gimp/libgimp/gimpexport.c

/* LIBGIMP - The GIMP Library
 * Copyright (C) 1995-1997 Peter Mattis and Spencer Kimball
 *
 * gimpexport.c
 * Copyright (C) 1999-2004 Sven Neumann <sven@gimp.org>
 *
 * This library is free software: you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 3 of the License, or (at your option) any later version.
 *
 * This library 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library.  If not, see
 * <https://www.gnu.org/licenses/>.
 */

#include "config.h"

#include <string.h>

#include <gtk/gtk.h>

#include "gimp.h"
#include "gimpui.h"

#include "libgimp-intl.h"


/**
 * SECTION: gimpexport
 * @title: gimpexport
 * @short_description: Export an image before it is saved.
 *
 * This function should be called by all save_plugins unless they are
 * able to save all image formats GIMP knows about. It takes care of
 * asking the user if she wishes to export the image to a format the
 * save_plugin can handle. It then performs the necessary conversions
 * (e.g. Flatten) on a copy of the image so that the image can be
 * saved without changing the original image.
 *
 * The capabilities of the save_plugin are specified by combining
 * #GimpExportCapabilities using a bitwise OR.
 *
 * Make sure you have initialized GTK+ before you call this function
 * as it will most probably have to open a dialog.
 **/


typedef void (* ExportFunc) (GimpImage    *image,
                             GList       **drawables);


/* the export action structure */
typedef struct
{
  ExportFunc   default_action;
  ExportFunc   alt_action;
  const gchar *reason;
  const gchar *possibilities[2];
  gint         choice;
} ExportAction;


/* the functions that do the actual export */

static void
export_merge (GimpImage  *image,
              GList     **drawables)
{
  GList  *layers;
  GList  *iter;
  gint32  nvisible = 0;

  layers = gimp_image_list_layers (image);

  for (iter = layers; iter; iter = g_list_next (iter))
    {
      if (gimp_item_get_visible (GIMP_ITEM (iter->data)))
        nvisible++;
    }

  if (nvisible <= 1)
    {
      GimpLayer     *transp;
      GimpImageType  layer_type;

      /* if there is only one (or zero) visible layer, add a new
       * transparent layer that has the same size as the canvas.  The
       * merge that follows will ensure that the offset, opacity and
       * size are correct
       */
      switch (gimp_image_get_base_type (image))
        {
        case GIMP_RGB:
          layer_type = GIMP_RGBA_IMAGE;
          break;
        case GIMP_GRAY:
          layer_type = GIMP_GRAYA_IMAGE;
          break;
        case GIMP_INDEXED:
          layer_type = GIMP_INDEXEDA_IMAGE;
          break;
        default:
          /* In case we add a new type in future. */
          g_return_if_reached ();
        }
      transp = gimp_layer_new (image, "-",
                               gimp_image_get_width (image),
                               gimp_image_get_height (image),
                               layer_type,
                               100.0, GIMP_LAYER_MODE_NORMAL);
      gimp_image_insert_layer (image, transp, NULL, 1);
      gimp_selection_none (image);
      gimp_drawable_edit_clear (GIMP_DRAWABLE (transp));
      nvisible++;
    }

  if (nvisible > 1)
    {
      GimpLayer *merged;

      merged = gimp_image_merge_visible_layers (image, GIMP_CLIP_TO_IMAGE);

      g_return_if_fail (merged != NULL);

      *drawables = g_list_prepend (NULL, merged);

      g_list_free (layers);

      layers = gimp_image_list_layers (image);

      /*  make sure that the merged drawable matches the image size  */
      if (gimp_drawable_get_width   (GIMP_DRAWABLE (merged)) !=
          gimp_image_get_width  (image) ||
          gimp_drawable_get_height  (GIMP_DRAWABLE (merged)) !=
          gimp_image_get_height (image))
        {
          gint off_x, off_y;

          gimp_drawable_get_offsets (GIMP_DRAWABLE (merged), &off_x, &off_y);
          gimp_layer_resize (merged,
                             gimp_image_get_width (image),
                             gimp_image_get_height (image),
                             off_x, off_y);
        }
    }

  /* remove any remaining (invisible) layers */
  for (iter = layers; iter; iter = iter->next)
    {
      if (! g_list_find (*drawables, iter->data))
        gimp_image_remove_layer (image, iter->data);
    }

  g_list_free (layers);
}

static void
export_flatten (GimpImage  *image,
                GList     **drawables)
{
  GimpLayer *flattened;

  flattened = gimp_image_flatten (image);

  if (flattened != NULL)
    *drawables = g_list_prepend (NULL, flattened);
}

static void
export_remove_alpha (GimpImage  *image,
                     GList     **drawables)
{
  GList  *layers;
  GList  *iter;

  layers = gimp_image_list_layers (image);

  for (iter = layers; iter; iter = iter->next)
    {
      if (gimp_drawable_has_alpha (GIMP_DRAWABLE (iter->data)))
        gimp_layer_flatten (iter->data);
    }

