From 6f2e74de8120837ae9cfa0f90764a82c071731b3 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Mon, 23 Mar 2009 17:38:14 +0000
Subject: [PATCH] stuff

---
 ChangeLog                   |  2 ++
 TODO                        |  7 +++++++
 libsrc/resample/im_affine.c |  4 ++--
 libsrc/resample/transform.c | 13 +++++++------
 4 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index c7e0be7d..29aeede4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -6,6 +6,8 @@
 - saner im_buildlut() behaviour
 - added im_gauss_imask_sep()
 - allow open of truncated images, but block pixel access
+- revising rounding on im_affine*() coordinate transforms to make them more
+  stable
 
 3/3/09 started 7.17.2
 - im_magick2vips.c: allow funky bit depths, like 14 (thanks Mikkel)
diff --git a/TODO b/TODO
index 5a0e3aa9..e9e68b60 100644
--- a/TODO
+++ b/TODO
@@ -1,3 +1,10 @@
+- try
+
+	 vips im_affinei_all ~/in.v ~/out.v bilinear 1.0928961748633881 0 0 1 0 0
+
+  where in.v is a 366 pixel wide image, and 1.092... is (400 / 366)
+
+
 - mask subscript in Pythion seems to be broken
 
 	>>> from vipsCC import *
diff --git a/libsrc/resample/im_affine.c b/libsrc/resample/im_affine.c
index 96f7a169..66eaea4c 100644
--- a/libsrc/resample/im_affine.c
+++ b/libsrc/resample/im_affine.c
@@ -231,9 +231,9 @@ affinei_gen( REGION *or, void *seq, void *a, void *b )
 	need.left += iarea->left;
 	need.top += iarea->top;
 
-	/* Add a border for interpolation. 
+	/* Add a border for interpolation. Plus one for rounding errors.
 	 */
-	im_rect_marginadjust( &need, half_window_size );
+	im_rect_marginadjust( &need, half_window_size + 1 );
 
 	/* Clip against the size of (2).
 	 */
diff --git a/libsrc/resample/transform.c b/libsrc/resample/transform.c
index 8aadf033..20abddfa 100644
--- a/libsrc/resample/transform.c
+++ b/libsrc/resample/transform.c
@@ -181,7 +181,7 @@ typedef void (*transform_fn)( const Transformation *,
  */
 static void
 transform_rect( const Transformation *trn, transform_fn transform,
-	const Rect *in, 		/* In input space */
+	const Rect *in,		/* In input space */
 	Rect *out )		/* In output space */
 {
 	double x1, y1;		/* Map corners */
@@ -197,17 +197,18 @@ transform_rect( const Transformation *trn, transform_fn transform,
 	transform( trn, IM_RECT_RIGHT( in ), in->top, &x2, &y2 );
 	transform( trn, IM_RECT_RIGHT( in ), IM_RECT_BOTTOM( in ), &x4, &y4 );
 
-	/* Find bounding box for these four corners.
+	/* Find bounding box for these four corners. Round-to-nearest to try
+	 * to stop rounding errors growing images.
 	 */
 	left = IM_MIN( x1, IM_MIN( x2, IM_MIN( x3, x4 ) ) );
 	right = IM_MAX( x1, IM_MAX( x2, IM_MAX( x3, x4 ) ) );
 	top = IM_MIN( y1, IM_MIN( y2, IM_MIN( y3, y4 ) ) );
 	bottom = IM_MAX( y1, IM_MAX( y2, IM_MAX( y3, y4 ) ) );
 
-	out->left = floor( left );
-	out->top = floor( top );
-	out->width = ceil( right ) - out->left;
-	out->height = ceil( bottom ) - out->top;
+	out->left = IM_RINT( left );
+	out->top = IM_RINT( top );
+	out->width = IM_RINT( right - left );
+	out->height = IM_RINT( bottom - top );
 }
 
 /* Given an area in the input image, calculate the bounding box for those