napi系列学习高阶篇——通过IDE集成C/C++三方库并开发napi接口

简介

应用在调用系统固件集成的C/C++三方库时，可能会由于系统固件集成端与IDE的NDK中libc++版本不一致导致调用失败，而且系统固件集成的C/C++三方库对于应用的调式也很不友好，需要多方编译调试，很不方便。因此本文将通过在IDE上适配openjpeg 三方库为例介绍IDE上适配一个C/C++三方库的具体流程。

创建工程

在开发进行三方库适配以及napi接口开发前，我们需要创建一个三方库对应的工程，具体创建工程方法可以参照文档通过IDE开发一个Napi工程。

IDE上三方库的适配

本文中我们以适配 openjpeg 为例介绍整个适配流程 。

原生库准备

下载代码

通过openjpeg github网址，通过Code>>Download ZIP选项下载最新版本的源码包，并将其解压后放在IDE工程中的CPP目录下。

• 下载openjpeg 2.5.0版本的库：

• 将库放在IDE工程：

分析编译依赖

• 分析CMakeLists.txt 对于库不是很复杂且目录结构简单的库可以通过分析CMakeLists.txt文件来获取库的依赖。在openjpeg库中， 通过分析最外层CMakeLists.txt文件，可以得知编译openjpeg核心代码以及需要依赖编译库自带thirdparty，如下图：

而分析thirdparty/CMakeLists.txt文件，如果BUILD_THIRDPARTY开关未打开，将会通过FindPkgConfig自动搜索系统(IDE工具的SDK编译链)中的库文件，如下图：

并由此文件可以分析出该库非强制依赖了libz, libpng, libtiff以及liblcms2，如对libpng依赖的分析中：

IDE工具的SDK编译链中只有libz库，其他三个库是没有的，所以如果需要其他三个库的功能，我们需要将BUILD_THIRDPARTY开关打开，此开关在库顶层目录的CMakeLists.txt文件中，如下图：

到此，本库的依赖就已经分析完了。

• 通过运行cmake分析 我们除了分析CMakeLists.txt文件外，也可以通过在linux中通过cmake过程来分析对应的依赖。

我们在执行cmake的时候，会有对相关的依赖库的提示：

-- Large File support - found
-- Looking for include file malloc.h
-- Looking for include file malloc.h - found
-- Looking for _aligned_malloc
-- Looking for _aligned_malloc - not found
-- Looking for posix_memalign
-- Looking for posix_memalign - found
-- Looking for memalign
-- Looking for memalign - found
-- Found PkgConfig: /usr/bin/pkg-config (found version "0.29.1")
-- Found ZLIB: /usr/lib/x86_64-linux-gnu/libz.so (found version "1.2.11")
-- Your system seems to have a Z lib available, we will use it to generate PNG lib
-- Found PNG: /usr/lib/x86_64-linux-gnu/libpng.so (found version "1.6.37")
-- Your system seems to have a PNG lib available, we will use it
-- Found TIFF: /usr/lib/x86_64-linux-gnu/libtiff.so (found version "4.1.0")
-- Your system seems to have a TIFF lib available, we will use it
-- Could NOT find LCMS2 (missing: LCMS2_LIBRARY LCMS2_INCLUDE_DIR)
-- Could NOT find LCMS (missing: LCMS_LIBRARY LCMS_INCLUDE_DIR)
-- LCMS2 or LCMS lib not found, activate BUILD_THIRDPARTY if you want build it
-- Configuring done
-- Generating done

由以上信息可以查看到，编译此库需要依赖libz(found version "1.2.11")，libpng(found version "1.6.37")，libtiff(found version "4.1.0")以及liblcms2(LCMS2 or LCMS lib not found, activate BUILD_THIRDPARTY if you want build it)。从提示中可以看到，如果想要使能对应的功能且系统库中未包含该依赖的话，需要打开BUILD_THIRDPARTY 开关。

除了cmake中获取的依赖，我们也可以通过分析make编译过程获取更多的信息，具体方法可以参照三方库适配依赖分析。

重构CMakeLists

对于不复杂的库且没有其他四方库依赖的三方库，我们可以使用原生库的CMakeLists.txt文件，但是对于一些复杂的，且强制依赖其他四方库的库，使用其原生CMakeLists.txt文件，无法解决四方库依赖的问题。此时，我们就需要对三方库的CMakeLists.txt文件进行重构。

