add "interlace" option to vips_jpegsave()

see https://github.com/jcupitt/libvips/issues/77

ChangeLog

@@ -2,6 +2,7 @@
 - redone im_rotate_*mask45(), im_gauss_*mask*(), im_log_*mask() as classes
 - vips_init() now does some ABI compat checking, though this change requires
   an ABI break
+- add "interlace" option to vips_jpegsave()
 
 18/10/13	started 7.36.3
 - fix compiler warnings in ubuntu 13.10

libvips/foreign/foreign.c

@@ -1988,6 +1988,7 @@ vips_jpegload( const char *filename, VipsImage **out, ... )
  * @Q: quality factor
  * @profile: attach this ICC profile
  * @optimize_coding: compute optimal Huffman coding tables
+ * @interlace: write an interlaced (progressive) jpeg
  *
  * Write a VIPS image to a file as JPEG.
  *
@@ -2012,6 +2013,13 @@ vips_jpegload( const char *filename, VipsImage **out, ... )
  * IPCT as @VIPS_META_IPCT_NAME ("ipct-data") and XMP as VIPS_META_XMP_NAME
  * ("xmp-data") are coded and attached. 
  *
+ * If @optimize_coding is set, the Huffman tables are optimised. This is
+ * sllightly slower and produces slightly smaller files. 
+ *
+ * If @interlace is set, the jpeg files will be interlaced (progressive jpeg,
+ * in jpg parlance). These files may be better for display over a slow network
+ * conection, but need much more memory to encode and decode. 
+ *
  * See also: vips_jpegsave_buffer(), vips_image_write_file().
  *
  * Returns: 0 on success, -1 on error.
@@ -2041,6 +2049,7 @@ vips_jpegsave( VipsImage *in, const char *filename, ... )
  * @Q: JPEG quality factor
  * @profile: attach this ICC profile
  * @optimize_coding: compute optimal Huffman coding tables
+ * @interlace: write an interlaced (progressive) jpeg
  *
  * As vips_jpegsave(), but save to a memory buffer. 
  *

libvips/foreign/jpegsave.c

@@ -83,6 +83,10 @@ typedef struct _VipsForeignSaveJpeg {
 	 */
 	gboolean optimize_coding;
 
+	/* Generate an interlaced (progressive, in jpg terminology) file.
+	 */
+	gboolean interlace;
+
 } VipsForeignSaveJpeg;
 
 typedef VipsForeignSaveClass VipsForeignSaveJpegClass;
@@ -135,6 +139,13 @@ vips_foreign_save_jpeg_class_init( VipsForeignSaveJpegClass *class )
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
 		G_STRUCT_OFFSET( VipsForeignSaveJpeg, optimize_coding ),
 		FALSE );
+
+	VIPS_ARG_BOOL( class, "interlace", 13,
+		_( "interlace" ),
+		_( "Generate an interlaced (progressive) jpeg" ),
+		VIPS_ARGUMENT_OPTIONAL_INPUT,
+		G_STRUCT_OFFSET( VipsForeignSaveJpeg, interlace ),
+		FALSE );
 }
 
 static void
@@ -169,7 +180,8 @@ vips_foreign_save_jpeg_file_build( VipsObject *object )
 		return( -1 );
 
 	if( vips__jpeg_write_file( save->ready, file->filename,
-		jpeg->Q, jpeg->profile, jpeg->optimize_coding ) )
+		jpeg->Q, jpeg->profile, jpeg->optimize_coding, 
+		jpeg->interlace ) )
 		return( -1 );
 
 	return( 0 );
@@ -234,7 +246,8 @@ vips_foreign_save_jpeg_buffer_build( VipsObject *object )
 		return( -1 );
 
 	if( vips__jpeg_write_buffer( save->ready, 
-		&obuf, &olen, jpeg->Q, jpeg->profile, jpeg->optimize_coding ) )
+		&obuf, &olen, jpeg->Q, jpeg->profile, jpeg->optimize_coding, 
+		jpeg->interlace ) )
 		return( -1 );
 
 	area = vips_area_new_blob( (VipsCallbackFn) vips_free, obuf, olen );
@@ -295,7 +308,8 @@ vips_foreign_save_jpeg_mime_build( VipsObject *object )
 		return( -1 );
 
 	if( vips__jpeg_write_buffer( save->ready, 
-		&obuf, &olen, jpeg->Q, jpeg->profile, jpeg->optimize_coding ) )
+		&obuf, &olen, jpeg->Q, jpeg->profile, jpeg->optimize_coding, 
+		jpeg->interlace ) )
 		return( -1 );
 
 	printf( "Content-length: %zd\r\n", olen );

libvips/foreign/vips2jpeg.c

@@ -841,7 +841,7 @@ write_jpeg_block( REGION *region, Rect *area, void *a )
  */
 static int
 write_vips( Write *write, int qfac, const char *profile, 
-	gboolean optimize_coding )
+	gboolean optimize_coding, gboolean progressive )
 {
 	VipsImage *in;
 	J_COLOR_SPACE space;
@@ -898,6 +898,11 @@ write_vips( Write *write, int qfac, const char *profile,
 	 */
 	write->cinfo.optimize_coding = optimize_coding;
 
+	/* Enable progressive write.
+	 */
+	if( progressive ) 
+		jpeg_simple_progression( &write->cinfo ); 
+
 	/* Build compress tables.
 	 */
 	jpeg_start_compress( &write->cinfo, TRUE );
@@ -941,7 +946,7 @@ write_vips( Write *write, int qfac, const char *profile,
 int
 vips__jpeg_write_file( VipsImage *in, 
 	const char *filename, int Q, const char *profile, 
-	gboolean optimize_coding )
+	gboolean optimize_coding, gboolean progressive )
 {
 	Write *write;
 
@@ -971,7 +976,7 @@ vips__jpeg_write_file( VipsImage *in,
 
 	/* Convert!
 	 */
-	if( write_vips( write, Q, profile, optimize_coding ) ) {
+	if( write_vips( write, Q, profile, optimize_coding, progressive ) ) {
 		write_destroy( write );
 		return( -1 );
 	}
@@ -1218,7 +1223,7 @@ buf_dest( j_compress_ptr cinfo, void **obuf, size_t *olen )
 int
 vips__jpeg_write_buffer( VipsImage *in, 
 	void **obuf, size_t *olen, int Q, const char *profile, 
-	gboolean optimize_coding )
+	gboolean optimize_coding, gboolean progressive )
 {
 	Write *write;
 
@@ -1247,7 +1252,7 @@ vips__jpeg_write_buffer( VipsImage *in,
 
 	/* Convert!
 	 */
-	if( write_vips( write, Q, profile, optimize_coding ) ) {
+	if( write_vips( write, Q, profile, optimize_coding, progressive ) ) {
 		write_destroy( write );
 
 		return( -1 );

libvips/foreign/vipsjpeg.h

@@ -39,10 +39,10 @@ extern const char *vips__jpeg_suffs[];
 
 int vips__jpeg_write_file( VipsImage *in, 
 	const char *filename, int Q, const char *profile, 
-	gboolean optimize_coding );
+	gboolean optimize_coding, gboolean progressive );
 int vips__jpeg_write_buffer( VipsImage *in, 
 	void **obuf, size_t *olen, int Q, const char *profile, 
-	gboolean optimize_coding );
+	gboolean optimize_coding, gboolean progressive );
 
 int vips__isjpeg( const char *filename );
 int vips__jpeg_read_file( const char *name, VipsImage *out,