From ffb34c943cc28a5f31b9bf68117c66a6d4402758 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Mon, 26 Mar 2012 09:35:22 +0100
Subject: [PATCH] nearest0neighbor now rounds to nearest

before it just truncated x/y downs, now it rounds to nearest ... this
removes a 0.5 shift compared to the other interpolators

thanks Nicolas
---
 ChangeLog                      | 2 ++
 libvips/resample/interpolate.c | 9 +++------
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 72168e31..31c30359 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,8 @@
 19/3/12 started 7.29.0
 - better PNG alpha handling
 - sanity-check PNG read geometry
+- nearest-neighbor interpolation rounds coordinates to nearest instead of 
+  rounding down (thanks Nicolas)
 
 13/3/12 started 7.28.2
 - xres/yres tiffsave args were broken
diff --git a/libvips/resample/interpolate.c b/libvips/resample/interpolate.c
index 6c191d08..65ee20d5 100644
--- a/libvips/resample/interpolate.c
+++ b/libvips/resample/interpolate.c
@@ -331,15 +331,12 @@ static void
 vips_interpolate_nearest_interpolate( VipsInterpolate *interpolate,
 	void *out, REGION *in, double x, double y )
 {
-	/* Pel size and line size.
-	 */
 	const int ps = IM_IMAGE_SIZEOF_PEL( in->im );
 
-	/* Top left corner we interpolate from. We know x/y are always
-	 * positive, so we can just (int) them.
+	/* We know x/y are always positive, so we can just (int) them.
 	 */
-	const int xi = (int) x;
-	const int yi = (int) y;
+	const int xi = (int) (x + 0.5);
+	const int yi = (int) (y + 0.5);
 
 	const VipsPel *p = IM_REGION_ADDR( in, xi, yi );
 	VipsPel *q = (VipsPel *) out;