  g_list_free (layers);
}

static void
export_apply_masks (GimpImage  *image,
                    GList     **drawables)
{
  GList  *layers;
  GList  *iter;

  layers = gimp_image_list_layers (image);

  for (iter = layers; iter; iter = iter->next)
    {
      GimpLayerMask *mask;

      mask = gimp_layer_get_mask (iter->data);

      if (mask)
        {
          /* we can't apply the mask directly to a layer group, so merge it
           * first
           */
          if (gimp_item_is_group (iter->data))
            iter->data = gimp_image_merge_layer_group (image, iter->data);

          gimp_layer_remove_mask (iter->data, GIMP_MASK_APPLY);
        }
    }

  g_list_free (layers);
}

static void
export_convert_rgb (GimpImage  *image,
                    GList     **drawables)
{
  gimp_image_convert_rgb (image);
}

static void
export_convert_grayscale (GimpImage  *image,
                          GList     **drawables)
{
  gimp_image_convert_grayscale (image);
}

static void
export_convert_indexed (GimpImage  *image,
                        GList     **drawables)
{
  GList    *layers;
  GList    *iter;
  gboolean  has_alpha = FALSE;

  /* check alpha */
  layers = gimp_image_list_layers (image);

  for (iter = *drawables; iter; iter = iter->next)
    {
      if (gimp_drawable_has_alpha (iter->data))
        {
          has_alpha = TRUE;
          break;
        }
    }

  if (layers || has_alpha)
    gimp_image_convert_indexed (image,
                                GIMP_CONVERT_DITHER_NONE,
                                GIMP_CONVERT_PALETTE_GENERATE,
                                255, FALSE, FALSE, "");
  else
    gimp_image_convert_indexed (image,
                                GIMP_CONVERT_DITHER_NONE,
                                GIMP_CONVERT_PALETTE_GENERATE,
                                256, FALSE, FALSE, "");
  g_list_free (layers);
}

static void
export_convert_bitmap (GimpImage  *image,
                       GList     **drawables)
{
  if (gimp_image_get_base_type (image) == GIMP_INDEXED)
    gimp_image_convert_rgb (image);

  gimp_image_convert_indexed (image,
                              GIMP_CONVERT_DITHER_FS,
                              GIMP_CONVERT_PALETTE_GENERATE,
                              2, FALSE, FALSE, "");
}

static void
export_add_alpha (GimpImage  *image,
                  GList     **drawables)
{
  GList  *layers;
  GList  *iter;

  layers = gimp_image_list_layers (image);

  for (iter = layers; iter; iter = iter->next)
    {
      if (! gimp_drawable_has_alpha (GIMP_DRAWABLE (iter->data)))
        gimp_layer_add_alpha (GIMP_LAYER (iter->data));
    }

  g_list_free (layers);
}

static void
export_crop_image (GimpImage  *image,
                   GList     **drawables)
{
  gimp_image_crop (image,
                   gimp_image_get_width  (image),
                   gimp_image_get_height (image),
                   0, 0);
}

static void
export_resize_image (GimpImage  *image,
                     GList     **drawables)
{
  gimp_image_resize_to_layers (image);
}

static void
export_void (GimpImage  *image,
             GList     **drawables)
{
  /* do nothing */
}


/* a set of predefined actions */

static ExportAction export_action_merge =
{
  export_merge,
  NULL,
  N_("%s plug-in can't handle layers"),
  { N_("Merge Visible Layers"), NULL },
  0
};

static ExportAction export_action_merge_single =
{
  export_merge,
  NULL,
  N_("%s plug-in can't handle layer offsets, size or opacity"),
  { N_("Merge Visible Layers"), NULL },
  0
};

static ExportAction export_action_animate_or_merge =
{
  NULL,
  export_merge,
  N_("%s plug-in can only handle layers as animation frames"),
  { N_("Save as Animation"), N_("Merge Visible Layers") },
  0
};

static ExportAction export_action_animate_or_flatten =
{
  NULL,
  export_flatten,
  N_("%s plug-in can only handle layers as animation frames"),
  { N_("Save as Animation"), N_("Flatten Image") },
  0
};

static ExportAction export_action_merge_or_flatten =
{
  export_flatten,
  export_merge,
  N_("%s plug-in can't handle layers"),
  { N_("Flatten Image"), N_("Merge Visible Layers") },
  1
};

static ExportAction export_action_flatten =
{
  export_flatten,
  NULL,
  N_("%s plug-in can't handle transparency"),
  { N_("Flatten Image"), NULL },
  0
};

static ExportAction export_action_remove_alpha =
{
  export_remove_alpha,
  NULL,
  N_("%s plug-in can't handle transparent layers"),
  { N_("Flatten Image"), NULL },
  0
};

static ExportAction export_action_apply_masks =
{
  export_apply_masks,
  NULL,
  N_("%s plug-in can't handle layer masks"),
  { N_("Apply Layer Masks"), NULL },
  0
};

static ExportAction export_action_convert_rgb =
{
  export_convert_rgb,
  NULL,
  N_("%s plug-in can only handle RGB images"),
  { N_("Convert to RGB"), NULL },
  0
};

static ExportAction export_action_convert_grayscale =
{
  export_convert_grayscale,
  NULL,
  N_("%s plug-in can only handle grayscale images"),
  { N_("Convert to Grayscale"), NULL },
  0
};

static ExportAction export_action_convert_indexed =
{
  export_convert_indexed,
  NULL,
  N_("%s plug-in can only handle indexed images"),
  { N_("Convert to Indexed using default settings\n"
       "(Do it manually to tune the result)"), NULL },
  0
};

static ExportAction export_action_convert_bitmap =
{
  export_convert_bitmap,
  NULL,
  N_("%s plug-in can only handle bitmap (two color) indexed images"),
  { N_("Convert to Indexed using bitmap default settings\n"
       "(Do it manually to tune the result)"), NULL },
  0
};

static ExportAction export_action_convert_rgb_or_grayscale =
{
  export_convert_rgb,
  export_convert_grayscale,
  N_("%s plug-in can only handle RGB or grayscale images"),
  { N_("Convert to RGB"), N_("Convert to Grayscale")},
  0
};

static ExportAction export_action_convert_rgb_or_indexed =
{
  export_convert_rgb,
  export_convert_indexed,
  N_("%s plug-in can only handle RGB or indexed images"),
  { N_("Convert to RGB"), N_("Convert to Indexed using default settings\n"
                             "(Do it manually to tune the result)")},
  0
};

static ExportAction export_action_convert_indexed_or_grayscale =
{
  export_convert_indexed,
  export_convert_grayscale,
  N_("%s plug-in can only handle grayscale or indexed images"),
  { N_("Convert to Indexed using default settings\n"
       "(Do it manually to tune the result)"),
    N_("Convert to Grayscale") },
  0
};

static ExportAction export_action_add_alpha =
{
  export_add_alpha,
  NULL,
  N_("%s plug-in needs an alpha channel"),
  { N_("Add Alpha Channel"), NULL},
  0
};

static ExportAction export_action_crop_or_resize =
{
  export_crop_image,
  export_resize_image,
  N_("%s plug-in needs to crop the layers to the image bounds"),
  { N_("Crop Layers"), N_("Resize Image to Layers")},
  0
};


static ExportFunc
export_action_get_func (const ExportAction *action)
{
  if (action->choice == 0 && action->default_action)
    {
      return action->default_action;
    }

  if (action->choice == 1 && action->alt_action)
    {
      return action->alt_action;
    }

  return export_void;
}

static void
export_action_perform (const ExportAction *action,
                       GimpImage          *image,
                       GList             **drawables)
{
  export_action_get_func (action) (image, drawables);
}


/* dialog functions */

static void
export_toggle_callback (GtkWidget *widget,
                        gpointer   data)
{
  gint *choice = (gint *) data;

  if (gtk_toggle_button_get_active (GTK_TOGGLE_BUTTON (widget)))
    *choice = FALSE;
  else
    *choice = TRUE;
}

static GimpExportReturn
confirm_save_dialog (const gchar *message,
                     const gchar *format_name)
{
  GtkWidget        *dialog;
  GtkWidget        *hbox;
  GtkWidget        *image;
  GtkWidget        *main_vbox;
  GtkWidget        *label;
  gchar            *text;
  GimpExportReturn  retval;

  g_return_val_if_fail (message != NULL, GIMP_EXPORT_CANCEL);
  g_return_val_if_fail (format_name != NULL, GIMP_EXPORT_CANCEL);

  dialog = gimp_dialog_new (_("Confirm Save"), "gimp-export-image-confirm",
                            NULL, 0,
                            gimp_standard_help_func,
                            "gimp-export-confirm-dialog",

                            _("_Cancel"),  GTK_RESPONSE_CANCEL,
                            _("C_onfirm"), GTK_RESPONSE_OK,

                            NULL);

  gimp_dialog_set_alternative_button_order (GTK_DIALOG (dialog),
                                           GTK_RESPONSE_OK,
                                           GTK_RESPONSE_CANCEL,
                                           -1);

  gtk_window_set_resizable (GTK_WINDOW (dialog), FALSE);
  gimp_window_set_transient (GTK_WINDOW (dialog));

  hbox = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 12);
  gtk_box_pack_start (GTK_BOX (gtk_dialog_get_content_area (GTK_DIALOG (dialog))),
                      hbox, TRUE, TRUE, 0);
  gtk_container_set_border_width (GTK_CONTAINER (hbox), 12);
  gtk_widget_show (hbox);

  image = gtk_image_new_from_icon_name ("dialog-warning",
                                        GTK_ICON_SIZE_DIALOG);
  gtk_widget_set_valign (image, GTK_ALIGN_START);
  gtk_box_pack_start (GTK_BOX (hbox), image, FALSE, FALSE, 0);
  gtk_widget_show (image);

