---
title: In GPU we Rust
type: slide
description: Overview of GPU libraries in Rust.
slideOptions:
theme: Serif
transition: 'fade'
center: false
---


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## `whoami`


<!-- 12 years of experience -->

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## Agenda

1. Landscape of GPU abstractions
2. History of *wgpu*
3. *Blade* of difference

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## GPU abstractions


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### Map of Portability


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<!-- is it safe to access memory? Browser definition -->
<!-- underfined behavior vs undefined data -->

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### case: glow

Purity: :heavy_check_mark:
Safety: :grey_question:
- OpenGL is safe, but Rust API is not

Backends: *GL/GLES/WebGL*
- no compute on Apple platforms

Overhead: :question:
- API itself is close to zero overhead
- but actual platforms may involve translation

Ergonomics: *AA+*
- relatively small API
- boilerplate related to bindings and framebuffers

Downloads: every *8 seconds*

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### case: Ash

Purity: :heavy_check_mark: (no shader solution)
Safety: :x:
Backends: *Vulkan*
Overhead: :heavy_check_mark:
Ergonomics: *A*
Downloads: every *9 seconds*
- is a dependency of many others

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### case: Vulkano


Purity: :heavy_check_mark: host, :x: shader processing (3rd party C++)
Safety: :heavy_check_mark: host, :x: shaders, relies on robust buffer/image access
Backends: *Vulkan*
Overhead: :zzz:
- every draw/dispatch is iterating all the used resources
- actual commands are recorded at the end of the pass

Ergonomics: *AA*
- automatic barriers, bit of type sugar

Downloads: every *2.5 minutes*

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### case: wgpu


Purity: :heavy_check_mark: (includes shader solution via `naga`)
Safety: :heavy_check_mark: (includes shader instrumentation)
Backends: *Vulkan*, *D3D12*, *Metal*, *GL*, *WebGPU*, *WebGL2*
Overhead: :zzz:
- tracking every bind group setup
- actual commands are recorded at the end of the pass

Ergonomics: *AAA*
- simple specification
- automatic state tracking

Downloads: every *12 seconds*

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### case: wgpu-hal

Purity: :heavy_check_mark: (includes shader solution via `naga`)
Safety: :x:
Backends: *Vulkan*, *D3D12*, *Metal*, *GL/GLES/WebGL2*, *WebGPU*
Overhead: :heavy_check_mark: (directly mapped)
Ergonomics: *A+*
- a bit simpler than Vulkan

Downloads: every *12 seconds* (same as wgpu)

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### case: Blade


Purity: :heavy_check_mark: (includes shader solution via `naga`)
Safety: :x:
Backends: *Vulkan*, *Metal*, *GLES/WebGL2*
Overhead: :heavy_check_mark: (directly mapped)
GPU penalty: :question: (to be discussed)
Ergonomics: *AAA+*
- doesn't involve any bind group layout business
- no resource states or barriers
- but requires manual resource destruction

Downloads: every *15 minutes*

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### Ergonomics scale


<!-- drops portability and overhead -->

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### wgpu: Implementation of WebGPU


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### WebGPU: Targets

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### wgpu: History

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### wgpu: Architecture


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### wgpu: Safety

Core idea: *validating correctness takes as much computation as providing it*.

<!-- not obvious, needed to be experimentally proven -->

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### wgpu: Synchronization


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### WebGPU Shading Language


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#### WGSL: Motivation

- one of the drivers behind early Web was the ability to _inspect/edit/write_ pages directly.
- no shading language is designed for safety and lack of UB.
- GLSL is outdated, SPIR-V spec is difficult, everything else is poorly specified...

Naga shows GLSL -> SPIRV in just 1.5ms per shader.

<!-- in any case SPIR-V fork would require a spec -->

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#### naga: Architecture


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### wgpu: Conclusion

- most mature, portable, well specified
- pretty fast, and the only truly safe


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## blade

Lean and mean graphics API


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### blade: Motivation

- it's not always worth it to provide the driver with all the info ahead of time.
- lots of workflows are leaning to *compute-only*, e.g. 2D graphics rendering, ray tracing, neural networks.
- most API complexity is from rasterization.
- modern APIs are too verbose.

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### blade: Principles

1. hacking graphics should be fun!
- we can live without resource barriers
- shader resource layouts can be simpler
- uniforms are just data
2. simplicity >> safety
- no runtime validation
- copyable handles

<!-- user-facing abstraction should be safe,
the question is - at what level is this enforced?
Arguably, GPU API level isn't the best -->

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### blade: Look, ma, no bindings!

Shader:

var<storage,read_write> particles: array<Particle>;
var<uniform> parameters: Parameters;

Host:

pc.bind(0, &MainData {
    particles: particle_buffer.into(),
    parameters:  Parameters {
        my_uniform: [1,2,3,4],
    },
});
pc.dispatch([group_count, 1, 1]);

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### blade: Synchronization

if let mut pass = command_encoder.compute("fill-gbuf") {
    let mut pc = pass.with(&self.fill_pipeline);
    pc.bind(0, &FillData {...});
    pc.dispatch(groups);
}
// implicit barrier between passes
if let mut pass = command_encoder.compute("ray-trace") {
    let mut pc = pass.with(&self.main_pipeline);
    pc.bind(0, &MainData {...});
    pc.dispatch(groups);
}

----


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### blade: Performance

API translation and command recording: :zap:

Rasterization:
| GPU | blade | wgpu-hal |
| --- | ----- | -------- |
| Ryzen 3500U | 20K | 20K |
| Ryzen 6850U | 70K | 70K |
| GeForce 3050 | 100K | 100K |

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### blade: GPU Penalty

[@krOoze on Khronos forums](https://community.khronos.org/t/which-vulkan-implementations-really-care-about-image-layouts/6885/4):
>Supplying GENERAL everywhere sure is state-of-the-art weapons-grade laziness…

Drivers:
* NVIDIA: [irrelevant](https://d29g4g2dyqv443.cloudfront.net/sites/default/files/akamai/gameworks%2FVulkanDevDaypdaniel.pdf)
>Just leave images in the VK_IMAGE_LAYOUT_GENERAL layout
* AMD: comes down to [ac_surface_supports_dcc_image_stores](https://gitlab.freedesktop.org/mesa/mesa/-/blob/e18733300e65f97757150c6a670f80d032a2615d/src/amd/common/ac_surface.c#L149)
* roughly starts with RDNA
* experiments show no penalty on Vega
* Intel: unclear

Easy to mitigate by inserting transitions around render passes.

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### blade: conclusion

- easy to use, hackable
- very fast and portable


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## Thank you! :crab: :crab: :crab: