From 02327b621415059078272ef621b7832e5fac4dae Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Fri, 1 May 2020 16:05:48 +0100
Subject: [PATCH 01/19] add an experimental libspng reader

it compiles, but I've not tried running it yet heh
---
 ChangeLog                   |   1 +
 README.md                   |  24 ++
 configure.ac                |  22 +-
 libvips/foreign/Makefile.am |   1 +
 libvips/foreign/spngload.c  | 674 ++++++++++++++++++++++++++++++++++++
 5 files changed, 720 insertions(+), 2 deletions(-)
 create mode 100644 libvips/foreign/spngload.c

diff --git a/ChangeLog b/ChangeLog
index 350c63f3..4e70da6f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -18,6 +18,7 @@
 - add all to smartcrop 
 - flood fill could stop half-way for some very complex shapes
 - better handling of unaligned reads in multipage tiffs [petoor]
+- add experimental libspng reader 
 
 24/4/20 started 8.9.3
 - better iiif tile naming [IllyaMoskvin]
diff --git a/README.md b/README.md
index 03bab492..1b4c4e6d 100644
--- a/README.md
+++ b/README.md
@@ -4,6 +4,30 @@
 [![Fuzzing Status](https://oss-fuzz-build-logs.storage.googleapis.com/badges/libvips.svg)](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=2&q=proj:libvips)
 [![Coverity Status](https://scan.coverity.com/projects/6503/badge.svg)](https://scan.coverity.com/projects/jcupitt-libvips)
 
+# This branch
+
+Is for experiemtning with [libspng](https://github.com/randy408/libspng).
+
+## Notes
+
+Build libspng:
+
+```
+cd libspng
+meson build --prefix=/home/john/vips --libdir=/home/john/vips/lib
+cd build 
+ninja
+ninja install
+```
+
+Installs `spng.pc`.
+
+Sample code:
+
+https://github.com/randy408/libspng/blob/master/examples/example.c
+
+# Introduction
+
 libvips is a [demand-driven, horizontally
 threaded](https://github.com/libvips/libvips/wiki/Why-is-libvips-quick)
 image processing library. Compared to similar
diff --git a/configure.ac b/configure.ac
index 2c712caf..e44866e9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1175,6 +1175,22 @@ FIND_GIFLIB(
   ]
 )
 
+# Look for libspng first
+AC_ARG_WITH([spng], 
+  AS_HELP_STRING([--without-spng], [build without libspng (default: test)]))
+
+if test x"$with_spng" != x"no"; then
+  PKG_CHECK_MODULES(SPNG, spng >= 0.6,
+    [AC_DEFINE(HAVE_SPNG,1,[define if you have libspng installed.])
+     with_spng=yes
+     PACKAGES_USED="$PACKAGES_USED spng"
+     with_png=no
+    ],
+    [
+    ]
+  )
+fi
+
 # look for PNG with pkg-config ... fall back to our tester
 AC_ARG_WITH([png], 
   AS_HELP_STRING([--without-png], [build without libpng (default: test)]))
@@ -1298,10 +1314,10 @@ if test x"$LIB_FUZZING_ENGINE" = x; then
 fi
 
 # Gather all up for VIPS_CFLAGS, VIPS_INCLUDES, VIPS_LIBS
-VIPS_CFLAGS="$VIPS_CFLAGS $GTHREAD_CFLAGS $GIO_CFLAGS $REQUIRED_CFLAGS $EXPAT_CFLAGS $ZLIB_CFLAGS $PANGOFT2_CFLAGS $GSF_CFLAGS $FFTW_CFLAGS $MAGICK_CFLAGS $JPEG_CFLAGS $PNG_CFLAGS $IMAGEQUANT_CFLAGS $EXIF_CFLAGS $MATIO_CFLAGS $CFITSIO_CFLAGS $LIBWEBP_CFLAGS $LIBWEBPMUX_CFLAGS $GIFLIB_INCLUDES $RSVG_CFLAGS $PDFIUM_INCLUDES $POPPLER_CFLAGS $OPENEXR_CFLAGS $OPENSLIDE_CFLAGS $ORC_CFLAGS $TIFF_CFLAGS $LCMS_CFLAGS $HEIF_CFLAGS"
+VIPS_CFLAGS="$VIPS_CFLAGS $GTHREAD_CFLAGS $GIO_CFLAGS $REQUIRED_CFLAGS $EXPAT_CFLAGS $ZLIB_CFLAGS $PANGOFT2_CFLAGS $GSF_CFLAGS $FFTW_CFLAGS $MAGICK_CFLAGS $JPEG_CFLAGS $SPNG_CFLAGS $PNG_CFLAGS $IMAGEQUANT_CFLAGS $EXIF_CFLAGS $MATIO_CFLAGS $CFITSIO_CFLAGS $LIBWEBP_CFLAGS $LIBWEBPMUX_CFLAGS $GIFLIB_INCLUDES $RSVG_CFLAGS $PDFIUM_INCLUDES $POPPLER_CFLAGS $OPENEXR_CFLAGS $OPENSLIDE_CFLAGS $ORC_CFLAGS $TIFF_CFLAGS $LCMS_CFLAGS $HEIF_CFLAGS"
 VIPS_CFLAGS="$VIPS_DEBUG_FLAGS $VIPS_CFLAGS"
 VIPS_INCLUDES="$ZLIB_INCLUDES $PNG_INCLUDES $TIFF_INCLUDES $JPEG_INCLUDES $NIFTI_INCLUDES" 
-VIPS_LIBS="$ZLIB_LIBS $HEIF_LIBS $MAGICK_LIBS $PNG_LIBS $IMAGEQUANT_LIBS $TIFF_LIBS $JPEG_LIBS $GTHREAD_LIBS $GIO_LIBS $REQUIRED_LIBS $EXPAT_LIBS $PANGOFT2_LIBS $GSF_LIBS $FFTW_LIBS $ORC_LIBS $LCMS_LIBS $GIFLIB_LIBS $RSVG_LIBS $NIFTI_LIBS $PDFIUM_LIBS $POPPLER_LIBS $OPENEXR_LIBS $OPENSLIDE_LIBS $CFITSIO_LIBS $LIBWEBP_LIBS $LIBWEBPMUX_LIBS $MATIO_LIBS $EXIF_LIBS -lm"
+VIPS_LIBS="$ZLIB_LIBS $HEIF_LIBS $MAGICK_LIBS $SPNG_LIBS $PNG_LIBS $IMAGEQUANT_LIBS $TIFF_LIBS $JPEG_LIBS $GTHREAD_LIBS $GIO_LIBS $REQUIRED_LIBS $EXPAT_LIBS $PANGOFT2_LIBS $GSF_LIBS $FFTW_LIBS $ORC_LIBS $LCMS_LIBS $GIFLIB_LIBS $RSVG_LIBS $NIFTI_LIBS $PDFIUM_LIBS $POPPLER_LIBS $OPENEXR_LIBS $OPENSLIDE_LIBS $CFITSIO_LIBS $LIBWEBP_LIBS $LIBWEBPMUX_LIBS $MATIO_LIBS $EXIF_LIBS -lm"
 
 AC_SUBST(VIPS_LIBDIR)
 
