Adding upstream version 2.10.22.upstream/2.10.22upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1956 insertions, 0 deletions

diff --git a/app/core/gimpchannel.c b/app/core/gimpchannel.c
new file mode 100644
index 0000000..a9b7546
--- /dev/null
+++ b/app/core/gimpchannel.c
@@ -0,0 +1,1956 @@
+/* GIMP - The GNU Image Manipulation Program
+ * Copyright (C) 1995 Spencer Kimball and Peter Mattis
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include <string.h>
+
+#include <cairo.h>
+#include <gegl.h>
+#include <gdk-pixbuf/gdk-pixbuf.h>
+
+#include "libgimpbase/gimpbase.h"
+#include "libgimpmath/gimpmath.h"
+#include "libgimpcolor/gimpcolor.h"
+
+#include "core-types.h"
+
+#include "paint/gimppaintcore-stroke.h"
+#include "paint/gimppaintoptions.h"
+
+#include "gegl/gimp-gegl-apply-operation.h"
+#include "gegl/gimp-gegl-loops.h"
+#include "gegl/gimp-gegl-mask.h"
+#include "gegl/gimp-gegl-nodes.h"
+
+#include "gimp.h"
+#include "gimp-utils.h"
+#include "gimpboundary.h"
+#include "gimpcontainer.h"
+#include "gimperror.h"
+#include "gimpimage.h"
+#include "gimpimage-quick-mask.h"
+#include "gimpimage-undo.h"
+#include "gimpimage-undo-push.h"
+#include "gimpchannel.h"
+#include "gimpchannel-select.h"
+#include "gimpcontext.h"
+#include "gimpdrawable-fill.h"
+#include "gimpdrawable-stroke.h"
+#include "gimpmarshal.h"
+#include "gimppaintinfo.h"
+#include "gimppickable.h"
+#include "gimpstrokeoptions.h"
+
+#include "gimp-intl.h"
+
+
+#define RGBA_EPSILON 1e-6
+
+enum
+{
+  COLOR_CHANGED,
+  LAST_SIGNAL
+};
+
+
+static void gimp_channel_pickable_iface_init (GimpPickableInterface *iface);
+
+static void       gimp_channel_finalize      (GObject           *object);
+
+static gint64     gimp_channel_get_memsize   (GimpObject        *object,
+                                              gint64            *gui_size);
+
+static gchar  * gimp_channel_get_description (GimpViewable      *viewable,
+                                              gchar            **tooltip);
+
+static GeglNode * gimp_channel_get_node      (GimpFilter        *filter);
+
+static gboolean   gimp_channel_is_attached   (GimpItem          *item);
+static GimpItemTree * gimp_channel_get_tree  (GimpItem          *item);
+static gboolean   gimp_channel_bounds        (GimpItem          *item,
+                                              gdouble           *x,
+                                              gdouble           *y,
+                                              gdouble           *width,
+                                              gdouble           *height);
+static GimpItem * gimp_channel_duplicate     (GimpItem          *item,
+                                              GType              new_type);
+static void       gimp_channel_convert       (GimpItem          *item,
+                                              GimpImage         *dest_image,
+                                              GType              old_type);
+static void       gimp_channel_translate     (GimpItem          *item,
+                                              gdouble            off_x,
+                                              gdouble            off_y,
+                                              gboolean           push_undo);
+static void       gimp_channel_scale         (GimpItem          *item,
+                                              gint               new_width,
+                                              gint               new_height,
+                                              gint               new_offset_x,
+                                              gint               new_offset_y,
+                                              GimpInterpolationType interp_type,
+                                              GimpProgress      *progress);
+static void       gimp_channel_resize        (GimpItem          *item,
+                                              GimpContext       *context,
+                                              GimpFillType       fill_type,
+                                              gint               new_width,
+                                              gint               new_height,
+                                              gint               offset_x,
+                                              gint               offset_y);
+static GimpTransformResize
+                  gimp_channel_get_clip      (GimpItem          *item,
+                                              GimpTransformResize clip_result);
+static gboolean   gimp_channel_fill          (GimpItem          *item,
+                                              GimpDrawable      *drawable,
+                                              GimpFillOptions   *fill_options,
+                                              gboolean           push_undo,
+                                              GimpProgress      *progress,
+                                              GError           **error);
+static gboolean   gimp_channel_stroke        (GimpItem          *item,
+                                              GimpDrawable      *drawable,
+                                              GimpStrokeOptions *stroke_options,
+                                              gboolean           push_undo,
+                                              GimpProgress      *progress,
+                                              GError           **error);
+static void       gimp_channel_to_selection  (GimpItem          *item,
+                                              GimpChannelOps     op,
+                                              gboolean           antialias,
+                                              gboolean           feather,
+                                              gdouble            feather_radius_x,
+                                              gdouble            feather_radius_y);
+
+static void       gimp_channel_convert_type  (GimpDrawable      *drawable,
+                                              GimpImage         *dest_image,
+                                              const Babl        *new_format,
+                                              GimpColorProfile  *dest_profile,
+                                              GeglDitherMethod   layer_dither_type,
+                                              GeglDitherMethod   mask_dither_type,
+                                              gboolean           push_undo,
+                                              GimpProgress      *progress);
+static void gimp_channel_invalidate_boundary   (GimpDrawable       *drawable);
+static void gimp_channel_get_active_components (GimpDrawable       *drawable,
+                                                gboolean           *active);
+
+static void      gimp_channel_set_buffer     (GimpDrawable        *drawable,
+                                              gboolean             push_undo,
+                                              const gchar         *undo_desc,
+                                              GeglBuffer          *buffer,
+                                              const GeglRectangle *bounds);
+
+static gdouble   gimp_channel_get_opacity_at (GimpPickable        *pickable,
+                                              gint                 x,
+                                              gint                 y);
+
+static gboolean   gimp_channel_real_boundary (GimpChannel         *channel,
+                                              const GimpBoundSeg **segs_in,
+                                              const GimpBoundSeg **segs_out,
+                                              gint                *num_segs_in,
+                                              gint                *num_segs_out,
+                                              gint                 x1,
+                                              gint                 y1,
+                                              gint                 x2,
+                                              gint                 y2);
+static gboolean   gimp_channel_real_is_empty (GimpChannel         *channel);
+static void       gimp_channel_real_feather  (GimpChannel         *channel,
+                                              gdouble              radius_x,
+                                              gdouble              radius_y,
+                                              gboolean             edge_lock,
+                                              gboolean             push_undo);
+static void       gimp_channel_real_sharpen  (GimpChannel         *channel,
