How to build libwebp for Java JNI in windows?

[dave.j...@gmail.com]

Hello,
I've been trying to build libwebp to be used in Java. But currently I don't know the steps to do it properly.
I downloaded the libwebp-0.4.3.tar.gz. In the readme file, it says to run this command:

>nmake /f Makefile.vc CFG=release-static RTLIBCFG=static OBJDIR=output

So first I did the command, and it created a folder containing some '.exe', '.obj' and '.lib' files.

The readme also mention SWIG binding for java jni? So I downloaded it too (swigwin-3.0.7). After extracting it, I added them to environment-variable path.
Inside the \swig directory there is another readme that says to run this command:

$ gcc -shared -fPIC -fno-strict-aliasing -O2 \
       -I/path/to/your/jdk/includes \
       libwebp_java_wrap.c \
       -lwebp \
       -o libwebp_jni.so

Why is the output 'libwebp_jni.so', shouldn't it be '.dll' for jni? And so I modified that command to :

>gcc -shared -fPIC -fno-strict-aliasing -O2 -I"C:\Program Files\Java\jdk1.7.0_04\include" -I"C:\Program Files\Java\jdk1.7.0_04\include\win32" -I"C:\libwebp-0.4.3\src" -L"C:\libwebp-0.4.3\output\release-static\x86\lib" libwebp_java_wrap.c -lwebp -o libwebp_jni.dll

But I get this error:
C:\libwebp-0.4.3\swig>gcc -shared -fPIC -fno-strict-aliasing -O2 -I"C:\Program Files\Java\jdk1.7.0_04\include" -I"C:\Program Files\Jav\jdk1.7.0_04\include\win32" -I"C:\libwebp-0.4.3\src" -L"C:\libwebp-0.4.3\output\release-static\x86\lib" libwebp_java_wrap.c -lwebp -o libwebp_jni.dll
libwebp_java_wrap.c:1:0: warning: -fPIC ignored for target (all code is position independent) [enabled by default]
c:/mingw/bin/../lib/gcc/mingw32/4.6.2/../../../../mingw32/bin/ld.exe: cannot find -lwebp
collect2: ld returned 1 exit status

What is the correct way to build libwebp in Windows?


Sorry if this is a nooby question.
Thanks in advance!

[Pepijn Van Eeckhoudt]

Using https://bitbucket.org/luciad/webp-imageio might be easier. It provides a Java binding and an ImageIO plugin which makes it pretty easy to encode/decode WebP images in JavaSE. 

There are precompiled binaries for libwebp 0.4.2. I haven’t had a chance to build binaries for 0.4.3 yet.

Pepijn

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[James Zern]

Hi,

On Tuesday, August 18, 2015 at 1:57:08 AM UTC-7, dave.j...@gmail.com wrote:

Hello,
I've been trying to build libwebp to be used in Java. But currently I don't know the steps to do it properly.
I downloaded the libwebp-0.4.3.tar.gz. In the readme file, it says to run this command:

>nmake /f Makefile.vc CFG=release-static RTLIBCFG=static OBJDIR=output

So first I did the command, and it created a folder containing some '.exe', '.obj' and '.lib' files.

The readme also mention SWIG binding for java jni? So I downloaded it too (swigwin-3.0.7). After extracting it, I added them to environment-variable path.
Inside the \swig directory there is another readme that says to run this command:

$ gcc -shared -fPIC -fno-strict-aliasing -O2 \
       -I/path/to/your/jdk/includes \
       libwebp_java_wrap.c \
       -lwebp \
       -o libwebp_jni.so


Why is the output 'libwebp_jni.so', shouldn't it be '.dll' for jni?

The README was written with an eye toward linux, I hadn't tried building the jni for windows.

 

And so I modified that command to :

>gcc -shared -fPIC -fno-strict-aliasing -O2 -I"C:\Program Files\Java\jdk1.7.0_04\include" -I"C:\Program Files\Java\jdk1.7.0_04\include\win32" -I"C:\libwebp-0.4.3\src" -L"C:\libwebp-0.4.3\output\release-static\x86\lib" libwebp_java_wrap.c -lwebp -o libwebp_jni.dll

But I get this error:
C:\libwebp-0.4.3\swig>gcc -shared -fPIC -fno-strict-aliasing -O2 -I"C:\Program Files\Java\jdk1.7.0_04\include" -I"C:\Program Files\Jav\jdk1.7.0_04\include\win32" -I"C:\libwebp-0.4.3\src" -L"C:\libwebp-0.4.3\output\release-static\x86\lib" libwebp_java_wrap.c -lwebp -o libwebp_jni.dll
libwebp_java_wrap.c:1:0: warning: -fPIC ignored for target (all code is position independent) [enabled by default]
c:/mingw/bin/../lib/gcc/mingw32/4.6.2/../../../../mingw32/bin/ld.exe: cannot find -lwebp
collect2: ld returned 1 exit status

msvc libs and mingw probably won't mix well. You can probably build the swig jni wrapper (libwebp_java_wrap.c) with cl.exe, let me see if I can get some instructions together.

[James Zern]

The following should work if you're working within the libwebp tree, have JDK set to the top of your jdk install and use the simple example from swig/README. I tested with vs2013 & jdk1.7.0_40.

libwebp> nmake /f Makefile.vc CFG=release-static RTLIBCFG=static
libwebp> cd swig
libwebp> cl /I../src /I"%JDK%\include" /I"%JDK\include\win32" ^
  libwebp_java_wrap.c ^
  /MT /LD /Fe:webp_jni.dll ^
  ..\..\obj\release-static\x64\lib\libwebp.lib
libwebp> "%JDK%\bin\javac.exe" -cp libwebp.jar libwebp_jni_example.java
libwebp> "%JDK%\bin\java.exe" -Djava.library.path=. -cp libwebp.jar;. libwebp_jni_example

Let me know if it helps and I'll update the README.