Compiling multiple .metal files into one .metallib

I’m currently writing some custom Core Image filters using Metal. For the sake of structure I want to put the different kernels into different

.metal

files with some common includes like you would do with “normal” source files.

However, when the

metallib

tool bundles the different

.air

files created by the Metal compiler into one

.metallib

file, only the kernel functions defined in the first input

.air

file given to

metallib

are visible. Functions from the other

.air

files don’t seem to be included. What’s the reason for this?

I thought (as is the default compilation behavior for Metal files) all Metal sources get compiled into one library that is then used by every custom

CIFilter

class to instantiate their internal

CIKernel

with the function they need.

I now ended up compiling a

.metallib

file for each custom filter with custom build rules and copying all of them them into my framework within a custom build phase. This don’t seem to be the intended way…