+                                              gboolean             push_undo);
+static void       gimp_channel_real_clear    (GimpChannel         *channel,
+                                              const gchar         *undo_desc,
+                                              gboolean             push_undo);
+static void       gimp_channel_real_all      (GimpChannel         *channel,
+                                              gboolean             push_undo);
+static void       gimp_channel_real_invert   (GimpChannel         *channel,
+                                              gboolean             push_undo);
+static void       gimp_channel_real_border   (GimpChannel         *channel,
+                                              gint                 radius_x,
+                                              gint                 radius_y,
+                                              GimpChannelBorderStyle style,
+                                              gboolean             edge_lock,
+                                              gboolean             push_undo);
+static void       gimp_channel_real_grow     (GimpChannel         *channel,
+                                              gint                 radius_x,
+                                              gint                 radius_y,
+                                              gboolean             push_undo);
+static void       gimp_channel_real_shrink   (GimpChannel         *channel,
+                                              gint                 radius_x,
+                                              gint                 radius_y,
+                                              gboolean             edge_lock,
+                                              gboolean             push_undo);
+static void       gimp_channel_real_flood    (GimpChannel         *channel,
+                                              gboolean             push_undo);
+
+
+static void      gimp_channel_buffer_changed (GeglBuffer          *buffer,
+                                              const GeglRectangle *rect,
+                                              GimpChannel         *channel);
+
+
+G_DEFINE_TYPE_WITH_CODE (GimpChannel, gimp_channel, GIMP_TYPE_DRAWABLE,
+                         G_IMPLEMENT_INTERFACE (GIMP_TYPE_PICKABLE,
+                                                gimp_channel_pickable_iface_init))
+
+#define parent_class gimp_channel_parent_class
+
+static guint channel_signals[LAST_SIGNAL] = { 0 };
+
+
+static void
+gimp_channel_class_init (GimpChannelClass *klass)
+{
+  GObjectClass      *object_class      = G_OBJECT_CLASS (klass);
+  GimpObjectClass   *gimp_object_class = GIMP_OBJECT_CLASS (klass);
+  GimpViewableClass *viewable_class    = GIMP_VIEWABLE_CLASS (klass);
+  GimpFilterClass   *filter_class      = GIMP_FILTER_CLASS (klass);
+  GimpItemClass     *item_class        = GIMP_ITEM_CLASS (klass);
+  GimpDrawableClass *drawable_class    = GIMP_DRAWABLE_CLASS (klass);
+
+  channel_signals[COLOR_CHANGED] =
+    g_signal_new ("color-changed",
+                  G_TYPE_FROM_CLASS (klass),
+                  G_SIGNAL_RUN_FIRST,
+                  G_STRUCT_OFFSET (GimpChannelClass, color_changed),
+                  NULL, NULL,
+                  gimp_marshal_VOID__VOID,
+                  G_TYPE_NONE, 0);
+
+  object_class->finalize            = gimp_channel_finalize;
+
+  gimp_object_class->get_memsize    = gimp_channel_get_memsize;
+
+  viewable_class->get_description   = gimp_channel_get_description;
+  viewable_class->default_icon_name = "gimp-channel";
+
+  filter_class->get_node            = gimp_channel_get_node;
+
+  item_class->is_attached          = gimp_channel_is_attached;
+  item_class->get_tree             = gimp_channel_get_tree;
+  item_class->bounds               = gimp_channel_bounds;
+  item_class->duplicate            = gimp_channel_duplicate;
+  item_class->convert              = gimp_channel_convert;
+  item_class->translate            = gimp_channel_translate;
+  item_class->scale                = gimp_channel_scale;
+  item_class->resize               = gimp_channel_resize;
+  item_class->get_clip             = gimp_channel_get_clip;
+  item_class->fill                 = gimp_channel_fill;
+  item_class->stroke               = gimp_channel_stroke;
+  item_class->to_selection         = gimp_channel_to_selection;
+  item_class->default_name         = _("Channel");
+  item_class->rename_desc          = C_("undo-type", "Rename Channel");
+  item_class->translate_desc       = C_("undo-type", "Move Channel");
+  item_class->scale_desc           = C_("undo-type", "Scale Channel");
+  item_class->resize_desc          = C_("undo-type", "Resize Channel");
+  item_class->flip_desc            = C_("undo-type", "Flip Channel");
+  item_class->rotate_desc          = C_("undo-type", "Rotate Channel");
+  item_class->transform_desc       = C_("undo-type", "Transform Channel");
+  item_class->fill_desc            = C_("undo-type", "Fill Channel");
+  item_class->stroke_desc          = C_("undo-type", "Stroke Channel");
+  item_class->to_selection_desc    = C_("undo-type", "Channel to Selection");
+  item_class->reorder_desc         = C_("undo-type", "Reorder Channel");
+  item_class->raise_desc           = C_("undo-type", "Raise Channel");
+  item_class->raise_to_top_desc    = C_("undo-type", "Raise Channel to Top");
+  item_class->lower_desc           = C_("undo-type", "Lower Channel");
+  item_class->lower_to_bottom_desc = C_("undo-type", "Lower Channel to Bottom");
+  item_class->raise_failed         = _("Channel cannot be raised higher.");
+  item_class->lower_failed         = _("Channel cannot be lowered more.");
+
+  drawable_class->convert_type          = gimp_channel_convert_type;
+  drawable_class->invalidate_boundary   = gimp_channel_invalidate_boundary;
+  drawable_class->get_active_components = gimp_channel_get_active_components;
+  drawable_class->set_buffer            = gimp_channel_set_buffer;
+
+  klass->boundary       = gimp_channel_real_boundary;
+  klass->is_empty       = gimp_channel_real_is_empty;
+  klass->feather        = gimp_channel_real_feather;
+  klass->sharpen        = gimp_channel_real_sharpen;
+  klass->clear          = gimp_channel_real_clear;
+  klass->all            = gimp_channel_real_all;
+  klass->invert         = gimp_channel_real_invert;
+  klass->border         = gimp_channel_real_border;
+  klass->grow           = gimp_channel_real_grow;
+  klass->shrink         = gimp_channel_real_shrink;
+  klass->flood          = gimp_channel_real_flood;
+
+  klass->feather_desc   = C_("undo-type", "Feather Channel");
+  klass->sharpen_desc   = C_("undo-type", "Sharpen Channel");
+  klass->clear_desc     = C_("undo-type", "Clear Channel");
+  klass->all_desc       = C_("undo-type", "Fill Channel");
+  klass->invert_desc    = C_("undo-type", "Invert Channel");
+  klass->border_desc    = C_("undo-type", "Border Channel");
+  klass->grow_desc      = C_("undo-type", "Grow Channel");
+  klass->shrink_desc    = C_("undo-type", "Shrink Channel");
+  klass->flood_desc     = C_("undo-type", "Flood Channel");
+}
+
+static void
+gimp_channel_init (GimpChannel *channel)
+{
+  gimp_rgba_set (&channel->color, 0.0, 0.0, 0.0, GIMP_OPACITY_OPAQUE);
+
+  channel->show_masked    = FALSE;
+
+  /*  Selection mask variables  */
+  channel->boundary_known = FALSE;
+  channel->segs_in        = NULL;
+  channel->segs_out       = NULL;
+  channel->num_segs_in    = 0;
+  channel->num_segs_out   = 0;
+  channel->empty          = FALSE;
+  channel->bounds_known   = FALSE;
+  channel->x1             = 0;
+  channel->y1             = 0;
+  channel->x2             = 0;
+  channel->y2             = 0;
+}
+
+static void
+gimp_channel_pickable_iface_init (GimpPickableInterface *iface)
+{
+  iface->get_opacity_at = gimp_channel_get_opacity_at;
+}
+
+static void
+gimp_channel_finalize (GObject *object)
+{
+  GimpChannel *channel = GIMP_CHANNEL (object);
+
+  g_clear_pointer (&channel->segs_in,  g_free);
+  g_clear_pointer (&channel->segs_out, g_free);
+
+  G_OBJECT_CLASS (parent_class)->finalize (object);
+}
+
+static gint64
+gimp_channel_get_memsize (GimpObject *object,
+                          gint64     *gui_size)
+{
+  GimpChannel *channel = GIMP_CHANNEL (object);
+
+  *gui_size += channel->num_segs_in  * sizeof (GimpBoundSeg);
+  *gui_size += channel->num_segs_out * sizeof (GimpBoundSeg);
+
+  return GIMP_OBJECT_CLASS (parent_class)->get_memsize (object, gui_size);
+}
+
+static gchar *
+gimp_channel_get_description (GimpViewable  *viewable,
+                              gchar        **tooltip)
+{
+  if (! strcmp (GIMP_IMAGE_QUICK_MASK_NAME,
