[gegl] spherize: reduce sphere radius to avoid out-of-bounds sampling

[N/A <ell src gnome org>]

commit 3f5dafe1e6b7fc5f4ff45baa58ebdcd004f38cb6
Author: Ell <ell_se yahoo com>
Date:   Wed Oct 11 12:03:42 2017 -0400

    spherize: reduce sphere radius to avoid out-of-bounds sampling
    
    Use (width-1)/2 and (height-1)/2 as the radii, rather than width/2
    and height/2, to avoid sampling beyond the center of the outermost
    pixels of the input buffer, so that the abyss color doesn't leak
    in.

 operations/workshop/spherize.c |   24 +++++++++++++++++++++---
 1 files changed, 21 insertions(+), 3 deletions(-)
---
diff --git a/operations/workshop/spherize.c b/operations/workshop/spherize.c
index 05e1cd8..342addb 100644
--- a/operations/workshop/spherize.c
+++ b/operations/workshop/spherize.c
@@ -73,8 +73,26 @@ static gboolean
 is_nop (GeglOperation *operation)
 {
   GeglProperties *o = GEGL_PROPERTIES (operation);
+  GeglRectangle  *in_rect;
 
-  return fabs (o->curvature) < EPSILON || fabs (o->amount) < EPSILON;
+  if (fabs (o->curvature) < EPSILON || fabs (o->amount) < EPSILON)
+    return TRUE;
+
+  in_rect = gegl_operation_source_get_bounding_box (operation, "input");
+
+  switch (o->mode)
+    {
+    case GEGL_SPHERIZE_MODE_RADIAL:
+      return in_rect->width < 1 || in_rect->height < 1;
+
+    case GEGL_SPHERIZE_MODE_HORIZONTAL:
+      return in_rect->width < 1;
+
+    case GEGL_SPHERIZE_MODE_VERTICAL:
+      return in_rect->height < 1;
+    }
+
+  g_return_val_if_reached (TRUE);
 }
 
 static void
@@ -187,12 +205,12 @@ process (GeglOperation       *operation,
   if (o->mode == GEGL_SPHERIZE_MODE_RADIAL ||
       o->mode == GEGL_SPHERIZE_MODE_HORIZONTAL)
     {
-      dx = 2.0 / in_extent->width;
+      dx = 2.0 / (in_extent->width - 1);
     }
   if (o->mode == GEGL_SPHERIZE_MODE_RADIAL ||
       o->mode == GEGL_SPHERIZE_MODE_VERTICAL)
     {
-      dy = 2.0 / in_extent->height;
+      dy = 2.0 / (in_extent->height - 1);
     }
 
   coangle_of_view_2 = MAX (180.0 - o->angle_of_view, 0.01) * G_PI / 360.0;