  main_vbox = gtk_box_new (GTK_ORIENTATION_VERTICAL, 12);
  gtk_box_pack_start (GTK_BOX (hbox), main_vbox, FALSE, FALSE, 0);
  gtk_widget_show (main_vbox);

  text = g_strdup_printf (message, format_name);
  label = gtk_label_new (text);
  g_free (text);

  gimp_label_set_attributes (GTK_LABEL (label),
                             PANGO_ATTR_SCALE,  PANGO_SCALE_LARGE,
                             PANGO_ATTR_WEIGHT, PANGO_WEIGHT_BOLD,
                             -1);
  gtk_label_set_xalign (GTK_LABEL (label), 0.0);
  gtk_label_set_line_wrap (GTK_LABEL (label), TRUE);
  gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_LEFT);
  gtk_box_pack_start (GTK_BOX (main_vbox), label, FALSE, FALSE, 0);
  gtk_widget_show (label);

  gtk_widget_show (dialog);

  switch (gimp_dialog_run (GIMP_DIALOG (dialog)))
    {
    case GTK_RESPONSE_OK:
      retval = GIMP_EXPORT_EXPORT;
      break;

    default:
      retval = GIMP_EXPORT_CANCEL;
      break;
    }

  gtk_widget_destroy (dialog);

  return retval;
}

static GimpExportReturn
export_dialog (GSList      *actions,
               const gchar *format_name)
{
  GtkWidget        *dialog;
  GtkWidget        *hbox;
  GtkWidget        *image;
  GtkWidget        *main_vbox;
  GtkWidget        *label;
  GSList           *list;
  gchar            *text;
  GimpExportReturn  retval;

  g_return_val_if_fail (actions != NULL, GIMP_EXPORT_CANCEL);
  g_return_val_if_fail (format_name != NULL, GIMP_EXPORT_CANCEL);

  dialog = gimp_dialog_new (_("Export File"), "gimp-export-image",
                            NULL, 0,
                            gimp_standard_help_func, "gimp-export-dialog",

                            _("_Ignore"), GTK_RESPONSE_NO,
                            _("_Cancel"), GTK_RESPONSE_CANCEL,
                            _("_Export"), GTK_RESPONSE_OK,

                            NULL);

  gimp_dialog_set_alternative_button_order (GTK_DIALOG (dialog),
                                           GTK_RESPONSE_NO,
                                           GTK_RESPONSE_OK,
                                           GTK_RESPONSE_CANCEL,
                                           -1);

  gtk_window_set_resizable (GTK_WINDOW (dialog), FALSE);
  gimp_window_set_transient (GTK_WINDOW (dialog));

  hbox = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 12);
  gtk_box_pack_start (GTK_BOX (gtk_dialog_get_content_area (GTK_DIALOG (dialog))),
                      hbox, TRUE, TRUE, 0);
  gtk_container_set_border_width (GTK_CONTAINER (hbox), 12);
  gtk_widget_show (hbox);

  image = gtk_image_new_from_icon_name ("dialog-information",
                                        GTK_ICON_SIZE_DIALOG);
  gtk_widget_set_valign (image, GTK_ALIGN_START);
  gtk_box_pack_start (GTK_BOX (hbox), image, FALSE, FALSE, 0);
  gtk_widget_show (image);

  main_vbox = gtk_box_new (GTK_ORIENTATION_VERTICAL, 12);
  gtk_box_pack_start (GTK_BOX (hbox), main_vbox, FALSE, FALSE, 0);
  gtk_widget_show (main_vbox);

  /* the headline */
  text = g_strdup_printf (_("Your image should be exported before it "
                            "can be saved as %s for the following reasons:"),
                          format_name);
  label = gtk_label_new (text);
  g_free (text);

  gimp_label_set_attributes (GTK_LABEL (label),
                             PANGO_ATTR_SCALE,  PANGO_SCALE_LARGE,
                             -1);
  gtk_label_set_xalign (GTK_LABEL (label), 0.0);
  gtk_label_set_line_wrap (GTK_LABEL (label), TRUE);
  gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_LEFT);
  gtk_box_pack_start (GTK_BOX (main_vbox), label, FALSE, FALSE, 0);
  gtk_widget_show (label);

  for (list = actions; list; list = g_slist_next (list))
    {
      ExportAction *action = list->data;
      GtkWidget    *frame;
      GtkWidget    *vbox;

      text = g_strdup_printf (gettext (action->reason), format_name);
      frame = gimp_frame_new (text);
      g_free (text);

      gtk_box_pack_start (GTK_BOX (main_vbox), frame, FALSE, FALSE, 0);
      gtk_widget_show (frame);

      vbox = gtk_box_new (GTK_ORIENTATION_VERTICAL, 6);
      gtk_container_add (GTK_CONTAINER (frame), vbox);