+                gimp_object_get_name (viewable)))
+    {
+      return g_strdup (_("Quick Mask"));
+    }
+
+  return GIMP_VIEWABLE_CLASS (parent_class)->get_description (viewable,
+                                                              tooltip);
+}
+
+static GeglNode *
+gimp_channel_get_node (GimpFilter *filter)
+{
+  GimpDrawable *drawable = GIMP_DRAWABLE (filter);
+  GimpChannel  *channel  = GIMP_CHANNEL (filter);
+  GeglNode     *node;
+  GeglNode     *source;
+  GeglNode     *mode_node;
+  const Babl   *color_format;
+
+  node = GIMP_FILTER_CLASS (parent_class)->get_node (filter);
+
+  source = gimp_drawable_get_source_node (drawable);
+  gegl_node_add_child (node, source);
+
+  g_warn_if_fail (channel->color_node == NULL);
+
+  if (gimp_drawable_get_linear (drawable))
+    color_format = babl_format ("RGBA float");
+  else
+    color_format = babl_format ("R'G'B'A float");
+
+  channel->color_node = gegl_node_new_child (node,
+                                             "operation", "gegl:color",
+                                             "format",    color_format,
+                                             NULL);
+  gimp_gegl_node_set_color (channel->color_node,
+                            &channel->color);
+
+  g_warn_if_fail (channel->mask_node == NULL);
+
+  channel->mask_node = gegl_node_new_child (node,
+                                            "operation", "gegl:opacity",
+                                            NULL);
+  gegl_node_connect_to (channel->color_node, "output",
+                        channel->mask_node,  "input");
+
+  g_warn_if_fail (channel->invert_node == NULL);
+
+  channel->invert_node = gegl_node_new_child (node,
+                                              "operation", "gegl:invert-linear",
+                                              NULL);
+
+  if (channel->show_masked)
+    {
+      gegl_node_connect_to (source,               "output",
+                            channel->invert_node, "input");
+      gegl_node_connect_to (channel->invert_node, "output",
+                            channel->mask_node,   "aux");
+    }
+  else
+    {
+      gegl_node_connect_to (source,             "output",
+                            channel->mask_node, "aux");
+    }
+
+  mode_node = gimp_drawable_get_mode_node (drawable);
+
+  gegl_node_connect_to (channel->mask_node, "output",
+                        mode_node,          "aux");
+
+  return node;
+}
+
+static gboolean
+gimp_channel_is_attached (GimpItem *item)
+{
+  GimpImage *image = gimp_item_get_image (item);
+
+  return (GIMP_IS_IMAGE (image) &&
+          gimp_container_have (gimp_image_get_channels (image),
+                               GIMP_OBJECT (item)));
+}
+
+static GimpItemTree *
+gimp_channel_get_tree (GimpItem *item)
+{
+  if (gimp_item_is_attached (item))
+    {
+      GimpImage *image = gimp_item_get_image (item);
+
+      return gimp_image_get_channel_tree (image);
+    }
+
+  return NULL;
+}
+
+static gboolean
+gimp_channel_bounds (GimpItem *item,
+                     gdouble  *x,
+                     gdouble  *y,
+                     gdouble  *width,
+                     gdouble  *height)
+{
+  GimpChannel *channel = GIMP_CHANNEL (item);
+
+  if (! channel->bounds_known)
+    {
+      GeglBuffer *buffer = gimp_drawable_get_buffer (GIMP_DRAWABLE (channel));
+
+      channel->empty = ! gimp_gegl_mask_bounds (buffer,
+                                                &channel->x1,
+                                                &channel->y1,
+                                                &channel->x2,
+                                                &channel->y2);
+
+      channel->bounds_known = TRUE;
+    }
+
+  *x      = channel->x1;
+  *y      = channel->y1;
+  *width  = channel->x2 - channel->x1;
+  *height = channel->y2 - channel->y1;
+
+  return ! channel->empty;
+}
+
+static GimpItem *
+gimp_channel_duplicate (GimpItem *item,
+                        GType     new_type)
+{
+  GimpItem *new_item;
+
+  g_return_val_if_fail (g_type_is_a (new_type, GIMP_TYPE_DRAWABLE), NULL);
+
+  new_item = GIMP_ITEM_CLASS (parent_class)->duplicate (item, new_type);
+
+  if (GIMP_IS_CHANNEL (new_item))
+    {
+      GimpChannel *channel     = GIMP_CHANNEL (item);
+      GimpChannel *new_channel = GIMP_CHANNEL (new_item);
+
+      new_channel->color        = channel->color;
+      new_channel->show_masked  = channel->show_masked;
+
+      /*  selection mask variables  */
+      new_channel->bounds_known = channel->bounds_known;
+      new_channel->empty        = channel->empty;
+      new_channel->x1           = channel->x1;
+      new_channel->y1           = channel->y1;
+      new_channel->x2           = channel->x2;
+      new_channel->y2           = channel->y2;
+
+      if (new_type == GIMP_TYPE_CHANNEL)
+        {
+          /*  8-bit channel hack: make sure pixels between all sorts
+           *  of channels of an image is always copied without any
+           *  gamma conversion
+           */
+          GimpDrawable *new_drawable = GIMP_DRAWABLE (new_item);
+          GimpImage    *image        = gimp_item_get_image (item);
+          const Babl   *format       = gimp_image_get_channel_format (image);
+
+          if (format != gimp_drawable_get_format (new_drawable))
+            {
+              GeglBuffer *new_buffer;
+
+              new_buffer =
+                gegl_buffer_new (GEGL_RECTANGLE (0, 0,
+                                                 gimp_item_get_width  (new_item),
+                                                 gimp_item_get_height (new_item)),
+                                 format);
+
+              gegl_buffer_set_format (new_buffer,
+                                      gimp_drawable_get_format (new_drawable));
+              gimp_gegl_buffer_copy (gimp_drawable_get_buffer (new_drawable),
+                                     NULL, GEGL_ABYSS_NONE,
+                                     new_buffer, NULL);
+              gegl_buffer_set_format (new_buffer, NULL);
+
+              gimp_drawable_set_buffer (new_drawable, FALSE, NULL, new_buffer);
+              g_object_unref (new_buffer);
+            }
+        }
+    }
+
+  return new_item;
+}
+
+static void
+gimp_channel_convert (GimpItem  *item,
+                      GimpImage *dest_image,
+                      GType      old_type)
+{
+  GimpChannel  *channel  = GIMP_CHANNEL (item);
+  GimpDrawable *drawable = GIMP_DRAWABLE (item);
+
+  if (! gimp_drawable_is_gray (drawable))
+    {
+      gimp_drawable_convert_type (drawable, dest_image,
+                                  GIMP_GRAY,
+                                  gimp_image_get_precision (dest_image),
+                                  gimp_drawable_has_alpha (drawable),
+                                  NULL,
+                                  GEGL_DITHER_NONE, GEGL_DITHER_NONE,
+                                  FALSE, NULL);
+    }
+
+  if (gimp_drawable_has_alpha (drawable))
+    {
+      GeglBuffer *new_buffer;
+      const Babl *format;
+      GimpRGB     background;
+
+      format = gimp_drawable_get_format_without_alpha (drawable);
+
+      new_buffer =
+        gegl_buffer_new (GEGL_RECTANGLE (0, 0,
+                                         gimp_item_get_width (item),
+                                         gimp_item_get_height (item)),
+                         format);
+
+      gimp_rgba_set (&background, 0.0, 0.0, 0.0, 0.0);
+
+      gimp_gegl_apply_flatten (gimp_drawable_get_buffer (drawable),
+                               NULL, NULL,
+                               new_buffer, &background,
+                               GIMP_LAYER_COLOR_SPACE_RGB_LINEAR);
+
+      gimp_drawable_set_buffer_full (drawable, FALSE, NULL,
+                                     new_buffer,
+                                     GEGL_RECTANGLE (
+                                       gimp_item_get_offset_x (item),
+                                       gimp_item_get_offset_y (item),
+                                       0, 0),
+                                     TRUE);
+      g_object_unref (new_buffer);
+    }
+
+  if (G_TYPE_FROM_INSTANCE (channel) == GIMP_TYPE_CHANNEL)
+    {
+      gint width  = gimp_image_get_width  (dest_image);
+      gint height = gimp_image_get_height (dest_image);
+
+      gimp_item_set_offset (item, 0, 0);
+
+      if (gimp_item_get_width  (item) != width ||
+          gimp_item_get_height (item) != height)
+        {
+          gimp_item_resize (item, gimp_get_user_context (dest_image->gimp),
+                            GIMP_FILL_TRANSPARENT,
+                            width, height, 0, 0);