@@ -1397,6 +1413,8 @@ 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
+  (requires libspng-0.6 or later)
 file import/export with libpng: 	$with_png
   (requires libpng-1.2.9 or later)
 support 8bpp PNG quantisation:		$with_imagequant
diff --git a/libvips/foreign/Makefile.am b/libvips/foreign/Makefile.am
index d9a68585..759df2e5 100644
--- a/libvips/foreign/Makefile.am
+++ b/libvips/foreign/Makefile.am
@@ -39,6 +39,7 @@ libforeign_la_SOURCES = \
 	magickload.c \
 	magick7load.c \
 	magicksave.c \
+	spngload.c \
 	pngload.c \
 	pngsave.c \
 	vipspng.c \
diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
new file mode 100644
index 00000000..e89566d2
--- /dev/null
+++ b/libvips/foreign/spngload.c
@@ -0,0 +1,674 @@
+/* load PNG with libspng
+ *
+ * 5/12/11
+ * 	- from pngload.c
+ */
+
+/*
+
+    This file is part of VIPS.
+    
+    VIPS is free software; you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+    02110-1301  USA
+
+ */
+
+/*
+
+    These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk
+
+ */
+
+/* Notes:
+ *
+ * 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)
+ */
+
+/*
+#define DEBUG
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif /*HAVE_CONFIG_H*/
+#include <vips/intl.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <vips/vips.h>
+#include <vips/buf.h>
+#include <vips/internal.h>
+
+#include "pforeign.h"
+
+#ifdef HAVE_SPNG
+
+#include <spng.h>
+
+typedef struct _VipsForeignLoadPng {
+	VipsForeignLoad parent_object;
+
+	/* Set by subclasses.
+	 */
+	VipsSource *source;
+
+	spng_ctx *ctx;
+	struct spng_ihdr ihdr;
+	enum spng_format fmt;
+	int bands;
+	VipsInterpretation interpretation;
+	VipsBandFormat format;
+	size_t out_size;
+	size_t out_line_size;
+	int y_pos;
+
+} VipsForeignLoadPng;
+
+typedef VipsForeignLoadClass VipsForeignLoadPngClass;
+
+G_DEFINE_ABSTRACT_TYPE( VipsForeignLoadPng, vips_foreign_load_png, 
+	VIPS_TYPE_FOREIGN_LOAD );
+
+static void
+vips_foreign_load_png_dispose( GObject *gobject )
+{
+	VipsForeignLoadPng *png = (VipsForeignLoadPng *) gobject;
+
+	VIPS_FREEF( spng_ctx_free, png->ctx );
+	VIPS_UNREF( png->source );
+
+	G_OBJECT_CLASS( vips_foreign_load_png_parent_class )->
+		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 )
+{
+	VipsSource *source = VIPS_SOURCE( user );
+
+	gint64 bytes_read;
+
+	bytes_read = vips_source_read( source, dest, length );
+	if( bytes_read < 0 )
+		return( SPNG_IO_ERROR );
+	if( bytes_read < length )
+		return( SPNG_IO_EOF);
+
+	return( 0 );
+}
+
+static VipsForeignFlags
+vips_foreign_load_png_get_flags_source( VipsSource *source )
+{
+	spng_ctx *ctx;
+	struct spng_ihdr ihdr;
+	VipsForeignFlags flags;
+
+	ctx = spng_ctx_new( 0 );
+	spng_set_crc_action( ctx, SPNG_CRC_USE, SPNG_CRC_USE );
+	spng_set_png_stream( ctx, 
+		vips_foreign_load_png_stream, source );
+	if( spng_get_ihdr( ctx, &ihdr ) ) {
+		spng_ctx_free( ctx );
+		return( 0 );
+	}
+	spng_ctx_free( ctx );
+
+	flags = 0;
+	if( ihdr.interlace_method != 0 )
+		flags |= VIPS_FOREIGN_PARTIAL;
+	else
+		flags |= VIPS_FOREIGN_SEQUENTIAL;
+
+	return( flags );
+}
+
+static VipsForeignFlags
+vips_foreign_load_png_get_flags( VipsForeignLoad *load )
+{
+	VipsForeignLoadPng *png = (VipsForeignLoadPng *) load;
+
+	return( vips_foreign_load_png_get_flags_source( png->source ) );
+}
+
+static VipsForeignFlags
+vips_foreign_load_png_get_flags_filename( const char *filename )
+{
+	VipsSource *source;
+	VipsForeignFlags flags;
+
+	if( !(source = vips_source_new_from_file( filename )) )
+		return( 0 );
+	flags = vips_foreign_load_png_get_flags_source( source );
+	VIPS_UNREF( source );
+
+	return( flags );
+}
+
+static void
+vips_foreign_load_png_set_header( VipsForeignLoadPng *png, VipsImage *image )
+{
+	vips_image_init_fields( image,
+		png->ihdr.width, png->ihdr.height, png->bands,
+		png->format, VIPS_CODING_NONE, png->interpretation, 
+		1.0, 1.0 );
+	VIPS_SETSTR( image->filename, 
+		vips_connection_filename( VIPS_CONNECTION( png->source ) ) );
+
+	/* 0 is no interlace.
+	 */
+	if( png->ihdr.interlace_method == 0 ) 
+		/* Sequential mode needs thinstrip to work with things like
+		 * vips_shrink().
+		 */
+		vips_image_pipelinev( image, 
+			VIPS_DEMAND_STYLE_THINSTRIP, NULL );
+	else 
+		/* Interlaced images are read via a huge memory buffer.
+		 */
+		vips_image_pipelinev( image, VIPS_DEMAND_STYLE_ANY, NULL );
+}
+
+static int
+vips_foreign_load_png_header( VipsForeignLoad *load )
+{
+	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( load );
+	VipsForeignLoadPng *png = (VipsForeignLoadPng *) load;
+
+	int error;
+
+	/* Flags can be eg. SPNG_CTX_IGNORE_ADLER32 to ignore CRC chaekcs in
+	 * deflate.
+	 *
+	 * FIXME ... fail handling
+	 */
+	png->ctx = spng_ctx_new( 0 );
+	spng_set_crc_action( png->ctx, SPNG_CRC_USE, SPNG_CRC_USE );
+
+	spng_set_png_stream( png->ctx, 
+		vips_foreign_load_png_stream, png->source );
+	if( (error = spng_get_ihdr( png->ctx, &png->ihdr )) ) {
+		vips_error( class->nickname, "%s", spng_strerror( error ) ); 
+		return( -1 );
+	}
+
+	printf(" width: %d\nheight: %d\nbit depth: %d\ncolor type: %d\n",
+		png->ihdr.width, png->ihdr.height,
+		png->ihdr.bit_depth, png->ihdr.color_type );
+	printf( "compression method: %d\nfilter method: %d\n"
+		"interlace method: %d\n",
+		png->ihdr.compression_method, png->ihdr.filter_method,
+		png->ihdr.interlace_method );
+
+	switch( png->ihdr.color_type ) {
+	case SPNG_COLOR_TYPE_GRAYSCALE:
+		png->interpretation = VIPS_INTERPRETATION_B_W;
+		png->bands = 1;
+		break;
+
+	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
+		png->interpretation = VIPS_INTERPRETATION_B_W;
+		png->bands = 2;
+		break;
+
+	case SPNG_COLOR_TYPE_TRUECOLOR:
+	case SPNG_COLOR_TYPE_INDEXED:
+		png->interpretation = VIPS_INTERPRETATION_sRGB;
+		png->bands = 3;
+		break;
+
+	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
+		png->interpretation = VIPS_INTERPRETATION_sRGB;
+		png->bands = 4;
+		break;
+
+	default:
+		vips_error( class->nickname, "%s", "unknown color_type" ); 
+		return( -1 );
+	}
+
+	if( png->ihdr.bit_depth == 16 ) {
+		png->fmt = SPNG_FMT_RGBA16;
+		png->format = VIPS_FORMAT_USHORT;
+		if( png->interpretation == VIPS_INTERPRETATION_B_W )
+			png->interpretation = VIPS_INTERPRETATION_GREY16;
+		if( png->interpretation == VIPS_INTERPRETATION_sRGB )
+			png->interpretation = VIPS_INTERPRETATION_RGB16;
+	}
+	else {
+		png->fmt = SPNG_FMT_RGBA8;
+		png->format = VIPS_FORMAT_UCHAR;
+	}
+
+	/* FIXME ... get resolution.
+	 */
+
+	vips_source_minimise( png->source );
+
+	vips_foreign_load_png_set_header( png, load->out );
+
+	return( 0 );
+}
+
+static int
+vips_foreign_load_png_interlace( VipsForeignLoadPng *png, VipsImage *image )
+{
+	/* FIXME ... load interlaced PNG to huge memory image.
+	 */
+
+	return( 0 );
+}
+
+static int
+vips_foreign_load_png_generate( VipsRegion *or, 
+	void *seq, void *a, void *b, gboolean *stop )
+{
+        VipsRect *r = &or->valid;
+	VipsForeignLoad *load = VIPS_FOREIGN_LOAD( a );
+	VipsForeignLoadPng *png = (VipsForeignLoadPng *) load;
+	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( png );
+
+	int y;
+	int error;
+
+#ifdef DEBUG
+	printf( "vips_foreign_load_png_generate: line %d, %d rows\n", 
+		r->top, r->height );
+	printf( "vips_foreign_load_png_generate: y_top = %d\n", png->y_pos );
+#endif /*DEBUG*/
+
+	/* We're inside a tilecache where tiles are the full image width, so
+	 * this should always be true.
+	 */
+	g_assert( r->left == 0 );
+	g_assert( r->width == or->im->Xsize );
+	g_assert( VIPS_RECT_BOTTOM( r ) <= or->im->Ysize );
+
+	/* Tiles should always be a strip in height, unless it's the final
+	 * strip.
+	 */
+	g_assert( r->height == VIPS_MIN( VIPS__FATSTRIP_HEIGHT, 
+		or->im->Ysize - r->top ) ); 
+
+	/* And check that y_pos is correct. It should be, since we are inside
+	 * a vips_sequential().
+	 */
+	if( r->top != png->y_pos ) {
+		vips_error( class->nickname, 
+			_( "out of order read at line %d" ), png->y_pos );
+		return( -1 );
+	}
+
+	for( y = 0; y < r->height; y++ ) {
+		error = spng_decode_row( png->ctx, 
+			VIPS_REGION_ADDR( or, 0, r->top + y ),
+			VIPS_REGION_SIZEOF_LINE( or ) );
+
+		/* FIXME .. should allow SPNG_EOI here?
+		 */
+		if( error ) { 
+			/* We've failed to read some pixels. Knock this 
+			 * operation out of cache. 
+			 */
+			vips_operation_invalidate( VIPS_OPERATION( png ) ); 
+
+#ifdef DEBUG
+			printf( "vips_foreign_load_png_generate:\n" ); 
+			printf( "  spng_decode_row() failed, line %d\n", 
+				r->top + y ); 
+			printf( "  file %s\n", read->name );
+			printf( "  thread %p\n", g_thread_self() );
+#endif /*DEBUG*/
+
+			/* And bail if fail is on. We have to add an error
+			 * message, since the handler we install just does
+			 * g_warning().
+			 */
+			if( load->fail ) {
+				vips_error( class->nickname, 
+					"%s", _( "libpng read error" ) ); 
+				return( -1 );
+			}
