widgets: implement unique color count

This patch reintroduce the unique color counting in an image,
an old feature from old color-cube-analyze plug-in.
See #13026

app/core/gimphistogram.c

@@ -37,6 +37,7 @@
 #include "gimp-atomic.h"
 #include "gimp-parallel.h"
 #include "gimpasync.h"
+#include "gimpdrawable.h"
 #include "gimphistogram.h"
 #include "gimpwaitable.h"
 
@@ -119,6 +120,9 @@ static void       gimp_histogram_calculate_area           (const GeglRectangle
                                                            CalculateData        *data);
 static void       gimp_histogram_calculate_async_callback (GimpAsync            *async,
                                                            CalculateContext     *context);
+static guint      hash_color_bytes                        (gpointer             *key);
+static gboolean   color_bytes_equal                       (gpointer             *key1,
+                                                           gpointer             *key2);
 
 
 G_DEFINE_TYPE_WITH_PRIVATE (GimpHistogram, gimp_histogram, GIMP_TYPE_OBJECT)
@@ -229,6 +233,49 @@ gimp_histogram_get_memsize (GimpObject *object,
                                                                   gui_size);
 }
 
+static guint
+hash_color_bytes (gpointer *key)
+{
+  GBytes       *bytes     = (GBytes *) key;
+  gsize         size;
+  const guint8 *data;
+  guint64       max_value = 0;
+  guint64       value     = 0;
+  guint         hash;
+
+  data = g_bytes_get_data (bytes, &size);
+
+  for (gsize i = 0; i < size; ++i)
+    {
+      value     = value * 256 + data[i];
+      max_value = max_value * 256 + 255;
+    }
+
+  if (max_value == 0)
+    return 0;
+
+  hash = (guint) ((value * (guint64) G_MAXUINT) / max_value);
+
+  return hash;
+}
+
+static gboolean
+color_bytes_equal (gpointer *key1,
+                   gpointer *key2)
+{
+  GBytes       *bytes1 = (GBytes *) key1;
+  GBytes       *bytes2 = (GBytes *) key2;
+  gsize         size1;
+  gsize         size2;
+  const guint8 *data1  = g_bytes_get_data (bytes1, &size1);
+  const guint8 *data2  = g_bytes_get_data (bytes2, &size2);
+
+  if (size1 != size2)
+    return FALSE;
+
+  return memcmp (data1, data2, size1) == 0;
+}
+
 /*  public functions  */
 
 GimpHistogram *
@@ -1230,3 +1277,52 @@ gimp_histogram_calculate_async_callback (GimpAsync        *async,
 
   g_slice_free (CalculateContext, context);
 }
+
+guint
+gimp_histogram_unique_colors (GimpDrawable *drawable)
+{
+  const Babl         *format;
+  guint               bpp;
+  GeglBufferIterator *iter;
+  GHashTable         *hash_table;
+  GBytes             *key     = NULL;
+  guint               uniques = 0;
+
+  g_return_val_if_fail (GIMP_IS_DRAWABLE (drawable), 0);
+
+  format = gimp_drawable_get_format (drawable);
+  bpp    = babl_format_get_bytes_per_pixel (format);
+
+  iter = gegl_buffer_iterator_new (gimp_drawable_get_buffer (drawable),
+                                   NULL, 0, format,
+                                   GEGL_ACCESS_READ, GEGL_ABYSS_NONE, 1);
+
+
+  hash_table = g_hash_table_new ((GHashFunc)  hash_color_bytes,
+                                 (GEqualFunc) color_bytes_equal);
+
+  while (gegl_buffer_iterator_next (iter))
+    {
+      guint8 *data   = iter->items[0].data;
+      guint   length = iter->length;
+
+      while (length--)
+        {
+          key = g_bytes_new (data, bpp);
+
+          if (! g_hash_table_lookup (hash_table, key))
+            {
+              g_hash_table_insert (hash_table, key, key);
+              key = NULL;
+              uniques++;
+            }
+
+          data += bpp;
+        }
+    }
+
+  g_hash_table_destroy (hash_table);
+  g_bytes_unref (key);
+
+  return uniques;
+}

app/core/gimphistogram.h

@@ -100,6 +100,7 @@ gint            gimp_histogram_n_components    (GimpHistogram        *histogram)
 gint            gimp_histogram_n_bins          (GimpHistogram        *histogram);
 gboolean        gimp_histogram_has_channel     (GimpHistogram        *histogram,
                                                 GimpHistogramChannel  channel);
+guint           gimp_histogram_unique_colors   (GimpDrawable         *drawable);
 
 
 #endif /* __GIMP_HISTOGRAM_H__ */

app/widgets/gimphistogrameditor.c

@@ -221,6 +221,30 @@ gimp_histogram_editor_init (GimpHistogramEditor *editor)
       gtk_grid_attach (GTK_GRID (grid), label, x + 1, y, 1, 1);
       gtk_widget_show (label);
     }
+
+  editor->toggle = gtk_check_button_new_with_label (_("Compute unique colors:"));
+  gimp_label_set_attributes (GTK_LABEL (gtk_bin_get_child (GTK_BIN (editor->toggle))),
+                             PANGO_ATTR_SCALE, PANGO_SCALE_SMALL,
+                             -1);
+  gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (editor->toggle), FALSE);
+  g_signal_connect_swapped (editor->toggle, "toggled",
+                            G_CALLBACK (gimp_histogram_editor_info_update),
+                            editor);
+  gtk_widget_set_margin_start (gtk_bin_get_child (GTK_BIN (editor->toggle)), 6);
+  gtk_widget_set_halign (editor->toggle, GTK_ALIGN_END);
+  gtk_grid_attach (GTK_GRID (grid), editor->toggle, 0, 3, 1, 1);
+  gtk_widget_show (editor->toggle);
+
+  editor->labels[6] = label = g_object_new (GTK_TYPE_LABEL,
+                                            "xalign",      0.0,
+                                            "yalign",      0.5,
+                                            "width-chars", 9,
+                                            NULL);
+  gimp_label_set_attributes (GTK_LABEL (label),
+                             PANGO_ATTR_SCALE, PANGO_SCALE_SMALL,
+                             -1);
+  gtk_grid_attach (GTK_GRID (grid), label, 1, 3, 1, 1);
+  gtk_widget_show (label);
 }
 
 static void
@@ -767,12 +791,23 @@ gimp_histogram_editor_info_update (GimpHistogramEditor *editor)
                                                  (100.0 * count / pixels) :
                                                  0.0));
       gtk_label_set_text (GTK_LABEL (editor->labels[5]), text);
+
+      if (gtk_toggle_button_get_active (GTK_TOGGLE_BUTTON (editor->toggle)))
+        {
+          g_snprintf (text, sizeof (text), "%d",
+                      gimp_histogram_unique_colors (editor->drawable));
+          gtk_label_set_text (GTK_LABEL (editor->labels[6]), text);
+        }
+      else
+        {
+          gtk_label_set_text (GTK_LABEL (editor->labels[6]), "n/a");
+        }
     }
   else
     {
       gint i;
 
-      for (i = 0; i < 6; i++)
+      for (i = 0; i < 7; i++)
         gtk_label_set_text (GTK_LABEL (editor->labels[i]), NULL);
     }
 }

app/widgets/gimphistogrameditor.h

@@ -51,7 +51,8 @@ struct _GimpHistogramEditor
 
   GtkWidget            *menu;
   GtkWidget            *box;
-  GtkWidget            *labels[6];
+  GtkWidget            *labels[7];
+  GtkWidget            *toggle;
 };
 
 struct _GimpHistogramEditorClass