      if (action->possibilities[0] && action->possibilities[1])
        {
          GtkWidget *button;
          GSList    *radio_group = NULL;

          button = gtk_radio_button_new_with_label (radio_group,
                                                    gettext (action->possibilities[0]));
          gtk_label_set_justify (GTK_LABEL (gtk_bin_get_child (GTK_BIN (button))),
                                 GTK_JUSTIFY_LEFT);
          radio_group = gtk_radio_button_get_group (GTK_RADIO_BUTTON (button));
          gtk_box_pack_start (GTK_BOX (vbox), button, FALSE, FALSE, 0);
          g_signal_connect (button, "toggled",
                            G_CALLBACK (export_toggle_callback),
                            &action->choice);
          gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (button),
                                        (action->choice == 0));
          gtk_widget_show (button);

          button = gtk_radio_button_new_with_label (radio_group,
                                                    gettext (action->possibilities[1]));
          gtk_label_set_justify (GTK_LABEL (gtk_bin_get_child (GTK_BIN (button))),
                                 GTK_JUSTIFY_LEFT);
          radio_group = gtk_radio_button_get_group (GTK_RADIO_BUTTON (button));
          gtk_box_pack_start (GTK_BOX (vbox), button, FALSE, FALSE, 0);
          gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (button),
                                        (action->choice == 1));
          gtk_widget_show (button);
        }
      else if (action->possibilities[0])
        {
          label = gtk_label_new (gettext (action->possibilities[0]));
          gtk_label_set_xalign (GTK_LABEL (label), 0.0);
          gtk_label_set_line_wrap (GTK_LABEL (label), TRUE);
          gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_LEFT);
          gtk_box_pack_start (GTK_BOX (vbox), label, FALSE, FALSE, 0);
          gtk_widget_show (label);
          action->choice = 0;
        }

      gtk_widget_show (vbox);
    }

  /* the footline */
  label = gtk_label_new (_("The export conversion won't modify your "
                           "original image."));
  gimp_label_set_attributes (GTK_LABEL (label),
                             PANGO_ATTR_STYLE, PANGO_STYLE_ITALIC,
                             -1);
  gtk_label_set_xalign (GTK_LABEL (label), 0.0);
  gtk_label_set_line_wrap (GTK_LABEL (label), TRUE);
  gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_LEFT);
  gtk_box_pack_start (GTK_BOX (main_vbox), label, FALSE, FALSE, 0);
  gtk_widget_show (label);

  gtk_widget_show (dialog);

  switch (gimp_dialog_run (GIMP_DIALOG (dialog)))
    {
    case GTK_RESPONSE_OK:
      retval = GIMP_EXPORT_EXPORT;
      break;

    case GTK_RESPONSE_NO:
      retval = GIMP_EXPORT_IGNORE;
      break;

    default:
      retval = GIMP_EXPORT_CANCEL;
      break;
    }

  gtk_widget_destroy (dialog);

  return retval;
}

/**
 * gimp_export_image:
 * @image:        Pointer to the image.
 * @n_drawables:  Size of @drawables.
 * @drawables: (array length=n_drawables): Array of pointers to drawables.
 * @format_name:  The (short) name of the image_format (e.g. JPEG or GIF).
 * @capabilities: What can the image_format do?
 *
 * Takes an image and a drawable to be saved together with a
 * description of the capabilities of the image_format. If the
 * type of image doesn't match the capabilities of the format
 * a dialog is opened that informs the user that the image has
 * to be exported and offers to do the necessary conversions.
 *
 * If the user chooses to export the image, a copy is created.
 * This copy is then converted, @image and @drawables are changed to
 * point to the new image and the procedure returns GIMP_EXPORT_EXPORT.
 * The save_plugin has to take care of deleting the created image using
 * gimp_image_delete() and the drawables list with g_free() once the
 * image has been saved.
 *
 * If the user chooses to Ignore the export problem, @image and
 * @drawables are not altered, GIMP_EXPORT_IGNORE is returned and the
 * save_plugin should try to save the original image. If the user
 * chooses Cancel, GIMP_EXPORT_CANCEL is returned and the save_plugin
 * should quit itself with status %GIMP_PDB_CANCEL.
 *
 * If @format_name is NULL, no dialogs will be shown and this function
 * will behave as if the user clicked on the 'Export' button, if a
 * dialog would have been shown.
 *
 * Returns: An enum of #GimpExportReturn describing the user_action.
 **/
GimpExportReturn
gimp_export_image (GimpImage               **image,
                   gint                     *n_drawables,
                   GimpDrawable           ***drawables,
                   const gchar              *format_name,
                   GimpExportCapabilities    capabilities)
{
  GSList            *actions = NULL;
  GimpImageBaseType  type;
  GList             *layers;
  GList             *iter;
  GType              drawables_type       = G_TYPE_NONE;
  gboolean           interactive          = FALSE;
  gboolean           added_flatten        = FALSE;
  gboolean           has_layer_masks      = FALSE;
  gboolean           background_has_alpha = TRUE;
  GimpExportReturn   retval               = GIMP_EXPORT_CANCEL;
  gint               i;