+        }
+    }
+
+  GIMP_ITEM_CLASS (parent_class)->convert (item, dest_image, old_type);
+}
+
+static void
+gimp_channel_translate (GimpItem *item,
+                        gdouble   off_x,
+                        gdouble   off_y,
+                        gboolean  push_undo)
+{
+  GimpChannel *channel = GIMP_CHANNEL (item);
+  gint         x, y, width, height;
+
+  gimp_item_bounds (GIMP_ITEM (channel), &x, &y, &width, &height);
+
+  /*  update the old area  */
+  gimp_drawable_update (GIMP_DRAWABLE (item), x, y, width, height);
+
+  if (push_undo)
+    gimp_channel_push_undo (channel, NULL);
+
+  if (gimp_rectangle_intersect (x + SIGNED_ROUND (off_x),
+                                y + SIGNED_ROUND (off_y),
+                                width, height,
+                                0, 0,
+                                gimp_item_get_width  (GIMP_ITEM (channel)),
+                                gimp_item_get_height (GIMP_ITEM (channel)),
+                                &x, &y, &width, &height))
+    {
+      /*  copy the portion of the mask we will keep to a temporary
+       *  buffer
+       */
+      GeglBuffer *tmp_buffer =
+        gegl_buffer_new (GEGL_RECTANGLE (0, 0, width, height),
+                         gimp_drawable_get_format (GIMP_DRAWABLE (channel)));
+
+      gimp_gegl_buffer_copy (gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                             GEGL_RECTANGLE (x - SIGNED_ROUND (off_x),
+                                             y - SIGNED_ROUND (off_y),
+                                             width, height),
+                             GEGL_ABYSS_NONE,
+                             tmp_buffer,
+                             GEGL_RECTANGLE (0, 0, 0, 0));
+
+      /*  clear the mask  */
+      gegl_buffer_clear (gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                         NULL);
+
+      /*  copy the temp mask back to the mask  */
+      gimp_gegl_buffer_copy (tmp_buffer, NULL, GEGL_ABYSS_NONE,
+                             gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                             GEGL_RECTANGLE (x, y, 0, 0));
+
+      /*  free the temporary mask  */
+      g_object_unref (tmp_buffer);
+
+      channel->x1 = x;
+      channel->y1 = y;
+      channel->x2 = x + width;
+      channel->y2 = y + height;
+    }
+  else
+    {
+      /*  clear the mask  */
+      gegl_buffer_clear (gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                         NULL);
+
+      channel->empty = TRUE;
+      channel->x1    = 0;
+      channel->y1    = 0;
+      channel->x2    = gimp_item_get_width  (GIMP_ITEM (channel));
+      channel->y2    = gimp_item_get_height (GIMP_ITEM (channel));
+    }
+
+  /*  update the new area  */
+  gimp_drawable_update (GIMP_DRAWABLE (item),
+                        channel->x1, channel->y1,
+                        channel->x2 - channel->x1,
+                        channel->y2 - channel->y1);
+}
+
+static void
+gimp_channel_scale (GimpItem              *item,
+                    gint                   new_width,
+                    gint                   new_height,
+                    gint                   new_offset_x,
+                    gint                   new_offset_y,
+                    GimpInterpolationType  interpolation_type,
+                    GimpProgress          *progress)
+{
+  GimpChannel *channel = GIMP_CHANNEL (item);
+
+  if (G_TYPE_FROM_INSTANCE (item) == GIMP_TYPE_CHANNEL)
+    {
+      new_offset_x = 0;
+      new_offset_y = 0;
+    }
+
+  /*  don't waste CPU cycles scaling an empty channel  */
+  if (channel->bounds_known && channel->empty)
+    {
+      GimpDrawable *drawable = GIMP_DRAWABLE (item);
+      GeglBuffer   *new_buffer;
+
+      new_buffer =
+        gegl_buffer_new (GEGL_RECTANGLE (0, 0, new_width, new_height),
+                         gimp_drawable_get_format (drawable));
+
+      gimp_drawable_set_buffer_full (drawable,
+                                     gimp_item_is_attached (item), NULL,
+                                     new_buffer,
+                                     GEGL_RECTANGLE (new_offset_x, new_offset_y,
+                                                     0,            0),
+                                     TRUE);
+      g_object_unref (new_buffer);
+
+      gimp_channel_clear (GIMP_CHANNEL (item), NULL, FALSE);
+    }
+  else
+    {
+      GIMP_ITEM_CLASS (parent_class)->scale (item, new_width, new_height,
+                                             new_offset_x, new_offset_y,
+                                             interpolation_type, progress);
+    }
+}
+
+static void
+gimp_channel_resize (GimpItem     *item,
+                     GimpContext  *context,
+                     GimpFillType  fill_type,
+                     gint          new_width,
+                     gint          new_height,
+                     gint          offset_x,
+                     gint          offset_y)
+{
+  GIMP_ITEM_CLASS (parent_class)->resize (item, context, GIMP_FILL_TRANSPARENT,
+                                          new_width, new_height,
+                                          offset_x, offset_y);
+
+  if (G_TYPE_FROM_INSTANCE (item) == GIMP_TYPE_CHANNEL)
+    {
+      gimp_item_set_offset (item, 0, 0);
+    }
+}
+
+static GimpTransformResize
+gimp_channel_get_clip (GimpItem            *item,
+                       GimpTransformResize  clip_result)
+{
+  return GIMP_TRANSFORM_RESIZE_CLIP;
+}
+
+static gboolean
+gimp_channel_fill (GimpItem         *item,
+                   GimpDrawable     *drawable,
+                   GimpFillOptions  *fill_options,
+                   gboolean          push_undo,
+                   GimpProgress     *progress,
+                   GError          **error)
+{
+  GimpChannel        *channel = GIMP_CHANNEL (item);
+  const GimpBoundSeg *segs_in;
+  const GimpBoundSeg *segs_out;
+  gint                n_segs_in;
+  gint                n_segs_out;
+  gint                offset_x, offset_y;
+
+  if (! gimp_channel_boundary (channel, &segs_in, &segs_out,
+                               &n_segs_in, &n_segs_out,
+                               0, 0, 0, 0))
+    {
+      g_set_error_literal (error, GIMP_ERROR, GIMP_FAILED,
+                           _("Cannot fill empty channel."));
+      return FALSE;
+    }
+
+  gimp_item_get_offset (item, &offset_x, &offset_y);
+
+  gimp_drawable_fill_boundary (drawable,
+                               fill_options,
+                               segs_in, n_segs_in,
+                               offset_x, offset_y,
+                               push_undo);
+
+  return TRUE;
+}
+
+static gboolean
+gimp_channel_stroke (GimpItem           *item,
+                     GimpDrawable       *drawable,
+                     GimpStrokeOptions  *stroke_options,
+                     gboolean            push_undo,
+                     GimpProgress       *progress,
+                     GError            **error)
+{
+  GimpChannel        *channel = GIMP_CHANNEL (item);
+  const GimpBoundSeg *segs_in;
+  const GimpBoundSeg *segs_out;
+  gint                n_segs_in;
+  gint                n_segs_out;
+  gboolean            retval = FALSE;
+  gint                offset_x, offset_y;
+
+  if (! gimp_channel_boundary (channel, &segs_in, &segs_out,
+                               &n_segs_in, &n_segs_out,
+                               0, 0, 0, 0))
+    {
+      g_set_error_literal (error, GIMP_ERROR, GIMP_FAILED,
+                           _("Cannot stroke empty channel."));
+      return FALSE;
+    }
+
+  gimp_item_get_offset (item, &offset_x, &offset_y);
+
+  switch (gimp_stroke_options_get_method (stroke_options))
+    {
+    case GIMP_STROKE_LINE:
+      gimp_drawable_stroke_boundary (drawable,
+                                     stroke_options,
+                                     segs_in, n_segs_in,
+                                     offset_x, offset_y,
+                                     push_undo);
+      retval = TRUE;
+      break;
+
+    case GIMP_STROKE_PAINT_METHOD:
+      {
+        GimpPaintInfo    *paint_info;
+        GimpPaintCore    *core;
+        GimpPaintOptions *paint_options;
+        gboolean          emulate_dynamics;
+
+        paint_info = gimp_context_get_paint_info (GIMP_CONTEXT (stroke_options));
+
+        core = g_object_new (paint_info->paint_type, NULL);
+
+        paint_options = gimp_stroke_options_get_paint_options (stroke_options);
+        emulate_dynamics = gimp_stroke_options_get_emulate_dynamics (stroke_options);
+
+        retval = gimp_paint_core_stroke_boundary (core, drawable,
