[gimp] plug-ins: add a Lua goat-exercise.

[Jehan <jehanp src gnome org>]

commit a09b7a9c92a2a8dfddf31023898f1b8de4e7d081
Author: Jehan <jehan girinstud io>
Date:   Fri Aug 16 16:57:34 2019 +0200

    plug-ins: add a Lua goat-exercise.
    
    It is working fine except that it crashes at the end when running
    procedure:new_return_values(). I have not understood why yet, but it may
    be a bug in lua LGI. Maybe we'll have to create the returned
    GimpValueArray by hand in Lua.
    Also the dialog does not show the source yet.
    
    This is not installed yet (and lua interpreter is not checked at
    configure) because of these issues which I will have to figure out. In
    the meantime, I commit this work-in-progress.

 plug-ins/goat-exercises/goat-exercise-lua.lua | 163 ++++++++++++++++++++++++++
 1 file changed, 163 insertions(+)
---
diff --git a/plug-ins/goat-exercises/goat-exercise-lua.lua b/plug-ins/goat-exercises/goat-exercise-lua.lua
new file mode 100755
index 0000000000..1e55f48484
--- /dev/null
+++ b/plug-ins/goat-exercises/goat-exercise-lua.lua
@@ -0,0 +1,163 @@
+#!/usr/bin/env luajit
+
+-- GIMP - The GNU Image Manipulation Program
+-- Copyright (C) 1995 Spencer Kimball and Peter Mattis
+--
+-- goat-exercise-lua.lua
+-- Copyright (C) Jehan
+--
+-- 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/>.
+
+local lgi = require 'lgi'
+
+local GLib    = lgi.GLib
+local GObject = lgi.GObject
+local Gio     = lgi.Gio
+local Gegl    = lgi.Gegl
+local Gimp    = lgi.Gimp
+local Gtk     = lgi.Gtk
+local Gdk     = lgi.Gdk
+
+local Goat = lgi.package 'Goat'
+local Goat = lgi.Goat
+
+function run(procedure, args, data)
+  local run_mode = GObject.Value.get_enum(args:index(0))
+  if run_mode == Gimp.RunMode.INTERACTIVE then
+    Gimp.ui_init("goat-exercise-lua", false);
+    local dialog = Gimp.Dialog {
+      title          = "Exercise a goat (Lua)",
+      role           = "goat-exercise-Lua",
+      use_header_bar = 1
+    }
+    dialog:add_button("_Cancel", Gtk.ResponseType.CANCEL);
+    dialog:add_button("_Source", Gtk.ResponseType.APPLY);
+    dialog:add_button("_OK", Gtk.ResponseType.OK);
+
+    local geometry = Gdk.Geometry()
+    geometry.min_aspect = 0.5;
+    geometry.max_aspect = 1.0;
+    dialog:set_geometry_hints (nil, geometry, Gdk.WindowHints.ASPECT);
+
+    local box = Gtk.Box {
+      orientation = Gtk.Orientation.VERTICAL,
+      spacing     = 2
+    }
+    dialog:get_content_area():add(box)
+    box:show()
+
+    local lang = "Lua"
+    local head_text = "This plug-in is an exercise in '%s' to demo plug-in creation.\n" ..
+                      "Check out the last version of the source code online by clicking the \"Source\" 
button."
+
+    local label = Gtk.Label { label = string.format(head_text, lang) }
+    box:pack_start(label, false, false, 1)
+    label:show()
+
+    -- TODO: show source.
+
+    while (true) do
+      local response = dialog:run()
+      local url = 
'https://gitlab.gnome.org/GNOME/gimp/blob/master/plug-ins/goat-exercises/goat-exercise-lua.lua'
+
+      if response == Gtk.ResponseType.OK then
+        dialog:destroy()
+        break
+      elseif (response == Gtk.ResponseType.APPLY)  then
+        Gio.app_info_launch_default_for_uri(url, nil);
+      else -- CANCEL, CLOSE, DELETE_EVENT
+        dialog:destroy()
+        return procedure:new_return_values(Gimp.PDBStatusType.CANCEL, nil)
+      end
+    end
+  end
+
+  local drawable_id = args:index(2):get_int()
+  local x, y, width, height = Gimp.drawable_mask_intersect (drawable_id)
+  if width > 0 and height > 0 then
+    Gegl.init(nil)
+
+    local buffer = Gimp.drawable_get_buffer (drawable_id)
+    local shadow_buffer = Gimp.drawable_get_shadow_buffer (drawable_id)
+
+    local graph = Gegl.Node()
+    local input = graph:create_child("gegl:buffer-source")
+    input:set_property("buffer", GObject.Value(Gegl.Buffer, buffer))
+    local invert = graph:create_child("gegl:invert")
+    local output = graph:create_child("gegl:write-buffer")
+    output:set_property("buffer", GObject.Value(Gegl.Buffer, shadow_buffer))
+    input:link(invert)
+    invert:link(output)
+    output:process()
+
+    shadow_buffer:flush()
+
+    Gimp.drawable_merge_shadow(drawable_id, true)
+    Gimp.drawable_update(drawable_id, x, y, width, height)
+    Gimp.displays_flush()
+  else
+    local err = GLib.Error.new_literal(GLib.quark_from_string("goat-error-quark"), 0,
+                                       "No pixels to process in the selected area.")
+    return procedure:new_return_values(Gimp.PDBStatusType.CALLING_ERROR, err)
+  end
+
+  return procedure:new_return_values(Gimp.PDBStatusType.SUCCESS, 0)
+end
+
+Goat:class('Exercise', Gimp.PlugIn)
+
+function Goat.Exercise:do_query_procedures()
+  return { 'goat-exercise-lua' }
+end
+
+function Goat.Exercise:do_create_procedure(name)
+  local procedure = Gimp.Procedure.new(self, name,
+                                       Gimp.PDBProcType.PLUGIN,
+                                       run, nil)
+  procedure:set_image_types("RGB*, INDEXED*, GRAY*");
+  procedure:set_menu_label("Exercise a Lua goat");
+  procedure:set_documentation("Exercise a goat in the Lua language",
+                              "Takes a goat for a walk in Lua",
+                              "");
+  procedure:add_menu_path('<Image>/Filters/Development/Goat exercises/');
+  procedure:set_attribution("Jehan", "Jehan", "2019");
+  procedure:add_argument(GObject.param_spec_enum("run-mode",
+                                                 "Run mode",
+                                                 "The run mode",
+                                                 GObject.Type.name(Gimp.RunMode),
+                                                 Gimp.RunMode.NONINTERACTIVE,
+                                                 GObject.ParamFlags.READWRITE));
+  procedure:add_argument(Gimp.param_spec_image_id ("image",
+                                                   "Image",
+                                                   "The input image",
+                                                   false,
+                                                   GObject.ParamFlags.READWRITE));
+  procedure:add_argument(Gimp.param_spec_drawable_id ("drawable",
+                                                      "Drawable",
+                                                      "The input drawable",
+                                                      false,
+                                                      GObject.ParamFlags.READWRITE));
+
+  return procedure
+end
+
+-- 'arg' is a Lua table. When automatically converted to an array, the
+-- value 0 is deleted (because Lua arrays start at 1!), which breaks
+-- Gimp.main() call. So let's create our own array starting at 1.
+argv = {}
+for k, v in pairs(arg) do
+  argv[k+1] = v
+end
+
+Gimp.main(GObject.Type.name(Goat.Exercise), argv)