Are shaders limited to $input $output?

[TMIndust]

Hi,

Background

I have a project with which one can write shaders in a high level language (including IDE support that comes with it) which is then transpiled to C-Style GLSL and classes by the compiler. Currently targeting OpenGL but since that one is a dying API I would love to support Vulkan instead. However, Vulkan is time consuming.

So I am searching for a sufficient graphics API which my project can target.

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Actual Question

When I read the shaderc doc, shaders sound super limiting, like everything needs to be a float or a vec4, or

$input tokens for vertex shader can be only following: [List of predefined stuff]

https://bkaradzic.github.io/bgfx/tools.html#shader-compiler-shaderc

Mind you, I have no experience using bgfx at all. Bgfx sounds super promising but that looks severly limiting to do anything "fancy". My lib on the other hand is meant to enable programers to do complicated stuff on a GPU without thinking about shaders.

Am I misinterpreting that?

Thank you all :)