Function pack_instances 

pub fn pack_instances(visible_slots: &[u32], morphs: &[f32]) -> Vec<u8> 

Pack per-instance data for the chunk MultiMesh into a byte buffer.

Each instance is 16 f32 values (64 bytes) matching Godot’s TRANSFORM_3D + custom_data multimesh format:

floats [0..3]   — transform row 0  (identity: 1 0 0 0)
floats [4..7]   — transform row 1  (identity: 0 1 0 0)
floats [8..11]  — transform row 2  (identity: 0 0 1 0)
float  [12]     — INSTANCE_CUSTOM.r = slot as f32    ← slot index here
float  [13]     — INSTANCE_CUSTOM.g = geomorph factor ← morph here
floats [14..15] — INSTANCE_CUSTOM.b/a = 0

visible_slots and morphs are parallel arrays (one entry per drawn instance, same order); morphs[i] is the geomorph factor for the chunk in slot visible_slots[i] (1 = full detail, 0 = parent resolution). Pass 1.0 for every entry to disable morphing.

The identity transform is intentional: the vertex shader reads vertex positions from the vertex-pool texture using the slot, so no CPU-side transform is needed.

Panics

Panics (debug) if morphs.len() != visible_slots.len().