whoami

Agenda

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

GPU abstractions

Map of Portability

case: glow

Purity:

• OpenGL is safe, but Rust API is not

Backends: GL/GLES/WebGL

• no compute on Apple platforms

Overhead:

• 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

case: Ash

Purity:

• is a dependency of many others

case: Vulkano

Purity:

• 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

case: wgpu

Purity:

• 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

case: wgpu-hal

Purity:

• a bit simpler than Vulkan

Downloads: every 12 seconds (same as wgpu)

case: Blade

Purity:

• doesn't involve any bind group layout business
• no resource states or barriers
• but requires manual resource destruction

Downloads: every 15 minutes

Ergonomics scale

wgpu: Implementation of WebGPU

WebGPU: Targets

wgpu: History

wgpu: Architecture

wgpu: Safety

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

wgpu: Synchronization

WebGPU Shading Language

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• GLSL is outdated, SPIR-V spec is difficult, everything else is poorly specified…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.

naga: Architecture

wgpu: Conclusion

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

blade

Lean and mean graphics API

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.

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

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]);

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);
}

blade: Performance

API translation and command recording:

Rasterization:

blade: GPU Penalty

@krOoze on Khronos forums:

Supplying GENERAL everywhere sure is state-of-the-art weapons-grade laziness…

Drivers:

• NVIDIA: irrelevant

  Just leave images in the VK_IMAGE_LAYOUT_GENERAL layout

• AMD: comes down to ac_surface_supports_dcc_image_stores
  • roughly starts with RDNA
  • experiments show no penalty on Vega
• Intel: unclear

Easy to mitigate by inserting transitions around render passes.

blade: conclusion

• easy to use, hackable
• very fast and portable

Thank you!

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