[gegl] panorama-projection: fix off by half error in sampling

[Øyvind Kolås <ok src gnome org>]

commit c87c5a3f3de514835330a7929479ba6b11fc32fd
Author: Øyvind Kolås <pippin gimp org>
Date:   Mon Apr 9 21:36:32 2018 +0200

    panorama-projection: fix off by half error in sampling

 operations/common/panorama-projection.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/operations/common/panorama-projection.c b/operations/common/panorama-projection.c
index f17b310..6cb6b95 100644
--- a/operations/common/panorama-projection.c
+++ b/operations/common/panorama-projection.c
@@ -477,7 +477,8 @@ process (GeglOperation       *operation,
                 gegl_unmap(u,v, cx, cy);
 #undef gegl_unmap
                 gegl_sampler_get (sampler,
-                                  cx * transform.in_width, cy * transform.in_height,
+                                  cx * transform.in_width + 0.5f,
+                                  cy * transform.in_height + 0.5f,
                                   scale, out, abyss_mode);
                 out += 4;
 
@@ -501,7 +502,8 @@ process (GeglOperation       *operation,
 
                 transform.mapfun (&transform, u, v, &cx, &cy);
                 gegl_sampler_get (sampler,
-                                  cx * transform.in_width, cy * transform.in_height,
+                                  cx * transform.in_width + 0.5f,
+                                  cy * transform.in_height + 0.5f,
                                   scale, out, abyss_mode);
                 out += 4;