Hi, lead author here. You're definitely getting at the core of the issue. An effective shader programming models needs to support modularity and composition of shader code, while also supporting GPU code specialization and interop between host and GPU code. Large game engines provide layered tools that aim to provide these features, and they are very useful especially for users who aren't experts in graphics programming (e.g., artists and technical artists). I'll use this opportunity to shamelessly plug our prior work, which explores these aspects of shader systems in more detail: https://dl.acm.org/doi/10.1145/3355089.3356554 (preprint here: https://escholarship.org/uc/item/2f8448n2 )
Even with these layered tools, the host-GPU interop is still something that shader programming systems have to contend with directly, in contrast to "unified" systems like CUDA and C++ AMP in the GPU compute world. As you point out, translating C++ to GPU-compatible code is just one step in the process. Our work looks at the next step: once we can write both host and GPU shader code in C++, what's missing? What we discovered is that by merging the host and GPU halves together in C++, we inadvertently broke the critical shader specialization optimization. So our work presents a method to support shader specialization in a first class way, while also meeting our other design goals.
Even with these layered tools, the host-GPU interop is still something that shader programming systems have to contend with directly, in contrast to "unified" systems like CUDA and C++ AMP in the GPU compute world. As you point out, translating C++ to GPU-compatible code is just one step in the process. Our work looks at the next step: once we can write both host and GPU shader code in C++, what's missing? What we discovered is that by merging the host and GPU halves together in C++, we inadvertently broke the critical shader specialization optimization. So our work presents a method to support shader specialization in a first class way, while also meeting our other design goals.