+                                                  paint_options,
+                                                  emulate_dynamics,
+                                                  segs_in, n_segs_in,
+                                                  offset_x, offset_y,
+                                                  push_undo, error);
+
+        g_object_unref (core);
+      }
+      break;
+
+    default:
+      g_return_val_if_reached (FALSE);
+    }
+
+  return retval;
+}
+
+static void
+gimp_channel_to_selection (GimpItem       *item,
+                           GimpChannelOps  op,
+                           gboolean        antialias,
+                           gboolean        feather,
+                           gdouble         feather_radius_x,
+                           gdouble         feather_radius_y)
+{
+  GimpChannel *channel = GIMP_CHANNEL (item);
+  GimpImage   *image   = gimp_item_get_image (item);
+  gint         off_x, off_y;
+
+  gimp_item_get_offset (item, &off_x, &off_y);
+
+  gimp_channel_select_channel (gimp_image_get_mask (image),
+                               GIMP_ITEM_GET_CLASS (item)->to_selection_desc,
+                               channel, off_x, off_y,
+                               op,
+                               feather, feather_radius_x, feather_radius_x);
+}
+
+static void
+gimp_channel_convert_type (GimpDrawable     *drawable,
+                           GimpImage        *dest_image,
+                           const Babl       *new_format,
+                           GimpColorProfile *dest_profile,
+                           GeglDitherMethod  layer_dither_type,
+                           GeglDitherMethod  mask_dither_type,
+                           gboolean          push_undo,
+                           GimpProgress     *progress)
+{
+  GeglBuffer *dest_buffer;
+
+  dest_buffer =
+    gegl_buffer_new (GEGL_RECTANGLE (0, 0,
+                                     gimp_item_get_width  (GIMP_ITEM (drawable)),
+                                     gimp_item_get_height (GIMP_ITEM (drawable))),
+                     new_format);
+
+  if (mask_dither_type == GEGL_DITHER_NONE)
+    {
+      gimp_gegl_buffer_copy (gimp_drawable_get_buffer (drawable), NULL,
+                             GEGL_ABYSS_NONE,
+                             dest_buffer, NULL);
+    }
+  else
+    {
+      gint bits;
+
+      bits = (babl_format_get_bytes_per_pixel (new_format) * 8 /
+              babl_format_get_n_components (new_format));
+
+      gimp_gegl_apply_dither (gimp_drawable_get_buffer (drawable),
+                              NULL, NULL,
+                              dest_buffer, 1 << bits, mask_dither_type);
+    }
+
+  gimp_drawable_set_buffer (drawable, push_undo, NULL, dest_buffer);
+  g_object_unref (dest_buffer);
+}
+
+static void
+gimp_channel_invalidate_boundary (GimpDrawable *drawable)
+{
+  GimpChannel *channel = GIMP_CHANNEL (drawable);
+
+  channel->boundary_known = FALSE;
+  channel->bounds_known   = FALSE;
+}
+
+static void
+gimp_channel_get_active_components (GimpDrawable *drawable,
+                                    gboolean     *active)
+{
+  /*  Make sure that the alpha channel is not valid.  */
+  active[GRAY]    = TRUE;
+  active[ALPHA_G] = FALSE;
+}
+
+static void
+gimp_channel_set_buffer (GimpDrawable        *drawable,
+                         gboolean             push_undo,
+                         const gchar         *undo_desc,
+                         GeglBuffer          *buffer,
+                         const GeglRectangle *bounds)
+{
+  GimpChannel *channel    = GIMP_CHANNEL (drawable);
+  GeglBuffer  *old_buffer = gimp_drawable_get_buffer (drawable);
+
+  if (old_buffer)
+    {
+      g_signal_handlers_disconnect_by_func (old_buffer,
+                                            gimp_channel_buffer_changed,
+                                            channel);
+    }
+
+  GIMP_DRAWABLE_CLASS (parent_class)->set_buffer (drawable,
+                                                  push_undo, undo_desc,
+                                                  buffer, bounds);
+
+  gegl_buffer_signal_connect (buffer, "changed",
+                              G_CALLBACK (gimp_channel_buffer_changed),
+                              channel);
+
+  if (gimp_filter_peek_node (GIMP_FILTER (channel)))
+    {
+      const Babl *color_format;
+
+      if (gimp_drawable_get_linear (drawable))
+        color_format = babl_format ("RGBA float");
+      else
+        color_format = babl_format ("R'G'B'A float");
+
+      gegl_node_set (channel->color_node,
+                     "format", color_format,
+                     NULL);
+    }
+}
+
+static gdouble
+gimp_channel_get_opacity_at (GimpPickable *pickable,
+                             gint          x,
+                             gint          y)
+{
+  GimpChannel *channel = GIMP_CHANNEL (pickable);
+  gdouble      value   = GIMP_OPACITY_TRANSPARENT;
+
+  if (x >= 0 && x < gimp_item_get_width  (GIMP_ITEM (channel)) &&
+      y >= 0 && y < gimp_item_get_height (GIMP_ITEM (channel)))
+    {
+      if (! channel->bounds_known ||
+          (! channel->empty &&
+           x >= channel->x1 &&
+           x <  channel->x2 &&
+           y >= channel->y1 &&
+           y <  channel->y2))
+        {
+          gegl_buffer_sample (gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                              x, y, NULL, &value, babl_format ("Y double"),
+                              GEGL_SAMPLER_NEAREST, GEGL_ABYSS_NONE);
+        }
+    }
+
+  return value;
+}
+
+static gboolean
+gimp_channel_real_boundary (GimpChannel         *channel,
+                            const GimpBoundSeg **segs_in,
+                            const GimpBoundSeg **segs_out,
+                            gint                *num_segs_in,
+                            gint                *num_segs_out,
+                            gint                 x1,
+                            gint                 y1,
+                            gint                 x2,
+                            gint                 y2)
+{
+  if (! channel->boundary_known)
+    {
+      gint x3, y3, x4, y4;
+
+      /* free the out of date boundary segments */
+      g_free (channel->segs_in);
+      g_free (channel->segs_out);
+
+      if (gimp_item_bounds (GIMP_ITEM (channel), &x3, &y3, &x4, &y4))
+        {
+          GeglBuffer    *buffer;
+          GeglRectangle  rect = { x3, y3, x4, y4 };
+
+          x4 += x3;
+          y4 += y3;
+
+          buffer = gimp_drawable_get_buffer (GIMP_DRAWABLE (channel));
+
+          channel->segs_out = gimp_boundary_find (buffer, &rect,
+                                                  babl_format ("Y float"),
+                                                  GIMP_BOUNDARY_IGNORE_BOUNDS,
+                                                  x1, y1, x2, y2,
+                                                  GIMP_BOUNDARY_HALF_WAY,
+                                                  &channel->num_segs_out);
+          x1 = MAX (x1, x3);
+          y1 = MAX (y1, y3);
+          x2 = MIN (x2, x4);
+          y2 = MIN (y2, y4);
+
+          if (x2 > x1 && y2 > y1)
+            {
+              channel->segs_in = gimp_boundary_find (buffer, NULL,
+                                                     babl_format ("Y float"),
+                                                     GIMP_BOUNDARY_WITHIN_BOUNDS,
+                                                     x1, y1, x2, y2,
+                                                     GIMP_BOUNDARY_HALF_WAY,
+                                                     &channel->num_segs_in);
+            }
+          else
+            {
+              channel->segs_in     = NULL;
+              channel->num_segs_in = 0;
+            }
+        }
+      else
+        {
+          channel->segs_in      = NULL;
+          channel->segs_out     = NULL;
+          channel->num_segs_in  = 0;
+          channel->num_segs_out = 0;
+        }
+
+      channel->boundary_known = TRUE;
+    }
+
+  *segs_in      = channel->segs_in;
+  *segs_out     = channel->segs_out;
+  *num_segs_in  = channel->num_segs_in;
+  *num_segs_out = channel->num_segs_out;
+
+  return (! channel->empty);
+}
+
+static gboolean
+gimp_channel_real_is_empty (GimpChannel *channel)
+{
+  GeglBuffer *buffer;
+
+  if (channel->bounds_known)
+    return channel->empty;
+
+  buffer = gimp_drawable_get_buffer (GIMP_DRAWABLE (channel));
+
+  if (! gimp_gegl_mask_is_empty (buffer))
+    return FALSE;
+
+  /*  The mask is empty, meaning we can set the bounds as known  */