  g_return_val_if_fail (gimp_image_is_valid (*image) && drawables &&
                        n_drawables && *n_drawables > 0, FALSE);

  for (i = 0; i < *n_drawables; i++)
    {
      g_return_val_if_fail (gimp_item_is_valid (GIMP_ITEM ((*drawables)[i])), FALSE);

      if (drawables_type == G_TYPE_NONE ||
          g_type_is_a (drawables_type, G_OBJECT_TYPE ((*drawables)[i])))
        drawables_type = G_OBJECT_TYPE ((*drawables)[i]);
      else
        g_return_val_if_fail (g_type_is_a (G_OBJECT_TYPE ((*drawables)[i]), drawables_type), FALSE);
    }

  /* do some sanity checks */
  if (capabilities & GIMP_EXPORT_NEEDS_ALPHA)
    capabilities |= GIMP_EXPORT_CAN_HANDLE_ALPHA;

  if (capabilities & GIMP_EXPORT_CAN_HANDLE_LAYERS_AS_ANIMATION)
    capabilities |= GIMP_EXPORT_CAN_HANDLE_LAYERS;

  if (capabilities & GIMP_EXPORT_CAN_HANDLE_LAYER_MASKS)
    capabilities |= GIMP_EXPORT_CAN_HANDLE_LAYERS;

  if (format_name && g_getenv ("GIMP_INTERACTIVE_EXPORT"))
    interactive = TRUE;

  /* ask for confirmation if the user is not saving a layer (see bug #51114) */
  if (interactive &&
      ! g_type_is_a (drawables_type, GIMP_TYPE_LAYER) &&
      ! (capabilities & GIMP_EXPORT_CAN_HANDLE_LAYERS))
    {
      if (g_type_is_a (drawables_type, GIMP_TYPE_LAYER_MASK))
        {
          retval = confirm_save_dialog
            (_("You are about to save a layer mask as %s.\n"
               "This will not save the visible layers."), format_name);
        }
      else if (g_type_is_a (drawables_type, GIMP_TYPE_CHANNEL))
        {
          retval = confirm_save_dialog
            (_("You are about to save a channel (saved selection) as %s.\n"
               "This will not save the visible layers."), format_name);
        }
      else
        {
          /* this should not happen */
          g_warning ("%s: unknown drawable type!", G_STRFUNC);
        }

      /* cancel - the user can then select an appropriate layer to save */
      if (retval == GIMP_EXPORT_CANCEL)
        return GIMP_EXPORT_CANCEL;
    }


  /* check alpha and layer masks */
  layers = gimp_image_list_layers (*image);

  for (iter = layers; iter; iter = iter->next)
    {
      GimpLayer *layer = GIMP_LAYER (iter->data);

      if (gimp_drawable_has_alpha (GIMP_DRAWABLE (layer)))
        {
          if (! (capabilities & GIMP_EXPORT_CAN_HANDLE_ALPHA))
            {
              if (! (capabilities & GIMP_EXPORT_CAN_HANDLE_LAYERS))
                {
                  actions = g_slist_prepend (actions, &export_action_flatten);
                  added_flatten = TRUE;
                  break;
                }
              else
                {
                  actions = g_slist_prepend (actions, &export_action_remove_alpha);
                  break;
                }
            }
        }
      else
        {
          /*  If this is the last layer, it's visible and has no alpha
           *  channel, then the image has a "flat" background
           */
          if (iter->next == NULL && gimp_item_get_visible (GIMP_ITEM (layer)))
            background_has_alpha = FALSE;

          if (capabilities & GIMP_EXPORT_NEEDS_ALPHA)
            {
              actions = g_slist_prepend (actions, &export_action_add_alpha);
              break;
            }
        }
    }

  if (! added_flatten)
    {
      for (iter = layers; iter; iter = iter->next)
        {
          if (gimp_layer_get_mask (iter->data))
            has_layer_masks = TRUE;
        }
    }

  if (! added_flatten)
    {
      GimpLayer *layer = GIMP_LAYER (layers->data);
      GList     *children;

      children = gimp_item_list_children (GIMP_ITEM (layer));

      if ((capabilities & GIMP_EXPORT_CAN_HANDLE_LAYERS) &&
          (capabilities & GIMP_EXPORT_NEEDS_CROP))
        {
          GeglRectangle image_bounds;
          gboolean      needs_crop = FALSE;

          image_bounds.x      = 0;
          image_bounds.y      = 0;
          image_bounds.width  = gimp_image_get_width  (*image);
          image_bounds.height = gimp_image_get_height (*image);

          for (iter = layers; iter; iter = iter->next)
            {
              GimpDrawable  *drawable = iter->data;
              GeglRectangle  layer_bounds;

              gimp_drawable_get_offsets (drawable,
                                     &layer_bounds.x, &layer_bounds.y);

              layer_bounds.width  = gimp_drawable_get_width  (drawable);
              layer_bounds.height = gimp_drawable_get_height (drawable);

              if (! gegl_rectangle_contains (&image_bounds, &layer_bounds))
                {
                  needs_crop = TRUE;

                  break;
                }
            }

          if (needs_crop)
            {
              actions = g_slist_prepend (actions,
                                         &export_action_crop_or_resize);
            }
        }

