Added WGVK webgpu backend

[r-lyeh]

Hello Omar,

• Here is a preliminary PR that adds a new webgpu backend (WGVK) targetting Vulkan.
• By default, WGVK can only consume SPIRV shaders: WGSL and GLSL shaders can be enabled by linking against extra libs. The fastest way to have WGSL shaders enabled is to link against Simple_WGSL and add their -DSUPPORT_WGSL directive to the build commands.
• In order to simplify adoption and minimize build problems I have decided to support both modes: vanilla WGVK(SPIRV) and WGVK+WGSL support.
  • If the end-user decides to link only against the vanilla wgvk.c file, then the webgpu backend will load some new embedded WGSL->SPIRV shaders which can be found now in the implementation.
  • If the end-user decides to link against wgvk.c AND Simple_WGSL AND add the -DSUPPORT_WGSL directive, then the backend will consume the existing WGSL shaders and the current backend is probably on parity with Dawn and WGPU.
  • To simplify the process in the future, it would be probably good to try loading WGSL first, and switching to SPIRV as a fallback if shader compilation fails, I guess.
• While integrating the new backend some problems in the GLFW3/SDL2/SDL3 examples were found, mostly about setting up the device and some UB logic regarding the async/futures setup. Why this was not crashing for WGPU/Dawn is not known to me, but apparently passing a adapterCallbackInfo.mode = 0 to the spec is invalid (the enumeration starts from 1).
• The backend has been tested against latest WGVK (with and without Simple_WGSL) and SDL2/SDL3/GLFW3 backends.
• No hurries to merge this PR at the moment, but it is probably a good time to start discussing the proposed changes.

[procedural]

rip r-lyeh, let Omar's wrath be merciful

[ocornut]

Before I have a chance to look at this, I have an immediate problem which is that I noticed today that latest Emscripten the WGPU backend doesn't compile anymore:
https://github.com/ocornut/imgui/actions/runs/22069146278/job/63768805098

Which version of Emcripten did you build with?

The new version is 5.0.1 but even if I replace to use the defines html5_webgpu.h is missing.
It works with 5.0.0 (!) but not 5.0.1.
It works with 4.0.23.
And here I thought 4.0 was the end of our problems, nope 😭 cc @BrutPitt

I cannot find where proper Emscripten/WGPU changelog are published.
Many major open-source projects don't seem to care about exposing reliable changelogs apparently (neither Emscripten neither SDL3 do).

[ocornut]

• Can you confirm Emscripten (and potentially WGVK) version used?
• Did you test building and/or running changes with WGPU and DAWN? (preferably yes, but if you didn't I'd appreciate to know)
• If that's easy for you could you squash everything into 1 commit, so we don't have to carry a bunch of unrelated stuff in history?
• I don't know where the shader sources are?
• Could the same shaders sources in backends/vulkan/* and stored binary in backends/imgui_impl_vulkan.cpp be used for some of the path?
• Best to not make ImGui_ImplWGPU_CreateShaderModule() a template and simply use e.g. void*
• If SUPPORT_WGSL is not a standard define then the name should presumably use a IMGUI_IMPL_WEBGPU_XXX prefix? But it seems like this could be a runtime flag rather than a compile-time one? Would a ImGui_ImplWGPU_SetShaderSourceType(WGPUSType shader_source_type) be more adequate?

While integrating the new backend some problems in the GLFW3/SDL2/SDL3 examples were found, mostly about setting up the device and some UB logic regarding the async/futures setup

• Could this be isolated in a dedicated commit? So we can make and tests with other backends.