移植opencv2.4.9到android过程记录

在移植到arm开发板的时候已经说过，opencv已经为各平台准备了一套cmake交叉编译脚本。为android移植的脚本在opencv目录/platforms/android/android.toolchain.cmake。
这个脚本里面有很详细的过程介绍，按照它里面的说明，配置好ndk的路径，就可以了。
但我们还需要实现其他目的：
1、使用fpu，neon,且Tag_FP_arch: VFPv4
2、动态库的形式编译

这些通过阅读android.toolchain.cmake文件，以及opencv目录下的CMakeLists.txt文件可以知道。例如关于abi的说明（在交叉编译脚本）：

 # ABI-specific flags
 if( ARMEABI_V7A )
  set( ANDROID_CXX_FLAGS "${ANDROID_CXX_FLAGS} -march=armv7-a -mfloat-abi=softfp" )
  if( NEON )
   set( ANDROID_CXX_FLAGS "${ANDROID_CXX_FLAGS} -mfpu=neon" )
  elseif( VFPV3 )
   set( ANDROID_CXX_FLAGS "${ANDROID_CXX_FLAGS} -mfpu=vfpv3" )
  else()
   set( ANDROID_CXX_FLAGS "${ANDROID_CXX_FLAGS} -mfpu=vfpv3-d16" )
  endif()
 elseif( ARMEABI_V6 )
  set( ANDROID_CXX_FLAGS "${ANDROID_CXX_FLAGS} -march=armv6 -mfloat-abi=softfp -mfpu=vfp" ) # vfp == vfpv2
 elseif( ARMEABI )
  set( ANDROID_CXX_FLAGS "${ANDROID_CXX_FLAGS} -march=armv5te -mtune=xscale -msoft-float" )
 endif()

看上面没有vfpv4的，先不更改了。

而关于编译动态库的，则在opencv/CMakeLists.txt内：

169 # OpenCV build components
 170 # ===================================================
 171 OCV_OPTION(BUILD_SHARED_LIBS        "Build shared libraries (.dll/.so) instead of static ones (.lib/.a)" NOT (ANDROID OR IOS) )
 172 OCV_OPTION(BUILD_opencv_apps        "Build utility applications (used for example to train classifiers)" (NOT ANDROID) IF (NOT IOS) )
 173 OCV_OPTION(BUILD_ANDROID_EXAMPLES   "Build examples for Android platform"         ON  IF ANDROID )
 174 OCV_OPTION(BUILD_DOCS               "Create build rules for OpenCV Documentation" ON )
 175 OCV_OPTION(BUILD_EXAMPLES           "Build all examples"                          OFF )
 176 OCV_OPTION(BUILD_PACKAGE            "Enables 'make package_source' command"       ON )
 177 OCV_OPTION(BUILD_PERF_TESTS         "Build performance tests"                     ON  IF (NOT IOS) )
 178 OCV_OPTION(BUILD_TESTS              "Build accuracy & regression tests"           ON  IF (NOT IOS) )
 179 OCV_OPTION(BUILD_WITH_DEBUG_INFO    "Include debug info into debug libs (not MSCV only)" ON )
 180 OCV_OPTION(BUILD_WITH_STATIC_CRT    "Enables use of staticaly linked CRT for staticaly linked OpenCV" ON IF MSVC )
 181 OCV_OPTION(BUILD_FAT_JAVA_LIB       "Create fat java wrapper containing the whole OpenCV library" ON IF NOT BUILD_SHARED_LIBS AND CMAKE_COMPILER_IS_GNUCXX )
 182 OCV_OPTION(BUILD_ANDROID_SERVICE    "Build OpenCV Manager for Google Play" OFF IF ANDROID AND ANDROID_SOURCE_TREE )
 183 OCV_OPTION(BUILD_ANDROID_PACKAGE    "Build platform-specific package for Google Play" OFF IF ANDROID )

执行cmake指令：

cmake -DCMAKE_INSTALL_PREFIX=../install_neon_dir -DCMAKE_BUILD_TYPE=RELEASE -DBUILD_SHARED_LIBS=1 -DCMAKE_TOOLCHAIN_FILE=../android.toolchain.cmake -DANDROID_ABI="armeabi-v7a with NEON" ../../../

