vipsthumbnail knows about pdfload

woo, fast!

ChangeLog

@@ -3,6 +3,7 @@
 - vips_resize() and vips_similarity() use it when they can
 - bicubic is better on 32-bit int images
 - add pdfload for PDF rendering ... file and buffer input are supported
+- vipsthumbnail knows about pdfload
 
 27/1/16 started 8.2.3
 - fix a crash with SPARC byte-order labq vips images

libvips/foreign/foreign.c

@@ -2863,12 +2863,13 @@ vips_matload( const char *filename, VipsImage **out, ... )
  * @dpi: %gdouble, render at this DPI
  * @scale: %gdouble, scale render by this factor
  *
- * Render a PDF file into a VIPS image. 
+ * Render a PDF file into a VIPS image.  Rendering uses the libpoppler library
+ * and should be fast.
  *
  * Use @page to select a page to render, numbering from zero.
  *
  * Use @dpi to set the rendering resolution. The default is 72. Alternatively,
- * you can scale the rendering by @scale.
+ * you can scale the rendering from the default 1 point == 1 pixel by @scale.
  *
  * The operation fills a number of header fields with metadata, for example
  * "pdf-author". They may be useful. 

tools/vipsthumbnail.c

@@ -70,6 +70,8 @@
  * 	- premultiply alpha
  * 30/7/15
  * 	- warn if you autorot and there's no exif support
+ * 9/2/16
+ * 	- add PDF --size support
  */
 
 #ifdef HAVE_CONFIG_H
@@ -274,8 +276,34 @@ thumbnail_open( VipsObject *process, const char *filename )
 			NULL )) )
 			return( NULL );
 	}
+	else if( strcmp( loader, "VipsForeignLoadPdfFile" ) == 0 ) {
+		double shrink;
+
+		/* This will just read in the header and is quick.
+		 */
+		if( !(im = vips_image_new_from_file( filename, NULL )) )
+			return( NULL );
+
+		shrink = calculate_shrink( im ); 
+
+		g_object_unref( im );
+
+		vips_info( "vipsthumbnail", 
+			"loading PDF with factor %g pre-shrink", 
+			shrink ); 
+
+		/* We can't use UNBUFERRED safely on very-many-core systems.
+		 */
+		if( !(im = vips_image_new_from_file( filename, 
+			"access", VIPS_ACCESS_SEQUENTIAL,
+			"scale", 1.0 / shrink,
+			NULL )) )
+			return( NULL );
+
+	}
 	else {
-		/* All other formats.
+		/* All other formats. We can't use UNBUFERRED safely on 
+		 * very-many-core systems.
 		 */
 		if( !(im = vips_image_new_from_file( filename, 
 			"access", VIPS_ACCESS_SEQUENTIAL,