Feature cmake basic structure for compilation

[kalwalt]

CMAKE implementation

Preamble

I will provide a minimal cmake implementation to compile the library.
If the library can be compiled with cmake i will provide also some basic test with googletest as i already started.

Final considerations

The library now can be compiled with the CMakeLists.txt file in the WebARKit directory. The result will be the WebARKitLib static lib (libWebARKitLib.a). The static lib is used to make some basic test, i would improve this, adding more of them. I haven't tested on Windows or Mac, i used the linux environment for simplicity. I haven't ttried to compile the libWebARKitLib.a with Emscripten ( with emcmake) but i think the cmake script should be a bit different, because we link the 3dparty zlib (included with OpenCV) but Emscripten has its own zlib. Anyway this will be space for another PR.

[kalwalt]

I have tested under Windows and i always i get a SEH error, maybe is related to the platform. I made some improvements in the code that i will commit soon, but for now i'm testing under Ubuntu(WSL) to see if i get the same error or not.

[kalwalt]

Under Ubuntu(WSL) i got a similar error:

./hello_test
Running main() from /mnt/c/Users/perda/kalwalt-github/webarkit-testing/emscripten/WebARKitLib/tests/build/_deps/googletest-src/googletest/src/gtest_main.cc
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from HelloTest
[ RUN      ] HelloTest.BasicAssertions
[info] Webarkit C++ lib v1.0.0 initalised.
free(): invalid size
Aborted

I think the issue is in the destructor and the versionString variable. I will try to fix this.

[kalwalt]

with commit d292c57 i solved the issue see the log running the test:

./hello_test
Running main() from /mnt/c/Users/perda/kalwalt-github/webarkit-testing/emscripten/WebARKitLib/tests/build/_deps/googletest-src/googletest/src/gtest_main.cc
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from InitTest
[ RUN      ] InitTest.InitialiseBaseTest
[info] Webarkit C++ lib v1.0.0 initalised.
[       OK ] InitTest.InitialiseBaseTest (0 ms)
[----------] 1 test from InitTest (0 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (1 ms total)
[  PASSED  ] 1 test.

I need to test under windows but i think it will be fine. I have to change some cmake target includes because they are pointing to opencv and opencv_contrib folder cloned with webarkit_testing repository (they are submodules in there), instead they should be related to them from cmake FetchContent.

[kalwalt]

I'm not sure that cmake FetchContent is the best approach for compiling a lib, and i'm not sure that it always compile correctly, at least on Windows. Most of the time i had to re run the cmage configuration step to avoid missing includes from xfeatuers2d module.
I will make other tests and i can also prepare a github action script to run the test.
Based on these tests i will conider to opt to another approach: create opencv and opencv_contrib git submodule in this repository and adequate the cmake script, easier solution but has the downside to increase the size of the repository.

[kalwalt]

Now the action cript can run the build (cmake) but fails with this message:

fatal error: opencv2/xfeatures2d.hpp: No such file or directory
    6 | #include <opencv2/xfeatures2d.hpp>

this is the same message as i encountered compiling locally. i will see if this can be solved or i will found another solution.

[kalwalt]

from the action github log:
To be built: calib3d core features2d flann imgcodecs imgproc java video
you cam see that xfeatures2d is not added even i added twice here:

WebARKitLib/WebARKit/CMakeLists.txt

Line 42 in d338779

set(BUILD_opencv_xfeatures2d ON)

and:

WebARKitLib/WebARKit/CMakeLists.txt

Line 74 in d338779

set(BUILD_opencv_xfeatures2d ON)

and also the OPENCV_EXTRA_MODULES_PATH:

WebARKitLib/WebARKit/CMakeLists.txt

Line 52 in d338779

set(OPENCV_EXTRA_MODULES_PATH ../opencv_contrib-src/modules/)

and:

WebARKitLib/WebARKit/CMakeLists.txt

Line 72 in d338779

set(OPENCV_EXTRA_MODULES_PATH ../${opencv_contrib_SOURCE_DIR}/modules/)

[kalwalt]

Now it build process fails at the final stage:

[ 98%] Linking CXX executable bin/webarkit_test
/usr/bin/ld: cannot find -lopencv_xfeatures2d: No such file or directory
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/webarkit_test.dir/build.make:121: bin/webarkit_test] Error 1
make[1]: *** [CMakeFiles/Makefile2:1148: CMakeFiles/webarkit_test.dir/all] Error 2

this because the xfeatures2d static lib is not generated.

[kalwalt]

I can't find a solution to the last issue: with FetchContent i can't compile the xfeatures2d external module, maybe this is possible but i find very complicated. As i did for webrakit-testing i will create opencv and opencv_contrib git submodules and the libs will be compiled as i already did. The advantage with the FetchContent proces was to avoid to grow the size of the repository but i think better to create a strong basis for the future development.

[kalwalt]

So inside the WebARKitLib folder i will create a deps (dependencies folder) where opencv and opencv_contrib will be cloned as submodules. Of course our opencv and opencv_contrib forks because we did our modifications in the code.

[kalwalt]

I will make a step back because opencv + opencv_contrib are more than one Gb when downloaded, so maybe i will found an alternative option. I can provide binaries and static libs as i already did in opencv-em for other projects. I can develop a script and a github action to upload precompiled libs and headers for opencv and opencv_contrib with opencv-em and then when someone wants compile WebARKitLib will download these.

[kalwalt]

i can build opencv builds with opencv-em webarkit/opencv-em#6 i have tested the tests with the new opencv pre-binaries, see this gist
Now i will make a new opencv-em release so it can be downloaded as a .zip file, and maybe we can grab with FetcContent? or at least populated with a shell script...

[kalwalt]

Tests failing because the last command was for Windows OS, i will fix and surely it will work.

[kalwalt]

Now, i think this PR is on the good track to be merged.

[kalwalt]

During the tests phase we get this warning:

CMake Warning (dev) at /home/kalwalt/.local/lib/python3.10/site-packages/cmake/data/share/cmake-3.27/Modules/FetchContent.cmake:1316 (message):
  The DOWNLOAD_EXTRACT_TIMESTAMP option was not given and policy CMP0135 is
  not set.  The policy's OLD behavior will be used.  When using a URL
  download, the timestamps of extracted files should preferably be that of
  the time of extraction, otherwise code that depends on the extracted
  contents might not be rebuilt if the URL changes.  The OLD behavior
  preserves the timestamps from the archive instead, but this is usually not
  what you want.  Update your project to the NEW behavior or specify the
  DOWNLOAD_EXTRACT_TIMESTAMP option with a value of true to avoid this
  robustness issue.
Call Stack (most recent call first):
  /mnt/c/Users/perda/kalwalt-github/webarkit-testing/emscripten/WebARKitLib/WebARKit/CMakeLists.txt:9 (FetchContent_Declare)      
This warning is for project developers.  Use -Wno-dev to suppress it.

I will see to solve this one and then i can merge it.