float, y: Float, z: Float): Modifier3D

// Overload 2 — typed Distance values (preferred)
fun position(x: Distance, y: Distance, z: Distance): Modifier3D

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rotateX / rotateY / rotateZ

Rotates the element around the named world axis. The Angle type is constructed with the .deg extension: 
fun rotateX(angle: Angle): Modifier3D
fun rotateY(angle: Angle): Modifier3D
fun rotateZ(angle: Angle): Modifier3D

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scale

Multiplies the element’s size relative to its unit mesh dimensions: 
fun scale(x: Distance, y: Distance, z: Distance): Modifier3D

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size — uniform

Sets all three dimensions to the same absolute size in meters: 
fun size(all: Distance): Modifier3D

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size — non-uniform

Sets width, height, and depth independently: 
fun size(width: Distance, height: Distance, depth: Distance): Modifier3D

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Chaining

Chain calls left-to-right, starting from Modifier3D.Default. The order follows the model matrix composition (T × Rz × Ry × Rx × S), so rotation is applied before translation: 
Element.Cube(
    modifier = Modifier3D.Default
        .rotateY(45f.deg)
        .size(2f.meters)
        .position(0f.meters, 0f.meters, (-5f).meters),
)
This places a 2 m cube 5 m in front of the camera, rotated 45° around the Y-axis.

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Coordinate System

Spatial uses a standard right-handed coordinate system:
AxisDirection
+XRight
+YUp
+ZToward the viewer (out of the screen)
−ZInto the scene (away from the viewer)
Objects in front of the default camera position sit at negative Z. Use (-5f).meters, (-4f).meters, etc. for the Z component of position() so elements appear in the viewport.

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size vs scale

size(...)scale(...)
SemanticsSets absolute world-space dimensions in metersMultiplies relative to the unit mesh
Example.size(2f.meters) → always 2 m.scale(2.meters, 2.meters, 2.meters) → 2× the mesh default
Use whenYou know the exact real-world dimensionsYou want proportional scaling relative to the base mesh
When size is set it overrides scale during model matrix resolution. If size is not set, scale is used instead.

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Units Reference

Spatial uses two typed unit classes from the spatial-units module: 
// Distance — constructed with .meters or .cm extension properties
val d: Distance = 1.5f.meters
val c: Distance = 50f.cm       // same as 0.5f.meters

// Angle — constructed with .deg extension property
val a: Angle = 45f.deg
  • Elements — apply Modifier3D to Element.Cube, Element.Sphere, and Element.Plane
  • Units — full reference for Distance and Angle typed units

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