【Android 内存优化】libjpeg-turbo 函数库交叉编译与使用 ( 交叉编译脚本编写 | 函数库头文件拷贝 | 构建脚本配置 | Android Studio 测试函数库 )（二）

cmake_minimum_required(VERSION 3.4.1)
add_library( # 函数库名称
        native-lib
        # 动态库类型
        SHARED
        # 源文件
        native-lib.cpp)
find_library( # 日志库
        log-lib
        log )
find_library( # JNI 图形库
        jnigraphics-lib
        jnigraphics )
# 设置头文件搜索路径
include_directories(include)
# 通过设置编译选项, 设置函数库的搜索路径
# 此处的 ANDROID_ABI 是在
# build.gradle android->defaultConfig->externalNativeBuild->cmake
# 下的 abiFilters 中设置
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -L${CMAKE_SOURCE_DIR}/libs/${ANDROID_ABI}")
target_link_libraries( # 链接动态库
        native-lib
        # 查找到的 libturbojpeg 静态库
        turbojpeg
        ${log-lib}
        ${jnigraphics-lib} )

apply plugin: 'com.android.application'
android {
    compileSdkVersion 29
    defaultConfig {
        applicationId "kim.hsl.pc"
        minSdkVersion 16
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ""
                abiFilters 'armeabi-v7a'
            }
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
            //version "3.10.2"
        }
    }
}
dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

#include <jni.h>
#include <string>
#include <jpeglib.h>
#include <android/bitmap.h>
#include <malloc.h>
#include <android/log.h>
#include <bitset>
#include <iosfwd>
extern "C" JNIEXPORT jstring JNICALL
Java_kim_hsl_pc_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    // 测试 libturbojpeg.a 函数库
    jpeg_compress_struct jcs;
    __android_log_print(ANDROID_LOG_INFO, "JPEG", "jpeg_compress_struct jcs = %d", jcs.image_width);
    hello = hello + " , jpeg_compress_struct jcs = " + std::to_string(jcs.image_width);
    return env->NewStringUTF(hello.c_str());
}