可以看到结果为：

--   C/C++:
--     Built as dynamic libs?:      YES
--     C++ Compiler:                /home/gumh/software/android-ndk-r9d/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-g++  (ver 4.8)
--     C++ flags (Release):         -fexceptions -frtti -Wno-psabi --sysroot=/home/gumh/software/android-ndk-r9d/platforms/android-8/arch-arm -fpic -funwind-tables -finline-limit=64 -fsigned-char -no-canonical-prefixes -march=armv7-a -mfloat-abi=softfp -mfpu=neon -fdata-sections -ffunction-sections -Wa,--noexecstack    -fsigned-char -W -Wall -Werror=return-type -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wno-narrowing -Wno-delete-non-virtual-dtor -fdiagnostics-show-option -fomit-frame-pointer -mfpu=neon -mthumb -fomit-frame-pointer -fno-strict-aliasing -O3 -DNDEBUG  -DNDEBUG
--     C++ flags (Debug):           -fexceptions -frtti -Wno-psabi --sysroot=/home/gumh/software/android-ndk-r9d/platforms/android-8/arch-arm -fpic -funwind-tables -finline-limit=64 -fsigned-char -no-canonical-prefixes -march=armv7-a -mfloat-abi=softfp -mfpu=neon -fdata-sections -ffunction-sections -Wa,--noexecstack    -fsigned-char -W -Wall -Werror=return-type -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wno-narrowing -Wno-delete-non-virtual-dtor -fdiagnostics-show-option -fomit-frame-pointer -mfpu=neon -marm -fno-omit-frame-pointer -fno-strict-aliasing -O0 -g -DDEBUG -D_DEBUG  -O0 -DDEBUG -D_DEBUG
--     C Compiler:                  /home/gumh/software/android-ndk-r9d/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc
--     C flags (Release):           -fexceptions -Wno-psabi --sysroot=/home/gumh/software/android-ndk-r9d/platforms/android-8/arch-arm -fpic -funwind-tables -finline-limit=64 -fsigned-char -no-canonical-prefixes -march=armv7-a -mfloat-abi=softfp -mfpu=neon -fdata-sections -ffunction-sections -Wa,--noexecstack    -fsigned-char -W -Wall -Werror=return-type -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wno-narrowing -fdiagnostics-show-option -fomit-frame-pointer -mfpu=neon -mthumb -fomit-frame-pointer -fno-strict-aliasing -O3 -DNDEBUG  -DNDEBUG
--     C flags (Debug):             -fexceptions -Wno-psabi --sysroot=/home/gumh/software/android-ndk-r9d/platforms/android-8/arch-arm -fpic -funwind-tables -finline-limit=64 -fsigned-char -no-canonical-prefixes -march=armv7-a -mfloat-abi=softfp -mfpu=neon -fdata-sections -ffunction-sections -Wa,--noexecstack    -fsigned-char -W -Wall -Werror=return-type -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wno-narrowing -fdiagnostics-show-option -fomit-frame-pointer -mfpu=neon -marm -fno-omit-frame-pointer -fno-strict-aliasing -O0 -g -DDEBUG -D_DEBUG  -O0 -DDEBUG -D_DEBUG
--     Linker flags (Release):      -Wl,--fix-cortex-a8 -Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now 
--     Linker flags (Debug):        -Wl,--fix-cortex-a8 -Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now 
--     Precompiled headers:         YES

在arm的编译时，设置-mfpu是：-mfpu=neon-vfpv4，这里只是neon.

最后编译的结果为：

[zzz@localhost build_neon]$ readelf -a lib/armeabi-v7a/libopencv_core.so 
...
Attribute Section: aeabi
File Attributes
  Tag_CPU_name: "ARM v7"
  Tag_CPU_arch: v7
  Tag_CPU_arch_profile: Application
  Tag_ARM_ISA_use: Yes
  Tag_THUMB_ISA_use: Thumb-2
  Tag_FP_arch: VFPv3
  Tag_Advanced_SIMD_arch: NEONv1
  Tag_ABI_PCS_wchar_t: 4
  Tag_ABI_FP_denormal: Needed
  Tag_ABI_FP_exceptions: Needed
  Tag_ABI_FP_number_model: IEEE 754
  Tag_ABI_align_needed: 8-byte
  Tag_ABI_enum_size: int
  Tag_ABI_HardFP_use: SP and DP
  Tag_ABI_optimization_goals: Aggressive Speed
  Tag_CPU_unaligned_access: v6
  Tag_DIV_use: Not allowed