重构CMakeLists文件主要需涉及以下几点：

• 动态生成配置文件 查看原生CMakeLists.txt文件中是否有configure_file配置项，如果没有可直接跳过此步骤。
  在openjpeg库的原生CMakeLists.txt文件中，有2个配置文件需要动态生成：

  opj_config.h generation (2/2)

  configure_file(
  ${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/opj_config.h.cmake.in
  ${CMAKE_CURRENT_BINARY_DIR}/src/lib/openjp2/opj_config.h
  @ONLY
  )

  configure_file(
  ${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/opj_config_private.h.cmake.in
  ${CMAKE_CURRENT_BINARY_DIR}/src/lib/openjp2/opj_config_private.h
  @ONLY
  )

configure_file带了@ONLY参数，该参数限制了变量替换，让其只替换被@VAR@引用的变量。因此我们需要分析两个文件中对应的@VAR@配置规则。首先在opj_config.h.cmake.in文件定义的对应@VAR@的定义：

/* create opj_config.h for CMake */
#cmakedefine OPJ_HAVE_STDINT_H   @OPJ_HAVE_STDINT_H@
/*--------------------------------------------------------------------------*/
/* OpenJPEG Versioning                                                      */

/* Version number. */
#define OPJ_VERSION_MAJOR @OPENJPEG_VERSION_MAJOR@
#define OPJ_VERSION_MINOR @OPENJPEG_VERSION_MINOR@
#define OPJ_VERSION_BUILD @OPENJPEG_VERSION_BUILD@

在分析@VAR@的赋值规则，在顶层CMakeLists.txt中：

# opj_config.h generation (1/2)

# Check if some include files are provided by the system
include(EnsureFileInclude)
# These files are mandatory
ensure_file_include("string.h"   HAVE_STRING_H YES)
ensure_file_include("memory.h"   HAVE_MEMORY_H YES)
ensure_file_include("stdlib.h"   HAVE_STDLIB_H YES)
ensure_file_include("stdio.h"    HAVE_STDIO_H  YES)
ensure_file_include("math.h"     HAVE_MATH_H   YES)
ensure_file_include("float.h"    HAVE_FLOAT_H  YES)
ensure_file_include("time.h"     HAVE_TIME_H   YES)
ensure_file_include("stdarg.h"   HAVE_STDARG_H YES)
ensure_file_include("ctype.h"    HAVE_CTYPE_H  YES)
ensure_file_include("assert.h"   HAVE_ASSERT_H YES)

# For the following files, we provide an alternative, they are not mandatory
ensure_file_include("stdint.h"   OPJ_HAVE_STDINT_H   NO)
ensure_file_include("inttypes.h" OPJ_HAVE_INTTYPES_H NO)

从以上内容通过分析ensure_file_include可以知道，在执行cmake时从系统中查找stdint.h文件，如果查找到则将OPJ_HAVE_STDINT_H置起，否则不会改变。而IDE上是没有stdint.h文件的，因此我们需要在配置文件之前手动将OPJ_HAVE_STDINT_H置起，如下：

set(OPJ_HAVE_STDINT_H TRUE)

其他变量也是通过类似的方法分析。

• 相关宏定义的设置 通过add_definitions设置三方库的相关宏定义，如下所示：

  add_definitions(-DOPJ_HAVE_PNG_H=0 -DOPJ_HAVE_TIFF_H=1 -DOPJ_HAVE_LCMS2_H=1)

• 源码文件编译 三方库编译的源码可以通过在linux执行make的时候查看分析到：

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  [ 99%] Building C object src/bin/jp2/CMakeFiles/opj_decompress.dir/converttif.c.o
  [ 99%] Building C object src/bin/jp2/CMakeFiles/opj_decompress.dir/convertpng.c.o
  [100%] Linking C executable ../../../bin/opj_decompress
  [100%] Built target opj_decompress

由上面过程可看出，每个编译目标(Built target)所依赖的文件由上一个目标(如果上一个目标由的话)生成后以及该目标生成前的文件组成，如生成libopenjp2.so（Built target openjp）的文件是Built target openjp2_static之后以及Built target openjp之前的文件：

[ 14%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/thread.c.o
[ 15%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/bio.c.o
[ 16%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/cio.c.o
[ 16%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/dwt.c.o
[ 17%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/event.c.o
[ 18%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/ht_dec.c.o
[ 18%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/image.c.o
[ 19%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/invert.c.o
[ 20%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/j2k.c.o
[ 20%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/jp2.c.o
[ 21%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/mct.c.o
[ 22%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/mqc.c.o
[ 22%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/openjpeg.c.o
[ 23%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/opj_clock.c.o
[ 23%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/pi.c.o
[ 24%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/t1.c.o
[ 25%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/t2.c.o
[ 25%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/tcd.c.o
[ 26%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/tgt.c.o
[ 27%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/function_list.c.o
[ 27%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/opj_malloc.c.o
[ 28%] Building C object src/lib/openjp2/CMakeFiles/openjp2.dir/sparse_array.c.o

