使用Emscripten编译含CGAL的C++项目至Wasm失败求助

我克隆了一个依赖CGAL的C++项目，尝试用Emscripten将其编译为WebAssembly格式。单独用cmake ../在自建build目录中能成功配置，但执行emcmake cmake ../时编译失败，错误提示找不到CGAL的配置文件CGALConfig.cmake或cgal-config.cmake。

成功的本地CMake配置日志 #

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

Emscripten编译错误日志 #

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)

1. 先指定CGAL配置文件路径 #

普通CMake能找到系统安装的CGAL，是因为默认搜索了/usr/lib/x86_64-linux-gnu/cmake/CGAL/目录。交叉编译时需要显式告诉Emscripten的CMake工具链这个路径：

emcmake cmake ../ -DCGAL_DIR=/usr/lib/x86_64-linux-gnu/cmake/CGAL/

执行后大概率会遇到GMP/MPFR找不到的新错误——系统安装的GMP/MPFR是x86架构的，无法被Emscripten的交叉编译环境使用，需要为WebAssembly编译这两个依赖库。

2. 编译Emscripten版本的GMP和MPFR #

编译GMP #

1. 下载GMP源码并解压，进入源码目录：

   wget https://gmplib.org/download/gmp/gmp-6.3.0.tar.xz
   tar -xf gmp-6.3.0.tar.xz
   cd gmp-6.3.0
   

2. 用Emscripten配置编译：

   emconfigure ./configure --host=asmjs-unknown-emscripten --prefix=$HOME/emsdk/ports/gmp
   emmake make -j$(nproc)
   emmake make install
   

编译MPFR #

1. 下载MPFR源码并解压，进入源码目录：

   wget https://www.mpfr.org/mpfr-current/mpfr-4.2.1.tar.xz
   tar -xf mpfr-4.2.1.tar.xz
   cd mpfr-4.2.1
   

2. 用Emscripten配置编译（依赖已编译好的GMP）：

   emconfigure ./configure --host=asmjs-unknown-emscripten --with-gmp=$HOME/emsdk/ports/gmp --prefix=$HOME/emsdk/ports/mpfr
   emmake make -j$(nproc)
   emmake make install
   

3. 带依赖路径执行Emscripten CMake配置 #

现在在cmake命令中同时指定CGAL、GMP、MPFR的路径：

emcmake cmake ../ \
  -DCGAL_DIR=/usr/lib/x86_64-linux-gnu/cmake/CGAL/ \
  -DGMP_INCLUDE_DIR=$HOME/emsdk/ports/gmp/include \
  -DGMP_LIBRARY=$HOME/emsdk/ports/gmp/lib/libgmp.a \
  -DMPFR_INCLUDE_DIR=$HOME/emsdk/ports/mpfr/include \
  -DMPFR_LIBRARY=$HOME/emsdk/ports/mpfr/lib/libmpfr.a \
  -DCMAKE_BUILD_TYPE=Release

备选方案：编译Emscripten版本的CGAL #

如果上面的方法仍有问题，可以直接编译针对WebAssembly的CGAL源码：

1. 克隆CGAL源码：

   git clone https://github.com/CGAL/cgal.git
   cd cgal
   mkdir build-emscripten && cd build-emscripten
   

2. 用Emscripten编译CGAL：

   emcmake cmake ../ \
     -DCMAKE_BUILD_TYPE=Release \
     -DGMP_INCLUDE_DIR=$HOME/emsdk/ports/gmp/include \
     -DGMP_LIBRARY=$HOME/emsdk/ports/gmp/lib/libgmp.a \
     -DMPFR_INCLUDE_DIR=$HOME/emsdk/ports/mpfr/include \
     -DMPFR_LIBRARY=$HOME/emsdk/ports/mpfr/lib/libmpfr.a
   emmake make -j$(nproc)
   

3. 在你的项目中指定CGAL_DIR为编译后的目录：

   emcmake cmake ../ \
     -DCGAL_DIR=/path/to/cgal/build-emscripten \
     -DGMP_INCLUDE_DIR=$HOME/emsdk/ports/gmp/include \
     -DGMP_LIBRARY=$HOME/emsdk/ports/gmp/lib/libgmp.a \
     -DMPFR_INCLUDE_DIR=$HOME/emsdk/ports/mpfr/include \
     -DMPFR_LIBRARY=$HOME/emsdk/ports/mpfr/lib/libmpfr.a \
     -DCMAKE_BUILD_TYPE=Release
   

注意事项 #

• 确保已正确激活Emscripten环境：source $HOME/emsdk/emsdk_env.sh（路径根据你的emsdk安装位置调整）
• 如果项目依赖Boost，同样需要确认Boost是否能被Emscripten找到，或者编译Emscripten版本的Boost

内容的提问来源于stack exchange，提问作者YI-CHENG LI