Setting flags/defines for building a library's dependency

1

I have Project A that I’m currently developing.
Project A has dependency of Library B that I made.
Library B has dependency of Library C that i did not make.

Library C requires a ton of flags being supplied through build_flags in platformio.ini:

-DTFT_SWRST=1
-DTFT_CASET=42
-DTFT_PASET=43
-DTFT_RAMWR=44
-DTFT_RAMRD=46

…And the list goes on. How do I, in Library B, imbed these defines so Project A does not need to know about them? Can I also do that as part of Library B’s platformio.ini? Just supplying them as #define’s in Library B does not work, it’s not picked up by Library C.

2

Libraries usually don´t have a platformio.ini but a library.json file.
The build flags can be specified in this file like so:

{
  "name": "libraryc",
  "version": "0.0.1",
  "build": {
    "flags": [
      "-DTFT_SWRST=1",
      "-DTFT_CASET=42",
      "-DTFT_PASET=43",
      "-DTFT_RAMWR=44",
      "-DTFT_RAMRD=46"
    ]
  }
}

Take a look at the README in the lib directory.

3

Thank you for your response, @sivar2311

It doesn’t seem to work as I want it. When added to Library B’s library.json, Library C (which i have no control over) doesn’t see the defines when building.

I’m not sure how the dependency building works - but i would expect it to be something like this:

Building Project A, it will build Library B. As Library C is a dependency of LIbrary B, it will be build with Library B’s build settings.

If i directly copy the build flags from Library B to Project A then everything works as expected - but that was kinda the whole point wrapping it up in LIbrary B in the first place, so that’s no good.

4

The build flags in library.json only apply locally for the respective library.
The build flags in platformio.ini apply to the entire project.

If it is the task of library B to configure library C, I don’t see a solution.

I think the only way to configure library C is to use the build flags in platformio.ini, which then apply to the entire project.

5

A working solution is to make library C a part of library B (copy library C into your library B), as follows:

libb
|--src
|  |--libc
|  |  |--src
|  |     |-libc.h
|  |     |-libc.cpp
|  |-libb.h
|  |-libb.cpp
|-library.json

To include library C through library B, use: #include "./libc/src/libc.h".
The settings in the library.json of library B also apply to library C

6

I checked if I could use extra_scripts and create a python script that does something like this:

Import("env")
for lb in env.GetLibBuilders():
    if (lb.name == "Library C"):
        lb.env.Append(CPPDEFINES=[
            ("MY_DEFINE", 123)
        ])

While the code executes correctly it doesn’t seem to work. Library C is not build with those defines -_-