在javascript中,Array有很多内置的功能,比如Array.map,Array.filter,Array.find等等,能用内置的功能就用内置的功能,最好不要自己实现一套,因为底层调用的可能压根就不是js语言本身,底层的实现可能由C/C++实现的。如果我们要做的一些功能,需要高性能密集计算,但是JavaScript内置函数无法满足我们要求的时候,这时候我们就要自己用C/C++编写一个程序,然后封装成wasm文件给JavaScript调用了,此时wasm还包含了.a文件这样的第三方库。
我们这里有个需求,就是在地球上有两艘船,船A和船B在某个经纬度位置触发,以某个航向、速度行驶,求它们间最小距离是多少,达到最小距离的时候,经过时间是多少秒?
首先这个功能用C/C++来编写,并且还要用到开源第三方库。
下图的红圈注释里面有几个参数,分别表示经度、纬度、速度、航向,当然getCPA最后一个参数6.5表示6.5分钟的时间长度。表示计算6.5分钟以内,两船最小距离是多少,并且到达最小距离时,经过时间是多少。
打开Visual Studio 2022,新建一个cmake工程,项目名称为GeoCompute。这仅仅是一个测试项目,如果测试通过,没有问题了,就把该代码交给emcc或者em++去编译。
CMakeLists.txt文件内容如下:
在这里,我采用vcpkg来安装GeographicLib库
可以执行如下命令安装。
vcpkg install GeographicLib:x64-windows
# CMakeList.txt: GeoCompute 的 CMake 项目,在此处包括源代码并定义
# 项目特定的逻辑。
#
cmake_minimum_required (VERSION 3.8)
set(VCPKG_ROOT "D:/CppPkg/WinVcpkg/vcpkg" CACHE PATH "")
set(CMAKE_TOOLCHAIN_FILE "${VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake")
# Enable Hot Reload for MSVC compilers if supported.
if (POLICY CMP0141)
cmake_policy(SET CMP0141 NEW)
set(CMAKE_MSVC_DEBUG_INFORMATION_FORMAT "$,$>,$<$:EditAndContinue>,$<$:ProgramDatabase>>" )
endif()
project ("GeoCompute")
# 将源代码添加到此项目的可执行文件。
add_executable (GeoCompute "GeoCompute.cpp" )
find_package (GeographicLib CONFIG REQUIRED)
target_link_libraries (GeoCompute PRIVATE ${GeographicLib_LIBRARIES})
if (CMAKE_VERSION VERSION_GREATER 3.12)
set_property(TARGET GeoCompute PROPERTY CXX_STANDARD 20)
endif()
# TODO: 如有需要,请添加测试并安装目标。
然后编写一个GeoCompute.cpp文件
#include
#include
#include
#include
#include
const double EARTH_RADIUS = 6377830.0; // 地球的平均半径,单位为千米
const double M_PI = 3.14159265359;
struct LatLon {
double first;
double second;
};
double deg2rad(double deg) {
return deg * M_PI / 180.0;
}
double haversine_distance(double lat1, double lon1, double lat2, double lon2) {
double dlat = deg2rad(lat2 - lat1);
double dlon = deg2rad(lon2 - lon1);
double a = std::sin(dlat / 2) * std::sin(dlat / 2) +
std::cos(deg2rad(lat1)) * std::cos(deg2rad(lat2)) *
std::sin(dlon / 2) * std::sin(dlon / 2);
double c = 2 * std::atan2(std::sqrt(a), std::sqrt(1 - a));
return EARTH_RADIUS * c;
}
LatLon new_position_with_geolib(double lat, double lon, double speed, double cog, double T) {
const GeographicLib::Geodesic& geod = GeographicLib::Geodesic::WGS84();
double s12 = speed * T;
double lat2, lon2;
// Direct method gives the destination point given start point, initial azimuth, and distance
geod.Direct(lat, lon, cog, s12, lat2, lon2);
return { lat2, lon2 };
}
double new_distance(double T, double latA, double lonA, double speedA, double cogA, double latB, double lonB, double speedB, double cogB) {
auto resA = new_position_with_geolib(latA, lonA, speedA, cogA, T);
auto resB = new_position_with_geolib(latB, lonB, speedB, cogB, T);
return haversine_distance(resA.first, resA.second, resB.first, resB.second);
