computer-graphics | Beginners Guide to Computer Graphics | Graphics library

You are looking for the Vulkan-Loader/LoaderAndLayerInterface.md documentation.

The app interfaces with The Loader (sometimes called Vulkan RT, or Vulkan Runtime). That is the vulkan-1.dll (or so).

The Loader also has vulkan-1.lib, which is classic dll shim. It is where the loading of core version and WSI commands happens, but you can skip the lib and do it all manually directly from the dll using vkGetInstanceProcAddr.

Then you have ICDs (Installable Client Drivers). Those are something like nvoglv64.dll, and you can have more of them on your PC (e.g. Intel iGPU + NV). The name is arbitrary and vendor specific. The Loader finds them via config files.

Now when you call something to a command obtained with vkGetInstanceProcAddress (which is everything if you use the *.lib only), you get onto a loader trampoline, which calls a chain of layers, after which the relevant ICD (or all of them) are called. Then the callstack is unwound, so it goes the other direction until the returned to the app. The loader mutexes and merges the the input and output to the ICD.

Commands obtained with vkGetDeviceProcAddress are little bit more streamlined, as they do not require to be mutexed or merged and are meant to be passed to the ICD without much intervention from the Loader.

The code is also at the same repo: trampoline.c, and loader.c. It's pretty straightforward; every layer just calls the layer below it. Starts at the trampoline, and ends with the terminator layer which in turn will call the ICD layer.