From c0637d9969488ac3e87bf69d246318371435ff38 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Thu, 11 Aug 2022 16:49:40 +0100
Subject: [PATCH] jp2ksave saves as jp2

Confusingly we previously saved jp2 images as a jpeg2000 codestream rather
than as a jp2 file.

See https://github.com/libvips/libvips/issues/2977
---
 ChangeLog                  |  4 +++-
 libvips/foreign/jp2ksave.c | 45 +++++++++++++++++++++++++++++++++-----
 2 files changed, 42 insertions(+), 7 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index ea0729ae..8dce962a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,7 +2,9 @@ master
 
 - version bump to 8.14
 - remove autotools
-- jp2ksave defaults to chroma subsample off
+- remove various obsolete scripts
+- remove benchmark 
+- jp2ksave defaults to chroma subsample off, and jp2 write
 - don't minimise sink_screen input after expose ... improves caching during
   interactive use
 
diff --git a/libvips/foreign/jp2ksave.c b/libvips/foreign/jp2ksave.c
index 5802fc39..4ed398c3 100644
--- a/libvips/foreign/jp2ksave.c
+++ b/libvips/foreign/jp2ksave.c
@@ -141,7 +141,7 @@ vips_foreign_save_jp2k_dispose( GObject *gobject )
 }
 
 static OPJ_SIZE_T
-vips_foreign_save_jp2k_write_target( void *buffer, size_t length, void *client )
+vips_foreign_save_jp2k_target_write( void *buffer, size_t length, void *client )
 {
 	VipsTarget *target = VIPS_TARGET( client );
 
@@ -151,6 +151,28 @@ vips_foreign_save_jp2k_write_target( void *buffer, size_t length, void *client )
 	return( length );
 }
 
+static OPJ_BOOL
+vips_foreign_save_jp2k_target_seek( off_t position, void *client )
+{
+	VipsTarget *target = VIPS_TARGET( client );
+
+	if( vips_target_seek( target, position, SEEK_SET ) < 0 )
+		return( FALSE );
+
+	return( TRUE );
+}
+
+static OPJ_OFF_T 
+vips_foreign_save_jp2k_target_skip( off_t offset, void *client)
+{
+	VipsTarget *target = VIPS_TARGET( client );
+
+	if( vips_target_seek( target, offset, SEEK_CUR ) < 0 )
+		return( -1 );
+
+        return( offset );
+}
+
 /* Make a libopenjp2 output stream that wraps a VipsTarget.
  */
 static opj_stream_t *
@@ -165,7 +187,11 @@ vips_foreign_save_jp2k_target( VipsTarget *target )
 
 	opj_stream_set_user_data( stream, target, NULL );
 	opj_stream_set_write_function( stream,
-		vips_foreign_save_jp2k_write_target );
+		vips_foreign_save_jp2k_target_write );
+	opj_stream_set_seek_function( stream,
+		vips_foreign_save_jp2k_target_seek );
+	opj_stream_set_skip_function( stream,
+		vips_foreign_save_jp2k_target_skip );
 
 	return( stream );
 }
@@ -182,16 +208,16 @@ static void
 vips_foreign_save_jp2k_warning_callback( const char *msg, void *client )
 {
 #ifdef DEBUG
-	g_warning( "jp2ksave: %s", msg );
 #endif /*DEBUG*/
+	g_warning( "jp2ksave: %s", msg );
 }
 
 static void
 vips_foreign_save_jp2k_info_callback( const char *msg, void *client )
 {
 #ifdef DEBUG
-	g_info( "jp2ksave: %s", msg );
 #endif /*DEBUG*/
+	g_info( "jp2ksave: %s", msg );
 }
 
 static void
@@ -849,8 +875,11 @@ vips_foreign_save_jp2k_build( VipsObject *object )
 	/* Set up compressor.
 	 */
 
-	jp2k->codec = opj_create_compress( OPJ_CODEC_J2K );
+        /* Save as a jp2 file.
+         */
+	jp2k->codec = opj_create_compress( OPJ_CODEC_JP2 );
 	vips_foreign_save_jp2k_attach_handlers( jp2k->codec );
+
 	/* FALSE means don't alloc memory for image planes (we write in
 	 * tiles, not whole images).
 	 */
@@ -1343,6 +1372,8 @@ vips__foreign_load_jp2k_compress( VipsRegion *region,
 		return( -1 );
 	}
 
+        /* tiff needs a jpeg2000 codestream, not a jp2 file.
+         */
 	compress.codec = opj_create_compress( OPJ_CODEC_J2K );
 	vips_foreign_save_jp2k_attach_handlers( compress.codec );
         if( !opj_setup_encoder( compress.codec,
@@ -1432,7 +1463,9 @@ vips__foreign_load_jp2k_compress( VipsRegion *region,
  * Use @tile_width and @tile_height to set the tile size. The default is 512.
  *
  * Chroma subsampling is normally disabled for compatibility. Set
- * @subsample_mode to auto to enable chroma subsample for Q < 90.
+ * @subsample_mode to auto to enable chroma subsample for Q < 90. Subsample
+ * mode uses YCC rather than RGB colourspace, and many jpeg2000 decoders do
+ * not support this.
  *
  * This operation always writes a pyramid.
  *