因此生成libopenjpeg.so的源文件我们就可以这样写：

set(SHARED_LIB_SRC "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/thread.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/bio.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/cio.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/dwt.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/event.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/ht_dec.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/image.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/invert.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/j2k.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/jp2.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/mct.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/mqc.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/openjpeg.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/opj_clock.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/pi.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/t1.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/t2.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/tcd.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/tgt.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/function_list.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/opj_malloc.c"
                  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/sparse_array.c")

其中CMAKE_CURRENT_SOURCE_DIR是代表当前CMakeLists.txt文件所在的路径。

• 目标文件生成 这里我们调用add_library生成一个目标文件libopenjpeg_shared.so，其依赖上面分析的源码share_lib_src：

  add_library(openjp2 SHARED ${SHARED_LIB_SRC})

• 添加其他四方库依赖 如果三方库有对其他四方库依赖的话，需要通过target_link_libraries()方法添加对应的依赖。如在工程CPP目录下的CMakeLists.txt文件中的:

  target_link_libraries(entry PUBLIC libace_napi.z.so openjg2) # libace_napi.z.so-系统napi库, openjg2-依赖的openjpeg库

• 完整的CMakeLists.txt

  the minimum version of CMake.

  cmake_minimum_required(VERSION 3.4.1)
  set(CMAKE_CXX_STANDARD 17)
  project(openjpeg)

  set(OPJ_HAVE_STDINT_H TRUE)
  set(OPJ_HAVE_INTTYPES_H TRUE)
  set(OPENJPEG_VERSION_MAJOR 2)
  set(OPENJPEG_VERSION_MINOR 5)
  set(OPENJPEG_VERSION_BUILD 0)
  set(OPENJPEG_VERSION
  "{OPENJPEG_VERSION_MAJOR}.{OPENJPEG_VERSION_MINOR}.{OPENJPEG_VERSION_BUILD}") set(PACKAGE_VERSION "{OPENJPEG_VERSION_MAJOR}.{OPENJPEG_VERSION_MINOR}.{OPENJPEG_VERSION_BUILD}")

  configure_file(
  ${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/opj_config.h.cmake.in
  ${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/opj_config.h
  @ONLY
  )

  configure_file(
  ${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/opj_config_private.h.cmake.in
  ${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/opj_config_private.h
  @ONLY
  )

  add_definitions(-DOPJ_HAVE_PNG_H=0 -DOPJ_HAVE_TIFF_H=1 -DOPJ_HAVE_LCMS2_H=1)
  set(INCLUDE_DIR "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2") set(SHARED_LIB_SRC "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/thread.c"
  "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/bio.c" "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/cio.c"
  "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/dwt.c" "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/event.c"
  "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/ht_dec.c" "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/image.c"
  "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/invert.c" "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/j2k.c"
  "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/jp2.c" "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/mct.c"
  "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/mqc.c" "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/openjpeg.c"
  "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/opj_clock.c" "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/pi.c"
  "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/t1.c" "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/t2.c"
  "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/tcd.c" "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/tgt.c"
  "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/function_list.c" "{CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/opj_malloc.c"
  "${CMAKE_CURRENT_SOURCE_DIR}/src/lib/openjp2/sparse_array.c")

  add_library(openjp2 SHARED ${SHARED_LIB_SRC})
  target_include_directories(openjp2 PRIVATE ${INCLUDE_DIR})

加入编译构建

原生库源码准备完后，我们需要将库加入到工程的编译构建中。在工程目录CPP下的CMakeLists.txt文件中，通过add_subdirectory将openjpeg加入到编译中，并通过target_link_libraries添加对openjpeg的链接，如下图：

特别说明：

如果使用原生库的CMakeLists文件，编译时会提示添加目标时需要重新更改目标路径：

此时我们就需要在顶层目录的CMakeLists.txt文件中添加

set(CMAKE_BUILD_WITH_INSTALL_RPATH TRUE)

到此，我们的三方库适配已经完成并可以正常编译成功。

三方库napi接口开发

三方库napi的接口一般是由需求方提供的，对于无需求或需要自己定义接口的，我们可以根据三方库对外导出的API接口进行封装或是根据原生库的测试用例对外封装测试接口。本文中我们已封装2个openjpeg测试接口为例详细说明napi接口开发的具体流程。