+		}
+
+		png->y_pos += 1;
+	}
+
+	return( 0 );
+}
+
+static int
+vips_foreign_load_png_load( VipsForeignLoad *load )
+{
+	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( load );
+	VipsForeignLoadPng *png = (VipsForeignLoadPng *) load;
+	VipsImage **t = (VipsImage **) 
+		vips_object_local_array( VIPS_OBJECT( load ), 3 );
+
+	int error;
+
+	if( (error = spng_decoded_image_size( png->ctx, 
+		png->fmt, &png->out_size )) ) {
+		vips_error( class->nickname, "%s", spng_strerror( error ) ); 
+		return( -1 );
+	}
+	png->out_line_size = png->out_size / png->ihdr.height;
+
+	/* Initialize for progressive decoding.
+	 */
+	if( (error = spng_decode_image( png->ctx, NULL, 0, 
+		png->fmt, SPNG_DECODE_PROGRESSIVE )) ) {
+		vips_error( class->nickname, "%s", spng_strerror( error ) ); 
+		return( -1 );
+	}
+
+	t[0] = vips_image_new_memory();
+	vips_foreign_load_png_set_header( png, t[0] );
+	if( vips_source_decode( png->source ) )
+		return( -1 );
+
+	if( png->ihdr.interlace_method != 0 ) {
+		/* Arg awful interlaced image. We have to load to a huge mem 
+		 * buffer, then copy to out.
+		 */
+		if( vips_foreign_load_png_interlace( png, t[0] ) ||
+			vips_image_write( t[0], load->real ) )
+			return( -1 );
+	}
+	else {
+		if( vips_image_generate( t[0], 
+				NULL, vips_foreign_load_png_generate, NULL, 
+				read, NULL ) ||
+			vips_sequential( t[0], &t[1], 
+				"tile_height", VIPS__FATSTRIP_HEIGHT, 
+				NULL ) ||
+			vips_image_write( t[1], load->real ) )
+			return( -1 );
+	}
+
+	return( 0 );
+}
+
+static void
+vips_foreign_load_png_class_init( VipsForeignLoadPngClass *class )
+{
+	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
+	VipsObjectClass *object_class = (VipsObjectClass *) class;
+	VipsForeignClass *foreign_class = (VipsForeignClass *) class;
+	VipsForeignLoadClass *load_class = (VipsForeignLoadClass *) class;
+
+	gobject_class->dispose = vips_foreign_load_png_dispose;
+
+	object_class->nickname = "pngload_base";
+	object_class->description = _( "load png base class" );
+
+	/* We are fast at is_a(), so high priority.
+	 */
+	foreign_class->priority = 200;
+
+	load_class->get_flags_filename = 
+		vips_foreign_load_png_get_flags_filename;
+	load_class->get_flags = vips_foreign_load_png_get_flags;
+	load_class->header = vips_foreign_load_png_header;
+	load_class->load = vips_foreign_load_png_load;
+
+}
+
+static void
+vips_foreign_load_png_init( VipsForeignLoadPng *png )
+{
+}
+
+typedef struct _VipsForeignLoadPngSource {
+	VipsForeignLoadPng parent_object;
+
+	/* Load from a source.
+	 */
+	VipsSource *source;
+
+} VipsForeignLoadPngSource;
+
+typedef VipsForeignLoadPngClass VipsForeignLoadPngSourceClass;
+
+G_DEFINE_TYPE( VipsForeignLoadPngSource, vips_foreign_load_png_source, 
+	vips_foreign_load_png_get_type() );
+
+static int
+vips_foreign_load_png_source_build( VipsObject *object )
+{
+	VipsForeignLoadPng *png = (VipsForeignLoadPng *) object;
+	VipsForeignLoadPngSource *source = (VipsForeignLoadPngSource *) object;
+
+	if( source->source ) {
+		png->source = source->source;
+		g_object_ref( png->source );
+	}
+
+	if( VIPS_OBJECT_CLASS( vips_foreign_load_png_source_parent_class )->
+		build( object ) )
+		return( -1 );
+
+	return( 0 );
+}
+
+static gboolean
+vips_foreign_load_png_source_is_a_source( VipsSource *source )
+{
+	static unsigned char signature[8] = { 137, 80, 78, 71, 13, 10, 26, 10 };
+
+	const unsigned char *p;
+
+	if( (p = vips_source_sniff( source, 8 )) &&
+		memcmp( p, signature, 8 ) == 0 )
+		return( TRUE ); 
+
+	return( FALSE ); 
+}
+
+static void
+vips_foreign_load_png_source_class_init( VipsForeignLoadPngSourceClass *class )
+{
+	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
+	VipsObjectClass *object_class = (VipsObjectClass *) class;
+	VipsForeignLoadClass *load_class = (VipsForeignLoadClass *) class;
+
+	gobject_class->set_property = vips_object_set_property;
+	gobject_class->get_property = vips_object_get_property;
+
+	object_class->nickname = "pngload_source";
+	object_class->description = _( "load png from source" );
+	object_class->build = vips_foreign_load_png_source_build;
+
+	load_class->is_a_source = vips_foreign_load_png_source_is_a_source;
+
+	VIPS_ARG_OBJECT( class, "source", 1,
+		_( "Source" ),
+		_( "Source to load from" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT, 
+		G_STRUCT_OFFSET( VipsForeignLoadPngSource, source ),
+		VIPS_TYPE_SOURCE );
+
+}
+
+static void
+vips_foreign_load_png_source_init( VipsForeignLoadPngSource *source )
+{
+}
+
+typedef struct _VipsForeignLoadPngFile {
+	VipsForeignLoadPng parent_object;
+
+	/* Filename for load.
+	 */
+	char *filename; 
+
+} VipsForeignLoadPngFile;
+
+typedef VipsForeignLoadPngClass VipsForeignLoadPngFileClass;
+
+G_DEFINE_TYPE( VipsForeignLoadPngFile, vips_foreign_load_png_file, 
+	vips_foreign_load_png_get_type() );
+
+static int
+vips_foreign_load_png_file_build( VipsObject *object )
+{
+	VipsForeignLoadPng *png = (VipsForeignLoadPng *) object;
+	VipsForeignLoadPngFile *file = (VipsForeignLoadPngFile *) object;
+
+	if( file->filename &&
+		!(png->source = vips_source_new_from_file( file->filename )) )
+		return( -1 );
+
+	if( VIPS_OBJECT_CLASS( vips_foreign_load_png_file_parent_class )->
+		build( object ) )
+		return( -1 );
+
+	return( 0 );
+}
+
+static gboolean
+vips_foreign_load_png_file_is_a( const char *filename )
+{
+	VipsSource *source;
+	gboolean result;
+
+	if( !(source = vips_source_new_from_file( filename )) )
+		return( FALSE );
+	result = vips_foreign_load_png_source_is_a_source( source );
+	VIPS_UNREF( source );
+
+	return( result );
+}
+
+const char *vips_foreign_load_png_file_suffs[] = { ".png", NULL };
+
+static void
+vips_foreign_load_png_file_class_init( VipsForeignLoadPngFileClass *class )
+{
+	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
+	VipsObjectClass *object_class = (VipsObjectClass *) class;
+	VipsForeignClass *foreign_class = (VipsForeignClass *) class;
+	VipsForeignLoadClass *load_class = (VipsForeignLoadClass *) class;
+
+	gobject_class->set_property = vips_object_set_property;
+	gobject_class->get_property = vips_object_get_property;
+
+	object_class->nickname = "pngload";
+	object_class->description = _( "load png from file" );
+	object_class->build = vips_foreign_load_png_file_build;
+
+	foreign_class->suffs = vips_foreign_load_png_file_suffs;
+
+	load_class->is_a = vips_foreign_load_png_file_is_a;
+
+	VIPS_ARG_STRING( class, "filename", 1, 
+		_( "Filename" ),
+		_( "Filename to load from" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT, 
+		G_STRUCT_OFFSET( VipsForeignLoadPngFile, filename ),
+		NULL );
+}
+
+static void
+vips_foreign_load_png_file_init( VipsForeignLoadPngFile *file )
+{
+}
+
+typedef struct _VipsForeignLoadPngBuffer {
+	VipsForeignLoadPng parent_object;
+
+	/* Load from a buffer.
+	 */
+	VipsBlob *blob;
+
+} VipsForeignLoadPngBuffer;
+
+typedef VipsForeignLoadPngClass VipsForeignLoadPngBufferClass;
+
+G_DEFINE_TYPE( VipsForeignLoadPngBuffer, vips_foreign_load_png_buffer, 
+	vips_foreign_load_png_get_type() );
+
+static int
+vips_foreign_load_png_buffer_build( VipsObject *object )
+{
+	VipsForeignLoadPng *png = (VipsForeignLoadPng *) object;
+	VipsForeignLoadPngBuffer *buffer = (VipsForeignLoadPngBuffer *) object;
+
+	if( buffer->blob &&
+		!(png->source = vips_source_new_from_memory( 
+			VIPS_AREA( buffer->blob )->data, 
+			VIPS_AREA( buffer->blob )->length )) )
+		return( -1 );
+
+	if( VIPS_OBJECT_CLASS( vips_foreign_load_png_buffer_parent_class )->
+		build( object ) )
+		return( -1 );
+
+	return( 0 );
+}
+
+static gboolean
+vips_foreign_load_png_buffer_is_a_buffer( const void *buf, size_t len )
+{
+	VipsSource *source;
+	gboolean result;
+
+	if( !(source = vips_source_new_from_memory( buf, len )) )
+		return( FALSE );
+	result = vips_foreign_load_png_source_is_a_source( source );
+	VIPS_UNREF( source );
+
+	return( result );
+}
+
+static void
+vips_foreign_load_png_buffer_class_init( VipsForeignLoadPngBufferClass *class )
+{
+	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
+	VipsObjectClass *object_class = (VipsObjectClass *) class;
+	VipsForeignLoadClass *load_class = (VipsForeignLoadClass *) class;
+
+	gobject_class->set_property = vips_object_set_property;
+	gobject_class->get_property = vips_object_get_property;
+
+	object_class->nickname = "pngload_buffer";
+	object_class->description = _( "load png from buffer" );
+	object_class->build = vips_foreign_load_png_buffer_build;
+
+	load_class->is_a_buffer = vips_foreign_load_png_buffer_is_a_buffer;
+
+	VIPS_ARG_BOXED( class, "buffer", 1, 
+		_( "Buffer" ),
+		_( "Buffer to load from" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT, 
+		G_STRUCT_OFFSET( VipsForeignLoadPngBuffer, blob ),
+		VIPS_TYPE_BLOB );
+
+}
+
+static void
+vips_foreign_load_png_buffer_init( VipsForeignLoadPngBuffer *buffer )
+{
+}
+
+#endif /*HAVE_SPNG*/