+  g_clear_pointer (&channel->segs_in,  g_free);
+  g_clear_pointer (&channel->segs_out, g_free);
+
+  channel->empty          = TRUE;
+  channel->num_segs_in    = 0;
+  channel->num_segs_out   = 0;
+  channel->bounds_known   = TRUE;
+  channel->boundary_known = TRUE;
+  channel->x1             = 0;
+  channel->y1             = 0;
+  channel->x2             = gimp_item_get_width  (GIMP_ITEM (channel));
+  channel->y2             = gimp_item_get_height (GIMP_ITEM (channel));
+
+  return TRUE;
+}
+
+static void
+gimp_channel_real_feather (GimpChannel *channel,
+                           gdouble      radius_x,
+                           gdouble      radius_y,
+                           gboolean     edge_lock,
+                           gboolean     push_undo)
+{
+  gint x1, y1, x2, y2;
+
+  if (radius_x <= 0.0 && radius_y <= 0.0)
+    return;
+
+  if (! gimp_item_bounds (GIMP_ITEM (channel), &x1, &y1, &x2, &y2))
+    return;
+
+  x2 += x1;
+  y2 += y1;
+
+  if (gimp_channel_is_empty (channel))
+    return;
+
+  x1 = MAX (0, x1 - ceil (radius_x));
+  y1 = MAX (0, y1 - ceil (radius_y));
+
+  x2 = MIN (gimp_item_get_width  (GIMP_ITEM (channel)), x2 + ceil (radius_x));
+  y2 = MIN (gimp_item_get_height (GIMP_ITEM (channel)), y2 + ceil (radius_y));
+
+  if (push_undo)
+    gimp_channel_push_undo (channel,
+                            GIMP_CHANNEL_GET_CLASS (channel)->feather_desc);
+
+  gimp_gegl_apply_feather (gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                           NULL, NULL,
+                           gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                           GEGL_RECTANGLE (x1, y1, x2 - x1, y2 - y1),
+                           radius_x,
+                           radius_y,
+                           edge_lock);
+
+  gimp_drawable_update (GIMP_DRAWABLE (channel), 0, 0, -1, -1);
+}
+
+static void
+gimp_channel_real_sharpen (GimpChannel *channel,
+                           gboolean     push_undo)
+{
+  GimpDrawable *drawable = GIMP_DRAWABLE (channel);
+
+  if (push_undo)
+    gimp_channel_push_undo (channel,
+                            GIMP_CHANNEL_GET_CLASS (channel)->sharpen_desc);
+
+  gimp_gegl_apply_threshold (gimp_drawable_get_buffer (drawable),
+                             NULL, NULL,
+                             gimp_drawable_get_buffer (drawable),
+                             0.5);
+
+  gimp_drawable_update (GIMP_DRAWABLE (channel), 0, 0, -1, -1);
+}
+
+static void
+gimp_channel_real_clear (GimpChannel *channel,
+                         const gchar *undo_desc,
+                         gboolean     push_undo)
+{
+  GeglBuffer    *buffer;
+  GeglRectangle  rect;
+  GeglRectangle  aligned_rect;
+
+  if (channel->bounds_known && channel->empty)
+    return;
+
+  if (push_undo)
+    {
+      if (! undo_desc)
+        undo_desc = GIMP_CHANNEL_GET_CLASS (channel)->clear_desc;
+
+      gimp_channel_push_undo (channel, undo_desc);
+    }
+
+  buffer = gimp_drawable_get_buffer (GIMP_DRAWABLE (channel));
+
+  if (channel->bounds_known)
+    {
+      rect.x      = channel->x1;
+      rect.y      = channel->y1;
+      rect.width  = channel->x2 - channel->x1;
+      rect.height = channel->y2 - channel->y1;
+    }
+  else
+    {
+      rect.x      = 0;
+      rect.y      = 0;
+      rect.width  = gimp_item_get_width  (GIMP_ITEM (channel));
+      rect.height = gimp_item_get_height (GIMP_ITEM (channel));
+    }
+
+  gegl_rectangle_align_to_buffer (&aligned_rect, &rect, buffer,
+                                  GEGL_RECTANGLE_ALIGNMENT_SUPERSET);
+
+  gegl_buffer_clear (buffer, &aligned_rect);
+
+  /*  we know the bounds  */
+  channel->bounds_known = TRUE;
+  channel->empty        = TRUE;
+  channel->x1           = 0;
+  channel->y1           = 0;
+  channel->x2           = gimp_item_get_width  (GIMP_ITEM (channel));
+  channel->y2           = gimp_item_get_height (GIMP_ITEM (channel));
+
+  gimp_drawable_update (GIMP_DRAWABLE (channel),
+                        rect.x, rect.y, rect.width, rect.height);
+}
+
+static void
+gimp_channel_real_all (GimpChannel *channel,
+                       gboolean     push_undo)
+{
+  GeglColor *color;
+
+  if (push_undo)
+    gimp_channel_push_undo (channel,
+                            GIMP_CHANNEL_GET_CLASS (channel)->all_desc);
+
+  /*  clear the channel  */
+  color = gegl_color_new ("#fff");
+  gegl_buffer_set_color (gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                         NULL, color);
+  g_object_unref (color);
+
+  /*  we know the bounds  */
+  channel->bounds_known = TRUE;
+  channel->empty        = FALSE;
+  channel->x1           = 0;
+  channel->y1           = 0;
+  channel->x2           = gimp_item_get_width  (GIMP_ITEM (channel));
+  channel->y2           = gimp_item_get_height (GIMP_ITEM (channel));
+
+  gimp_drawable_update (GIMP_DRAWABLE (channel), 0, 0, -1, -1);
+}
+
+static void
+gimp_channel_real_invert (GimpChannel *channel,
+                          gboolean     push_undo)
+{
+  GimpDrawable *drawable = GIMP_DRAWABLE (channel);
+
+  if (push_undo)
+    gimp_channel_push_undo (channel,
+                            GIMP_CHANNEL_GET_CLASS (channel)->invert_desc);
+
+  if (channel->bounds_known && channel->empty)
+    {
+      gimp_channel_all (channel, FALSE);
+    }
+  else
+    {
+      gimp_gegl_apply_invert_linear (gimp_drawable_get_buffer (drawable),
+                                     NULL, NULL,
+                                     gimp_drawable_get_buffer (drawable));
+
+      gimp_drawable_update (GIMP_DRAWABLE (channel), 0, 0, -1, -1);
+    }
+}
+
+static void
+gimp_channel_real_border (GimpChannel            *channel,
+                          gint                    radius_x,
+                          gint                    radius_y,
+                          GimpChannelBorderStyle  style,
+                          gboolean                edge_lock,
+                          gboolean                push_undo)
+{
+  gint x1, y1, x2, y2;
+
+  if (radius_x == 0 && radius_y == 0)
+    {
+      /* The relevant GEGL operations require radius_x and radius_y to be > 0.
+       * When both are 0 (currently can only be achieved by the user through
+       * PDB), the effect should be to clear the channel.
+       */
+      gimp_channel_clear (channel,
+                          GIMP_CHANNEL_GET_CLASS (channel)->border_desc,
+                          push_undo);
+      return;
+    }
+  else if (radius_x <= 0 || radius_y <= 0)
+    {
+      /* FIXME: Implement the case where only one of radius_x and radius_y is 0.
+       * Currently, should never happen.
+       */
+      g_return_if_reached();
+    }
+
+  if (! gimp_item_bounds (GIMP_ITEM (channel), &x1, &y1, &x2, &y2))
+    return;
+
+  x2 += x1;
+  y2 += y1;
+
+  if (gimp_channel_is_empty (channel))
+    return;
+
+  if (x1 - radius_x < 0)
+    x1 = 0;
+  else
+    x1 -= radius_x;
+
+  if (x2 + radius_x > gimp_item_get_width (GIMP_ITEM (channel)))
+    x2 = gimp_item_get_width (GIMP_ITEM (channel));
+  else
+    x2 += radius_x;
+
+  if (y1 - radius_y < 0)
+    y1 = 0;
+  else
+    y1 -= radius_y;
+
+  if (y2 + radius_y > gimp_item_get_height (GIMP_ITEM (channel)))
+    y2 = gimp_item_get_height (GIMP_ITEM (channel));
+  else
+    y2 += radius_y;
+
+  if (push_undo)
+    gimp_channel_push_undo (channel,
+                            GIMP_CHANNEL_GET_CLASS (channel)->border_desc);
+
+  gimp_gegl_apply_border (gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                          NULL, NULL,
+                          gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                          GEGL_RECTANGLE (x1, y1, x2 - x1, y2 - y1),
+                          radius_x, radius_y, style, edge_lock);
+
+  gimp_drawable_update (GIMP_DRAWABLE (channel), 0, 0, -1, -1);
+}
+
+static void
+gimp_channel_real_grow (GimpChannel *channel,
+                        gint         radius_x,
+                        gint         radius_y,
+                        gboolean     push_undo)
+{
+  gint x1, y1, x2, y2;
+
+  if (radius_x == 0 && radius_y == 0)
+    return;
+
+  if (radius_x <= 0 && radius_y <= 0)
+    {
+      gimp_channel_shrink (channel, -radius_x, -radius_y, FALSE, push_undo);
+      return;
+    }
+
+  if (radius_x < 0 || radius_y < 0)
+    return;
+
+  if (! gimp_item_bounds (GIMP_ITEM (channel), &x1, &y1, &x2, &y2))
+    return;
+
+  x2 += x1;
+  y2 += y1;
+
+  if (gimp_channel_is_empty (channel))
+    return;
+
+  if (x1 - radius_x > 0)
+    x1 = x1 - radius_x;
+  else
+    x1 = 0;
+
+  if (y1 - radius_y > 0)
+    y1 = y1 - radius_y;
+  else
+    y1 = 0;
+
+  if (x2 + radius_x < gimp_item_get_width (GIMP_ITEM (channel)))
