From f5d76b42fc889d6db74f256a53a54d56b73a22a3 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Mon, 3 Dec 2018 17:13:57 +0000
Subject: [PATCH] fix centre sampling for non-int nearest upscale

we were not disabling the input offset for NEAREST, whcih is always
centre

thanks edwjusti

see https://github.com/lovell/sharp/issues/1479
---
 libvips/resample/resize.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/libvips/resample/resize.c b/libvips/resample/resize.c
index fd5f4c37..c22135ed 100644
--- a/libvips/resample/resize.c
+++ b/libvips/resample/resize.c
@@ -28,6 +28,9 @@
  * 	- make LINEAR and CUBIC adaptive
  * 25/11/17
  * 	- deprecate --centre ... it's now always on, thanks tback
+ * 3/12/18 [edwjusti]
+ * 	- disable the centre sampling offset for nearest upscale, since the
+ * 	  affine nearest interpolator is always centre 
  */
 
 /*
@@ -241,9 +244,12 @@ vips_resize_build( VipsObject *object )
 			vips_resize_interpolate( resize->kernel );
 
 		/* Input displacement. For centre sampling, shift by 0.5 down
-		 * and right.
+		 * and right. Except if this is nearest, which is always
+		 * centre.
 		 */
-		const double id = 0.5;
+		const double id = 
+			resize->kernel == VIPS_KERNEL_NEAREST ? 
+			0.0 : 0.5;
 
 		VipsInterpolate *interpolate;