}
LatLon getCPA(double latA, double lonA, double speedA, double cogA, double latB, double lonB, double speedB, double cogB, double tcpa) {
double RES_TCPA = INFINITY;
double RES_DCPA = INFINITY;
double prev_dist = INFINITY;
double cur_dist = INFINITY;
std::vector<int> status;
int t_lim = tcpa * 60;
int step = 1;
if (t_lim > 600) {
step = int(double(t_lim) / 300.0);
}
for (int t = 0;t < t_lim; t += step) {
prev_dist = new_distance(t, latA, lonA, speedA, cogA, latB, lonB, speedB, cogB);
cur_dist = new_distance(t + step, latA, lonA, speedA, cogA, latB, lonB, speedB, cogB);
if (prev_dist < RES_DCPA) {
RES_DCPA = prev_dist;
}
if (cur_dist - prev_dist <= 0) {
if (status.size() == 0) {
status.emplace_back(-1);
}
}
else {
if (status.size() == 0) {
status.emplace_back(1);
break;
}
else {
if (status[0] == -1) {
status.emplace_back(1);
}
}
}
if (status.size() == 2 && status[0] == -1 && status[1] == 1) {
RES_TCPA = t;
break;
}
}
return { RES_TCPA, RES_DCPA };
}
//1. 一开始距离就变大
// 2. 从0时刻到指定tcpa一直减小
// 3. 从0时刻到指定tcpa,先减小后增大
int main() {
double lat = 40, lon = 100, speed = 10, cog = 45, T = 3600;
auto result = new_position_with_geolib(lat, lon, speed, cog, T);
std::cout << "New Latitude: " << result.first << ", New Longitude: " << result.second << std::endl;
/*
latA, lonA, speedA, cogA = 21.3058, 109.1014, 15.12, 187.13
latB, lonB, speedB, cogB = 21.288205, 109.118725, 3.909777, 254.42
*/
int i = 0;
while (true) {
// 先减小后增大
auto res_ = getCPA(21.3058, 109.1014, 15.12, 187.13, 21.288205, 109.118725, 3.909777, 254.42, 6.5);
//auto res_ = getCPA(22.3058, 108.1014, 15.12, 187.13, 21.288205, 109.118725, 3.909777, 254.42, 6.0);
//auto res_ = getCPA(0.0, 0.0, 15.12, 225.0, 0.0000001, 0.0000001, 3.909777, 45.0, 6.0);
std::cout << res_.first << " --- " << res_.second << std::endl;
i++;
printf("%d\n", i);
}
return 0;
}
好了,如果代码测试完成了。现在我们创建一个cmake工程,项目名为EmscriptenTest,这是用来生成wasm文件和js文件来给JavaScript调用的。
由于JavaScript运行在浏览器,不能直接支持windows的lib静态库,所以想办法得到.a库。
首先从github拉取geographiclib库的源码
git clone https://github.com/geographiclib/geographiclib.git
然后进入到根目录:
cd geographiclib
最后用emcmake和emmake命令编译代码(前提是要安装emsdk:官网有教程说明:https://emscripten.org/docs/getting_started/downloads.html)
emcmake cmake .
emmake make
编译完成之后:
转到目录geographiclib/src
找到libGeographicLib.a文件,然后把该文件拷贝到EmscriptenTest项目的lib目录下(如果没有lib目录则自己新建)
然后是CMakeLists.txt文件:
# CMakeList.txt: EmscriptenTest 的 CMake 项目,在此处包括源代码并定义
# 项目特定的逻辑。
#
cmake_minimum_required (VERSION 3.8)
set(CMAKE_TOOLCHAIN_FILE "D:/CppPkg/emsdk/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake")
# 手动设置GeographicLib的路径
set(GEOGRAPHICLIB_INCLUDE_DIR "/path/to/vcpkg/installed/x64-windows/include")
#set(GEOGRAPHICLIB_LIB_DIR "/path/to/vcpkg/installed/x64-windows/lib")
set(GEOGRAPHICLIB_LIB_DIR "填写你的EmscriptenTest/lib目录的绝对路径")