      /* check if layer size != canvas size, opacity != 100%, or offsets != 0 */
      if (g_list_length (layers) == 1       &&
          ! children                        &&
          g_type_is_a (drawables_type, GIMP_TYPE_LAYER) &&
          ! (capabilities & GIMP_EXPORT_CAN_HANDLE_LAYERS))
        {
          GimpDrawable *drawable = (*drawables)[0];
          gint          offset_x;
          gint          offset_y;

          gimp_drawable_get_offsets (drawable, &offset_x, &offset_y);

          if ((gimp_layer_get_opacity (GIMP_LAYER (drawable)) < 100.0) ||
              (gimp_image_get_width (*image) !=
               gimp_drawable_get_width (drawable))            ||
              (gimp_image_get_height (*image) !=
               gimp_drawable_get_height (drawable))           ||
              offset_x || offset_y)
            {
              if (capabilities & GIMP_EXPORT_CAN_HANDLE_ALPHA)
                {
                  actions = g_slist_prepend (actions,
                                             &export_action_merge_single);
                }
              else
                {
                  actions = g_slist_prepend (actions,
                                             &export_action_flatten);
                }
            }
        }
      /* check multiple layers */
      else if (layers && layers->next != NULL)
        {
          if (capabilities & GIMP_EXPORT_CAN_HANDLE_LAYERS_AS_ANIMATION)
            {
              if (background_has_alpha ||
                  capabilities & GIMP_EXPORT_NEEDS_ALPHA)
                actions = g_slist_prepend (actions,
                                           &export_action_animate_or_merge);
              else
                actions = g_slist_prepend (actions,
                                           &export_action_animate_or_flatten);
            }
          else if (! (capabilities & GIMP_EXPORT_CAN_HANDLE_LAYERS))
            {
              if (capabilities & GIMP_EXPORT_NEEDS_ALPHA)
                actions = g_slist_prepend (actions,
                                           &export_action_merge);
              else
                actions = g_slist_prepend (actions,
                                           &export_action_merge_or_flatten);
            }
        }
      /* check for a single toplevel layer group */
      else if (children)
        {
          if (! (capabilities & GIMP_EXPORT_CAN_HANDLE_LAYERS))
            {
              if (capabilities & GIMP_EXPORT_NEEDS_ALPHA)
                actions = g_slist_prepend (actions,
                                           &export_action_merge);
              else
                actions = g_slist_prepend (actions,
                                           &export_action_merge_or_flatten);
            }
        }

      g_list_free (children);

      /* check layer masks */
      if (has_layer_masks &&
          ! (capabilities & GIMP_EXPORT_CAN_HANDLE_LAYER_MASKS))
        actions = g_slist_prepend (actions, &export_action_apply_masks);
    }

  g_list_free (layers);

  /* check the image type */
  type = gimp_image_get_base_type (*image);
  switch (type)
    {
    case GIMP_RGB:
      if (! (capabilities & GIMP_EXPORT_CAN_HANDLE_RGB))
        {
          if ((capabilities & GIMP_EXPORT_CAN_HANDLE_INDEXED) &&
              (capabilities & GIMP_EXPORT_CAN_HANDLE_GRAY))
            actions = g_slist_prepend (actions,
                                       &export_action_convert_indexed_or_grayscale);
          else if (capabilities & GIMP_EXPORT_CAN_HANDLE_INDEXED)
            actions = g_slist_prepend (actions,
                                       &export_action_convert_indexed);
          else if (capabilities & GIMP_EXPORT_CAN_HANDLE_GRAY)
            actions = g_slist_prepend (actions,
                                       &export_action_convert_grayscale);
          else if (capabilities & GIMP_EXPORT_CAN_HANDLE_BITMAP)
            actions = g_slist_prepend (actions,
                                       &export_action_convert_bitmap);
        }
      break;

    case GIMP_GRAY:
      if (! (capabilities & GIMP_EXPORT_CAN_HANDLE_GRAY))
        {
          if ((capabilities & GIMP_EXPORT_CAN_HANDLE_RGB) &&
              (capabilities & GIMP_EXPORT_CAN_HANDLE_INDEXED))
            actions = g_slist_prepend (actions,
                                       &export_action_convert_rgb_or_indexed);
          else if (capabilities & GIMP_EXPORT_CAN_HANDLE_RGB)
            actions = g_slist_prepend (actions,
                                       &export_action_convert_rgb);
          else if (capabilities & GIMP_EXPORT_CAN_HANDLE_INDEXED)
            actions = g_slist_prepend (actions,
                                       &export_action_convert_indexed);
          else if (capabilities & GIMP_EXPORT_CAN_HANDLE_BITMAP)
            actions = g_slist_prepend (actions,
                                       &export_action_convert_bitmap);
        }
      break;

