add "page-height" save property

ChangeLog

@@ -8,6 +8,7 @@
 - add FORCE resize mode to break aspect ratio
 - add vips_thumbnail_image()
 - better prefix guessing on Windows, thanks tumagonx
+- savers support a "page_height" option for multipage save
 
 12/6/17 started 8.5.7
 - transform cmyk->rgb automatically on write if there's an embedded profile

libvips/foreign/foreign.c

@@ -16,6 +16,8 @@
  * 	- remove max-alpha stuff, this is now automatic
  * 12/6/17
  * 	- transform cmyk->rgb if there's an embedded profile
+ * 16/6/17
+ * 	- add page_height
  */
 
 /*
@@ -1485,6 +1487,10 @@ vips_foreign_save_build( VipsObject *object )
 			save->background ) )
 			return( -1 );
 
+		if( save->page_height )
+			vips_image_set_int( ready, 
+				VIPS_META_PAGE_HEIGHT, save->page_height );
+
 		VIPS_UNREF( save->ready );
 		save->ready = ready;
 	}
@@ -1570,6 +1576,13 @@ vips_foreign_save_class_init( VipsForeignSaveClass *class )
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
 		G_STRUCT_OFFSET( VipsForeignSave, background ),
 		VIPS_TYPE_ARRAY_DOUBLE );
+
+	VIPS_ARG_INT( class, "page_height", 8, 
+		_( "Page height" ), 
+		_( "Set page height for multipage save" ),
+		VIPS_ARGUMENT_OPTIONAL_INPUT,
+		G_STRUCT_OFFSET( VipsForeignSave, page_height ),
+		0, VIPS_MAX_COORD, 0 ); 
 }
 
 static void

libvips/foreign/tiffsave.c

@@ -472,6 +472,7 @@ vips_foreign_save_tiff_buffer_init( VipsForeignSaveTiffBuffer *buffer )
  * * @bigtiff: set %TRUE to write a BigTiff file
  * * @properties: set %TRUE to write an IMAGEDESCRIPTION tag
  * * @strip: set %TRUE to block metadata save
+ * * @page_height: %gint for page height for multi-page save
  *
  * Write a VIPS image to a file as TIFF.
  *
@@ -587,6 +588,7 @@ vips_tiffsave( VipsImage *in, const char *filename, ... )
  * * @bigtiff: set %TRUE to write a BigTiff file
  * * @properties: set %TRUE to write an IMAGEDESCRIPTION tag
  * * @strip: set %TRUE to block metadata save
+ * * @page_height: %gint for page height for multi-page save
  *
  * As vips_tiffsave(), but save to a memory buffer. 
  *

libvips/include/vips/foreign.h

@@ -279,6 +279,10 @@ typedef struct _VipsForeignSave {
 	 */
 	VipsArrayDouble *background;
 
+	/* Set to non-zero to set the page size for multi-page save.
+	 */
+	int page_height;
+
 	/*< public >*/
 
 	/* The image we are to save, as supplied by our caller.