[gegl] operations: make aux buffer of watershed-transform optional.

[Jehan <jehanp src gnome org>]

commit 5feeee4c66008e4695f771e64f815b4f8f3492ef
Author: Jehan <jehan girinstud io>
Date:   Tue Nov 20 15:43:22 2018 +0100

    operations: make aux buffer of watershed-transform optional.
    
    No auxiliary buffer will simply mean that all pixels have the same
    priority; since the algorithm queues newly labelled pixels (by
    propagation) in FIFO, it is also equivalent to having an aux buffer with
    all labelled pixels having the same higher priority (i.e. lower value)
    and all flagged pixels having the same lower priority.
    
    This doesn't change the output for any existing use of this operation,
    while making basic usage simpler (and potentially a bit faster, even
    though tests did not really show extraordinary gain).

 operations/common/watershed-transform.c | 65 ++++++++++++++++++---------------
 1 file changed, 35 insertions(+), 30 deletions(-)
---
diff --git a/operations/common/watershed-transform.c b/operations/common/watershed-transform.c
index 869e57b2b..5a1105f5c 100644
--- a/operations/common/watershed-transform.c
+++ b/operations/common/watershed-transform.c
@@ -226,7 +226,7 @@ process (GeglOperation       *operation,
   gint    j;
   gint    x, y;
   GeglBufferIterator  *iter;
-  GeglSampler         *gradient_sampler;
+  GeglSampler         *gradient_sampler = NULL;
   const GeglRectangle *extent = gegl_buffer_get_extent (input);
 
   const Babl  *gradient_format = babl_format ("Y u8");
@@ -243,10 +243,8 @@ process (GeglOperation       *operation,
   HQ_init (&hq);
 
   iter = gegl_buffer_iterator_new (input, extent, 0, labels_format,
-                                   GEGL_ACCESS_READ, GEGL_ABYSS_NONE, 11);
-
-  gegl_buffer_iterator_add (iter, aux, extent, 0, gradient_format,
-                            GEGL_ACCESS_READ, GEGL_ABYSS_NONE);
+                                   GEGL_ACCESS_READ, GEGL_ABYSS_NONE,
+                                   aux ? 11 : 10);
 
   gegl_buffer_iterator_add (iter, output, extent, 0, labels_format,
                             GEGL_ACCESS_WRITE, GEGL_ABYSS_NONE);
@@ -276,23 +274,28 @@ process (GeglOperation       *operation,
   gegl_buffer_iterator_add (iter, input,
                             GEGL_RECTANGLE (1, 1, extent->width, extent->height),
                             0, labels_format, GEGL_ACCESS_READ, GEGL_ABYSS_NONE);
+  /* Priority map: lower is higher priority. */
+  if (aux)
+    gegl_buffer_iterator_add (iter, aux, extent, 0, gradient_format,
+                              GEGL_ACCESS_READ, GEGL_ABYSS_NONE);
+
   while (gegl_buffer_iterator_next (iter))
     {
-      guint8   *label    = iter->items[0].data;
-      guint8   *pixel    = iter->items[1].data;
-      guint8   *outlabel = iter->items[2].data;
-      guint8   *n[8]     =
+      GeglRectangle *roi      = &iter->items[0].roi;
+      guint8        *label    = iter->items[0].data;
+      guint8        *outlabel = iter->items[1].data;
+      guint8        *n[8]     =
         {
+          iter->items[2].data,
           iter->items[3].data,
           iter->items[4].data,
           iter->items[5].data,
           iter->items[6].data,
           iter->items[7].data,
           iter->items[8].data,
-          iter->items[9].data,
-          iter->items[10].data
+          iter->items[9].data
         };
-      GeglRectangle *roi = &iter->items[0].roi;
+      guint8        *prio    = aux ? iter->items[10].data : NULL;
 
       for (y = roi->y; y < roi->y + roi->height; y++)
         for (x = roi->x; x < roi->x + roi->width; x++)
@@ -337,14 +340,15 @@ process (GeglOperation       *operation,
                     p->x = x;
                     p->y = y;
 
-                    HQ_push (&hq, *pixel, p);
+                    HQ_push (&hq, prio ? *prio : 0, p);
                   }
               }
 
             for (i = 0; i < bpp; i++)
               outlabel[i] = label[i];
 
-            pixel++;
+            if (prio)
+              prio++;
             label    += bpp;
             outlabel += bpp;
             for (j = 0; j < 8; j++)
@@ -352,10 +356,11 @@ process (GeglOperation       *operation,
           }
     }
 
-  gradient_sampler = gegl_buffer_sampler_new_at_level (aux,
-                                                       gradient_format,
-                                                       GEGL_SAMPLER_NEAREST,
-                                                       level);
+  if (aux)
+    gradient_sampler = gegl_buffer_sampler_new_at_level (aux,
+                                                         gradient_format,
+                                                         GEGL_SAMPLER_NEAREST,
+                                                         level);
   while (!HQ_is_empty (&hq))
     {
       PixelCoords *p = (PixelCoords *) HQ_pop (&hq);
@@ -391,16 +396,17 @@ process (GeglOperation       *operation,
               }
           if (flagged)
             {
-              guint8 gradient_value;
+              guint8 gradient_value = 0;
               GeglRectangle n_rect = {nx, ny, 1, 1};
               PixelCoords *n = g_new (PixelCoords, 1);
               n->x = nx;
               n->y = ny;
 
-              gegl_sampler_get (gradient_sampler,
-                                (gdouble) nx,
-                                (gdouble) ny,
-                                NULL, &gradient_value, GEGL_ABYSS_NONE);
+              if (gradient_sampler)
+                gegl_sampler_get (gradient_sampler,
+                                  (gdouble) nx,
+                                  (gdouble) ny,
+                                  NULL, &gradient_value, GEGL_ABYSS_NONE);
 
               HQ_push (&hq, gradient_value, n);
 
@@ -415,7 +421,8 @@ process (GeglOperation       *operation,
 
       g_free (p);
     }
-  g_object_unref (gradient_sampler);
+  if (gradient_sampler)
+    g_object_unref (gradient_sampler);
 
   HQ_clean (&hq);
   return  TRUE;
@@ -445,11 +452,6 @@ operation_process (GeglOperation        *operation,
                  n_comp, o->flag_component);
       success = FALSE;
     }
-  else if (! aux)
-    {
-      g_warning ("Missing priority buffer");
-      success = FALSE;
-    }
   else
     {
       gint flag_idx = o->flag_component < 0 ? n_comp + o->flag_component : o->flag_component;
@@ -492,7 +494,10 @@ gegl_op_class_init (GeglOpClass *klass)
                      "Output buffer will keep the input format. "
                      "Unlabelled pixels are marked with a given flag value "
                      "(by default: last component with NULL value). "
-                     "The mandatory aux buffer is a \"Y u8\" image representing the priority levels."),
+                     "The aux buffer is a \"Y u8\" image representing the priority levels "
+                     "(lower value is higher priority). If aux is absent, "
+                     "all labellized pixels have the same priority "
+                     "and propagated labels have a lower priority."),
     NULL);
 }