From d61a85f6c9c5400d8fbdd8f3ff67d5f82a9d6604 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Tue, 27 Aug 2019 14:47:36 +0100
Subject: [PATCH] prevent over-pre-shrink in thumbnail

We could pre-shrink so much that an axis went to 0.

See https://github.com/lovell/sharp/issues/1782#issuecomment-525249430
---
 ChangeLog                    |  1 +
 libvips/resample/thumbnail.c | 33 ++++++++++++++-------------------
 2 files changed, 15 insertions(+), 19 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 61d84138..edb52682 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -13,6 +13,7 @@
 - better feof() handling in GIF load
 - clip coding and interpretation on vips image read
 - check image bounds for GIF load
+- prevent over-pre-shrink in thumbnail [kleisauke]
 
 24/5/19 started 8.8.1
 - improve realpath() use on older libc
diff --git a/libvips/resample/thumbnail.c b/libvips/resample/thumbnail.c
index 89fbf48a..22838ae4 100644
--- a/libvips/resample/thumbnail.c
+++ b/libvips/resample/thumbnail.c
@@ -22,6 +22,8 @@
  * 	- don't force import CMYK, since colourspace knows about it now
  * 24/4/19
  * 	- support multi-page (animated) images
+ * 27/8/19 kleisauke
+ *	- prevent over-pre-shrink in thumbnail
  */
 
 /*
@@ -464,36 +466,24 @@ vips_thumbnail_open( VipsThumbnail *thumbnail )
 
 	factor = 1.0;
 
-	if( vips_isprefix( "VipsForeignLoadJpeg", thumbnail->loader ) ) {
+	if( vips_isprefix( "VipsForeignLoadJpeg", thumbnail->loader ) ) 
 		factor = vips_thumbnail_find_jpegshrink( thumbnail, 
 			thumbnail->input_width, thumbnail->input_height );
-
-		g_info( "loading jpeg with factor %g pre-shrink", factor ); 
-	}
 	else if( vips_isprefix( "VipsForeignLoadTiff", thumbnail->loader ) ||
 		vips_isprefix( "VipsForeignLoadOpenslide", 
-		thumbnail->loader ) ) {
+		thumbnail->loader ) ) 
 		factor = vips_thumbnail_find_pyrlevel( thumbnail, 
 			thumbnail->input_width, thumbnail->input_height );
-
-		g_info( "loading pyr level %g", factor ); 
-	}
-	else if( vips_isprefix( "VipsForeignLoadPdf", thumbnail->loader ) ) {
+	else if( vips_isprefix( "VipsForeignLoadPdf", thumbnail->loader ) ) 
 		factor = 1.0 / 
 			vips_thumbnail_calculate_common_shrink( thumbnail, 
 				thumbnail->input_width, 
 				thumbnail->page_height );
-
-		g_info( "loading PDF with factor %g pre-scale", factor ); 
-	}
-	else if( vips_isprefix( "VipsForeignLoadSvg", thumbnail->loader ) ) {
+	else if( vips_isprefix( "VipsForeignLoadSvg", thumbnail->loader ) ) 
 		factor = 1.0 / 
 			vips_thumbnail_calculate_common_shrink( thumbnail, 
 				thumbnail->input_width, 
 				thumbnail->input_height );
-
-		g_info( "loading SVG with factor %g pre-scale", factor ); 
-	}
 	else if( vips_isprefix( "VipsForeignLoadHeif", thumbnail->loader ) ) {
 		/* 'factor' is a gboolean which enables thumbnail load instead
 		 * of image load.
@@ -507,14 +497,19 @@ vips_thumbnail_open( VipsThumbnail *thumbnail )
 			factor = 0.0;
 
 	}
-	else if( vips_isprefix( "VipsForeignLoadWebp", thumbnail->loader ) ) {
+	else if( vips_isprefix( "VipsForeignLoadWebp", thumbnail->loader ) ) 
 		factor = 1.0 /
 			vips_thumbnail_calculate_common_shrink( thumbnail, 
 				thumbnail->input_width, 
 				thumbnail->page_height ); 
 
-		g_info( "loading webp with factor %g pre-scale", factor ); 
-	}
+	/* We don't want to pre-shrink so much that we send an axis to 0.
+	 */
+	if( factor > thumbnail->input_width ||
+		factor > thumbnail->input_height )
+		factor = 1.0;
+
+	g_info( "loading with factor %g pre-shrink", factor ); 
 
 	if( !(im = class->open( thumbnail, factor )) )
 		return( NULL );