opencv.js编译
一. 官方版本
后面发现官方有给https://github.com/opencv/opencv/releases
想查看支持哪些函数，即看./opencv-4.5.3/platforms/js/opencv_js.config.py
二.自己编译
参考https://docs.opencv.org/master/d4/da1/tutorial_js_setup.html
1.安装emsdk
https://github.com/emscripten-core/emsdk
首先下载：
git clone https://github.com/emscripten-core/emsdk.git
安装：
cd emsdk
./emsdk install latest
./emsdk activate latest
最后一个命令后返回：
Next steps:
- To conveniently access emsdk tools from the command line,
consider adding the following directories to your PATH:
/var/user_download_data/remotedata/make_opencv_js/emsdk
/var/user_download_data/remotedata/make_opencv_js/emsdk/node/14.15.5_64bit/bin
/var/user_download_data/remotedata/make_opencv_js/emsdk/upstream/emscripten
- This can be done for the current shell by running:
source "/var/user_download_data/remotedata/make_opencv_js/emsdk/emsdk_env.sh"
- Configure emsdk in your shell startup scripts by running:
echo 'source "/var/user_download_data/remotedata/make_opencv_js/emsdk/emsdk_env.sh"' >> $HOME/.bash_profile
然后运行：
source ./emsdk_env.sh
现在重新尝试在103机器上安装，返回：
(base) [root@machine emsdk]# source ./emsdk_env.sh
Adding directories to PATH:
PATH += /var/user_download_data/remotedata/make_opencv_js/emsdk
PATH += /var/user_download_data/remotedata/make_opencv_js/emsdk/upstream/emscripten
PATH += /var/user_download_data/remotedata/make_opencv_js/emsdk/node/14.15.5_64bit/bin
Setting environment variables:
PATH = /var/user_download_data/remotedata/make_opencv_js/emsdk:/var/user_download_data/remotedata/make_opencv_js/emsdk/upstream/emscripten:/var/user_download_data/remotedata/make_opencv_js/emsdk/node/14.15.5_64bit/bin:/var/u01/hadoop/anaconda3/bin:/var/u01/hadoop/anaconda3/condabin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/cuda-10.1/bin
EMSDK = /var/user_download_data/remotedata/make_opencv_js/emsdk
EM_CONFIG = /var/user_download_data/remotedata/make_opencv_js/emsdk/.emscripten
EMSDK_NODE = /var/user_download_data/remotedata/make_opencv_js/emsdk/node/14.15.5_64bit/bin/node
然后发现有一个变量没有命名：
export EMSCRIPTEN=/var/user_download_data/remotedata/make_opencv_js/emsdk/upstream/emscripten
这样运行下面的build_js.py时就不会报：
EMSCRIPTEN environment variable is not available. Please properly activate Emscripten SDK and consider using 'emcmake' launcher
2.下载opencv
git clone https://github.com/opencv/opencv.git
运行：
(base) [root@machine make_opencv_js]# emcmake python ./opencv-4.5.3/platforms/js/build_js.py build_js
报错：
build_js.py: error: unrecognized arguments: -DCMAKE_TOOLCHAIN_FILE=/var/user_download_data/remotedata/make_opencv_js/emsdk/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DCMAKE_CROSSCOMPILING_EMULATOR=/var/user_download_data/remotedata/make_opencv_js/emsdk/node/14.15.5_64bit/bin/node
emcmake: error: 'python3 ./opencv-4.5.3/platforms/js/build_js.py build_js -DCMAKE_TOOLCHAIN_FILE=/var/user_download_data/remotedata/make_opencv_js/emsdk/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DCMAKE_CROSSCOMPILING_EMULATOR=/var/user_download_data/remotedata/make_opencv_js/emsdk/node/14.15.5_64bit/bin/node' failed (returned 2)
(base) [root@machine make_opencv_js]# exit
然后我看了下./opencv-4.5.3/platforms/js/build_js.py文件
直接添加进这两个参数即可：
parser.add_argument('-DCMAKE_TOOLCHAIN_FILE', default='', help='DCMAKE_TOOLCHAIN_FILE')
parser.add_argument('-DCMAKE_CROSSCOMPILING_EMULATOR', default='', help="DCMAKE_CROSSCOMPILING_EMULATOR")
但是又报错：
CMake Error at CMakeLists.txt:27 (cmake_minimum_required):
CMake 3.5.1 or higher is required. You are running version 2.8.11
-- Configuring incomplete, errors occurred!
Traceback (most recent call last):
File "./build_js.py", line 286, in <module>
builder.config()
File "./build_js.py", line 192, in config
execute(cmd)
File "./build_js.py", line 23, in execute
raise Fail("Child returned: %s" % retcode)
__main__.Fail: Child returned: 1
emcmake: error: 'python ./build_js.py build_js -DCMAKE_TOOLCHAIN_FILE=/var/user_download_data/remotedata/make_opencv_js/emsdk/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DCMAKE_CROSSCOMPILING_EMULATOR=/var/user_download_data/remotedata/make_opencv_js/emsdk/node/14.15.5_64bit/bin/node' failed (returned 1)
应该是cmake的版本太低了，更新新版本
现在是：
(base) [root@machine js]# cmake --version
cmake version 2.8.11
安装新的版本：
wget https://cmake.org/files/v3.9/cmake-3.9.2.tar.gz
然后：
cd cmake-3.9.2
./configure
make
sudo make install
然后这样子得到的cmake文件就能够使用了，更改build_js.py的：
def get_cmake_cmd(self):
cmd = [
"cmake",
"-DPYTHON_DEFAULT_EXECUTABLE=%s" % sys.executable,
为：
def get_cmake_cmd(self):
cmd = [
"/var/user_download_data/remotedata/make_opencv_js/cmake-3.9.2/bin/cmake",
"-DPYTHON_DEFAULT_EXECUTABLE=%s" % sys.executable,
指定使用新版本的cmake
然后再运行：
emcmake python /var/user_download_data/remotedata/make_opencv_js/opencv-4.5.3/platforms/js/build_js.py build_js
就成功生成了：
OpenCV.js location: /var/user_download_data/remotedata/make_opencv_js/opencv-4.5.3/platforms/js/build_js/bin/opencv.js
得到的opencv.js大小大概是8.3M
3.局部函数编译
如果你只想要编译opencv的一部分功能,可以通过更改/var/user_download_data/remotedata/make_opencv_js/opencv-4.5.3/platforms/js下的opencv_js.config.py,即只保留想要的函数即可
比如我只留下：
core = {'': ['gemm', 'norm']}
calib3d = {'': ['solvePnP']}
white_list = makeWhiteList([core, calib3d])
但是使用生成的opencv.js的时候报错：
cv.matFromArray is not a function
使用这个发现没有cv.matFromArray,
使用console.log(cv)，发现连这个都没有出来：
Uncaught ReferenceError: cv is not defined
参考：https://github.com/opencv/opencv/issues/17620
发现是加载的问题，但是使用上面说的方法也没有成功加载，反而是使用下面的写法能成功加载：
<script type='text/javascript'>
async function onOpenCvReady() {
console.log('hello');
console.log(cv);
if (cv instanceof Promise) {
cv = await cv;
console.log(cv.Mat);
console.log(cv.matFromArray);
}
}
</script>
<script src="js/opencv.js" onload="onOpenCvReady();" ></script>
可见，原因其实是cv还没有调用进来你就使用了，难怪没有调用到
这样就成功调用了opencv.js,现在这个模型的大小是2.1M
