如何将emscripten与cmake一起用于项目依赖？

Question

所以我试图用emscripten移植到WebAssembly（wasm）一个程序，开头有以下内容：

#include <Eigen/Geometry>
#include <boost/filesystem.hpp>
#include <dvo/core/intrinsic_matrix.h>
#include <dvo/core/surface_pyramid.h>
#include <dvo/dense_tracking.h>
#include <fstream>
#include <iostream>
#include <opencv2/opencv.hpp>

为了轻松开始，我尝试编译一个最小的hello world OpenCV程序：

#include <opencv2/opencv.hpp>
#include <stdio.h>
using namespace cv;
int main(int argc, char **argv) {
  Mat M(2, 2, CV_8UC3, Scalar(0, 0, 255));
  std::cout << "M = " << std::endl << " " << M << std::endl;
  return 0;
}

我有以下CMakeLists.txt：

cmake_minimum_required(VERSION 2.8)
project( DisplayImage )
find_package( OpenCV REQUIRED PATHS third-party/opencv-4.1.0/build_wasm NO_DEFAULT_PATH)
include_directories( ${OpenCV_INCLUDE_DIRS} )
add_executable( hello hello.cpp )
target_link_libraries( hello ${OpenCV_LIBS} )

其中third-party/opencv-4.1.0/build_wasm是我在其中构建OpenCV的文件夹（cf doc）：

python ./platforms/js/build_js.py build_wasm --build_wasm

现在，当我在我的项目上运行emconfigure cmake ..时，它找不到OpenCV（“找不到包配置......”）。我做错了什么，但我不知道是什么。不幸的是，关于使用带有cmake和依赖关系的emscripten的文档并不详细。或许这个问题特定于OpenCV，我不知道。

编辑

完成错误：

 ~/t/w/w/build  emconfigure cmake ..                                                  ven. 26 avril 2019 16:01:00 CEST
CMake Error at CMakeLists.txt:5 (find_package):
  Could not find a package configuration file provided by "OpenCV" with any
  of the following names:

    OpenCVConfig.cmake
    opencv-config.cmake

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


-- Configuring incomplete, errors occurred!
See also "/home/matthieu/temp/wasm/wasm-opencv/build/CMakeFiles/CMakeOutput.log".
shared:ERROR: Configure step failed with non-zero return code: 1.  Command line: cmake -DCMAKE_CROSSCOMPILING_EMULATOR="/home/matthieu/programs/emsdk/node/8.9.1_64bit/bin/node" .. -DCMAKE_TOOLCHAIN_FILE=/home/matthieu/programs/emsdk/emscripten/1.38.30/cmake/Modules/Platform/Emscripten.cmake at /home/matthieu/temp/wasm/wasm-opencv/build

CMakeFiles/CMakeOutput.log的内容：

The target system is: Emscripten - 1 - x86
The host system is: Linux - 4.19.36-1-lts - x86_64

Answer 1

所以我终于设法用cmake编译了这个例子。这很丑陋，因为我手动添加包含和库与一些GLOB。我希望OpenCV，在构建库时，将提供一个OpenCVConfig.cmake文件，其中完成了所有依赖项设置。它可以允许在定位时使用经典的${OpenCV_INCLUDE_DIRS}和${OpenCV_LIBS}。

cmake_minimum_required( VERSION 3.1 )
set( CMAKE_CXX_STANDARD 11 )
project( HelloCV )

# Does not work
# find_package( OpenCV REQUIRED PATHS third-party/opencv-4.1.0/build_wasm NO_DEFAULT_PATH)

# Needed for opencv2/opencv.hpp
include_directories( third-party/opencv-4.1.0/include )

# Needed by opencv.hpp for opencv2/opencv_modules.hpp
include_directories( third-party/opencv-4.1.0/build_wasm )

# Needed by opencv_modules.hpp for every module
file( GLOB opencv_include_modules "third-party/opencv-4.1.0/modules/*/include" )
include_directories( ${opencv_include_modules} )

# Our hello world executable
add_executable( hello hello.cpp )

# Link to opencv.js precompiled libraries
file( GLOB opencv_js "third-party/opencv-4.1.0/build_wasm/lib/*.a" )
target_link_libraries( hello ${opencv_js} )

使用emscripten编译到WebAssembly时，这很有效：

~/t/e/o/build  emconfigure cmake -DCMAKE_BUILD_TYPE=Release ..
...
~/t/e/o/build  emmake make
...
~/t/e/o/build  node hello.js
M =
 [  0,   0, 255,   0,   0, 255;
   0,   0, 255,   0,   0, 255]

我当前的CMakeLists.txt的一个烦人的问题是它不能在本机中成功编译，只有wasm。如果您有比这更好的cmake配置，那么可以轻松更改目标（x86或emscripten），请分享您的答案。