# Enable Hot Reload for MSVC compilers if supported.
if (POLICY CMP0141)
cmake_policy(SET CMP0141 NEW)
set(CMAKE_MSVC_DEBUG_INFORMATION_FORMAT "$,$>,$<$:EditAndContinue>,$<$:ProgramDatabase>>" )
endif()
project ("EmscriptenTest")
# 将源代码添加到此项目的可执行文件。
add_executable (EmscriptenTest "GeoCompute.cpp")
include_directories(D:/CppPkg/WinVcpkg/vcpkg/installed/x64-windows/include )
target_link_libraries(EmscriptenTest ${GEOGRAPHICLIB_LIB_DIR}/libGeographicLib.a)
add_library(GeoCompute STATIC GeoCompute.cpp)
set_target_properties(GeoCompute PROPERTIES SUFFIX ".wasm")
set_target_properties(GeoCompute PROPERTIES LINK_FLAGS "--bind -s WASM=1 -s MODULARIZE=1 -s EXPORT_NAME='GeoComputeModule' -s EXPORTED_FUNCTIONS='[\"getCPA\"]'")
if (CMAKE_VERSION VERSION_GREATER 3.12)
set_property(TARGET EmscriptenTest PROPERTY CXX_STANDARD 20)
endif()
# TODO: 如有需要,请添加测试并安装目标。
这个EmscriptenTest.cpp没什么用,里面写个main函数,直接return 0;就完事儿了。
在项目根目录下新建GeoCompute.cpp文件
GeoCompute.cpp文件的内容:
可能会提示报错,但是如果点击重新生成,生成成功的话,是没事儿的。
在这个文件中,我修改了getCPA函数的返回类型为double* , 因为直接返回TDCPA结构体,JavaScript是无法识别的,一定要返回一个指针。
#include
#include
#include
#include
#include
#include
const double EARTH_RADIUS = 6377830.0; // 地球的平均半径,单位为千米
const double _M_PI = 3.14159265359;
struct LatLon {
double lat;
double lon;
};
struct TDCPA {
double res_tcpa;
double res_dcpa;
};
extern "C" {
EMSCRIPTEN_KEEPALIVE
double deg2rad(double deg) {
return deg * _M_PI / 180.0;
}
EMSCRIPTEN_KEEPALIVE
double haversine_distance(double lat1, double lon1, double lat2, double lon2) {
double dlat = deg2rad(lat2 - lat1);
double dlon = deg2rad(lon2 - lon1);
double a = std::sin(dlat / 2) * std::sin(dlat / 2) +
std::cos(deg2rad(lat1)) * std::cos(deg2rad(lat2)) *
std::sin(dlon / 2) * std::sin(dlon / 2);
double c = 2 * std::atan2(std::sqrt(a), std::sqrt(1 - a));
return EARTH_RADIUS * c;
}
EMSCRIPTEN_KEEPALIVE
LatLon new_position_with_geolib(double lat, double lon, double speed, double cog, double T) {
const GeographicLib::Geodesic& geod = GeographicLib::Geodesic::WGS84();
double s12 = speed * T;
double lat2, lon2;
// Direct method gives the destination point given start point, initial azimuth, and distance
geod.Direct(lat, lon, cog, s12, lat2, lon2);
return { lat2, lon2 };
}
EMSCRIPTEN_KEEPALIVE
double new_distance(double T, double latA, double lonA, double speedA, double cogA, double latB, double lonB, double speedB, double cogB) {
auto resA = new_position_with_geolib(latA, lonA, speedA, cogA, T);
auto resB = new_position_with_geolib(latB, lonB, speedB, cogB, T);
return haversine_distance(resA.lat, resA.lon, resB.lat, resB.lon);
}
EMSCRIPTEN_KEEPALIVE
double* getCPA(double latA, double lonA, double speedA, double cogA, double latB, double lonB, double speedB, double cogB, double tcpa) {
double RES_TCPA = INFINITY;
double RES_DCPA = INFINITY;
double prev_dist = INFINITY;
double cur_dist = INFINITY;
double* tdcpaPtr = new double[2];
std::vector<int> status;
int t_lim = tcpa * 60;
int step = 1;
if (t_lim > 600) {
step = int(double(t_lim) / 300.0);
}
for (int t = 0; t < t_lim; t += step) {
