At some point (for basic rendering examples at least), you’re always going to have to define a data layout of some sort, have that reproduced or reflected between the cpu/gpu environments, and iterate through each vertex. How exactly that turns into GLSL’s in/out variables feels to me like a relatively unimportant implementation detail that should be assessed on performance alone rather than usability[†]. I wonder if what we’re ultimately heading toward is better shader compilation, directly to SPIR-V, to support both bound and unbound use cases.
Sort of related, but Gabriel Dechichi’s engine [1] reflects shader vertex layouts back to C, so you get compile-time error handling if the struct layouts don’t match between cpu/shader.
[0] https://github.com/rkevingibson/loon_gpu/blob/main/examples/...
[1] https://m.youtube.com/watch?v=NTuLfB2ex5Q&ra=m
[†] Edit: Specifically talking about the final compilation unit here, not the shader language or library interface