1. libjpeg-turbo

前面已经编译过1.5.91版本的libjpeg-turbo,现在版本升级到2.0.0,基于CMake编译。

依然还是一样,按照官网介绍，libjpeg-turbo比libjpeg快2-6倍,得益于它高度优化的哈夫曼算法。在许多情况下，libjpeg-turbo的性能可与专有的高速JPEG编解码器相媲美.

On such systems, libjpeg-turbo is generally 2-6x as fast as libjpeg, all else being equal. On other types of systems, libjpeg-turbo can still outperform libjpeg by a significant amount, by virtue of its highly-optimized Huffman coding routines. In many cases, the performance of libjpeg-turbo rivals that of proprietary high-speed JPEG codecs

2. 编译过程

2.1 编译环境

在Windows 10的虚拟机VM上的Ubuntu中编译
vm_Ubuntu

2.2 编译要求

我们将参照源码中的BUILDING.md编译，github地址BUILDING.md

NDK: Linux 64 位 (x86) / android-ndk-r15c
CMake: cmake-3.12.1-Linux-x86_64
NASM 或者 YASM: 如果需要编译 x86 或者 x86-64的库，需要安装 NASM 2.10及以上或者 YASM 2.10及以上版本。

安装工具

2.3 配置环境变量

把Cmake配置进系统环境变量，当然这不是必须的。
cmake环境变量

2.4 编译

2.4.1 下载源码

下载并解压源码https://github.com/libjpeg-turbo/libjpeg-turbo

2.4.2 编译脚本

# lib-name
MY_LIBS_NAME=libjpeg-turbo
MY_SOURCE_DIR=$(pwd)/libjpeg-turbo-master
#编译的过程中产生的中间件的存放目录，为了区分编译目录，源码目录，install目录
MY_BUILD_DIR=binary

export PATH=/home/as/Android/cmake-3.12.1-Linux-x86_64/bin:$PATH

NDK_PATH=/home/as/Android/android-ndk-r15c
BUILD_PLATFORM=linux-x86_64
TOOLCHAIN_VERSION=4.9
ANDROID_VERSION=24

ANDROID_ARMV5_CFLAGS="-march=armv5te"
ANDROID_ARMV7_CFLAGS="-march=armv7-a -mfloat-abi=softfp -mfpu=neon"  # -mfpu=vfpv3-d16  -fexceptions -frtti
ANDROID_ARMV8_CFLAGS="-march=armv8-a"   # -mfloat-abi=softfp -mfpu=neon -fexceptions -frtti
ANDROID_X86_CFLAGS="-march=i386 -mtune=intel -mssse3 -mfpmath=sse -m32"
ANDROID_X86_64_CFLAGS="-march=x86-64 -msse4.2 -mpopcnt -m64 -mtune=intel"

# params($1:arch,$2:arch_abi,$3:host,$4:compiler,$5:cflags,$6:processor)
build_bin() {

    echo "-------------------star build $2-------------------------"

    ARCH=$1                # arm arm64 x86 x86_64
    ANDROID_ARCH_ABI=$2    # armeabi armeabi-v7a x86 mips
    # 最终编译的安装目录
    PREFIX=$(pwd)/dist/${MY_LIBS_NAME}/${ANDROID_ARCH_ABI}/
    HOST=$3
    COMPILER=$4
    PROCESSOR=$6
    SYSROOT=${NDK_PATH}/platforms/android-${ANDROID_VERSION}/arch-${ARCH}
    CFALGS="$5"
    TOOLCHAIN=${NDK_PATH}/toolchains/${HOST}-${TOOLCHAIN_VERSION}/prebuilt/${BUILD_PLATFORM}

    # build 中间件
    BUILD_DIR=./${MY_BUILD_DIR}/${ANDROID_ARCH_ABI}

    export CFLAGS="$5 -O3 -D__ANDROID_API__=${ANDROID_VERSION} --sysroot=${SYSROOT} \
                   -isystem ${NDK_PATH}/sysroot/usr/include \
                   -isystem ${NDK_PATH}/sysroot/usr/include/${HOST} "
    export LDFLAGS=-pie

    echo "path==>$PATH"
    echo "build_dir==>$BUILD_DIR"
    echo "ARCH==>$ARCH"
    echo "ANDROID_ARCH_ABI==>$ANDROID_ARCH_ABI"
    echo "HOST==>$HOST"
    echo "CFALGS==>$CFALGS"
    echo "COMPILER==>$COMPILER-gcc"
    echo "PROCESSOR==>$PROCESSOR"

    mkdir -p ${BUILD_DIR}   #创建当前arch_abi的编译目录,比如:binary/armeabi-v7a
    cd ${BUILD_DIR}         #此处 进了当前arch_abi的2级编译目录


cat >toolchain.cmake << EOF 
set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR $6)
set(CMAKE_C_COMPILER ${TOOLCHAIN}/bin/${COMPILER}-gcc)
set(CMAKE_FIND_ROOT_PATH ${TOOLCHAIN}/${COMPILER})
EOF # 此处不顶格写脚本会报一个错误

    cmake -G"Unix Makefiles" \
          -DCMAKE_TOOLCHAIN_FILE=toolchain.cmake \
          -DCMAKE_POSITION_INDEPENDENT_CODE=1 \
          -DCMAKE_INSTALL_PREFIX=${PREFIX} \
          -DWITH_JPEG8=1 \
          ${MY_SOURCE_DIR}

    make clean
    make
    make install

    #从当前arch_abi编译目录跳出，对应上面的cd ${BUILD_DIR},以便function多次执行
    cd ../../

    echo "-------------------$2 build end-------------------------"
}

# build armeabi
build_bin arm armeabi arm-linux-androideabi arm-linux-androideabi "$ANDROID_ARMV5_CFLAGS" arm

#build armeabi-v7a
build_bin arm armeabi-v7a arm-linux-androideabi arm-linux-androideabi "$ANDROID_ARMV7_CFLAGS" arm

#build arm64-v8a
build_bin arm64 arm64-v8a aarch64-linux-android aarch64-linux-android "$ANDROID_ARMV8_CFLAGS" aarch64

#build x86
build_bin x86 x86 x86 i686-linux-android "$ANDROID_X86_CFLAGS" i386

#build x86_64
build_bin x86_64 x86_64 x86_64 x86_64-linux-android "$ANDROID_X86_64_CFLAGS" x86_64

2.4.3 执行编译脚本

sudo sh build.sh
编译执行

2.4.4 编译可能遇到的问题

1. Syntax error: end of file unexpected (expecting "}"): 编译脚本中 cat << EOF >文件名内容 EOF,最好顶格写，否则可能出现上述错误
2.未识别的 cflags参数: 一些cflags参数可能导致编译识别,修改编译出错的参数即可