From 53101929c5c7004a8c3a642e94795e4a3abb0cad Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Fri, 1 May 2020 20:28:03 +0100
Subject: [PATCH 02/19] workinig!

---
 libvips/foreign/foreign.c  |   6 ++
 libvips/foreign/spngload.c | 123 ++++++++++++++++---------------------
 2 files changed, 60 insertions(+), 69 deletions(-)

diff --git a/libvips/foreign/foreign.c b/libvips/foreign/foreign.c
index 895c999b..e0367c4d 100644
--- a/libvips/foreign/foreign.c
+++ b/libvips/foreign/foreign.c
@@ -2206,6 +2206,12 @@ vips_foreign_operation_init( void )
 	vips_foreign_save_png_target_get_type(); 
 #endif /*HAVE_PNG*/
 
+#ifdef HAVE_SPNG
+	vips_foreign_load_png_file_get_type(); 
+	vips_foreign_load_png_buffer_get_type(); 
+	vips_foreign_load_png_source_get_type(); 
+#endif /*HAVE_SPNG*/
+
 #ifdef HAVE_MATIO
 	vips_foreign_load_mat_get_type(); 
 #endif /*HAVE_MATIO*/
diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index e89566d2..dad90fc0 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -70,12 +70,11 @@ typedef struct _VipsForeignLoadPng {
 
 	spng_ctx *ctx;
 	struct spng_ihdr ihdr;
+	struct spng_trns trns;
 	enum spng_format fmt;
 	int bands;
 	VipsInterpretation interpretation;
 	VipsBandFormat format;
-	size_t out_size;
-	size_t out_line_size;
 	int y_pos;
 
 } VipsForeignLoadPng;
@@ -195,16 +194,22 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( load );
 	VipsForeignLoadPng *png = (VipsForeignLoadPng *) load;
 
+	int flags;
 	int error;
 
-	/* Flags can be eg. SPNG_CTX_IGNORE_ADLER32 to ignore CRC chaekcs in
-	 * deflate.
-	 *
-	 * FIXME ... fail handling
+	/* In non-fail mode, ignore CRC errors.
 	 */
-	png->ctx = spng_ctx_new( 0 );
-	spng_set_crc_action( png->ctx, SPNG_CRC_USE, SPNG_CRC_USE );
+	flags = 0;
+	if( !load->fail )
+		flags |= SPNG_CTX_IGNORE_ADLER32;
+	png->ctx = spng_ctx_new( flags );
+	if( !load->fail )
+		/* Ignore and don't calculate checksums.
+		 */
+		spng_set_crc_action( png->ctx, SPNG_CRC_USE, SPNG_CRC_USE );
 
+	if( vips_source_rewind( png->source ) ) 
+		return( -1 );
 	spng_set_png_stream( png->ctx, 
 		vips_foreign_load_png_stream, png->source );
 	if( (error = spng_get_ihdr( png->ctx, &png->ihdr )) ) {
@@ -212,40 +217,20 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		return( -1 );
 	}
 
-	printf(" width: %d\nheight: %d\nbit depth: %d\ncolor type: %d\n",
+	/*
+	printf( "width: %d\nheight: %d\nbit depth: %d\ncolor type: %d\n",
 		png->ihdr.width, png->ihdr.height,
 		png->ihdr.bit_depth, png->ihdr.color_type );
 	printf( "compression method: %d\nfilter method: %d\n"
 		"interlace method: %d\n",
 		png->ihdr.compression_method, png->ihdr.filter_method,
 		png->ihdr.interlace_method );
+	 */
 
