Beginner Question: what does Naga do?

[iampi31415]

I stumbled upon this recent post where it says:

[Naga] provides a common intermediate representation and supports translating between WGSL, SPIR-V, GLSL, MSL, and HLSL.

I got curious about the conceptual part of this. Is it saying that Naga does something like this diagram below?

                         +--------+
                         |  WGSL  |
                         +--------+
                             ↕
    +--------+         +-------------+         +--------+
    | SPIR-V | ↔       |             |       ↔ |  GLSL  |
    +--------+         |    NAGA     |         +--------+
                       | (Common IR) |
    +--------+         |             |         +--------+
    |  MSL   | ↔       |             |       ↔ |  HLSL  |
    +--------+         +-------------+         +--------+

Were we simply choose a source language, and it will translate to any supported by the platform.

And I think then one has an overall system like:

• WGPU translates API and shaders.
  • Uses Naga to do WGSL (source) => SomeShader (dest)

[ErichDonGubler]

This seems mostly right, minus a couple of details that I think are important for this high-level overview.

Your diagram suggests that Naga can ingest and emit all shader languages equally. But if you examine https://github.com/gfx-rs/wgpu/tree/1bf1671ed877a6a9ccf5f1a349ec167cd28af3d7/naga#supported-end-points, you'll see that only some languages are supported frontends, with a superset of them supported as a backend. In the language of your diagram, that means not all arrows between Common IR and the other languages are actually bidirectional links.

WGSL is the most common for the web world, but we have a fair number of WGPU users using other shader languages. Yet another interesting way they provide shaders for WGPU is via "passthrough" shaders, where (1) the user supplies a shader in the language of the platform's graphics runtime and which (2) the user promises (on penalty of undefined behavior) is compatible with their subsequent usage of the shader module.

[iampi31415]

Makes sense, I think a more accurate one would be (inward arrows are front-ends, some can be also output formats so they have double arrows, and some only output which have outward arrows.):

                         +--------+
                         |  WGSL  |
                         +--------+
                             ↕
    +--------+         +-------------+         +--------+
    | SPIR-V | ↔       |             |       ↔|  GLSL  |
    +--------+         |    NAGA     |         +--------+
                       | (Common IR) |
    +--------+         |             |         +--------+
    |  MSL   | ←       |             |       → |  HLSL  |
    +--------+         +-------------+         +--------+

I like to distinguish between Metal and MSL; WebGPU and WGSL and in general about what I consider the Driver API vs the Shading Language (but I am not a graphics programmer and this may be wrong.)

I'll soon checkout some of the wgpu tutorials since it seems fun and interesting.