This makes sense to me.
I am wondering if there is a way to check that the backend files present so that this check can be done automatically without adding extra CMake variables.

This makes sense to me.
I am wondering if there is a way to check that the backend files present so that this check can be done automatically without adding extra CMake variables.

This can easily be done in C++ with __has_include macro branching. An alternative is to check it on the cmake side and conditionally include the file and pass a definition with the filename.

Both slightly affect readability and cmake-based approach is probably logically more correct, but I would still prefer __has_include as it's more easy and transparent.
What do you think?

I actually prefer the CMake approach. Wondering, if something like this will work:

if(EXISTS "${DILIGENT_DEAR_IMGUI_PATH}/backends")

To me this seems to be the easiest way that does not require extra variables and just works automatically.

I actually prefer the CMake approach. Wondering, if something like this will work:

if(EXISTS "${DILIGENT_DEAR_IMGUI_PATH}/backends")

To me this seems to be the easiest way that does not require extra variables and just works automatically.

It's slightly less flexible, but it also works!