+    x2 = x2 + radius_x;
+  else
+    x2 = gimp_item_get_width (GIMP_ITEM (channel));
+
+  if (y2 + radius_y < gimp_item_get_height (GIMP_ITEM (channel)))
+    y2 = y2 + radius_y;
+  else
+    y2 = gimp_item_get_height (GIMP_ITEM (channel));
+
+  if (push_undo)
+    gimp_channel_push_undo (channel,
+                            GIMP_CHANNEL_GET_CLASS (channel)->grow_desc);
+
+  gimp_gegl_apply_grow (gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                        NULL, NULL,
+                        gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                        GEGL_RECTANGLE (x1, y1, x2 - x1, y2 - y1),
+                        radius_x, radius_y);
+
+  gimp_drawable_update (GIMP_DRAWABLE (channel), 0, 0, -1, -1);
+}
+
+static void
+gimp_channel_real_shrink (GimpChannel *channel,
+                          gint         radius_x,
+                          gint         radius_y,
+                          gboolean     edge_lock,
+                          gboolean     push_undo)
+{
+  gint x1, y1, x2, y2;
+
+  if (radius_x == 0 && radius_y == 0)
+    return;
+
+  if (radius_x <= 0 && radius_y <= 0)
+    {
+      gimp_channel_grow (channel, -radius_x, -radius_y, push_undo);
+      return;
+    }
+
+  if (radius_x < 0 || radius_y < 0)
+    return;
+
+  if (! gimp_item_bounds (GIMP_ITEM (channel), &x1, &y1, &x2, &y2))
+    return;
+
+  x2 += x1;
+  y2 += y1;
+
+  if (gimp_channel_is_empty (channel))
+    return;
+
+  if (x1 > 0)
+    x1--;
+  if (y1 > 0)
+    y1--;
+  if (x2 < gimp_item_get_width (GIMP_ITEM (channel)))
+    x2++;
+  if (y2 < gimp_item_get_height (GIMP_ITEM (channel)))
+    y2++;
+
+  if (push_undo)
+    gimp_channel_push_undo (channel,
+                            GIMP_CHANNEL_GET_CLASS (channel)->shrink_desc);
+
+  gimp_gegl_apply_shrink (gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                          NULL, NULL,
+                          gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                          GEGL_RECTANGLE (x1, y1, x2 - x1, y2 - y1),
+                          radius_x, radius_y, edge_lock);
+
+  gimp_drawable_update (GIMP_DRAWABLE (channel), 0, 0, -1, -1);
+}
+
+static void
+gimp_channel_real_flood (GimpChannel *channel,
+                         gboolean     push_undo)
+{
+  gint x, y, width, height;
+
+  if (! gimp_item_bounds (GIMP_ITEM (channel), &x, &y, &width, &height))
+    return;
+
+  if (gimp_channel_is_empty (channel))
+    return;
+
+  if (push_undo)
+    gimp_channel_push_undo (channel,
+                            GIMP_CHANNEL_GET_CLASS (channel)->flood_desc);
+
+  gimp_gegl_apply_flood (gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                         NULL, NULL,
+                         gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                         GEGL_RECTANGLE (x, y, width, height));
+
+  gimp_drawable_update (GIMP_DRAWABLE (channel), x, y, width, height);
+}
+
+static void
+gimp_channel_buffer_changed (GeglBuffer          *buffer,
+                             const GeglRectangle *rect,
+                             GimpChannel         *channel)
+{
+  gimp_drawable_invalidate_boundary (GIMP_DRAWABLE (channel));
+}
+
+
+/*  public functions  */
+
+GimpChannel *
+gimp_channel_new (GimpImage     *image,
+                  gint           width,
+                  gint           height,
+                  const gchar   *name,
+                  const GimpRGB *color)
+{
+  GimpChannel *channel;
+
+  g_return_val_if_fail (GIMP_IS_IMAGE (image), NULL);
+
+  channel =
+    GIMP_CHANNEL (gimp_drawable_new (GIMP_TYPE_CHANNEL,
+                                     image, name,
+                                     0, 0, width, height,
+                                     gimp_image_get_channel_format (image)));
+
+  if (color)
+    channel->color = *color;
+
+  channel->show_masked = TRUE;
+
+  /*  selection mask variables  */
+  channel->x2          = width;
+  channel->y2          = height;
+
+  return channel;
+}
+
+GimpChannel *
+gimp_channel_new_from_buffer (GimpImage     *image,
+                              GeglBuffer    *buffer,
+                              const gchar   *name,
+                              const GimpRGB *color)
+{
+  GimpChannel *channel;
+  GeglBuffer  *dest;
+
+  g_return_val_if_fail (GIMP_IS_IMAGE (image), NULL);
+  g_return_val_if_fail (GEGL_IS_BUFFER (buffer), NULL);
+
+  channel = gimp_channel_new (image,
+                              gegl_buffer_get_width  (buffer),
+                              gegl_buffer_get_height (buffer),
+                              name, color);
+
+  dest = gimp_drawable_get_buffer (GIMP_DRAWABLE (channel));
+  gimp_gegl_buffer_copy (buffer, NULL, GEGL_ABYSS_NONE, dest, NULL);
+
+  return channel;
+}
+
+GimpChannel *
+gimp_channel_new_from_alpha (GimpImage     *image,
+                             GimpDrawable  *drawable,
+                             const gchar   *name,
+                             const GimpRGB *color)
+{
+  GimpChannel *channel;
+  GeglBuffer  *dest_buffer;
+  gint         width;
+  gint         height;
+
+  g_return_val_if_fail (GIMP_IS_IMAGE (image), NULL);
+  g_return_val_if_fail (GIMP_IS_DRAWABLE (drawable), NULL);
+  g_return_val_if_fail (gimp_drawable_has_alpha (drawable), NULL);
+
+  width  = gimp_item_get_width  (GIMP_ITEM (drawable));
+  height = gimp_item_get_height (GIMP_ITEM (drawable));
+
+  channel = gimp_channel_new (image, width, height, name, color);
+
+  gimp_channel_clear (channel, NULL, FALSE);
+
+  dest_buffer = gimp_drawable_get_buffer (GIMP_DRAWABLE (channel));
+
+  gegl_buffer_set_format (dest_buffer,
+                          gimp_drawable_get_component_format (drawable,
+                                                              GIMP_CHANNEL_ALPHA));
+  gimp_gegl_buffer_copy (gimp_drawable_get_buffer (drawable), NULL,
+                         GEGL_ABYSS_NONE,
+                         dest_buffer, NULL);
+  gegl_buffer_set_format (dest_buffer, NULL);
+
+  return channel;
+}
+
+GimpChannel *
+gimp_channel_new_from_component (GimpImage       *image,
+                                 GimpChannelType  type,
+                                 const gchar     *name,
+                                 const GimpRGB   *color)
+{
+  GimpChannel *channel;
+  GeglBuffer  *src_buffer;
+  GeglBuffer  *dest_buffer;
+  gint         width;
+  gint         height;
+  const Babl  *format;
+
+  g_return_val_if_fail (GIMP_IS_IMAGE (image), NULL);
+
+  format = gimp_image_get_component_format (image, type);
+
+  g_return_val_if_fail (format != NULL, NULL);
+
+  gimp_pickable_flush (GIMP_PICKABLE (image));
+
+  src_buffer = gimp_pickable_get_buffer (GIMP_PICKABLE (image));
+  width  = gegl_buffer_get_width  (src_buffer);
+  height = gegl_buffer_get_height (src_buffer);
+
+  channel = gimp_channel_new (image, width, height, name, color);
+
+  dest_buffer = gimp_drawable_get_buffer (GIMP_DRAWABLE (channel));
+
+  gegl_buffer_set_format (dest_buffer, format);
+  gimp_gegl_buffer_copy (src_buffer, NULL, GEGL_ABYSS_NONE, dest_buffer, NULL);
+  gegl_buffer_set_format (dest_buffer, NULL);
+
+  return channel;
+}
+
+GimpChannel *
+gimp_channel_get_parent (GimpChannel *channel)
+{
+  g_return_val_if_fail (GIMP_IS_CHANNEL (channel), NULL);
+
+  return GIMP_CHANNEL (gimp_viewable_get_parent (GIMP_VIEWABLE (channel)));
+}
+
+void
+gimp_channel_set_color (GimpChannel   *channel,
+                        const GimpRGB *color,
+                        gboolean       push_undo)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+  g_return_if_fail (color != NULL);
+
+  if (gimp_rgba_distance (&channel->color, color) > RGBA_EPSILON)
+    {
+      if (push_undo && gimp_item_is_attached (GIMP_ITEM (channel)))
+        {
+          GimpImage *image = gimp_item_get_image (GIMP_ITEM (channel));
+
+          gimp_image_undo_push_channel_color (image, C_("undo-type", "Set Channel Color"),
+                                              channel);
+        }
+
+      channel->color = *color;
+
+      if (gimp_filter_peek_node (GIMP_FILTER (channel)))
+        {
+          gimp_gegl_node_set_color (channel->color_node,
+                                    &channel->color);
+        }
+
+      gimp_drawable_update (GIMP_DRAWABLE (channel), 0, 0, -1, -1);
+
+      g_signal_emit (channel, channel_signals[COLOR_CHANGED], 0);
+    }
+}
+
+void
+gimp_channel_get_color (GimpChannel *channel,
+                        GimpRGB     *color)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+  g_return_if_fail (color != NULL);
+
+  *color = channel->color;
+}
+
+gdouble
