[gegl] transform-core.c: comment explaining how to restore the 'boundary between pixels is owned by right/b

[Nicolas Robidoux <nrobidoux src gnome org>]

commit 8acd9bd4086f3a51bca29fbd3dac3ffb5d16d0a0
Author: Nicolas Robidoux <nrobidoux git gnome org>
Date:   Thu Dec 6 12:02:05 2012 -0500

    transform-core.c: comment explaining how to restore the 'boundary between pixels is owned by right/bottom' policy in bounding box computation

 operations/transform/transform-core.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/operations/transform/transform-core.c b/operations/transform/transform-core.c
index 15ebd66..8a8a2be 100644
--- a/operations/transform/transform-core.c
+++ b/operations/transform/transform-core.c
@@ -387,6 +387,11 @@ gegl_transform_bounding_box (const gdouble *points,
   /*
    * Warning: width may be 0 when min_x=max_x=integer. Same with
    * height.
+   *
+   * If you decide to enforce the "boundary between two pixels is
+   * owned by the right/bottom one" policy, replace ceil by floor +
+   * (gint) 1. This often enlarges result by one pixel at the right
+   * and bottom.
    */
   output->width  = (gint) ceil ((double) max_x) - output->x;
   output->height = (gint) ceil ((double) max_y) - output->y;