libpng的编译

jiujie
2,340 阅读2分钟
  • 源码下载地址
  • 参考链接
  • libpng依赖于zlib
  • 最关键的地方就在于在根项目的Application.mk中的APP_CFLAGS += -DPNG_ARM_NEON_OPT=0，因为如果不关闭neon在编译过程中会报错，网上资源相对较少，且有的会用APP_CPPFLAGS += -DPNG_ARM_NEON_OPT=0，导致问题一致的不到解决
    • 报错日志：/pngrtran.c:4782: undefined reference to png_riffle_palette_neon
  • 同时要分清楚Android.mk中的LOCAL_CFLAGS与Application.mk中的APP_CFLAGS的区别：
    • 前者是module_specific的cflags而后者是全局的clfags，在编译module的时候前者会覆盖后者
    • Application.mk

关于打包的参数设定

  • APP_CPPFLAGS和所有其他app_使变量应设置Application.mk，每个模块，使用LOCAL_CPPFLAGS或LOCAL_CFLAGS。
  • export CPPFLAGS="-DPNG_ARM_NEON_OPT=0"
  • PNG_ARM_NEON_IMPLEMENTATION
    • export CPPFLAGS="-DPNG_ARM_NEON_IMPLEMENTATION=2"
  • -mfpu=neon
  • Note that gcc-4.9 defines __ARM_NEON instead of the deprecated ARM_NEON, so we check both variants.
    • 如果支持neo，gcc编译器会传入__ARM_NEON或者__ARM_NEON__的宏，根据该宏来判断怎样选择代码

打包脚本

  • 目录解构：libpng-android/jni/，该目录下有libpng-1.6.37以及zlib-1.2.11目录，且在jni目录下有项目的Android.mk以及Application.mk，而libpng以及zlib目录下分别有自己的Android.mk用于各自的打包

  • libpng打包的Android.mk文件

    LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

LOCAL_MODULE := libpng
LOCAL_C_INCLUDES := 
# LOCAL_CFLAGS := -DPNG_ARM_NEON_IMPLEMENTATION=2 -DPNG_ARM_NEON_OPT=0
# LOCAL_CPPFLAGS := -DPNG_ARM_NEON_IMPLEMENTATION=2 -DPNG_ARM_NEON_OPT=0
LOCAL_LDLIBS := 
LOCAL_SHARED_LIBRARIES := 
LOCAL_STATIC_LIBRARIES := libz
LOCAL_PREBUILTS := 
LOCAL_SRC_FILES := ./png.c \
./pngerror.c \
./pngget.c \
./pngmem.c \
./pngpread.c \
./pngread.c \
./pngrio.c \
./pngrtran.c \
./pngrutil.c \
./pngset.c \
./pngtrans.c \
./pngwio.c \
./pngwrite.c \
./pngwtran.c \
./pngwutil.c \
./arm/arm_init.c \
./arm/filter_neon.S \
./arm/filter_neon_intrinsics.c

include $(BUILD_SHARED_LIBRARY)
# include $(BUILD_STATIC_LIBRARY)

# Auto-generated module by script
# include $(CLEAR_VARS)

# LOCAL_MODULE := pngtest
# LOCAL_C_INCLUDES := 
# LOCAL_CFLAGS := -DPNG_ARM_NEON_IMPLEMENTATION=2 -DPNG_ARM_NEON_OPT=0
# LOCAL_CPPFLAGS :=-DPNG_ARM_NEON_IMPLEMENTATION=2 -DPNG_ARM_NEON_OPT=0
# LOCAL_LDLIBS := 
# LOCAL_SHARED_LIBRARIES := 
# LOCAL_STATIC_LIBRARIES := libpng
# LOCAL_PREBUILTS := 
# LOCAL_SRC_FILES := ./pngtest.c

# include $(BUILD_EXECUTABLE)

  • libpng依赖于libz，打包libz的Android.mk

    LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

LOCAL_MODULE := libz
LOCAL_C_INCLUDES := 
LOCAL_CFLAGS := 
LOCAL_CPPFLAGS := 
LOCAL_LDLIBS := 
LOCAL_SHARED_LIBRARIES := 
LOCAL_STATIC_LIBRARIES := 
LOCAL_PREBUILTS := 
LOCAL_SRC_FILES := ./adler32.c \
./compress.c \
./crc32.c \
./deflate.c \
./gzclose.c \
./gzlib.c \
./gzread.c \
./gzwrite.c \
./infback.c \
./inffast.c \
./inflate.c \
./inftrees.c \
./trees.c \
./uncompr.c \
./zutil.c \

include $(BUILD_STATIC_LIBRARY)

  • 上层的Android.mk

    include $(all-subdir-makefiles)

  • 上层的Application.mk

    APP_PLATFORM := android-14
APP_CFLAGS += -DPNG_ARM_NEON_IMPLEMENTATION=2
APP_CFLAGS += -DPNG_ARM_NEON_OPT=0

libpng与zlib的版本对应关系

  • libpng与zlib的版本之间有一个对应关系，在libpng的pngpriv.h头文件中有如下代码：

    #if PNG_ZLIB_VERNUM != 0 && PNG_ZLIB_VERNUM != ZLIB_VERNUM
#  error ZLIB_VERNUM != PNG_ZLIB_VERNUM \
      "-I (include path) error: see the notes in pngpriv.h"
    • 注意：这里的#不是注释，是预编译指令
    • 其中ZLIB_VERNUM是zlib库中的zlib.h头文件中定义的一个宏# define ZLIB_VERNUM 0x1280，对应的版本是1.2.8
    • PNG_ZLIB_VERNUM是libpng库中定义的一个宏:#define PNG_ZLIB_VERNUM 0x1280
    • 要处理这个异常，要么将# error...一行注释掉，也就是不处理两个版本号不一致的情况，要么就是在源码中修改掉两个宏中任何一个让二者一致即可，要么根据需要去下载对应的zlib库
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