+gimp_channel_get_opacity (GimpChannel *channel)
+{
+  g_return_val_if_fail (GIMP_IS_CHANNEL (channel), GIMP_OPACITY_TRANSPARENT);
+
+  return channel->color.a;
+}
+
+void
+gimp_channel_set_opacity (GimpChannel *channel,
+                          gdouble      opacity,
+                          gboolean     push_undo)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+
+  opacity = CLAMP (opacity, GIMP_OPACITY_TRANSPARENT, GIMP_OPACITY_OPAQUE);
+
+  if (channel->color.a != opacity)
+    {
+      if (push_undo && gimp_item_is_attached (GIMP_ITEM (channel)))
+        {
+          GimpImage *image = gimp_item_get_image (GIMP_ITEM (channel));
+
+          gimp_image_undo_push_channel_color (image, C_("undo-type", "Set Channel Opacity"),
+                                              channel);
+        }
+
+      channel->color.a = opacity;
+
+      if (gimp_filter_peek_node (GIMP_FILTER (channel)))
+        {
+          gimp_gegl_node_set_color (channel->color_node,
+                                    &channel->color);
+        }
+
+      gimp_drawable_update (GIMP_DRAWABLE (channel), 0, 0, -1, -1);
+
+      g_signal_emit (channel, channel_signals[COLOR_CHANGED], 0);
+    }
+}
+
+gboolean
+gimp_channel_get_show_masked (GimpChannel *channel)
+{
+  g_return_val_if_fail (GIMP_IS_CHANNEL (channel), FALSE);
+
+  return channel->show_masked;
+}
+
+void
+gimp_channel_set_show_masked (GimpChannel *channel,
+                              gboolean     show_masked)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+
+  if (show_masked != channel->show_masked)
+    {
+      channel->show_masked = show_masked ? TRUE : FALSE;
+
+      if (channel->invert_node)
+        {
+          GeglNode *source;
+
+          source = gimp_drawable_get_source_node (GIMP_DRAWABLE (channel));
+
+          if (channel->show_masked)
+            {
+              gegl_node_connect_to (source,               "output",
+                                    channel->invert_node, "input");
+              gegl_node_connect_to (channel->invert_node, "output",
+                                    channel->mask_node,   "aux");
+            }
+          else
+            {
+              gegl_node_disconnect (channel->invert_node, "input");
+
+              gegl_node_connect_to (source,             "output",
+                                    channel->mask_node, "aux");
+            }
+        }
+
+      gimp_drawable_update (GIMP_DRAWABLE (channel), 0, 0, -1, -1);
+    }
+}
+
+void
+gimp_channel_push_undo (GimpChannel *channel,
+                        const gchar *undo_desc)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+  g_return_if_fail (gimp_item_is_attached (GIMP_ITEM (channel)));
+
+  gimp_image_undo_push_mask (gimp_item_get_image (GIMP_ITEM (channel)),
+                             undo_desc, channel);
+}
+
+
+/******************************/
+/*  selection mask functions  */
+/******************************/
+
+GimpChannel *
+gimp_channel_new_mask (GimpImage *image,
+                       gint       width,
+                       gint       height)
+{
+  GimpChannel *channel;
+
+  g_return_val_if_fail (GIMP_IS_IMAGE (image), NULL);
+
+  channel =
+    GIMP_CHANNEL (gimp_drawable_new (GIMP_TYPE_CHANNEL,
+                                     image, _("Selection Mask"),
+                                     0, 0, width, height,
+                                     gimp_image_get_mask_format (image)));
+
+  channel->show_masked = TRUE;
+  channel->x2          = width;
+  channel->y2          = height;
+
+  gegl_buffer_clear (gimp_drawable_get_buffer (GIMP_DRAWABLE (channel)),
+                     NULL);
+
+  return channel;
+}
+
+gboolean
+gimp_channel_boundary (GimpChannel         *channel,
+                       const GimpBoundSeg **segs_in,
+                       const GimpBoundSeg **segs_out,
+                       gint                *num_segs_in,
+                       gint                *num_segs_out,
+                       gint                 x1,
+                       gint                 y1,
+                       gint                 x2,
+                       gint                 y2)
+{
+  g_return_val_if_fail (GIMP_IS_CHANNEL (channel), FALSE);
+  g_return_val_if_fail (segs_in != NULL, FALSE);
+  g_return_val_if_fail (segs_out != NULL, FALSE);
+  g_return_val_if_fail (num_segs_in != NULL, FALSE);
+  g_return_val_if_fail (num_segs_out != NULL, FALSE);
+
+  return GIMP_CHANNEL_GET_CLASS (channel)->boundary (channel,
+                                                     segs_in, segs_out,
+                                                     num_segs_in, num_segs_out,
+                                                     x1, y1,
+                                                     x2, y2);
+}
+
+gboolean
+gimp_channel_is_empty (GimpChannel *channel)
+{
+  g_return_val_if_fail (GIMP_IS_CHANNEL (channel), FALSE);
+
+  return GIMP_CHANNEL_GET_CLASS (channel)->is_empty (channel);
+}
+
+void
+gimp_channel_feather (GimpChannel *channel,
+                      gdouble      radius_x,
+                      gdouble      radius_y,
+                      gboolean     edge_lock,
+                      gboolean     push_undo)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+
+  if (! gimp_item_is_attached (GIMP_ITEM (channel)))
+    push_undo = FALSE;
+
+  GIMP_CHANNEL_GET_CLASS (channel)->feather (channel, radius_x, radius_y,
+                                             edge_lock, push_undo);
+}
+
+void
+gimp_channel_sharpen (GimpChannel *channel,
+                      gboolean     push_undo)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+
+  if (! gimp_item_is_attached (GIMP_ITEM (channel)))
+    push_undo = FALSE;
+
+  GIMP_CHANNEL_GET_CLASS (channel)->sharpen (channel, push_undo);
+}
+
+void
+gimp_channel_clear (GimpChannel *channel,
+                    const gchar *undo_desc,
+                    gboolean     push_undo)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+
+  if (! gimp_item_is_attached (GIMP_ITEM (channel)))
+    push_undo = FALSE;
+
+  GIMP_CHANNEL_GET_CLASS (channel)->clear (channel, undo_desc, push_undo);
+}
+
+void
+gimp_channel_all (GimpChannel *channel,
+                  gboolean     push_undo)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+
+  if (! gimp_item_is_attached (GIMP_ITEM (channel)))
+    push_undo = FALSE;
+
+  GIMP_CHANNEL_GET_CLASS (channel)->all (channel, push_undo);
+}
+
+void
+gimp_channel_invert (GimpChannel *channel,
+                     gboolean     push_undo)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+
+  if (! gimp_item_is_attached (GIMP_ITEM (channel)))
+    push_undo = FALSE;
+
+  GIMP_CHANNEL_GET_CLASS (channel)->invert (channel, push_undo);
+}
+
+void
+gimp_channel_border (GimpChannel            *channel,
+                     gint                    radius_x,
+                     gint                    radius_y,
+                     GimpChannelBorderStyle  style,
+                     gboolean                edge_lock,
+                     gboolean                push_undo)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+
+  if (! gimp_item_is_attached (GIMP_ITEM (channel)))
+    push_undo = FALSE;
+
+  GIMP_CHANNEL_GET_CLASS (channel)->border (channel,
+                                            radius_x, radius_y, style, edge_lock,
+                                            push_undo);
+}
+
+void
+gimp_channel_grow (GimpChannel *channel,
+                   gint         radius_x,
+                   gint         radius_y,
+                   gboolean     push_undo)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+
+  if (! gimp_item_is_attached (GIMP_ITEM (channel)))
+    push_undo = FALSE;
+
+  GIMP_CHANNEL_GET_CLASS (channel)->grow (channel, radius_x, radius_y,
+                                          push_undo);
+}
+
+void
+gimp_channel_shrink (GimpChannel  *channel,
+                     gint          radius_x,
+                     gint          radius_y,
+                     gboolean      edge_lock,
+                     gboolean      push_undo)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+
+  if (! gimp_item_is_attached (GIMP_ITEM (channel)))
+    push_undo = FALSE;
+
+  GIMP_CHANNEL_GET_CLASS (channel)->shrink (channel, radius_x, radius_y,
+                                            edge_lock, push_undo);
+}
+
+void
+gimp_channel_flood (GimpChannel *channel,
+                    gboolean     push_undo)
+{
+  g_return_if_fail (GIMP_IS_CHANNEL (channel));
+
+  if (! gimp_item_is_attached (GIMP_ITEM (channel)))
+    push_undo = FALSE;
+
+  GIMP_CHANNEL_GET_CLASS (channel)->flood (channel, push_undo);
+}