Field Layout

FieldLayout

#![allow(unused)]
fn main() {
pub struct FieldLayout {
    pub name: &'static str,
    pub offset: usize,
    pub size: usize,
    pub alignment: usize,
    pub pad_after: usize,
}
}

Each entry in Layout::FIELDS describes one field of the struct.

pad_after Semantics

pad_after is the number of padding bytes between the end of this field's data and the start of the next field (or the end of the struct). When writing a struct to a buffer byte-by-byte:

1. Write the field's size bytes.
2. Write pad_after zero bytes.
3. Proceed to the next field.

The final field's pad_after accounts for struct-end padding so that the total equals SIZE.

RuntimeArray<T>

A runtime-sized array has no statically knowable size:

#![allow(unused)]
fn main() {
assert_eq!(<RuntimeArray<f32> as WgslLayout>::SIZE, 0);
}

SIZE is 0 because the array length is runtime-dependent. Such arrays may only appear as the last field of a storage-buffer struct.

Empty Structs

An empty struct is the identity element for layout:

#![allow(unused)]
fn main() {
assert_eq!(Empty::SIZE, 0);
assert_eq!(Empty::ALIGN, 1);
assert!(Empty::FIELDS.is_empty());
}

The WGSL spec does not define the empty-struct case; wgsl-rs-layout defines ALIGN = 1 so that roundUp(offset, 1) is a no-op and empty structs compose without disturbing surrounding layout.