[bug#41294] [PATCH] gnu: Add libfreenect.

[Ekaitz Zarraga <ekaitz@elenq.tech>]

> Inputs can also be defined with an extra argument for different outputs, right? It should be something like:
>
> `(inputs`("freeglut" ,freeglut "examples"))
>
> Am I right?

Nope!

I've been digging and I got this wrong. The third part in the tuple is the output of the dependency.
So there's no way to indicate which dependencies are needed for each output.

I also found a flag to compile OpenCV wrappers, which depends on OpenCV. OpenCV is huge and it's going to be downloaded regardless if its output is used or not. Best choice here seems to be to separate the package in multiple sub-packages.

I made this with the examples (see below), how does it look?
I used libfreenect as a dependency for examples too, so I needed to patch the CMakeLists.txt to avoid it compile the `src` folder again.
Is it cool if I do the same thing with OpenCV and Python?

(now we can move it to its own module because it's going to be long :) )

---

(define-public libfreenect
  (let ((version "0.6.1"))
    (package
      (name "libfreenect")
      (version version)
      (source (origin
                (method git-fetch)
                (uri (git-reference
                      (url "https://github.com/OpenKinect/libfreenect")
                      (commit (string-append "v" version))))
                (sha256
                 (base32 "0was1va167rqshmpn382h36yyprpfi9cwillb6ylppmnfdrfrhrr"))))
      (build-system cmake-build-system)
      (outputs '("out" "opencv" "examples"))
      (arguments
       '(#:tests? #f ; Project has not tests
         #:configure-flags '("-DBUILD_EXAMPLES=ON"
                             "-DBUILD_FAKENECT=ON"
                             "-DBUILD_CPP=ON"
                             "-DBUILD_CV=OFF"
                             "-DBUILD_C_SYNC=ON")
         #:phases
         (modify-phases %standard-phases
           (add-after 'install 'install-udev-rules
             (lambda* (#:key outputs #:allow-other-keys)
               (let* ((out (assoc-ref outputs "out"))
                      (rules-out (string-append out "/lib/udev/rules.d")))
                 (install-file "../source/platform/linux/udev/51-kinect.rules"
                               (string-append rules-out "51-kinect.rules"))
                 #t))))))
      (native-inputs
       `(("pkg-config" ,pkg-config)))
      (inputs
       `(("libusb" ,libusb)))
      (synopsis "Drivers and libraries for the Xbox Kinect device")
      (description "libfreenect is a userspace driver for the Microsoft Kinect.
It supports: RGB and Depth Images, Motors, Accelerometer, LED and Audio.")
      (home-page "https://openkinect.org/")
      (license license:gpl2+))))

(define-public libfreenect-examples
  (package
    (inherit libfreenect)
    (name "libfreenect-examples")
    (inputs
     `(("libusb" ,libusb)
       ("libfreenect" ,libfreenect)
       ("glut" ,freeglut)))
    (arguments
     '(#:tests? #f ; Project has not tests
       #:configure-flags '("-DBUILD_EXAMPLES=ON"
                           "-DBUILD_FAKENECT=OFF"
                           "-DBUILD_CPP=OFF"
                           "-DBUILD_C_SYNC=OFF")
       #:phases
       (modify-phases
         %standard-phases
         (add-after
           'unpack 'remove-sources
           (lambda* (#:key outputs #:allow-other-keys)
                    (substitute* "CMakeLists.txt"
                                 (("add_subdirectory \\(src\\)") "")
                                 ((".*libfreenectConfig.cmake.*") "")))))))
    (synopsis "Examples for libfreenect, the Xbox Kinect device library")))