Crate crabslab

Creating and crafting a tasty slab of memory.

What

crabslab is a slab implementation focused on marshalling data between CPUs and GPUs.

See the example below.

But Why?

It’s hard to get data onto GPUs in the form you expect.

To marshall your data correctly you must know about the alignment and sizes of the underlying representation of your data. This will often surprise you!

Working with a slab on the other hand, only requires that your types can be written into an array and read from an array.

Opinion

Working with shaders is much easier using a slab.

Shader code can be written in Rust with rust-gpu, which will enable you to use this crate on both CPU and GPU code.

rust-gpu

This crate was made to work with rust-gpu. Specifically, with this crate it is possible to pack your types into a buffer on the CPU and then read your types from the slab on the GPU (in Rust).

Other no-std platforms

Even though this crate was written with rust-gpu in mind, it should work in other no-std contexts.

And How

The idea is simple - crabslab helps you manage a heap of contiguous u32s (roughly in the form of Vec<u32>). Types implement the trait SlabItem which writes the type into an index of the slab as contiguous u32s and also reads them out symmetrically.

crabslab includes:

• a few traits:
  • Slab
  • GrowableSlab
  • SlabItem
• a derive macro for SlabItem for your types
• a few new structs for working with slabs
  • Id
  • Array
  • Offset
• a helper struct CpuSlab which wraps anything implementing GrowableSlab
• feature for deriving SlabItem for glam types

Example

use crabslab::{CpuSlab, Slab, GrowableSlab, SlabItem, Id};
use glam::{Vec3, Vec4};

#[derive(Debug, Default, SlabItem, PartialEq)]
struct Light {
    direction: Vec3,
    color: Vec4,
    inner_cutoff: f32,
    outer_cutoff: f32,
    is_on: bool
}

impl Light {
    fn standard() -> Self {
        Light {
            direction: Vec3::NEG_Z, // pointing down
            color: Vec4::ONE, // white
            inner_cutoff: 0.5,
            outer_cutoff: 2.6,
            is_on: true
        }
    }
}

fn cpu_code() -> (Id<Light>, Vec<u32>) {
    let light = Light::standard();
    // Create a new slab on the CPU-side.
    // Using CpuSlab make `append` unambiguous, as `Vec` has its own `append` function.
    let mut slab = CpuSlab::new(vec![]);
    let id = slab.append(&light);
    (id, slab.into_inner())
}

fn shader_code(light_id: Id<Light>, slab: &[u32]) {
    let light = slab.read(light_id);
    assert_eq!(Light::standard(), light);
}

let (light_id, slab) = cpu_code();
// marshalling your data depends on which GPU library you are using...
shader_code(light_id, &slab);

Modules

bits

Bitwise operations for creating tightly packed impls of SlabItem.

impl_slab_item

offset

Struct field identifiers.

Structs

Array

A pointer to contiguous T elements in a slab.

ArrayIter

Iterator over Ids in an Array.

CpuSlab

A wrapper around a GrowableSlab that provides convenience methods for working with CPU-side slabs.

Id

An identifier that can be used to read or write a type from/into the slab.

Constants

ID_NONE

u32 value of an Id that does not point to any item.

Traits

GrowableSlab

Trait for slabs of u32s that can store many types, and can grow to fit.

Slab

Trait for slabs of u32s that can store many types.

SlabItem

Determines the “size” of a type when stored in a slab of &[u32], and how to read/write it from/to the slab.

Functions

__saturating_sub

Proxy for u32::saturating_sub.

array_index

array_index_mut

slice_index

slice_index_mut

Derive Macros

IsContainer

Creates a proxy type to implement IsContainer for, where IsContainer::Container resolves to the type being derived.

SlabItem

Derives SlabItem for a struct.