定义napi接口

根据原生库的测试用例，我们封装2个测试用例接口

typedef struct {
   int comps_num;           // the number of components of the image.
    int comps_prec;         // number of bits per component per pixel
    int img_width;          // the image width
    int img_height;         // the image height
    int title_width;        // width of tile
    int title_height;       // height of title
    int irreversible;       // 1 : use the irreversible DWT 9-7
                            // 0 : use lossless compression (default)
    int cblockw_init;       // initial code block width, default to 64
    int cblockh_init;       // initial code block height, default to 64
    int numresolution;      // number of resolutions
    int offsetx;            // x component offset compared to the whole image
    int offsety;            // y component offset compared to the whole image
    int is_rand;            // Whether to generate data randomly
    char file[256];         // output filename
} J2K_Info;

int OpenjpegCompress(const char *input_file, char *output_file)   # 图片压缩成J2K格式
int openjpeg_create_j2k(J2K_Info *info)                # 创建一张J2K格式图片

注册接口

napi_property_descriptor desc[] = {
        {"openjpeg_compress", nullptr, OpenjpegCompress, nullptr, nullptr,
          nullptr, napi_default, nullptr},
        {"openjpeg_create_j2k", nullptr, OpenjpegCreateJ2K , nullptr, nullptr,
          nullptr, napi_default, nullptr}
    };

接口实现

• openjpeg_compress接口的实现

  static napi_value OpenjpegCompressMethod(napi_env env, napi_callback_info info)
  {
  napi_value result = nullptr;
  napi_get_undefined(env, &result);
  napi_value value;
  size_t argc = 2;
  napi_value args[2];
  size_t size;
  char input_file[256] = {0};
  char output_file[256] = {0};
  // 获取参数
  if (napi_get_cb_info(env, info, &argc, args, nullptr, nullptr) != napi_ok) {
  return result;
  }
  // js类型转换成C/C++类型
  if (napi_get_value_string_utf8(env, args[0], input_file, sizeof(input_file),
  &size) != napi_ok) {
  return result;
  }
  // js类型转换成C/C++类型
  if (napi_get_value_string_utf8(env, args[1], output_file, sizeof(output_file),
  &size) != napi_ok) {
  return result;
  }

    // 封装一个通过调用openjpeg接口实现编码的接口
    // 三方库实现调用的业务逻辑接口
    if (OpenjpegCompress(input_file, output_file) != 0) {
        return result;
    }
   // 创建返回的js类型参数
    if (napi_create_int64(env, 0, &result) != napi_ok) {
        std::cout << "napi_create_int64" << std::endl;
    }
    // 返回最终结果。
    return result;
  

  }

• openjpeg_create_j2k接口的实现

  static napi_value OpenjpegCreateJ2K(napi_env env, napi_callback_info info)
  {
  napi_value result = nullptr;
  napi_get_undefined(env, &result);
  napi_value value;
  size_t argc = 1;
  J2K_Info j2kInfo;
  // 获取参数
  if (napi_get_cb_info(env, info, &argc, &value, nullptr, nullptr) != napi_ok) {
  return result;
  }
  // 解析参数
  if (OpenjpegGetJ2kInfo(env, value, &j2kInfo) < 0) {
  return result;
  }
  // 封装一个通过调用openjpeg接口实现创建J2K文件的接口
  // 三方库实现调用的业务逻辑接口
  if (OpenjpegCreateJ2K(&j2kInfo) < 0) {
  return result;
  }

    if (napi_create_int64(env, 0, &result) != napi_ok) {
        std::cout << "napi_create_int64" << std::endl;
    }
    
    return result;
  

