Merge branch '8.6'

ChangeLog

@@ -16,8 +16,9 @@
 - set "interlaced=1" for interlaced JPG and PNG images
 
 12/3/18 started 8.6.4
-- better fitting of fonts with overhanging edges, thanks Adrià 
+- better fitting of fonts with overhanging edges [Adrià]
-- lower stack use in radsave to help musl [Jacob Thrane Lund]
+- revise C++ example [fangqiao]
+- strict round down on jpeg shrink on load [davidwood]
 
 12/2/18 started 8.6.3
 - use pkg-config to find libjpeg, if we can

doc/using-cpp.xml

@@ -26,7 +26,7 @@
 
 <programlisting language="cpp">
 /* compile with:
- *      g++ -g -Wall try.cc `pkg-config vips-cpp --cflags --libs`
+ *      g++ -g -Wall example.cc `pkg-config vips-cpp --cflags --libs`
  */
 
 #include &lt;vips/vips8&gt;
@@ -36,44 +36,26 @@ using namespace vips;
 int
 main (int argc, char **argv)
 { 
-  GOptionContext *context;
-  GOptionGroup *main_group;
-  GError *error = NULL;
-
   if (VIPS_INIT (argv[0])) 
     vips_error_exit (NULL);
   
-  context = g_option_context_new( "" ); 
+  if (argc != 3)
-
+    vips_error_exit ("usage: %s input-file output-file", argv[0]);
-  main_group = g_option_group_new( NULL, NULL, NULL, NULL, NULL );
-  g_option_context_set_main_group( context, main_group );
-  g_option_context_add_group( context, vips_get_option_group() );
-
-  if( !g_option_context_parse( context, &amp;argc, &amp;argv, &amp;error ) ) {
-    if( error ) {
-      fprintf( stderr, "%s\n", error->message );
-      g_error_free( error );
-    }
-
-    vips_error_exit( NULL );
-  }
 
   VImage in = VImage::new_from_file (argv[1],
-    VImage::option()->
+    VImage::option ()-&gt;set ("access", VIPS_ACCESS_SEQUENTIAL));
-      set( "access", VIPS_ACCESS_SEQUENTIAL ) ); 
   
   double avg = in.avg ();
   
   printf ("avg = %g\n", avg);
   printf ("width = %d\n", in.width ());
   
-  VImage in = VImage::new_from_file( argv[1],
+  in = VImage::new_from_file (argv[1],
-    VImage::option()->
+    VImage::option ()-&gt;set ("access", VIPS_ACCESS_SEQUENTIAL));
-      set( "access", VIPS_ACCESS_SEQUENTIAL ) ); 
   
   VImage out = in.embed (10, 10, 1000, 1000,
-    VImage::option()->
+    VImage::option ()-&gt;
-      set( "extend", "background" )->
+      set ("extend", "background")-&gt;
       set ("background", 128));
   
   out.write_to_file (argv[2]);
@@ -86,12 +68,13 @@ main( int argc, char **argv )
 
     <para>
       Everything before <code>VImage in = VImage::..</code> is exactly
-      as the C API. This boilerplate gives the example a set of standard
+      as the C API. vips_error_exit() just prints the arguments plus the 
-      command-line flags.
+      libvips error log and exits with an error code. 
     </para>
 
     <para>
-      This line is the C++ equivalent of vips_image_new_from_file(). It works 
+      <code>VImage in = VImage::..</code> is the C++ equivalent of 
+      vips_image_new_from_file(). It works 
       in the same way, the differences being:
 
       <itemizedlist>

libvips/foreign/jpeg2vips.c

@@ -96,6 +96,8 @@
  * 	  that
  * 9/4/18
  * 	- set interlaced=1 for interlaced images
+ * 10/4/18
+ * 	- strict round down on shrink-on-load
  */
 
 /*
@@ -153,8 +155,6 @@
 /* Stuff we track during a read.
  */
 typedef struct _ReadJpeg {
-	VipsImage *out;
-
 	/* Shrink by this much during load. 1, 2, 4, 8.
 	 */
 	int shrink;
@@ -179,6 +179,13 @@ typedef struct _ReadJpeg {
 	 * during load.
 	 */
 	gboolean autorotate;
+
+	/* cinfo->output_width and height can be larger than we want since
+	 * libjpeg rounds up on shrink-on-load. This is the real size we will
+	 * output, as opposed to the size we decompress to.
+	 */
+	int output_width;
+	int output_height;
 } ReadJpeg;
 
 /* This can be called many times.
@@ -230,7 +237,6 @@ readjpeg_new( VipsImage *out, int shrink, gboolean fail, gboolean autorotate )
 	if( !(jpeg = VIPS_NEW( out, ReadJpeg )) )
 		return( NULL );
 
-	jpeg->out = out;
 	jpeg->shrink = shrink;
 	jpeg->fail = fail;
 	jpeg->filename = NULL;
@@ -410,6 +416,18 @@ read_jpeg_header( ReadJpeg *jpeg, VipsImage *out )
 
 	vips_image_pipelinev( out, VIPS_DEMAND_STYLE_FATSTRIP, NULL );
 
+	/* cinfo->output_width and cinfo->output_height round up with
+	 * shrink-on-load. For example, if the image is 1801 pixels across and
+	 * we shrink by 4, the output will be 450.25 pixels across, 
+	 * cinfo->output_width with be 451, and libjpeg will write a black
+	 * column of pixels down the right.
+	 *
+	 * We must strictly round down, since we don't want fractional pixels
+	 * along the bottom and right.
+	 */
+	jpeg->output_width = cinfo->image_width / jpeg->shrink;
+	jpeg->output_height = cinfo->image_height / jpeg->shrink;
+
 	/* Interlaced jpegs need lots of memory to read, so our caller needs
 	 * to know.
 	 */
@@ -691,15 +709,20 @@ read_jpeg_image( ReadJpeg *jpeg, VipsImage *out )
 	printf( "read_jpeg_image: starting decompress\n" );
 #endif /*DEBUG*/
 
+	/* We must crop after the seq, or our generate may not be asked for
+	 * full lines of pixels and will attempt to write beyond the buffer.
+	 */
 	if( vips_image_generate( t[0], 
 		NULL, read_jpeg_generate, NULL, 
 		jpeg, NULL ) ||
 		vips_sequential( t[0], &t[1], 
 			"tile_height", 8,
-			NULL ) )
+			NULL ) ||
+		vips_extract_area( t[1], &t[2], 
+			0, 0, jpeg->output_width, jpeg->output_height, NULL ) )
 		return( -1 );
 
-	im = t[1];
+	im = t[2];
 	if( jpeg->autorotate )
 		im = read_jpeg_rotate( VIPS_OBJECT( out ), im );
 
@@ -738,6 +761,11 @@ vips__jpeg_read( ReadJpeg *jpeg, VipsImage *out, gboolean header_only )
 		if( read_jpeg_header( jpeg, out ) )
 			return( -1 ); 
 
+		/* Patch in the correct size.
+		 */
+		out->Xsize = jpeg->output_width;
+		out->Ysize = jpeg->output_height;
+
 		/* Swap width and height if we're going to rotate this image.
 		 */
 		if( jpeg->autorotate ) {