Hi, lead author here. The Rust GPU project is certainly some great work! We cite it in Section 7 of our paper.
The Rust GPU project is working to satisfy a necessary condition of unified shader programming in Rust: the ability to compile Rust code to GPU-executable kernels. However, in its current state, it does not provide interop between the host (CPU) code and GPU code in a unified way. Programmers still need to create separate host and GPU representations of parameters (and keep these two definitions in sync) and use API calls to communicate between the two halves of the code.
Similarly, Metal's GPU shader code is written in (a subset of) C++, but Metal does not meet our definition of a unified shader programming environment for the same reason.
Our work investigates the next step in this process: once we can translate host language X to GPU-compatible code, what else do we need to accomplish to unify the host and GPU halves of shader code into the same programming environment.
