[WM_LIB_CHECK([WEBP], ["-lwebp"], [VP8DecodeLayer], [$XLFLAGS $XLIBS],

[AS_IF([test "x$enable_webp" = "xno"],

    [wm_save_CFLAGS="$CFLAGS"

    [unsupported="$unsupported WebP"],

     AS_IF([wm_fn_lib_try_compile "webp/decode.h" "" "return 0" ""],

    [AC_CACHE_CHECK([for WebP support library], [wm_cv_imgfmt_webp],

         [],

        [wm_cv_imgfmt_webp=no

         [AC_MSG_ERROR([found $CACHEVAR but could not find appropriate header - are you missing libwebp-dev package?])])

         dnl

     CFLAGS="$wm_save_CFLAGS"],

         dnl The library is using a special trick on the functions to provide

    [supported_gfx], [GFXLIBS])dnl

         dnl compatibility between versions, so we cannot try linking against

]) dnl AC_DEFUN

         dnl a symbol without first using the header to handle it

         wm_save_LIBS="$LIBS"

         LIBS="$LIBS -lwebp"

         AC_TRY_LINK(

             [@%:@include <webp/decode.h>],

             [WebPGetFeatures(NULL, 1024, NULL);],

             [wm_cv_imgfmt_webp="-lwebp"])

         LIBS="$wm_save_LIBS"

         AS_IF([test "x$enable_webp$wm_cv_imgfmt_webp" = "xyesno"],

              [AC_MSG_ERROR([explicit WebP support requested but no library found])])dnl

        ])

     AS_IF([test "x$wm_cv_imgfmt_webp" = "xno"],

         [unsupported="$unsupported WebP"

          enable_webp="no"],

         [supported_gfx="$supported_gfx WebP"

          WM_APPEND_ONCE([$wm_cv_imgfmt_webp], [GFXLIBS])dnl

          AC_DEFINE([USE_WEBP], [1],

              [defined when valid Webp library with header was found])])dnl

    ])

AM_CONDITIONAL([USE_WEBP], [test "x$enable_webp" != "xno"])dnl

])