-	switch( png->ihdr.color_type ) {
-	case SPNG_COLOR_TYPE_GRAYSCALE:
-		png->interpretation = VIPS_INTERPRETATION_B_W;
-		png->bands = 1;
-		break;
-
-	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
-		png->interpretation = VIPS_INTERPRETATION_B_W;
-		png->bands = 2;
-		break;
-
-	case SPNG_COLOR_TYPE_TRUECOLOR:
-	case SPNG_COLOR_TYPE_INDEXED:
-		png->interpretation = VIPS_INTERPRETATION_sRGB;
-		png->bands = 3;
-		break;
-
-	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
-		png->interpretation = VIPS_INTERPRETATION_sRGB;
-		png->bands = 4;
-		break;
-
-	default:
-		vips_error( class->nickname, "%s", "unknown color_type" ); 
-		return( -1 );
-	}
+	/* For now, libspng always outputs RGBA.
+	 */
+	png->interpretation = VIPS_INTERPRETATION_sRGB;
+	png->bands = 4;
 
 	if( png->ihdr.bit_depth == 16 ) {
 		png->fmt = SPNG_FMT_RGBA16;
@@ -260,7 +245,7 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		png->format = VIPS_FORMAT_UCHAR;
 	}
 
-	/* FIXME ... get resolution.
+	/* FIXME ... get resolution, profile, exif, xmp, etc. etc.
 	 */
 
 	vips_source_minimise( png->source );
@@ -270,15 +255,6 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 	return( 0 );
 }
 
-static int
-vips_foreign_load_png_interlace( VipsForeignLoadPng *png, VipsImage *image )
-{
-	/* FIXME ... load interlaced PNG to huge memory image.
-	 */
-
-	return( 0 );
-}
-
 static int
 vips_foreign_load_png_generate( VipsRegion *or, 
 	void *seq, void *a, void *b, gboolean *stop )
@@ -323,10 +299,11 @@ vips_foreign_load_png_generate( VipsRegion *or,
 		error = spng_decode_row( png->ctx, 
 			VIPS_REGION_ADDR( or, 0, r->top + y ),
 			VIPS_REGION_SIZEOF_LINE( or ) );
-
-		/* FIXME .. should allow SPNG_EOI here?
+		/* libspng returns EOI when successfully reading the 
+		 * final line of input.
 		 */
-		if( error ) { 
+		if( error != 0 &&
+			error != SPNG_EOI ) { 
 			/* We've failed to read some pixels. Knock this 
 			 * operation out of cache. 
 			 */
@@ -336,8 +313,8 @@ vips_foreign_load_png_generate( VipsRegion *or,
 			printf( "vips_foreign_load_png_generate:\n" ); 
 			printf( "  spng_decode_row() failed, line %d\n", 
 				r->top + y ); 
-			printf( "  file %s\n", read->name );
 			printf( "  thread %p\n", g_thread_self() );
+			printf( "  error %s\n", spng_strerror( error ) ); 
 #endif /*DEBUG*/
 
 			/* And bail if fail is on. We have to add an error
@@ -367,23 +344,6 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 
 	int error;
 
-	if( (error = spng_decoded_image_size( png->ctx, 
-		png->fmt, &png->out_size )) ) {
-		vips_error( class->nickname, "%s", spng_strerror( error ) ); 
-		return( -1 );
-	}
-	png->out_line_size = png->out_size / png->ihdr.height;
-
-	/* Initialize for progressive decoding.
-	 */
-	if( (error = spng_decode_image( png->ctx, NULL, 0, 
-		png->fmt, SPNG_DECODE_PROGRESSIVE )) ) {
-		vips_error( class->nickname, "%s", spng_strerror( error ) ); 
-		return( -1 );
-	}
-
-	t[0] = vips_image_new_memory();
-	vips_foreign_load_png_set_header( png, t[0] );
 	if( vips_source_decode( png->source ) )
 		return( -1 );
 
@@ -391,14 +351,39 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		/* Arg awful interlaced image. We have to load to a huge mem 
 		 * buffer, then copy to out.
 		 */
-		if( vips_foreign_load_png_interlace( png, t[0] ) ||
-			vips_image_write( t[0], load->real ) )
+		t[0] = vips_image_new_memory();
+		vips_foreign_load_png_set_header( png, t[0] );
+		if( vips_image_write_prepare( t[0] ) )
+			return( -1 );
+
+		if( (error = spng_decode_image( png->ctx, 
+			VIPS_IMAGE_ADDR( t[0], 0, 0 ), 
+			VIPS_IMAGE_SIZEOF_IMAGE( t[0] ), 
+			png->fmt, 0 )) ) {
+			vips_error( class->nickname, 
+				"%s", spng_strerror( error ) ); 
+			return( -1 );
+		}
+
+		if( vips_image_write( t[0], load->real ) )
 			return( -1 );
 	}
 	else {
+		t[0] = vips_image_new();
+		vips_foreign_load_png_set_header( png, t[0] );
+
+		/* Initialize for progressive decoding.
+		 */
+		if( (error = spng_decode_image( png->ctx, NULL, 0, 
+			png->fmt, SPNG_DECODE_PROGRESSIVE )) ) {
+			vips_error( class->nickname, 
+				"%s", spng_strerror( error ) ); 
+			return( -1 );
+		}
+
 		if( vips_image_generate( t[0], 
 				NULL, vips_foreign_load_png_generate, NULL, 
-				read, NULL ) ||
+				png, NULL ) ||
 			vips_sequential( t[0], &t[1], 
 				"tile_height", VIPS__FATSTRIP_HEIGHT, 
 				NULL ) ||

From 10f1352f6fd798b832d03f8fc1ac693d88b81cbd Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Fri, 1 May 2020 23:20:48 +0100
Subject: [PATCH 03/19] clean up, add benchmarks

---
 README.md                  | 27 ++++++++++++++++++++++++++-
 configure.ac               | 10 +++++-----
 libvips/foreign/spngload.c | 17 +++++++++--------
 3 files changed, 40 insertions(+), 14 deletions(-)

diff --git a/README.md b/README.md
index 1b4c4e6d..44b5d3ce 100644
--- a/README.md
+++ b/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
diff --git a/configure.ac b/configure.ac
index e44866e9..90ca3d0a 100644
--- a/configure.ac
+++ b/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)
diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index dad90fc0..7d9e36ab 100644
--- a/libvips/foreign/spngload.c
+++ b/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, 

From d78480c84679a63f14365d6edf2638d39a052f6d Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Wed, 13 May 2020 15:25:01 +0100
Subject: [PATCH 04/19] update for SPNG_FMT_PNG

We can now decode PNG to g8/g16/ga8/ga16/rgb8/rgb16 etc.
---
 libvips/foreign/spngload.c | 62 +++++++++++++++++++++++++++++++-------
 1 file changed, 51 insertions(+), 11 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 7d9e36ab..d7b767d4 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -37,10 +37,10 @@
  *   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.
+ * test indexed decode
  *
- * Most metadata support (eg. XMP, ICC, etc. etc.) is missing.
+ * Most metadata support (eg. XMP, ICC, etc. etc.) is missing. We will need 
+ * to set a chunk size limit with spng_set_chunks_limits().
  *
  * Load only, there's no save support for now.
  */
@@ -211,6 +211,14 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		 */
 		spng_set_crc_action( png->ctx, SPNG_CRC_USE, SPNG_CRC_USE );
 
+	/* Set limits to avoid decompression bombs. We should set
+	 * spng_set_chunks_limits() as well, once that API goes in.
+	 *
+	 * No need to test the decoded image size -- the user can do that if
+	 * they wish.
+	 */
+	spng_set_image_limits( png->ctx, VIPS_MAX_COORD, VIPS_MAX_COORD );
+
 	if( vips_source_rewind( png->source ) ) 
 		return( -1 );
 	spng_set_png_stream( png->ctx, 
@@ -230,23 +238,55 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		png->ihdr.interlace_method );
 	 */
 
-	/* For now, libspng always outputs RGBA.
-	 */
-	png->interpretation = VIPS_INTERPRETATION_sRGB;
-	png->bands = 4;
+
+	switch( png->ihdr.color_type ) {
+	case SPNG_COLOR_TYPE_GRAYSCALE:
+		png->bands = 1;
+		png->interpretation = VIPS_INTERPRETATION_B_W;
+		png->fmt = SPNG_FMT_PNG;
+		break;
+
+	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
+		png->bands = 2;
+		png->interpretation = VIPS_INTERPRETATION_B_W;
+		png->fmt = SPNG_FMT_PNG;
+		break;
+
+	case SPNG_COLOR_TYPE_TRUECOLOR:
+		png->bands = 3;
+		png->interpretation = VIPS_INTERPRETATION_sRGB;
+		png->fmt = SPNG_FMT_PNG;
+		break;
+
+	case SPNG_COLOR_TYPE_INDEXED:
+		png->bands = 3;
+		png->interpretation = VIPS_INTERPRETATION_sRGB;
+
+		/* Expand indexed images to RGB8.
+		 */
+		png->fmt = SPNG_FMT_RGB8;
+		break;
+
+	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
+		png->bands = 4;
+		png->interpretation = VIPS_INTERPRETATION_sRGB;
+		png->fmt = SPNG_FMT_PNG;
+		break;
+
+	default:
+		vips_error( class->nickname, "%s", _( "unknown color type" ) );
+		return( -1 );
+	}
 
 	if( png->ihdr.bit_depth == 16 ) {
-		png->fmt = SPNG_FMT_RGBA16;
 		png->format = VIPS_FORMAT_USHORT;
 		if( png->interpretation == VIPS_INTERPRETATION_B_W )
 			png->interpretation = VIPS_INTERPRETATION_GREY16;
 		if( png->interpretation == VIPS_INTERPRETATION_sRGB )
 			png->interpretation = VIPS_INTERPRETATION_RGB16;
 	}
-	else {
-		png->fmt = SPNG_FMT_RGBA8;
+	else 
 		png->format = VIPS_FORMAT_UCHAR;
-	}
 
 	/* FIXME ... get resolution, profile, exif, xmp, etc. etc.
 	 */

From c2165671e25981a0e06925c36ddeb1e66610a9c1 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Wed, 13 May 2020 16:38:35 +0100
Subject: [PATCH 05/19] update benchmark result

---
 README.md                  | 10 ++++------
 libvips/foreign/spngload.c | 13 +++++++------
 2 files changed, 11 insertions(+), 12 deletions(-)

diff --git a/README.md b/README.md
index 44b5d3ce..89ae80a5 100644
--- a/README.md
+++ b/README.md
@@ -31,11 +31,11 @@ libspng benchmark:
 
 ```
 $ time vips avg wtc.png
-151.549325
+117.065766
 
-real	0m3.167s
-user	0m3.714s
-sys	0m0.194s
+real	0m2.972s
+user	0m3.376s
+sys	0m0.197s
 ```
 
