Emscripten with cgal failed

Question

First I clone this project: https://github.com/yushi-bot/CGAL_triangulation_demo.

Background: I am attempting to compile a C++ program that uses the CGAL library into WebAssembly (wasm) format using Emscripten technology to run it on a web page. The compilation is successful when using CMake alone. However, when I try to use the command emcmake make ../, the compilation process fails.

cmake ../        (at build folder which make by myself , it is success)

-- The C compiler identification is GNU 11.4.0
-- The CXX compiler identification is GNU 11.4.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Warning at /usr/lib/x86_64-linux-gnu/cmake/CGAL/CGALConfig.cmake:92 (message):
  CGAL_DATA_DIR cannot be deduced, set the variable CGAL_DATA_DIR to set the
  default value of CGAL::data_file_path()
Call Stack (most recent call first):
  CMakeLists.txt:4 (find_package)


-- Using header-only CGAL
-- Targetting Unix Makefiles
-- Using /usr/bin/c++ compiler.
-- Found GMP: /usr/lib/x86_64-linux-gnu/libgmp.so
-- Found MPFR: /usr/lib/x86_64-linux-gnu/libmpfr.so
-- Found Boost: /usr/lib/x86_64-linux-gnu/cmake/Boost-1.74.0/BoostConfig.cmake (found suitable version "1.74.0", minimum required is "1.48")
-- Boost include dirs: /usr/include
-- Boost libraries:
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE
-- Using gcc version 4 or later. Adding -frounding-math
-- Build type:
-- USING CXXFLAGS = ' '
-- USING EXEFLAGS = ' '
CMake Warning at /usr/lib/x86_64-linux-gnu/cmake/CGAL/CGAL_enable_end_of_configuration_hook.cmake:99 (message):
  =======================================================================

  CGAL performance notice:

  The variable CMAKE_BUILD_TYPE is set to "".  For performance reasons, you
  should set CMAKE_BUILD_TYPE to "Release".

  Set CGAL_DO_NOT_WARN_ABOUT_CMAKE_BUILD_TYPE to TRUE if you want to disable
  this warning.

  =======================================================================
Call Stack (most recent call first):
  CMakeLists.txt:9223372036854775807 (CGAL_run_at_the_end_of_configuration)


-- Configuring done
-- Generating done
-- Build files have been written to: /home/lyciih/github/CGAL_triangulation_demo/build

When I use this command.

emcmake cmake ../ 

configure: cmake ../ -DCMAKE_TOOLCHAIN_FILE=/usr/share/emscripten/cmake/Modules/Platform/Emscripten.cmake -DCMAKE_CROSSCOMPILING_EMULATOR=/usr/bin/node;--experimental-wasm-threads
CMake Error at CMakeLists.txt:4 (find_package):
  By not providing "FindCGAL.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "CGAL", but
  CMake did not find one.

  Could not find a package configuration file provided by "CGAL" with any of
  the following names:

    CGALConfig.cmake
    cgal-config.cmake

  Add the installation prefix of "CGAL" to CMAKE_PREFIX_PATH or set
  "CGAL_DIR" to a directory containing one of the above files.  If "CGAL"
  provides a separate development package or SDK, be sure it has been
  installed.


-- Configuring incomplete, errors occurred!
See also "/home/lyciih/github/CGAL_triangulation_demo/build/CMakeFiles/CMakeOutput.log".
emcmake: error: 'cmake ../ -DCMAKE_TOOLCHAIN_FILE=/usr/share/emscripten/cmake/Modules/Platform/Emscripten.cmake -DCMAKE_CROSSCOMPILING_EMULATOR=/usr/bin/node;--experimental-wasm-threads' failed (returned 1)

please tell me how to fix it.

Thanks for help

Answer 1

The issue is related to: https://github.com/emscripten-core/emscripten/issues/13310

In short: the toolchain file from emscripten restricts the search paths for packages and libraries, hence CGAL cannot be found. You can override this behaviour by setting -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=BOTH during your call to emcmake cmake ...

Also see: https://cmake.org/cmake/help/latest/variable/CMAKE_FIND_ROOT_PATH_MODE_PACKAGE.html#cmake-find-root-path-mode-package