gif2webp build support with autoconf tools

Change-Id: I51a007e7931f05f2eb2ac062038309c2127df3fd

configure.ac

@@ -148,6 +148,32 @@ AC_SUBST(TIFF_INCLUDES)
 CPPFLAGS=$SAVED_CPPFLAGS
 LIBS=$SAVED_LIBS
 
+dnl === check for GIF support ===
+
+WEBP_HAVE_GIF=""
+GIF_LIBS=""
+WITHLIB_OPTION([gif], [GIF])
+
+SAVED_LIBS=$LIBS
+LIBS="$GIF_LIBS $LIBS"
+
+AC_CHECK_HEADER(gif_lib.h,
+  AC_CHECK_LIB([gif], [DGifOpenFileHandle],
+               [GIF_LIBS="$GIF_LIBS -lgif"
+                WEBP_HAVE_GIF=1
+               ],
+               AC_MSG_WARN(Optional gif library not found),
+               [$MATH_LIBS]),
+  AC_MSG_WARN(gif library not available - no gif_lib.h)
+)
+AC_SUBST(GIF_LIBS)
+
+CPPFLAGS=$SAVED_CPPFLAGS
+LIBS=$SAVED_LIBS
+
+AM_CONDITIONAL([BUILD_GIF2WEBP], [test "$WEBP_HAVE_GIF" = "1" -a \
+                                  "$enable_experimental_libwebpmux" = "yes"])
+
 dnl === check for WIC support ===
 
 if test "$target_os" = "mingw32"; then

examples/Makefile.am

@@ -4,6 +4,11 @@ bin_PROGRAMS = dwebp cwebp
 if WANT_MUX
   bin_PROGRAMS += webpmux
 endif
+
+if BUILD_GIF2WEBP
+  bin_PROGRAMS += gif2webp
+endif
+
 noinst_LTLIBRARIES = libexampleutil.la
 
 libexampleutil_la_SOURCES = example_util.c
@@ -20,6 +25,11 @@ cwebp_CPPFLAGS  = $(AM_CPPFLAGS) $(USE_EXPERIMENTAL_CODE)
 cwebp_CPPFLAGS += $(JPEG_INCLUDES) $(PNG_INCLUDES) $(TIFF_INCLUDES)
 cwebp_LDADD = ../src/libwebp.la $(JPEG_LIBS) $(PNG_LIBS) $(TIFF_LIBS)
 
+gif2webp_SOURCES = gif2webp.c
+gif2webp_CPPFLAGS = $(AM_CPPFLAGS) $(USE_EXPERIMENTAL_CODE)
+gif2webp_LDADD  = libexampleutil.la ../src/mux/libwebpmux.la ../src/libwebp.la
+gif2webp_LDADD += $(GIF_LIBS)
+
 webpmux_SOURCES = webpmux.c
 webpmux_CPPFLAGS = $(AM_CPPFLAGS) $(USE_EXPERIMENTAL_CODE)
 webpmux_LDADD = libexampleutil.la ../src/mux/libwebpmux.la ../src/libwebp.la

examples/gif2webp.c

@@ -19,8 +19,6 @@
 #include "config.h"
 #endif
 
-// TODO(later): Use WEBP_USE_GIF flag here, determined at config time.
-
 #include <gif_lib.h>
 #include "webp/encode.h"
 #include "webp/mux.h"