 And for libpng:
@@ -49,8 +49,6 @@ user	0m4.177s
 sys	0m0.221s
 ```
 
-The avg is different since libspng is generating alpha 255.
-
 # Introduction
 
 libvips is a [demand-driven, horizontally
diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index d7b767d4..a037ada4 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -31,18 +31,19 @@
 
  */
 
-/* Notes:
+/* TODO
+ *
+ * an enum for interlace_method would be nice ... ADAM7 == 1, no interlace == 0
  *
- * 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)
  *
  * test indexed decode
  *
- * Most metadata support (eg. XMP, ICC, etc. etc.) is missing. We will need 
- * to set a chunk size limit with spng_set_chunks_limits().
+ * most metadata support (eg. XMP, ICC, etc. etc.) is missing ... we will need 
+ * to set a chunk size limit with spng_set_chunks_limits()
+ *
+ * load only, there's no save support for now
  *
- * Load only, there's no save support for now.
  */
 
 /*

From ef408d630bfec83ffe5446df4ddc656d85ed1b72 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Sun, 7 Jun 2020 14:00:10 +0100
Subject: [PATCH 06/19] start adding ICC and XMP support

not quite working though ... seems to need a fix in libspng still
---
 libvips/foreign/spngload.c | 36 +++++++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index a037ada4..0ed2330b 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -171,6 +171,11 @@ vips_foreign_load_png_get_flags_filename( const char *filename )
 static void
 vips_foreign_load_png_set_header( VipsForeignLoadPng *png, VipsImage *image )
 {
+	struct spng_iccp iccp;
+	struct spng_text *text;
+	guint32 n_text;
+	int ret;
+
 	vips_image_init_fields( image,
 		png->ihdr.width, png->ihdr.height, png->bands,
 		png->format, VIPS_CODING_NONE, png->interpretation, 
@@ -178,6 +183,34 @@ vips_foreign_load_png_set_header( VipsForeignLoadPng *png, VipsImage *image )
 	VIPS_SETSTR( image->filename, 
 		vips_connection_filename( VIPS_CONNECTION( png->source ) ) );
 
+	/* Attach ICC profile.
+	 */
+	if( !spng_get_iccp( png->ctx, &iccp ) ) {
+		printf( "attaching profile %s, %zd bytes\n", 
+			iccp.profile_name, iccp.profile_len );
+
+		vips_image_set_blob_copy( image, 
+			VIPS_META_ICC_NAME, iccp.profile, iccp.profile_len );
+	}
+
+	/*
+	spng_get_text( png->ctx, NULL, &n_text );
+	printf( "reading %" G_GUINT32_FORMAT " text chunks\n", n_text );
+	text = VIPS_ARRAY( VIPS_OBJECT( png ), n_text, struct spng_text );
+	if( !spng_get_text( png->ctx, text, &n_text ) ) {
+		guint32 i;
+
+		for( i = 0; i < n_text; i++ ) {
+			printf( "chunk %d: keyword %s, type %d, length %zd\n",
+				i, text[i].keyword, text[i].type, 
+				text[i].length );
+		}
+	}
+	 */
+
+	/* FIXME ... get resolution, exif, xmp, etc. etc.
+	 */
+
 	/* 0 is no interlace.
 	 */
 	if( png->ihdr.interlace_method == 0 ) 
@@ -289,9 +322,6 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 	else 
 		png->format = VIPS_FORMAT_UCHAR;
 
-	/* FIXME ... get resolution, profile, exif, xmp, etc. etc.
-	 */
-
 	vips_source_minimise( png->source );
 
 	vips_foreign_load_png_set_header( png, load->out );

From fc872421aa879154c86574203bcc1942261a6343 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Sun, 7 Jun 2020 15:17:37 +0100
Subject: [PATCH 07/19] add exif/icc/text text chunk read

using new libspng 0.6 features
---
 libvips/foreign/spngload.c | 102 ++++++++++++++++++++++++++-----------
 1 file changed, 73 insertions(+), 29 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 0ed2330b..9d1a7a29 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -168,49 +168,56 @@ vips_foreign_load_png_get_flags_filename( const char *filename )
 	return( flags );
 }
 
+/* Set the png text data as metadata on the vips image. These are always
+ * null-terminated strings.
+ */
+static void
+vips_foreign_load_png_set_text( VipsImage *out, 
+	int i, const char *key, const char *value ) 
+{
+#ifdef DEBUG
+	printf( "vips_foreign_load_png_set_text: key %s, value %s\n", 
+		key, value );
+#endif /*DEBUG*/
+
+	if( strcmp( key, "XML:com.adobe.xmp" ) == 0 ) {
+		/* Save as an XMP tag. This must be a BLOB, for compatibility
+		 * for things like the XMP blob that the tiff loader adds.
+		 *
+		 * Note that this will remove the null-termination from the
+		 * string. We must carefully reattach this.
+		 */
+		vips_image_set_blob_copy( out, 
+			VIPS_META_XMP_NAME, value, strlen( value ) );
+	}
+	else  {
+		char name[256];
+
+		/* Save as a string comment. Some PNGs have EXIF data as
+		 * text segments, unfortunately.
+		 */
+		vips_snprintf( name, 256, "png-comment-%d-%s", i, key );
+
+		vips_image_set_string( out, name, value );
+	}
+}
+
 static void
 vips_foreign_load_png_set_header( VipsForeignLoadPng *png, VipsImage *image )
 {
 	struct spng_iccp iccp;
 	struct spng_text *text;
+	struct spng_exif exif;
 	guint32 n_text;
-	int ret;
 
 	vips_image_init_fields( image,
 		png->ihdr.width, png->ihdr.height, png->bands,
 		png->format, VIPS_CODING_NONE, png->interpretation, 
 		1.0, 1.0 );
+
 	VIPS_SETSTR( image->filename, 
 		vips_connection_filename( VIPS_CONNECTION( png->source ) ) );
 
-	/* Attach ICC profile.
-	 */
-	if( !spng_get_iccp( png->ctx, &iccp ) ) {
-		printf( "attaching profile %s, %zd bytes\n", 
-			iccp.profile_name, iccp.profile_len );
-
-		vips_image_set_blob_copy( image, 
-			VIPS_META_ICC_NAME, iccp.profile, iccp.profile_len );
-	}
-
-	/*
-	spng_get_text( png->ctx, NULL, &n_text );
-	printf( "reading %" G_GUINT32_FORMAT " text chunks\n", n_text );
-	text = VIPS_ARRAY( VIPS_OBJECT( png ), n_text, struct spng_text );
-	if( !spng_get_text( png->ctx, text, &n_text ) ) {
-		guint32 i;
-
-		for( i = 0; i < n_text; i++ ) {
-			printf( "chunk %d: keyword %s, type %d, length %zd\n",
-				i, text[i].keyword, text[i].type, 
-				text[i].length );
-		}
-	}
-	 */
-
-	/* FIXME ... get resolution, exif, xmp, etc. etc.
-	 */
-
 	/* 0 is no interlace.
 	 */
 	if( png->ihdr.interlace_method == 0 ) 
@@ -223,6 +230,43 @@ vips_foreign_load_png_set_header( VipsForeignLoadPng *png, VipsImage *image )
 		/* Interlaced images are read via a huge memory buffer.
 		 */
 		vips_image_pipelinev( image, VIPS_DEMAND_STYLE_ANY, NULL );
+
+	if( !spng_get_iccp( png->ctx, &iccp ) ) 
+		vips_image_set_blob_copy( image, 
+			VIPS_META_ICC_NAME, iccp.profile, iccp.profile_len );
+
+	spng_get_text( png->ctx, NULL, &n_text );
+	text = VIPS_ARRAY( VIPS_OBJECT( png ), n_text, struct spng_text );
+	if( !spng_get_text( png->ctx, text, &n_text ) ) {
+		guint32 i;
+
+		for( i = 0; i < n_text; i++ ) 
+			/* .text is always a null-terminated C string.
+			 */
+			vips_foreign_load_png_set_text( image, 
+				i, text[i].keyword, text[i].text );
+	}
+
+	if( !spng_get_exif( png->ctx, &exif ) ) 
+		vips_image_set_blob_copy( image, VIPS_META_EXIF_NAME, 
+			exif.data, exif.length );
+
+	/* Attach original palette bit depth, if any, as metadata.
+	 *
+	 * FIXME ... when we get palette support done
+	 *
+	if( color_type == PNG_COLOR_TYPE_PALETTE )
+		vips_image_set_int( out, "palette-bit-depth", bit_depth );
+	 */
+
+	/* Let our caller know. These are very expensive to decode.
+	 */
+	if( png->ihdr.interlace_method != 0 ) 
+		vips_image_set_int( image, "interlaced", 1 ); 
+
+	/* FIXME ... get resolution, etc. etc.
+	 */
+
 }
 
 static int

From 6705ff85b5de76c49c1c527777a55a8ce1611ff0 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Sun, 7 Jun 2020 15:29:48 +0100
Subject: [PATCH 08/19] use INTERLACE_NONE

---
 libvips/foreign/spngload.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 9d1a7a29..319eafb2 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -32,15 +32,13 @@
  */
 
 /* TODO
- *
- * 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)
+ * would be useful
  *
  * test indexed decode
  *
- * most metadata support (eg. XMP, ICC, etc. etc.) is missing ... we will need 
- * to set a chunk size limit with spng_set_chunks_limits()
+ * set a chunk size limit with spng_set_chunks_limits() when that API is done
  *
  * load only, there's no save support for now
  *
@@ -138,7 +136,7 @@ vips_foreign_load_png_get_flags_source( VipsSource *source )
 	spng_ctx_free( ctx );
 
 	flags = 0;
-	if( ihdr.interlace_method != 0 )
+	if( ihdr.interlace_method != SPNG_INTERLACE_NONE )
 		flags |= VIPS_FOREIGN_PARTIAL;
 	else
 		flags |= VIPS_FOREIGN_SEQUENTIAL;
@@ -220,7 +218,7 @@ vips_foreign_load_png_set_header( VipsForeignLoadPng *png, VipsImage *image )
 
 	/* 0 is no interlace.
 	 */
-	if( png->ihdr.interlace_method == 0 ) 
+	if( png->ihdr.interlace_method == SPNG_INTERLACE_NONE ) 
 		/* Sequential mode needs thinstrip to work with things like
 		 * vips_shrink().
 		 */
@@ -261,7 +259,7 @@ vips_foreign_load_png_set_header( VipsForeignLoadPng *png, VipsImage *image )
 
 	/* Let our caller know. These are very expensive to decode.
 	 */
-	if( png->ihdr.interlace_method != 0 ) 
+	if( png->ihdr.interlace_method != SPNG_INTERLACE_NONE ) 
 		vips_image_set_int( image, "interlaced", 1 ); 
 
 	/* FIXME ... get resolution, etc. etc.
@@ -463,7 +461,7 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 	if( vips_source_decode( png->source ) )
 		return( -1 );
 
-	if( png->ihdr.interlace_method != 0 ) {
+	if( png->ihdr.interlace_method != SPNG_INTERLACE_NONE ) {
 		/* Arg awful interlaced image. We have to load to a huge mem 
 		 * buffer, then copy to out.
 		 */

From 20c9a7f7cc24965df486331738d181f641c075af Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Sun, 7 Jun 2020 17:27:24 +0100
Subject: [PATCH 09/19] improve transparency support

---
 libvips/foreign/spngload.c | 39 ++++++++++++++++++--------------------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 319eafb2..8b43aac9 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -41,12 +41,11 @@
  * set a chunk size limit with spng_set_chunks_limits() when that API is done
  *
  * load only, there's no save support for now
- *
  */
 
 /*
-#define DEBUG
  */
+#define DEBUG
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
@@ -316,37 +315,28 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 
 
 	switch( png->ihdr.color_type ) {
+	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
 	case SPNG_COLOR_TYPE_GRAYSCALE:
 		png->bands = 1;
-		png->interpretation = VIPS_INTERPRETATION_B_W;
-		png->fmt = SPNG_FMT_PNG;
-		break;
-
-	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
-		png->bands = 2;
+		if( !spng_get_trns( png->ctx ) ) 
+			png->bands += 1;
 		png->interpretation = VIPS_INTERPRETATION_B_W;
 		png->fmt = SPNG_FMT_PNG;
 		break;
 
 	case SPNG_COLOR_TYPE_TRUECOLOR:
+	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
 		png->bands = 3;
+		if( !spng_get_trns( png->ctx ) ) 
+			png->bands += 1;
 		png->interpretation = VIPS_INTERPRETATION_sRGB;
 		png->fmt = SPNG_FMT_PNG;
 		break;
 
 	case SPNG_COLOR_TYPE_INDEXED:
-		png->bands = 3;
-		png->interpretation = VIPS_INTERPRETATION_sRGB;
-
-		/* Expand indexed images to RGB8.
-		 */
-		png->fmt = SPNG_FMT_RGB8;
-		break;
-
-	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
 		png->bands = 4;
 		png->interpretation = VIPS_INTERPRETATION_sRGB;
-		png->fmt = SPNG_FMT_PNG;
+		png->fmt = SPNG_FMT_RGBA8;
 		break;
 
 	default:
@@ -457,10 +447,15 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		vips_object_local_array( VIPS_OBJECT( load ), 3 );
 
 	int error;
+	enum spng_decode_flags;
 
 	if( vips_source_decode( png->source ) )
 		return( -1 );
 
+	/* We want the alpha, if present.
+	 */
+	flags = SPNG_DECODE_TRNS;
+
 	if( png->ihdr.interlace_method != SPNG_INTERLACE_NONE ) {
 		/* Arg awful interlaced image. We have to load to a huge mem 
 		 * buffer, then copy to out.
@@ -473,7 +468,7 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		if( (error = spng_decode_image( png->ctx, 
 			VIPS_IMAGE_ADDR( t[0], 0, 0 ), 
 			VIPS_IMAGE_SIZEOF_IMAGE( t[0] ), 
-			png->fmt, 0 )) ) {
+			png->fmt, flags )) ) {
 			vips_error( class->nickname, 
 				"%s", spng_strerror( error ) ); 
 			return( -1 );
@@ -486,10 +481,12 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		t[0] = vips_image_new();
