add comments

git-svn-id: http://svn.code.sf.net/p/netpbm/code/trunk@1807 9d0c8265-081b-0410-96cb-a4ca84ce46f8

1 files changed, 6 insertions, 1 deletions

diff --git a/lib/libpamn.c b/lib/libpamn.c
index ff8af2fb..bd3fab21 100644
--- a/lib/libpamn.c
+++ b/lib/libpamn.c
@@ -541,7 +541,12 @@ static void
 applyopacityCommon(enum applyUnapply const applyUnapply,
                    struct pam *      const pamP,
                    tuplen *          const tuplenrow) {
-
+/*----------------------------------------------------------------------------
+   Either apply or unapply opacity to the row tuplenrow[], per
+   'applyUnapply'.  Apply means to multiply each foreground sample by
+   the opacity value for that pixel; Unapply means to do the inverse, as
+   if the foreground values had already been so multiplied.
+-----------------------------------------------------------------------------*/
     unsigned int opacityPlane;
     bool haveOpacity;