    case GIMP_INDEXED:
      if (! (capabilities & GIMP_EXPORT_CAN_HANDLE_INDEXED))
        {
          if ((capabilities & GIMP_EXPORT_CAN_HANDLE_RGB) &&
              (capabilities & GIMP_EXPORT_CAN_HANDLE_GRAY))
            actions = g_slist_prepend (actions,
                                       &export_action_convert_rgb_or_grayscale);
          else if (capabilities & GIMP_EXPORT_CAN_HANDLE_RGB)
            actions = g_slist_prepend (actions,
                                       &export_action_convert_rgb);
          else if (capabilities & GIMP_EXPORT_CAN_HANDLE_GRAY)
            actions = g_slist_prepend (actions,
                                       &export_action_convert_grayscale);
          else if (capabilities & GIMP_EXPORT_CAN_HANDLE_BITMAP)
            {
              gint n_colors;

              g_free (gimp_image_get_colormap (*image, NULL, &n_colors));

              if (n_colors > 2)
                actions = g_slist_prepend (actions,
                                           &export_action_convert_bitmap);
            }
        }
      break;
    }

  if (actions)
    {
      actions = g_slist_reverse (actions);

      if (interactive)
        retval = export_dialog (actions, format_name);
      else
        retval = GIMP_EXPORT_EXPORT;
    }
  else
    {
      retval = GIMP_EXPORT_IGNORE;
    }

  if (retval == GIMP_EXPORT_EXPORT)
    {
      GSList *list;
      GList  *drawables_in;
      GList  *drawables_out;
      gint    i;

      *image = gimp_image_duplicate (*image);
      drawables_in  = gimp_image_list_selected_layers (*image);
      drawables_out = drawables_in;

      gimp_image_undo_disable (*image);

      for (list = actions; list; list = list->next)
        {
          export_action_perform (list->data, *image, &drawables_out);

          if (drawables_in != drawables_out)
            {
              g_list_free (drawables_in);
              drawables_in = drawables_out;
            }
        }

      *n_drawables = g_list_length (drawables_out);
      *drawables = g_new (GimpDrawable *, *n_drawables);
      for (iter = drawables_out, i = 0; iter; iter = iter->next, i++)
        (*drawables)[i] = iter->data;

      g_list_free (drawables_out);
    }

  g_slist_free (actions);

  return retval;
}

/**
 * gimp_export_dialog_new:
 * @format_name: The short name of the image_format (e.g. JPEG or PNG).
 * @role:        The dialog's @role which will be set with
 *               gtk_window_set_role().
 * @help_id:     The GIMP help id.
 *
 * Creates a new export dialog. All file plug-ins should use this
 * dialog to get a consistent look on the export dialogs. Use
 * gimp_export_dialog_get_content_area() to get a vertical #GtkBox to be
 * filled with export options. The export dialog is a wrapped
 * #GimpDialog.
 *
 * The dialog response when the user clicks on the Export button is
 * %GTK_RESPONSE_OK, and when the Cancel button is clicked it is
 * %GTK_RESPONSE_CANCEL.
 *
 * Returns: (transfer full): The new export dialog.
 *
 * Since: 2.8
 **/
GtkWidget *
gimp_export_dialog_new (const gchar *format_name,
                        const gchar *role,
                        const gchar *help_id)
{
  GtkWidget *dialog;
  /* TRANSLATORS: the %s parameter is an image format name (ex: PNG). */
  gchar     *title  = g_strdup_printf (_("Export Image as %s"), format_name);

  dialog = gimp_dialog_new (title, role,
                            NULL, 0,
                            gimp_standard_help_func, help_id,

                            _("_Cancel"), GTK_RESPONSE_CANCEL,
                            _("_Export"), GTK_RESPONSE_OK,

                            NULL);

  gimp_dialog_set_alternative_button_order (GTK_DIALOG (dialog),
                                           GTK_RESPONSE_OK,
                                           GTK_RESPONSE_CANCEL,
                                           -1);

  gimp_window_set_transient (GTK_WINDOW (dialog));

  g_free (title);

  return dialog;
}

/**
 * gimp_export_dialog_get_content_area:
 * @dialog: A dialog created with gimp_export_dialog_new()
 *
 * Returns the vertical #GtkBox of the passed export dialog to be filled with
 * export options.
 *
 * Returns: (transfer none): The #GtkBox to fill with export options.
 *
 * Since: 2.8
 **/
GtkWidget *
gimp_export_dialog_get_content_area (GtkWidget *dialog)
{
  return gtk_dialog_get_content_area (GTK_DIALOG (dialog));
}