[gegl/samplers] comments

[Nicolas Robidoux <nrobidoux src gnome org>]

commit 957ca4a73421ca527e0fbd53f26540bf93976d3a
Author: Nicolas Robidoux <nicolas robidoux gmail com>
Date:   Sun Jun 26 09:56:42 2011 -0400

    comments

 gegl/buffer/gegl-sampler-lohalo.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)
---
diff --git a/gegl/buffer/gegl-sampler-lohalo.c b/gegl/buffer/gegl-sampler-lohalo.c
index 7ef6ba6..62f0c91 100644
--- a/gegl/buffer/gegl-sampler-lohalo.c
+++ b/gegl/buffer/gegl-sampler-lohalo.c
@@ -192,6 +192,14 @@
 #define LOHALO_FLOORED_DIVISION_BY_2(a) (((a) - ((a)>=0 ? 0 : 1)) / 2)
 
 /*
+ * General convention: Looking at the image as a (linear algebra)
+ * matrix, the index j has to do with the x-coordinate, that is,
+ * horizontal position, and the index i has to do with the
+ * y-coordinate (which runs from top to bottom), that is, the vertical
+ * position.
+ */
+
+/*
  * Convenience macro:
  */
 #define LOHALO_CALL_LEVEL_1_EWA_UPDATE(j,i) level_1_ewa_update ((j),           \