clean up, add benchmarks

README.md

@@ -14,7 +14,8 @@ Build libspng:
 
 ```
 cd libspng
-meson build --prefix=/home/john/vips --libdir=/home/john/vips/lib
+meson build --prefix=/home/john/vips --libdir=/home/john/vips/lib \
+    --buildtype=release
 cd build 
 ninja
 ninja install
@@ -26,6 +27,30 @@ Sample code:
 
 https://github.com/randy408/libspng/blob/master/examples/example.c
 
+libspng benchmark:
+
+```
+$ time vips avg wtc.png
+151.549325
+
+real	0m3.167s
+user	0m3.714s
+sys	0m0.194s
+```
+
+And for libpng:
+
+```
+$ time vips avg wtc.png
+117.065766
+
+real	0m3.816s
+user	0m4.177s
+sys	0m0.221s
+```
+
+The avg is different since libspng is generating alpha 255.
+
 # Introduction
 
 libvips is a [demand-driven, horizontally

configure.ac

@@ -1176,13 +1176,13 @@ FIND_GIFLIB(
 )
 
 # Look for libspng first
-AC_ARG_WITH([spng], 
-  AS_HELP_STRING([--without-spng], [build without libspng (default: test)]))
+AC_ARG_WITH([libspng], 
+  AS_HELP_STRING([--without-libspng], [build without libspng (default: test)]))
 
-if test x"$with_spng" != x"no"; then
+if test x"$with_libspng" != x"no"; then
   PKG_CHECK_MODULES(SPNG, spng >= 0.6,
     [AC_DEFINE(HAVE_SPNG,1,[define if you have libspng installed.])
-     with_spng=yes
+     with_libspng=yes
      PACKAGES_USED="$PACKAGES_USED spng"
      with_png=no
     ],
@@ -1413,7 +1413,7 @@ file import with cfitsio: 		$with_cfitsio
 file import/export with libwebp:	$with_libwebp
   (requires libwebp, libwebpmux, libwebpdemux 0.6.0 or later)
 text rendering with pangoft2: 		$with_pangoft2
-file import/export with libspng: 	$with_spng
+file import/export with libspng: 	$with_libspng
   (requires libspng-0.6 or later)
 file import/export with libpng: 	$with_png
   (requires libpng-1.2.9 or later)

libvips/foreign/spngload.c

@@ -36,6 +36,13 @@
  * an enum for interlace_method would be nice ... ADAM7 == 1, 
  *   no interlace == 0.
  * an equivalent of png_sig_cmp() from libpng (is_a_png on a memory area)
+ *
+ * This always reads RGBA8 or RGBA16. Other formst G8/G16/GA8 etc. etc. are
+ * in the roadmap.
+ *
+ * Most metadata support (eg. XMP, ICC, etc. etc.) is missing.
+ *
+ * Load only, there's no save support for now.
  */
 
 /*
@@ -70,7 +77,6 @@ typedef struct _VipsForeignLoadPng {
 
 	spng_ctx *ctx;
 	struct spng_ihdr ihdr;
-	struct spng_trns trns;
 	enum spng_format fmt;
 	int bands;
 	VipsInterpretation interpretation;
@@ -96,9 +102,6 @@ vips_foreign_load_png_dispose( GObject *gobject )
 		dispose( gobject );
 }
 
-/* libspng read callbacks should copy length bytes to dest and return 0 
- * or SPNG_IO_EOF/SPNG_IO_ERROR on error.
- */
 static int 
 vips_foreign_load_png_stream( spng_ctx *ctx, void *user, 
 	void *dest, size_t length )
@@ -123,7 +126,7 @@ vips_foreign_load_png_get_flags_source( VipsSource *source )
 	struct spng_ihdr ihdr;
 	VipsForeignFlags flags;
 
-	ctx = spng_ctx_new( 0 );
+	ctx = spng_ctx_new( SPNG_CTX_IGNORE_ADLER32 );
 	spng_set_crc_action( ctx, SPNG_CRC_USE, SPNG_CRC_USE );
 	spng_set_png_stream( ctx, 
 		vips_foreign_load_png_stream, source );
@@ -317,9 +320,7 @@ vips_foreign_load_png_generate( VipsRegion *or,
 			printf( "  error %s\n", spng_strerror( error ) ); 
 #endif /*DEBUG*/
 
-			/* And bail if fail is on. We have to add an error
-			 * message, since the handler we install just does
-			 * g_warning().
+			/* And bail if fail is on. 
 			 */
 			if( load->fail ) {
 				vips_error( class->nickname,