config: Add options to auto-scale imported layers

If enabled in Preferences, any image that's
dragged into an existing canvas (or
explicitly opened as a layer) will be scaled
to fit the current canvas size.

app/config/gimpcoreconfig.c

@@ -112,6 +112,7 @@ enum
   PROP_IMPORT_PROMOTE_FLOAT,
   PROP_IMPORT_PROMOTE_DITHER,
   PROP_IMPORT_ADD_ALPHA,
+  PROP_IMPORT_RESIZE_LAYERS,
   PROP_IMPORT_RAW_PLUG_IN,
   PROP_EXPORT_FILE_TYPE,
   PROP_EXPORT_COLOR_PROFILE,
@@ -724,6 +725,13 @@ gimp_core_config_class_init (GimpCoreConfigClass *klass)
                             FALSE,
                             GIMP_PARAM_STATIC_STRINGS);
 
+  GIMP_CONFIG_PROP_BOOLEAN (object_class, PROP_IMPORT_RESIZE_LAYERS,
+                            "import-resize-layers",
+                            "Import resize layers",
+                            IMPORT_RESIZE_LAYERS_BLURB,
+                            TRUE,
+                            GIMP_PARAM_STATIC_STRINGS);
+
   GIMP_CONFIG_PROP_PATH (object_class, PROP_IMPORT_RAW_PLUG_IN,
                          "import-raw-plug-in",
                          "Import raw plug-in",
@@ -1142,6 +1150,9 @@ gimp_core_config_set_property (GObject      *object,
     case PROP_IMPORT_ADD_ALPHA:
       core_config->import_add_alpha = g_value_get_boolean (value);
       break;
+    case PROP_IMPORT_RESIZE_LAYERS:
+      core_config->import_resize_layers = g_value_get_boolean (value);
+      break;
     case PROP_IMPORT_RAW_PLUG_IN:
       g_free (core_config->import_raw_plug_in);
       core_config->import_raw_plug_in = g_value_dup_string (value);
@@ -1408,6 +1419,9 @@ gimp_core_config_get_property (GObject    *object,
     case PROP_IMPORT_ADD_ALPHA:
       g_value_set_boolean (value, core_config->import_add_alpha);
       break;
+    case PROP_IMPORT_RESIZE_LAYERS:
+      g_value_set_boolean (value, core_config->import_resize_layers);
+      break;
     case PROP_IMPORT_RAW_PLUG_IN:
       g_value_set_string (value, core_config->import_raw_plug_in);
       break;

app/config/gimpcoreconfig.h

@@ -96,6 +96,7 @@ struct _GimpCoreConfig
   gboolean                import_promote_float;
   gboolean                import_promote_dither;
   gboolean                import_add_alpha;
+  gboolean                import_resize_layers;
   gchar                  *import_raw_plug_in;
   GimpExportFileType      export_file_type;
   gboolean                export_color_profile;

app/config/gimprc-blurbs.h

@@ -223,6 +223,10 @@ _("When promoting imported images to floating point precision, also add " \
 #define IMPORT_ADD_ALPHA_BLURB \
 _("Add an alpha channel to all layers of imported images.")
 
+#define IMPORT_RESIZE_LAYERS_BLURB \
+_("Resize imported layers to fit the existing image, retaining the " \
+  "imported layers' aspect ratio.")
+
 #define IMPORT_RAW_PLUG_IN_BLURB \
 _("Which plug-in to use for importing raw digital camera files.")
 

app/dialogs/preferences-dialog.c

@@ -1591,6 +1591,11 @@ prefs_dialog_new (Gimp       *gimp,
                                    _("_Add an alpha channel to imported images"),
                                    GTK_BOX (vbox2));
 
+  button = prefs_check_button_add (object, "import-resize-layers",
+                                   _("Resi_ze imported layers to fit the "
+                                     "existing canvas"),
+                                   GTK_BOX (vbox2));
+
   grid = prefs_grid_new (GTK_CONTAINER (vbox2));
   button = prefs_enum_combo_box_add (object, "color-profile-policy", 0, 0,
                                      _("Color _profile policy:"),

app/file/file-open.c

@@ -29,6 +29,8 @@
 
 #include "gegl/gimp-babl.h"
 
+#include "config/gimpcoreconfig.h"
+
 #include "core/gimp.h"
 #include "core/gimpcontext.h"
 #include "core/gimpdocumentlist.h"
@@ -630,7 +632,57 @@ file_open_layers (Gimp                *gimp,
 
       if (layers)
         {
-          gchar *basename;
+          GimpCoreConfig *config = dest_image->gimp->config;
+          gchar          *basename;
+
+          /* Scale imported layers to fit existing canvas.
+           * Adapted from ofnut's ofn-autoscale-layer.py */
+          if (config->import_resize_layers)
+            {
+              GList                *list;
+              gint                  image_width;
+              gint                  image_height;
+              gdouble               image_ratio;
+
+              image_width  = gimp_image_get_width (dest_image);
+              image_height = gimp_image_get_height (dest_image);
+
+              image_ratio = (gdouble) image_width / (gdouble) image_height;
+
+              for (list = layers; list; list = g_list_next (list))
+                {
+                  gdouble layer_ratio;
+                  gint    layer_width;
+                  gint    layer_height;
+                  gint    resized_width;
+                  gint    resized_height;
+
+                  layer_width  = gimp_item_get_width (GIMP_ITEM (list->data));
+                  layer_height = gimp_item_get_height (GIMP_ITEM (list->data));
+
+                  layer_ratio = (gdouble) layer_width / (gdouble) layer_height;
+
+                  if (layer_ratio > image_ratio)
+                    {
+                      resized_width = image_width;
+                      resized_height = image_width / layer_ratio;
+                    }
+                  else
+                    {
+                      resized_width = image_height * layer_ratio;
+                      resized_height = image_height;
+                    }
+
+                  gimp_item_scale_by_origin (GIMP_ITEM (list->data),
+                                             resized_width, resized_height,
+                                             config->interpolation_type,
+                                             progress, FALSE);
+                  gimp_item_set_offset (GIMP_ITEM (list->data),
+                                        (image_width / resized_width) / 2,
+                                        (image_height / resized_height) / 2);
+                }
+
+            }
 
           basename = g_path_get_basename (gimp_file_get_utf8_name (file));
           file_open_convert_items (dest_image, basename, layers);