add swig interface

Currently only supports a subset of decode functions and likely only
works fully for java.

For java bindings:
The generated java source can be compiled and the class files added to
libwebp.jar.
The generated jni source can be compiled to, e.g., libwebp_jni.so, which
can then be loaded via System.loadLibrary("webp_jni").

Change-Id: I8225933cbaf85c9cfa4b78c2e5f167cee8b62408

README

@@ -76,6 +76,26 @@ Note: The encoding and decoding libraries are compiled separately
 can be installed independently using a minor modifications in the
 corresponding Makefile.am configure files (see comments there).
 
+SWIG bindings:
+--------------
+
+To generate language bindings from swig/libwebp.i swig-1.3
+(http://www.swig.org) is required. 2.0 may work, but has not been tested.
+
+Currently from the decode interface the following functions are mapped:
+  WebPGetDecoderVersion
+  WebPGetInfo
+  WebPDecodeRGB
+  WebPDecodeRGBA
+  WebPDecodeBGR
+  WebPDecodeBGRA
+
+Java bindings:
+
+To build the swig-generated JNI wrapper code at least JDK-1.5 (or equivalent)
+is necessary for enum support. The output is intended to be a shared object /
+DLL that can be loaded via System.loadLibrary("webp_jni").
+
 Encoding tool:
 ==============
 

swig/libwebp.i

@@ -0,0 +1,115 @@
+// Copyright 2011 Google Inc.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// libwebp swig interface definition
+//
+// Author: James Zern (jzern@google.com)
+//
+// For java bindings compile with:
+//  $ mkdir -p java/com/google/webp
+//  $ swig -ignoremissing -I../src \
+//         -java \
+//         -package com.google.webp \
+//         -outdir java/com/google/webp \
+//         -o libwebp_java_wrap.c libwebp.i
+%module libwebp
+
+%include "constraints.i"
+%include "typemaps.i"
+
+%ignore WEBP_WEBP_DECODE_H_;
+// FIXME for these to be available returned_buffer_size() would need to be
+// made more intelligent.
+%ignore WebPDecodeRGBInto;
+%ignore WebPDecodeYUV;
+%ignore WebPDecodeRGBAInto;
+%ignore WebPDecodeBGRInto;
+%ignore WebPDecodeBGRAInto;
+%ignore WebPDecodeYUVInto;
+
+// incremental decoding
+%ignore WebPIDecGetYUV;
+%ignore WebPINew;
+%ignore WebPIDecoder;
+%ignore WebPIAppend;
+%ignore WebPIDecGetRGB;
+%ignore WebPIDelete;
+%ignore WebPINewRGB;
+%ignore WebPINewYUV;
+%ignore WebPIUpdate;
+%ignore WebPInitCustomIo;
+%ignore WebPInitDecParams;
+
+%apply int *OUTPUT { int *width, int *height }
+%apply int { uint32_t data_size }
+%apply Number NONNEGATIVE { uint32_t data_size }
+
+// free the buffer returned by these functions after copying into
+// the native type
+%newobject WebPDecodeRGB;
+%newobject WebPDecodeRGBA;
+%newobject WebPDecodeBGR;
+%newobject WebPDecodeBGRA;
+%typemap(newfree) uint8_t* "free($1);"
+
+#ifdef SWIGJAVA
+%include "arrays_java.i";
+%include "enums.swg" /*NB: requires JDK-1.5+
+                       See: http://www.swig.org/Doc1.3/Java.html#enumerations */
+
+// map uint8_t* such that a byte[] is used
+// this will generate a few spurious warnings in the wrapper code
+%apply signed char[] { uint8_t * }
+
+%{
+/* Work around broken gcj jni.h */
+#ifdef __GCJ_JNI_H__
+# undef JNIEXPORT
+# define JNIEXPORT
+# undef JNICALL
+# define JNICALL
+#endif
+%}
+#endif
+
+/*
+ * Wrapper code additions
+ */
+%{
+#include "webp/decode.h"
+
+#define FillMeInAsSizeCannotBeDeterminedAutomatically \
+    (result ? returned_buffer_size(__FUNCTION__, arg3, arg4) : 0)
+
+static jint returned_buffer_size(
+    const char *function, int *width, int *height) {
+  static const struct sizemap {
+    const char *function;
+    int size_multiplier;
+  } size_map[] = {
+    { "Java_com_google_webp_libwebpJNI_WebPDecodeRGB",  3 },
+    { "Java_com_google_webp_libwebpJNI_WebPDecodeRGBA", 4 },
+    { "Java_com_google_webp_libwebpJNI_WebPDecodeBGR",  3 },
+    { "Java_com_google_webp_libwebpJNI_WebPDecodeBGRA", 4 },
+    { NULL, 0 }
+  };
+  const struct sizemap *p;
+  jint size = -1;
+
+  for (p = size_map; p->function; p++) {
+    if (!strcmp(function, p->function)) {
+      size = *width * *height * p->size_multiplier;
+      break;
+    }
+  }
+
+  return size;
+}
+%}
+
+// All functions, constants, etc. not named above in %ignore will be wrapped
+%include "webp/decode.h"