more consistent behaviour for multi-page load

Some loaders were setting page-height even when the user was loading a
single page triggering unexpected multi-page behaviour from later
savers.

New rule: only set page-height when loading more than one page.

See https://github.com/libvips/libvips/issues/1318

ChangeLog

@@ -1,6 +1,7 @@
 24/5/19 started 8.8.1
 - improve realpath() use on older libc
 - better magickload error messages
+- more consistent behaviour for page-height metadata
 
 21/9/18 started 8.8.0
 - much faster smartcrop [lovell]

libvips/foreign/Makefile.am

@@ -11,7 +11,7 @@ libforeign_la_SOURCES = \
 	gifload.c \
 	cairo.c \
 	pdfload.c \
-	pdfload_pdfium.c \
+	pdfiumload.c \
 	svgload.c \
 	radiance.c \
 	radload.c \

libvips/foreign/gifload.c

@@ -571,11 +571,10 @@ vips_foreign_load_gif_set_header( VipsForeignLoadGif *gif, VipsImage *image )
 		1.0, 1.0 );
 	vips_image_pipelinev( image, VIPS_DEMAND_STYLE_FATSTRIP, NULL );
 
-	if( gif->n_pages > 1 ) {
+	if( gif->n > 1 ) 
 		vips_image_set_int( image, 
 			VIPS_META_PAGE_HEIGHT, gif->file->SHeight );
-		vips_image_set_int( image, VIPS_META_N_PAGES, gif->n_pages );
-	}
+	vips_image_set_int( image, VIPS_META_N_PAGES, gif->n_pages );
 	vips_image_set_int( image, "gif-delay", gif->delay );
 	vips_image_set_int( image, "gif-loop", gif->loop );
 	if( gif->comment ) 

libvips/foreign/heifload.c

@@ -382,7 +382,9 @@ vips_foreign_load_heif_set_header( VipsForeignLoadHeif *heif, VipsImage *out )
 
 	vips_image_set_int( out, "heif-primary", heif->primary_page );
 	vips_image_set_int( out, "n-pages", heif->n_top );
-	vips_image_set_int( out, "page-height", heif->page_height );
+	if( heif->n > 1 )
+		vips_image_set_int( out, 
+			VIPS_META_PAGE_HEIGHT, heif->page_height );
 
 	/* FIXME .. we always decode to RGB in generate. We should check for
 	 * all grey images, perhaps. 

libvips/foreign/pdfiumload.c

@@ -363,7 +363,8 @@ vips_foreign_load_pdf_header( VipsForeignLoad *load )
 	for( i = 1; i < pdf->n; i++ ) 
 		if( pdf->pages[i].height != pdf->pages[0].height )
 			break;
-	if( i == pdf->n ) 
+	if( i == pdf->n &&
+		pdf->n > 1 ) 
 		vips_image_set_int( load->out, 
 			VIPS_META_PAGE_HEIGHT, pdf->pages[0].height );
 

libvips/foreign/pdfload.c

@@ -317,7 +317,8 @@ vips_foreign_load_pdf_header( VipsForeignLoad *load )
 	for( i = 1; i < pdf->n; i++ ) 
 		if( pdf->pages[i].height != pdf->pages[0].height )
 			break;
-	if( i == pdf->n ) 
+	if( i == pdf->n &&
+		pdf->n > 1 ) 
 		vips_image_set_int( load->out, 
 			VIPS_META_PAGE_HEIGHT, pdf->pages[0].height );
 

libvips/foreign/webp2vips.c

@@ -467,7 +467,8 @@ read_header( Read *read, VipsImage *out )
 #endif /*DEBUG*/
 
 		vips_image_set_int( out, "gif-loop", loop_count );
-		vips_image_set_int( out, "page-height", read->frame_height );
+		vips_image_set_int( out, 
+			VIPS_META_PAGE_HEIGHT, read->frame_height );
 
 		/* We must get the first frame to get the delay. Frames number
 		 * from 1.