 		vips_foreign_load_png_set_header( png, t[0] );
 
-		/* Initialize for progressive decoding.
+		/* We can decode regular PNGs progressively.
 		 */
+		flags |= SPNG_DECODE_PROGRESSIVE;
+
 		if( (error = spng_decode_image( png->ctx, NULL, 0, 
-			png->fmt, SPNG_DECODE_PROGRESSIVE )) ) {
+			png->fmt, flags )) ) {
 			vips_error( class->nickname, 
 				"%s", spng_strerror( error ) ); 
 			return( -1 );

From 70a1dc09262be4dbe4ef4e6df45b0c2ed1dafce8 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Tue, 9 Jun 2020 02:04:55 +0100
Subject: [PATCH 10/19] Revert "improve transparency support"

This reverts commit 20c9a7f7cc24965df486331738d181f641c075af.
---
 libvips/foreign/spngload.c | 39 ++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 8b43aac9..319eafb2 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -41,11 +41,12 @@
  * set a chunk size limit with spng_set_chunks_limits() when that API is done
  *
  * load only, there's no save support for now
+ *
  */
 
 /*
- */
 #define DEBUG
+ */
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
@@ -315,28 +316,37 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 
 
 	switch( png->ihdr.color_type ) {
-	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
 	case SPNG_COLOR_TYPE_GRAYSCALE:
 		png->bands = 1;
-		if( !spng_get_trns( png->ctx ) ) 
-			png->bands += 1;
+		png->interpretation = VIPS_INTERPRETATION_B_W;
+		png->fmt = SPNG_FMT_PNG;
+		break;
+
+	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
+		png->bands = 2;
 		png->interpretation = VIPS_INTERPRETATION_B_W;
 		png->fmt = SPNG_FMT_PNG;
 		break;
 
 	case SPNG_COLOR_TYPE_TRUECOLOR:
-	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
 		png->bands = 3;
-		if( !spng_get_trns( png->ctx ) ) 
-			png->bands += 1;
 		png->interpretation = VIPS_INTERPRETATION_sRGB;
 		png->fmt = SPNG_FMT_PNG;
 		break;
 
 	case SPNG_COLOR_TYPE_INDEXED:
+		png->bands = 3;
+		png->interpretation = VIPS_INTERPRETATION_sRGB;
+
+		/* Expand indexed images to RGB8.
+		 */
+		png->fmt = SPNG_FMT_RGB8;
+		break;
+
+	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
 		png->bands = 4;
 		png->interpretation = VIPS_INTERPRETATION_sRGB;
-		png->fmt = SPNG_FMT_RGBA8;
+		png->fmt = SPNG_FMT_PNG;
 		break;
 
 	default:
@@ -447,15 +457,10 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		vips_object_local_array( VIPS_OBJECT( load ), 3 );
 
 	int error;
-	enum spng_decode_flags;
 
 	if( vips_source_decode( png->source ) )
 		return( -1 );
 
-	/* We want the alpha, if present.
-	 */
-	flags = SPNG_DECODE_TRNS;
-
 	if( png->ihdr.interlace_method != SPNG_INTERLACE_NONE ) {
 		/* Arg awful interlaced image. We have to load to a huge mem 
 		 * buffer, then copy to out.
@@ -468,7 +473,7 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		if( (error = spng_decode_image( png->ctx, 
 			VIPS_IMAGE_ADDR( t[0], 0, 0 ), 
 			VIPS_IMAGE_SIZEOF_IMAGE( t[0] ), 
-			png->fmt, flags )) ) {
+			png->fmt, 0 )) ) {
 			vips_error( class->nickname, 
 				"%s", spng_strerror( error ) ); 
 			return( -1 );
@@ -481,12 +486,10 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		t[0] = vips_image_new();
 		vips_foreign_load_png_set_header( png, t[0] );
 
-		/* We can decode regular PNGs progressively.
+		/* Initialize for progressive decoding.
 		 */
-		flags |= SPNG_DECODE_PROGRESSIVE;
-
 		if( (error = spng_decode_image( png->ctx, NULL, 0, 
-			png->fmt, flags )) ) {
+			png->fmt, SPNG_DECODE_PROGRESSIVE )) ) {
 			vips_error( class->nickname, 
 				"%s", spng_strerror( error ) ); 
 			return( -1 );

From f113e64515682f1bfca40cbf92914bbc48d32e86 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Tue, 9 Jun 2020 02:27:46 +0100
Subject: [PATCH 11/19] update for latest spng 1/2/4 bit handling

---
 libvips/foreign/spngload.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 319eafb2..05e33070 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -275,6 +275,7 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 
 	int flags;
 	int error;
+	struct spng_trns trns;
 
 	/* In non-fail mode, ignore CRC errors.
 	 */
@@ -354,6 +355,23 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		return( -1 );
 	}
 
+	if( !spng_get_trns( png->ctx, &trns ) ) {
+		if( png->ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR ) {
+			if( png->ihdr.bit_depth == 16 ) 
+				png->fmt = SPNG_FMT_RGBA16;
+			else 
+				png->fmt = SPNG_FMT_RGBA8;
+		}
+		else if( png->ihdr.color_type == SPNG_COLOR_TYPE_INDEXED ) 
+			png->fmt = SPNG_FMT_RGBA8;
+		else if( png->ihdr.color_type == SPNG_COLOR_TYPE_GRAYSCALE ) {
+			if( png->ihdr.bit_depth == 16 ) 
+				png->fmt = SPNG_FMT_GA16;
+			else 
+				png->fmt = SPNG_FMT_GA8;
+		}
+	}
+
 	if( png->ihdr.bit_depth == 16 ) {
 		png->format = VIPS_FORMAT_USHORT;
 		if( png->interpretation == VIPS_INTERPRETATION_B_W )

From ac96bb80b5a66b3662d405bb2e122e5f5f530b04 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Tue, 9 Jun 2020 02:38:38 +0100
Subject: [PATCH 12/19] try revising spng FMT handling again

---
 libvips/foreign/spngload.c | 52 +++++++++++++++++---------------------
 1 file changed, 23 insertions(+), 29 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 05e33070..2af0229a 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -318,21 +318,33 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 
 	switch( png->ihdr.color_type ) {
 	case SPNG_COLOR_TYPE_GRAYSCALE:
+	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
 		png->bands = 1;
 		png->interpretation = VIPS_INTERPRETATION_B_W;
 		png->fmt = SPNG_FMT_PNG;
-		break;
 
-	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
-		png->bands = 2;
-		png->interpretation = VIPS_INTERPRETATION_B_W;
-		png->fmt = SPNG_FMT_PNG;
+		if( !spng_get_trns( png->ctx, &trns ) ) {
+			png->bands += 1;
+
+			/* Expand 1/2/4 bit images to 8 bit.
+			 */
+			if( png->ihdr.bit_depth < 8 ) 
+				png->fmt = SPNG_FMT_GA8;
+		}
+		else {
+			if( png->ihdr.bit_depth < 8 ) 
+				png->fmt = SPNG_FMT_G8;
+		}
 		break;
 
 	case SPNG_COLOR_TYPE_TRUECOLOR:
+	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
 		png->bands = 3;
 		png->interpretation = VIPS_INTERPRETATION_sRGB;
 		png->fmt = SPNG_FMT_PNG;
+
+		if( !spng_get_trns( png->ctx, &trns ) ) 
+			png->bands += 1;
 		break;
 
 	case SPNG_COLOR_TYPE_INDEXED:
@@ -341,13 +353,12 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 
 		/* Expand indexed images to RGB8.
 		 */
-		png->fmt = SPNG_FMT_RGB8;
-		break;
-
-	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
-		png->bands = 4;
-		png->interpretation = VIPS_INTERPRETATION_sRGB;
-		png->fmt = SPNG_FMT_PNG;
+		if( !spng_get_trns( png->ctx, &trns ) ) {
+			png->bands += 1;
+			png->fmt = SPNG_FMT_RGBA8;
+		}
+		else
+			png->fmt = SPNG_FMT_RGB8;
 		break;
 
 	default:
@@ -355,23 +366,6 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		return( -1 );
 	}
 
-	if( !spng_get_trns( png->ctx, &trns ) ) {
-		if( png->ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR ) {
-			if( png->ihdr.bit_depth == 16 ) 
-				png->fmt = SPNG_FMT_RGBA16;
-			else 
-				png->fmt = SPNG_FMT_RGBA8;
-		}
-		else if( png->ihdr.color_type == SPNG_COLOR_TYPE_INDEXED ) 
-			png->fmt = SPNG_FMT_RGBA8;
-		else if( png->ihdr.color_type == SPNG_COLOR_TYPE_GRAYSCALE ) {
-			if( png->ihdr.bit_depth == 16 ) 
-				png->fmt = SPNG_FMT_GA16;
-			else 
-				png->fmt = SPNG_FMT_GA8;
-		}
-	}
-
 	if( png->ihdr.bit_depth == 16 ) {
 		png->format = VIPS_FORMAT_USHORT;
 		if( png->interpretation == VIPS_INTERPRETATION_B_W )

From ce63fc1145c51d5ddc8e9753c6067e7d595fd8b7 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Tue, 9 Jun 2020 14:38:04 +0100
Subject: [PATCH 13/19] use libspng for load, libpng for save

---
 configure.ac              | 1 -
 libvips/foreign/pngload.c | 4 ++--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/configure.ac b/configure.ac
index dda267bd..9843224d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1188,7 +1188,6 @@ if test x"$with_libspng" != x"no"; then
     [AC_DEFINE(HAVE_SPNG,1,[define if you have libspng installed.])
      with_libspng=yes
      PACKAGES_USED="$PACKAGES_USED spng"
-     with_png=no
     ],
     [
     ]
diff --git a/libvips/foreign/pngload.c b/libvips/foreign/pngload.c
index 1c4d34b0..8092078e 100644
--- a/libvips/foreign/pngload.c
+++ b/libvips/foreign/pngload.c
@@ -50,7 +50,7 @@
 
 #include "pforeign.h"
 
-#ifdef HAVE_PNG
+#if defined(HAVE_PNG) && !defined(HAVE_SPNG)
 
 typedef struct _VipsForeignLoadPng {
 	VipsForeignLoad parent_object;
@@ -387,7 +387,7 @@ vips_foreign_load_png_buffer_init( VipsForeignLoadPngBuffer *buffer )
 {
 }
 
-#endif /*HAVE_PNG*/
+#endif /*defined(HAVE_PNG) && !defined(HAVE_SPNG)*/
 
 /**
  * vips_pngload:

From 0ff30f972d736645f459d6a774f9f9c545f1b761 Mon Sep 17 00:00:00 2001
From: Randy <randy408@protonmail.com>
Date: Tue, 9 Jun 2020 19:56:23 +0200
Subject: [PATCH 14/19] revise spngload

---
 libvips/foreign/spngload.c | 106 +++++++++++++++++++++----------------
 1 file changed, 60 insertions(+), 46 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 2af0229a..37ecbee8 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -315,50 +315,23 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		png->ihdr.interlace_method );
 	 */
 
+    /* Just convert to host-endian if nothing else applies.
+	 */ 
+	png->fmt = SPNG_FMT_PNG;
 
 	switch( png->ihdr.color_type ) {
-	case SPNG_COLOR_TYPE_GRAYSCALE:
-	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
-		png->bands = 1;
-		png->interpretation = VIPS_INTERPRETATION_B_W;
-		png->fmt = SPNG_FMT_PNG;
-
-		if( !spng_get_trns( png->ctx, &trns ) ) {
-			png->bands += 1;
-
-			/* Expand 1/2/4 bit images to 8 bit.
-			 */
-			if( png->ihdr.bit_depth < 8 ) 
-				png->fmt = SPNG_FMT_GA8;
-		}
-		else {
-			if( png->ihdr.bit_depth < 8 ) 
-				png->fmt = SPNG_FMT_G8;
-		}
+	case SPNG_COLOR_TYPE_INDEXED: 
+		bands = 3; 
 		break;
 
-	case SPNG_COLOR_TYPE_TRUECOLOR:
-	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
-		png->bands = 3;
-		png->interpretation = VIPS_INTERPRETATION_sRGB;
-		png->fmt = SPNG_FMT_PNG;
-
-		if( !spng_get_trns( png->ctx, &trns ) ) 
-			png->bands += 1;
+	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA: 
+	case SPNG_COLOR_TYPE_GRAYSCALE: 
+		bands = 1; 
 		break;
 
-	case SPNG_COLOR_TYPE_INDEXED:
-		png->bands = 3;
-		png->interpretation = VIPS_INTERPRETATION_sRGB;
-
-		/* Expand indexed images to RGB8.
-		 */
-		if( !spng_get_trns( png->ctx, &trns ) ) {
-			png->bands += 1;
-			png->fmt = SPNG_FMT_RGBA8;
-		}
-		else
-			png->fmt = SPNG_FMT_RGB8;
+	case SPNG_COLOR_TYPE_RGB: 
+	case SPNG_COLOR_TYPE_RGB_ALPHA: 
+		bands = 3; 
 		break;
 
 	default:
@@ -366,15 +339,56 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		return( -1 );
 	}
 
-	if( png->ihdr.bit_depth == 16 ) {
-		png->format = VIPS_FORMAT_USHORT;
-		if( png->interpretation == VIPS_INTERPRETATION_B_W )
-			png->interpretation = VIPS_INTERPRETATION_GREY16;
-		if( png->interpretation == VIPS_INTERPRETATION_sRGB )
-			png->interpretation = VIPS_INTERPRETATION_RGB16;
+	if( bit_depth > 8 ) {
+		if( bands < 3 )
+			interpretation = VIPS_INTERPRETATION_GREY16;
+		else
+			interpretation = VIPS_INTERPRETATION_RGB16;
+	}
+	else {
+		if( bands < 3 )
+			interpretation = VIPS_INTERPRETATION_B_W;
+		else
+			interpretation = VIPS_INTERPRETATION_sRGB;
+	}
+
+	/* Expand palette images.
+	 */
+	if( png->ihdr.color_type == SPNG_COLOR_TYPE_INDEXED )
+		png->fmt = SPNG_FMT_RGB8;
+
+	/* Expand <8 bit images to full bytes.
+	 */
+	if( png->ihdr.color_type == SPNG_COLOR_TYPE_GRAYSCALE &&
+		    png->ihdr.bit_depth < 8 )
+			png->fmt = SPNG_FMT_G8;
+
+	/* Expand transparency.
+	 */
+	if( !spng_get_trns( png->ctx, &trns ) ) {
+		bands += 1;
+		if( png->ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR ) {
+			if( png->ihdr.bit_depth == 16 ) 
+				png->fmt = SPNG_FMT_RGBA16;
+			else 
+				png->fmt = SPNG_FMT_RGBA8;
+		}
+		else if( png->ihdr.color_type == SPNG_COLOR_TYPE_INDEXED ) 
+			png->fmt = SPNG_FMT_RGBA8;
+		else if( png->ihdr.color_type == SPNG_COLOR_TYPE_GRAYSCALE ) {
