Question

I am having problems trying to load libpng in my native android project.
It seems, that the compiler doesn’t recognize libpng functions, but does recognize types (like png_byte). It compiles normally with types, but throws errors if I add functions.

Here’s compile output (windows 7 cmd):

D:\Dropbox\Workspace\Eclipse\GhostEngine\jni>C:\android-ndk-r8\ndk-build
"Compile++ thumb : ghost <= ImagePng.cpp
"Compile++ thumb : ghost <= MainAndroid.cpp
"Compile++ thumb : ghost <= PlatformAndroid.cpp
make: Circular D:/Dropbox/Workspace/Eclipse/GhostEngine//obj/local/armeabi/libst
lport_static.a <- D:/Dropbox/Workspace/Eclipse/GhostEngine//obj/local/armeabi/li
bstlport_static.a dependency dropped.
SharedLibrary  : libghost.so
D:/Dropbox/Workspace/Eclipse/GhostEngine//obj/local/armeabi/objs/ghost/ImagePng.
o: In function `loadPngFile':
D:/Dropbox/Workspace/Eclipse/GhostEngine//jni/ghost/ImagePng.cpp:48: undefined r
eference to `png_sig_cmp'
D:/Dropbox/Workspace/Eclipse/GhostEngine//jni/ghost/ImagePng.cpp:55: undefined r
eference to `png_create_read_struct'
D:/Dropbox/Workspace/Eclipse/GhostEngine//jni/ghost/ImagePng.cpp:61: undefined r
eference to `png_create_info_struct'
D:/Dropbox/Workspace/Eclipse/GhostEngine//jni/ghost/ImagePng.cpp:68: undefined r
eference to `png_create_info_struct'
D:/Dropbox/Workspace/Eclipse/GhostEngine//jni/ghost/ImagePng.cpp:75: undefined r
eference to `png_set_longjmp_fn'
D:/Dropbox/Workspace/Eclipse/GhostEngine//jni/ghost/ImagePng.cpp:77: undefined r
eference to `png_destroy_read_struct'
D:/Dropbox/Workspace/Eclipse/GhostEngine//jni/ghost/ImagePng.cpp:63: undefined r
eference to `png_destroy_read_struct'
D:/Dropbox/Workspace/Eclipse/GhostEngine//jni/ghost/ImagePng.cpp:70: undefined r
eference to `png_destroy_read_struct'
collect2: ld returned 1 exit status
make: *** [D:/Dropbox/Workspace/Eclipse/GhostEngine//obj/local/armeabi/libghost.
so] Error 1

My android.mk in libpng looks like this:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_CFLAGS := 

LOCAL_MODULE    := libpng
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 

LOCAL_LDLIBS := -lz

include $(BUILD_STATIC_LIBRARY)

Application.mk:

APP_PLATFORM := android-10
STLPORT_FORCE_REBUILD := true
APP_STL := stlport_static
APP_MODULES := libpng ghost
#APP_CPPFLAGS += -fexceptions

Android.mk in my project folder:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE := ghost
FILE_LIST := $(wildcard $(LOCAL_PATH)/*.cpp)
LOCAL_SRC_FILES := $(FILE_LIST:$(LOCAL_PATH)/%=%)
LOCAL_LDLIBS := -llog -landroid -lEGL -lGLESv2

# Support for additional libraries
#LOCAL_CFLAGS := -DANDROID_NDK -Wno-psabi
LOCAL_STATIC_LIBRARIES := android_native_app_glue
LOCAL_C_INCLUDES := $(LOCAL_PATH)/../libpng/
LOCAL_LDLIBS += -L$(SYSROOT)/usr/lib -ldl
LOCAL_LDLIBS += -L$(SYSROOT)/usr/lib -lz

include $(BUILD_SHARED_LIBRARY)

$(call import-module,android/native_app_glue)

I appreciate your help regarding this subject.
Thanks, Martin.

Answer 1

I think you may need to add “libpng” to the LOCAL_STATIC_LIBRARIES variable.

If that doesn’t work, instead try adding -lpng to your LOCAL_LD_LIBS variable in your Android.mk file. (Which one is needed depends on where the libpng library is put.)