Vulkan, Direct3D, Metal and OpenGL are graphics APIs - the implementation comes with your GPU driver, and they're as close as you can reasonably get to writing code "directly for the GPU". When you call a Vulkan function you're directly calling driver code.
wgpu is a regular library that uses the native APIs above and abstracts them from you. I don't like calling it a graphics API because it implies it's the same as the vendor-provided APIs - it's a completely different beast.
WebGPU and WebGL are Web standards that the browser implements, and you program them via JS. Similarly to wgpu, they're implemented on top of the native graphics APIs.
The relationship between wgpu and WebGPU is that they're basically made by the same people, and in Firefox WebGPU is implemented on top of wgpu.
But saying "WebGPU runs everywhere" is plain wrong - it's a browser-exclusive API, and on top of that, at the point of writing this it doesn't even run on all browsers (71% support according to https://caniuse.com/webgpu)
> The relationship between wgpu and WebGPU is that they're basically made by the same people, and in Firefox WebGPU is implemented on top of wgpu.
I think that’s understating the relationship a bit. The wgpu API follows the WebGPU spec quite closely. It’s like saying “taffy isn’t flexbox”. You can make a technical argument that it’s not identical, and to be flexbox it must be in a browser, but anyone working with taffy will recognize that it’s implementing flexbox and will find that all their understands of flexbox apply to taffy.
Similarly, most of what I’m learning working with wgpu (outside of, maybe, threading), is directly transferable to WebGPU. And vice versa.
That's fair, my comment did understate their relation quite a lot. They are very closely linked, to the point stuff has been added to the WebGPU spec pretty-much because "eh, it's already in wgpu".
But the "knowledge is transferable to WebGPU" is key. Even when you're compiling your wgpu code to WASM, you're not using WebGPU directly - for every API call, you're going through generated bindings on the Rust side and then generated bindings on the JS side where the actual call is made. The JS wrappers aren't trivial either - Rust structs need to be converted to the nested JS objects required by WebGPU spec, numeric enums need to be converted strings, etc.
Considering that WebGPU is supposed to be the low-level graphics API for the Web, DX12/VK/Metal equivalent, all this is at least worth a mention, and "wgpu == WebGPU" brushes over a all that, to the point where we're now casually throwing statements like "[WebGPU] is guaranteed to run anywhere, including the browser".
wgpu is also not a graphics API, it's a library that abstracts the underlying graphics API.