[gegl] boxfilter: bail early if all pixels contributing are transparent

[Øyvind Kolås <ok src gnome org>]

commit b0bf192509a818fa67e44e013ccbf49f8c4ed9d0
Author: Øyvind Kolås <pippin gimp org>
Date:   Thu Oct 15 17:19:17 2015 +0200

    boxfilter: bail early if all pixels contributing are transparent

 gegl/gegl-algorithms-boxfilter.inc |   15 ++++++++++++++-
 1 files changed, 14 insertions(+), 1 deletions(-)
---
diff --git a/gegl/gegl-algorithms-boxfilter.inc b/gegl/gegl-algorithms-boxfilter.inc
index 6522635..4c79ee1 100644
--- a/gegl/gegl-algorithms-boxfilter.inc
+++ b/gegl/gegl-algorithms-boxfilter.inc
@@ -59,6 +59,19 @@ BOXFILTER_FUNCNAME (guchar              *dest_buf,
             src[0] -= 4;
             src[3] -= 4;
             src[6] -= 4;
+
+            if (src[0][3] == 0 &&  /* XXX: it would be even better to not call this at all for the abyss...  
*/
+                src[1][3] == 0 &&
+                src[2][3] == 0 &&
+                src[3][3] == 0 &&
+                src[4][3] == 0 &&
+                src[5][3] == 0 &&
+                src[6][3] == 0 &&
+                src[7][3] == 0)
+            {
+              dst[0] = dst[1] = dst[2] = dst[3] = 0;
+            }
+            else
             {
               const gfloat lt = left_weight[x] * top_weight;
               const gfloat lm = left_weight[x] * middle_weight;
@@ -69,6 +82,7 @@ BOXFILTER_FUNCNAME (guchar              *dest_buf,
               const gfloat rt = right_weight[x] * top_weight;
               const gfloat rm = right_weight[x] * middle_weight;
               const gfloat rb = right_weight[x] * bottom_weight;
+
                 dst[0] = BOXFILTER_ROUND(
                   src[0][0] * lt + src[3][0] * lm + src[6][0] * lb +
                   src[1][0] * ct + src[4][0] * cm + src[7][0] * cb +
@@ -225,6 +239,5 @@ BOXFILTER_FUNCNAME (guchar              *dest_buf,
         }
         break;
       }
-
     }
 }