prev_dist = new_distance(t, latA, lonA, speedA, cogA, latB, lonB, speedB, cogB);
cur_dist = new_distance(t + step, latA, lonA, speedA, cogA, latB, lonB, speedB, cogB);
if (prev_dist < RES_DCPA) {
RES_DCPA = prev_dist;
}
if (cur_dist - prev_dist <= 0) {
if (status.size() == 0) {
status.emplace_back(-1);
}
}
else {
if (status.size() == 0) {
status.emplace_back(1);
break;
}
else {
if (status[0] == -1) {
status.emplace_back(1);
}
}
}
if (status.size() == 2 && status[0] == -1 && status[1] == 1) {
RES_TCPA = t;
break;
}
}
tdcpaPtr[0] = RES_TCPA;
tdcpaPtr[1] = RES_DCPA;
return tdcpaPtr;
}
}
好了,现在就测试全部重新生成。如果没有报错,则通过测试。通过测试之后。证明可以大胆使用em++命令直接编译GeoCompute.cpp为wasm文件了。
打开cmd进入到EmscriptenTest工程根目录。
em++ GeoCompute.cpp -O1 -o libGeoCompute.js -s WASM=1 -s MODULARIZE=1 -s EXPORT_NAME="GeoComputeModule" -s "EXPORTED_FUNCTIONS=['_deg2rad', '_haversine_distance', '_new_position_with_geolib', '_new_distance', '_getCPA']" -s "EXPORTED_RUNTIME_METHODS=['ccall', 'cwrap']" -I D:/CppPkg/WinVcpkg/vcpkg/installed/x64-windows/include -L D:/HighPerformanceProjects/CppProjects/EmscriptenTest/lib -lGeographicLib
我这里导出了所有的函数,函数前面要加上下划线。但是在cmakelists.txt中不需要加下划线。
执行完成命令之后,会生成libGeoCompute.js和libGeoCompute.wasm文件。
现在可以使用npm创建一个原生的JavaScript项目。
这是工程目录结构:
最重要是main.js的写法:
const fs = require('fs');
const path = require('path');
// 加载 Emscripten 生成的模块
const Module = require('./libGeoCompute.js');
async function main() {
try {
const instance = await Module({
locateFile: (filename) => path.join(__dirname, filename),
});
console.log('Module instance:', instance);
console.log(typeof instance.cwrap)
// await new Promise((resolve) => {
// console.log('Waiting for runtime initialization...');
// instance.onRuntimeInitialized = () => {
// console.log('Runtime initialized.');
// resolve();
// };
// });
// 使用 cwrap 包装 getCPA 函数
const getCPA = instance.cwrap('getCPA', 'number', [
'number', 'number', 'number', 'number', 'number', 'number', 'number', 'number', 'number'
]);
console.log(typeof getCPA)
// 调用导出的 getCPA 函数
const resultPtr = getCPA(21.3058, 109.1014, 15.12, 187.13, 21.288205, 109.118725, 3.909777, 254.42, 6.5);
console.log(typeof resultPtr)
// 解析返回值(假设返回指向结构体的指针)
const res_tcpa = instance.HEAPF64[resultPtr >> 3]; // 读取double指针的第0个元素
const res_dcpa = instance.HEAPF64[(resultPtr >> 3) + 1]; // 读取地址偏移量+1
console.log('TCPA:', res_tcpa);
console.log('DCPA:', res_dcpa);
console.log('Continuing after runtime initialization.');
// 继续下面的逻辑...
} catch (error) {
console.error('Error:', error);
}
}
main();
index.html的内容:
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Blank Windowtitle>
head>
<body>
body>
html>
package.json的内容:
{
"name": "nodedevtest",
"version": "1.0.0",
"description": "A minimal Electron application",
"main": "main.js",
"scripts": {
"start": "node main.js"
},
"keywords": [],
"author": "",
"license": "ISC",
"dependencies": {
"axios": "^1.6.8",
"electron": "^30.0.1",
"pixi.js": "^8.1.0",
"request": "^2.88.2"
}
}
得出的结果:
得出的结果是154和1519.5687501879786
表示经过154秒以后,两船达到最小距离,并且最小距离为1519米多。