+			if( png->ihdr.bit_depth == 16 ) 
+				png->fmt = SPNG_FMT_GA16;
+			else 
+				png->fmt = SPNG_FMT_GA8;
+		}
+	}
+	else if( png->ihdr.color_type == PNG_COLOR_TYPE_GRAY_ALPHA || 
+		     png->ihdr.color_type == PNG_COLOR_TYPE_RGB_ALPHA ) {
+		/* Some images have their own alpha channel,
+		 * not just a transparent color.
+		 */
+		bands += 1;
 	}
-	else 
-		png->format = VIPS_FORMAT_UCHAR;
 
 	vips_source_minimise( png->source );
 

From 2457e6768a51655853377411f05c3bd5c0b2eebd Mon Sep 17 00:00:00 2001
From: Randy <randy408@protonmail.com>
Date: Tue, 9 Jun 2020 20:04:03 +0200
Subject: [PATCH 15/19] fix enums

---
 libvips/foreign/spngload.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 37ecbee8..74545756 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -382,8 +382,8 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 				png->fmt = SPNG_FMT_GA8;
 		}
 	}
-	else if( png->ihdr.color_type == PNG_COLOR_TYPE_GRAY_ALPHA || 
-		     png->ihdr.color_type == PNG_COLOR_TYPE_RGB_ALPHA ) {
+	else if( png->ihdr.color_type == SPNG_COLOR_TYPE_GRAYSCALE_ALPHA || 
+		     png->ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR_ALPHA ) {
 		/* Some images have their own alpha channel,
 		 * not just a transparent color.
 		 */

From 49df5f54c16e53d92aa2d1f9e250640931d6c9da Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Thu, 11 Jun 2020 12:17:58 +0100
Subject: [PATCH 16/19] Randy's loader patch compiles

---
 configure.ac               |  2 +-
 libvips/foreign/spngload.c | 42 +++++++++++++++++++-------------------
 2 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/configure.ac b/configure.ac
index 9843224d..3984100a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1189,7 +1189,7 @@ if test x"$with_libspng" != x"no"; then
      with_libspng=yes
      PACKAGES_USED="$PACKAGES_USED spng"
     ],
-    [
+    [with_libspng=no
     ]
   )
 fi
diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 74545756..362d3aa8 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -315,23 +315,23 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		png->ihdr.interlace_method );
 	 */
 
-    /* Just convert to host-endian if nothing else applies.
+	/* Just convert to host-endian if nothing else applies.
 	 */ 
 	png->fmt = SPNG_FMT_PNG;
 
 	switch( png->ihdr.color_type ) {
 	case SPNG_COLOR_TYPE_INDEXED: 
-		bands = 3; 
+		png->bands = 3; 
 		break;
 
 	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA: 
 	case SPNG_COLOR_TYPE_GRAYSCALE: 
-		bands = 1; 
+		png->bands = 1; 
 		break;
 
-	case SPNG_COLOR_TYPE_RGB: 
-	case SPNG_COLOR_TYPE_RGB_ALPHA: 
-		bands = 3; 
+	case SPNG_COLOR_TYPE_TRUECOLOR: 
+	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA: 
+		png->bands = 3; 
 		break;
 
 	default:
@@ -339,17 +339,17 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		return( -1 );
 	}
 
-	if( bit_depth > 8 ) {
-		if( bands < 3 )
-			interpretation = VIPS_INTERPRETATION_GREY16;
+	if( png->ihdr.bit_depth > 8 ) {
+		if( png->bands < 3 )
+			png->interpretation = VIPS_INTERPRETATION_GREY16;
 		else
-			interpretation = VIPS_INTERPRETATION_RGB16;
+			png->interpretation = VIPS_INTERPRETATION_RGB16;
 	}
 	else {
-		if( bands < 3 )
-			interpretation = VIPS_INTERPRETATION_B_W;
+		if( png->bands < 3 )
+			png->interpretation = VIPS_INTERPRETATION_B_W;
 		else
-			interpretation = VIPS_INTERPRETATION_sRGB;
+			png->interpretation = VIPS_INTERPRETATION_sRGB;
 	}
 
 	/* Expand palette images.
@@ -360,13 +360,14 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 	/* Expand <8 bit images to full bytes.
 	 */
 	if( png->ihdr.color_type == SPNG_COLOR_TYPE_GRAYSCALE &&
-		    png->ihdr.bit_depth < 8 )
-			png->fmt = SPNG_FMT_G8;
+		png->ihdr.bit_depth < 8 )
+		png->fmt = SPNG_FMT_G8;
 
 	/* Expand transparency.
 	 */
 	if( !spng_get_trns( png->ctx, &trns ) ) {
-		bands += 1;
+		png->bands += 1;
+
 		if( png->ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR ) {
 			if( png->ihdr.bit_depth == 16 ) 
 				png->fmt = SPNG_FMT_RGBA16;
@@ -383,12 +384,11 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		}
 	}
 	else if( png->ihdr.color_type == SPNG_COLOR_TYPE_GRAYSCALE_ALPHA || 
-		     png->ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR_ALPHA ) {
-		/* Some images have their own alpha channel,
-		 * not just a transparent color.
+		png->ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR_ALPHA ) 
+		/* Some images have an alpha channel, just not a transparent 
+		 * colour.
 		 */
-		bands += 1;
-	}
+		png->bands += 1;
 
 	vips_source_minimise( png->source );
 

From b8be8ec65977e8008a9856c8cda8fab3ff30b1bc Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Thu, 11 Jun 2020 12:53:46 +0100
Subject: [PATCH 17/19] pngsuite passes

---
 libvips/foreign/spngload.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 362d3aa8..3a8a6d28 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -339,17 +339,23 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		return( -1 );
 	}
 
+	/* Set libvips format and interpretation.
+	 */
 	if( png->ihdr.bit_depth > 8 ) {
 		if( png->bands < 3 )
 			png->interpretation = VIPS_INTERPRETATION_GREY16;
 		else
 			png->interpretation = VIPS_INTERPRETATION_RGB16;
+
+		png->format = VIPS_FORMAT_USHORT;
 	}
 	else {
 		if( png->bands < 3 )
 			png->interpretation = VIPS_INTERPRETATION_B_W;
 		else
 			png->interpretation = VIPS_INTERPRETATION_sRGB;
+
+		png->format = VIPS_FORMAT_UCHAR;
 	}
 
 	/* Expand palette images.
@@ -364,8 +370,15 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		png->fmt = SPNG_FMT_G8;
 
 	/* Expand transparency.
+	 *
+	 * The _ALPHA types should not have the optional trns chunk (they 
+	 * always have a transparent band), see 
+	 * https://www.w3.org/TR/2003/REC-PNG-20031110/#11tRNS
 	 */
-	if( !spng_get_trns( png->ctx, &trns ) ) {
+	if( png->ihdr.color_type == SPNG_COLOR_TYPE_GRAYSCALE_ALPHA || 
+		png->ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR_ALPHA ) 
+		png->bands += 1;
+	else if( !spng_get_trns( png->ctx, &trns ) ) {
 		png->bands += 1;
 
 		if( png->ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR ) {
@@ -383,12 +396,6 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 				png->fmt = SPNG_FMT_GA8;
 		}
 	}
-	else if( png->ihdr.color_type == SPNG_COLOR_TYPE_GRAYSCALE_ALPHA || 
-		png->ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR_ALPHA ) 
-		/* Some images have an alpha channel, just not a transparent 
-		 * colour.
-		 */
-		png->bands += 1;
 
 	vips_source_minimise( png->source );
 

From 61628eefdff38139ae0c4657e1555f9e0085e3b6 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Thu, 11 Jun 2020 13:24:27 +0100
Subject: [PATCH 18/19] final fixes for spng loader

---
 ChangeLog                  |  1 +
 libvips/foreign/spngload.c | 50 +++++++++++++++++---------------------
 2 files changed, 23 insertions(+), 28 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index e7968f23..31a52a17 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -27,6 +27,7 @@
 - thumbnail exploits subifd pyramids
 - handle all EXIF orientation cases, deprecate 
   vips_autorot_get_angle() [Elad-Laufer]
+- load PNGs with libspng, if possible
 
 24/4/20 started 8.9.3
 - better iiif tile naming [IllyaMoskvin]
diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 3a8a6d28..8ba77a4f 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -1,6 +1,6 @@
 /* load PNG with libspng
  *
- * 5/12/11
+ * 1/5/20
  * 	- from pngload.c
  */
 
@@ -31,19 +31,6 @@
 
  */
 
-/* TODO
- *
- * an equivalent of png_sig_cmp() from libpng (is_a_png on a memory area)
- * would be useful
- *
- * test indexed decode
- *
- * set a chunk size limit with spng_set_chunks_limits() when that API is done
- *
- * load only, there's no save support for now
- *
- */
-
 /*
 #define DEBUG
  */
@@ -203,21 +190,33 @@ vips_foreign_load_png_set_text( VipsImage *out,
 static void
 vips_foreign_load_png_set_header( VipsForeignLoadPng *png, VipsImage *image )
 {
+	double xres, yres;
 	struct spng_iccp iccp;
 	struct spng_text *text;
 	struct spng_exif exif;
+	struct spng_phys phys;
 	guint32 n_text;
 
+	/* Get resolution. Default to 72 pixels per inch.
+	 */
+	xres = (72.0 / 2.54 * 100.0);
+	yres = (72.0 / 2.54 * 100.0);
+	if( !spng_get_phys( png->ctx, &phys ) ) {
+		/* There's phys.units, but it's always 0, meaning pixels per
+		 * metre.
+		 */
+		xres = phys.ppu_x / 1000.0;
+		yres = phys.ppu_y / 1000.0;
+	}
+
 	vips_image_init_fields( image,
 		png->ihdr.width, png->ihdr.height, png->bands,
 		png->format, VIPS_CODING_NONE, png->interpretation, 
-		1.0, 1.0 );
+		xres, yres );
 
 	VIPS_SETSTR( image->filename, 
 		vips_connection_filename( VIPS_CONNECTION( png->source ) ) );
 
-	/* 0 is no interlace.
-	 */
 	if( png->ihdr.interlace_method == SPNG_INTERLACE_NONE ) 
 		/* Sequential mode needs thinstrip to work with things like
 		 * vips_shrink().
@@ -250,21 +249,15 @@ vips_foreign_load_png_set_header( VipsForeignLoadPng *png, VipsImage *image )
 			exif.data, exif.length );
 
 	/* Attach original palette bit depth, if any, as metadata.
-	 *
-	 * FIXME ... when we get palette support done
-	 *
-	if( color_type == PNG_COLOR_TYPE_PALETTE )
-		vips_image_set_int( out, "palette-bit-depth", bit_depth );
 	 */
+	if( png->ihdr.color_type == SPNG_COLOR_TYPE_INDEXED )
+		vips_image_set_int( image, 
+			"palette-bit-depth", png->ihdr.bit_depth );
 
 	/* Let our caller know. These are very expensive to decode.
 	 */
 	if( png->ihdr.interlace_method != SPNG_INTERLACE_NONE ) 
 		vips_image_set_int( image, "interlaced", 1 ); 
-
-	/* FIXME ... get resolution, etc. etc.
-	 */
-
 }
 
 static int
@@ -288,13 +281,14 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 		 */
 		spng_set_crc_action( png->ctx, SPNG_CRC_USE, SPNG_CRC_USE );
 
-	/* Set limits to avoid decompression bombs. We should set
-	 * spng_set_chunks_limits() as well, once that API goes in.
+	/* Set limits to avoid decompression bombs. Set chunk limits to 60mb
+	 * -- we've seen 50mb XMP blocks in the wild.
 	 *
 	 * No need to test the decoded image size -- the user can do that if
 	 * they wish.
 	 */
 	spng_set_image_limits( png->ctx, VIPS_MAX_COORD, VIPS_MAX_COORD );
+	spng_set_chunk_limits( png->ctx, 60 * 1024 * 1024, 60 * 1024 * 1024 );
 
 	if( vips_source_rewind( png->source ) ) 
 		return( -1 );

From f96f2d301492baaf206f5655694ca89c7f5c6085 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Thu, 11 Jun 2020 13:49:51 +0100
Subject: [PATCH 19/19] SPNG_DECODE_TRNS flag was missing

see https://github.com/libvips/libvips/pull/1682#pullrequestreview-428866084
---
 libvips/foreign/spngload.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 8ba77a4f..ac576e65 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -483,11 +483,16 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 	VipsImage **t = (VipsImage **) 
 		vips_object_local_array( VIPS_OBJECT( load ), 3 );
 
+	enum spng_decode_flags flags;
 	int error;
 
 	if( vips_source_decode( png->source ) )
 		return( -1 );
 
+	/* Decode transparency, if available.
+	 */
+	flags = SPNG_DECODE_TRNS;
+
 	if( png->ihdr.interlace_method != SPNG_INTERLACE_NONE ) {
 		/* Arg awful interlaced image. We have to load to a huge mem 
 		 * buffer, then copy to out.
@@ -500,7 +505,7 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		if( (error = spng_decode_image( png->ctx, 
 			VIPS_IMAGE_ADDR( t[0], 0, 0 ), 
 			VIPS_IMAGE_SIZEOF_IMAGE( t[0] ), 
-			png->fmt, 0 )) ) {
+			png->fmt, flags )) ) {
 			vips_error( class->nickname, 
 				"%s", spng_strerror( error ) ); 
 			return( -1 );
@@ -513,10 +518,12 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		t[0] = vips_image_new();
 		vips_foreign_load_png_set_header( png, t[0] );
 
-		/* Initialize for progressive decoding.
+		/* We can decode these progressively.
 		 */
+		flags |= SPNG_DECODE_PROGRESSIVE;
+
 		if( (error = spng_decode_image( png->ctx, NULL, 0, 
-			png->fmt, SPNG_DECODE_PROGRESSIVE )) ) {
+			png->fmt, flags )) ) {
 			vips_error( class->nickname, 
 				"%s", spng_strerror( error ) ); 
 			return( -1 );