  }

解析参数接口的实现：

static int OpenjpegGetJ2kInfo(napi_env env, napi_value value, J2K_Info *info)
{
  if (info == nullptr) {
        return -1;
    }
    if(GetObjectPropetry(env, value,"output_file", STRING, info->file) != napi_ok) {
        return -1;
    }
    if (GetObjectPropetry(env, value,"comps_prec", NUMBER, &info->comps_prec) !=
        napi_ok) {
        return -1;
    }
    if (GetObjectPropetry(env, value,"img_width", NUMBER, &info->img_width) !=
        napi_ok) {
        return -1;
    }
    if (GetObjectPropetry(env, value,"img_height", NUMBER, &info->img_height) !=
        napi_ok) {
        return -1;
    }
    if (GetObjectPropetry(env, value,"title_width", NUMBER, &info->title_width) !=
        napi_ok) {
        return -1;
    }
    if (GetObjectPropetry(env, value,"title_height", NUMBER, &info->title_height) !=
        napi_ok) {
        return -1;
    }
    if (GetObjectPropetry(env, value,"irreversible", NUMBER, &info->irreversible) !=
        napi_ok) {
        return -1;
    }
    GetObjectPropetry(env, value,"cblockw_init", NUMBER, &info->cblockw_init);
    GetObjectPropetry(env, value,"cblockh_init", NUMBER, &info->cblockh_init);
    GetObjectPropetry(env, value,"numresolution", NUMBER, &info->numresolution);
    GetObjectPropetry(env, value,"offsetx", NUMBER, &info->offsetx);
    GetObjectPropetry(env, value,"offsety", NUMBER, &info->offsety);
    GetObjectPropetry(env, value,"is_rand", BOOLEAN, &info->is_rand);
    
    return 0;
}

由上代码可以看出，OpenjpegGetJ2kInfo接扣调用了一个封装的接口GetObjectPropetry，该接口实现了通过调用napi的接口获取对应的数据：

static int GetObjectPropetry(napi_env env, napi_value object, std::string key, int keyType, void *retValue) {
    napi_value property = nullptr;
    napi_value result = nullptr;
    bool flag = false;
    int ret = -1;
  // 通过字符串获取napi_value对象
    if (napi_create_string_utf8(env, key.c_str(), strlen(key.c_str()), &property)
        != napi_ok) {
        return ret;
    }
    // 判断该字符串是否对应由属性值
    if (napi_has_property(env, object, property, &flag) != napi_ok && flag == true) {
        return ret;
    }
    // 获取字符串对应的属性值
    if (napi_get_property(env, object, property, &result) != napi_ok) {
        return ret;
    }
    
    if (keyType == NUMBER) {
        int64_t value = 0;
        // JS数据类型转换成C/C++的int数据类型
        if (napi_get_value_int64(env, result, &value) != napi_ok) {
            return ret;
        }
        *(int *)retValue = value;
        ret = 0;
    } else if (keyType == BOOLEAN) {
        bool value = false;
        // JS数据类型转换成C/C++ 的bool数据类型
        if (napi_get_value_bool(env, result, &value) != napi_ok) {
            return ret;
        }
        *(int *)retValue = (value == true ? 1 : 0);
    }else if (keyType == STRING) {
        size_t s = 0;
        char buf[256] = {0};
        // JS数据类型转换成C/C++的string数据类型
        if (napi_get_value_string_utf8(env, result, buf, sizeof(buf), &s) !=
            napi_ok) {
            return ret;
        }
        strncpy((char *)retValue, buf, strlen(buf));
        ret = 0;
    }

    return 0;
}

应用调用napi接口

• 应用申明接口 在确定需要封装的接口后，我们需要将这些接口定义在index.d.ts文件中(路径entry/src/main/cpp/types/libentry/index.d.ts)

  export const openjpeg_compress: (srcName:string, desName:string) =>number;
  interface openjpegOption{
  comps_num:number // the number of components of the image.
  comps_prec:number // number of bits per component per pixel
  img_width:number // the image width
  img_height:number // the image height
  title_width:number // width of tile
  title_height:number // height of title
  irreversible:number // 1 : use the irreversible DWT 9-7,
  // 0 : use lossless compression (default)
  output_file:string // output filename
  cblockw_init?:number // initial code block width, default to 64
  cblockh_init?:number // initial code block height, default to 64
  numresolution?:number // number of resolutions
  offsetx?:number // x component offset compared to the whole image
  offsety?:number // y component offset compared to the whole image
  is_rand?:boolean // Whether to generate data randomly
  }
  export const openjpeg_create_j2k: (option:openjpegOption) => number

• 应用调用接口 在ets工程中创建2个按钮，并通过按钮调用相关的接口，具体代码如下：

  Button(this.buttonTxt0)
  .fontSize(50)
  .margin({top:30})
  .fontWeight(FontWeight.Normal)
  .onClick(() => {
  testNapi.openjpeg_compress(this.dir + "test_pic.bmp", this.dir + "result.j2k")
  })
  Button(this.buttonTxt1)
  .fontSize(50)
  .margin({top:30})
  .fontWeight(FontWeight.Normal)
  .onClick(() => {
  testNapi.openjpeg_create_j2k({comps_num:3,comps_prec:8,
  img_width:2000,img_height:2000,
  title_width:1000,title_height:1000,
  irreversible:1, output_file:this.dir +
  "newImage.j2k"})
  })

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