[lua] Add get/set the foreground/background tile (fix #4403)

It's now possible to get/set the selected foreground/background tile
index. Example of use:

  app.fgTile = 1    -- the primary tile is '1'
  print(app.fgTile) -- this will show '1'
  app.fgTile = 0    -- the primery tile is 'no tile'
  print(app.fgTile) -- this will show '0'
  app.bgTile = 2    -- the secondary tile is '2'

src/app/script/app_object.cpp

@@ -644,6 +644,30 @@ int App_set_bgColor(lua_State* L)
   return 0;
 }
 
+int App_get_fgTile(lua_State* L)
+{
+  lua_pushinteger(L, Preferences::instance().colorBar.fgTile());
+  return 1;
+}
+
+int App_set_fgTile(lua_State* L)
+{
+  Preferences::instance().colorBar.fgTile(lua_tointeger(L, 2));
+  return 0;
+}
+
+int App_get_bgTile(lua_State* L)
+{
+  lua_pushinteger(L, Preferences::instance().colorBar.bgTile());
+  return 1;
+}
+
+int App_set_bgTile(lua_State* L)
+{
+  Preferences::instance().colorBar.bgTile(lua_tointeger(L, 2));
+  return 0;
+}
+
 int App_get_site(lua_State* L)
 {
   app::Context* ctx = App::instance()->context();
@@ -828,6 +852,8 @@ const Property App_properties[] = {
   { "sprites",        App_get_sprites,        nullptr },
   { "fgColor",        App_get_fgColor,        App_set_fgColor },
   { "bgColor",        App_get_bgColor,        App_set_bgColor },
+  { "fgTile",         App_get_fgTile,         App_set_fgTile },
+  { "bgTile",         App_get_bgTile,         App_set_bgTile },
   { "version",        App_get_version,        nullptr },
   { "apiVersion",     App_get_apiVersion,     nullptr },
   { "site",           App_get_site,           nullptr },

tests/scripts/tilemap.lua

@@ -1,4 +1,4 @@
--- Copyright (C) 2019-2023  Igara Studio S.A.
+-- Copyright (C) 2019-2024  Igara Studio S.A.
 --
 -- This file is released under the terms of the MIT license.
 -- Read LICENSE.txt for more information.
@@ -195,6 +195,79 @@ do
 
 end
 
+----------------------------------------------------------------------
+-- Tests of get/set app.fgTile and app.bgTile
+----------------------------------------------------------------------
+
+do
+  local spr = Sprite(32, 32, ColorMode.INDEXED)
+  spr.gridBounds = Rectangle{ 0, 0, 2, 2 }
+  assert(spr.layers[1].isImage)
+  assert(not spr.layers[1].isTilemap)
+
+  ----------------------------------------------------------------------
+  -- Create a tilemap
+  ----------------------------------------------------------------------
+
+  app.command.NewLayer{ tilemap=true }
+  assert(#spr.layers == 2)
+  app.layer = spr.layers[2]
+  assert(app.layer.isImage)
+  assert(app.layer.isTilemap)
+  assert(#app.layer.cels == 0)
+
+  ----------------------------------------------------------------------
+  -- Draw something on the tilemap so new tiles are created
+  ----------------------------------------------------------------------
+
+  app.useTool{
+    tool='pencil',
+    color=1,
+    tilesetMode=TilesetMode.STACK,
+    points={ Point(2, 0), Point(4, 0), Point(5,1) }
+  }
+  assert(#app.layer.cels == 1)
+  assert(app.layer:cel(1).image.colorMode == ColorMode.TILEMAP)
+  local tilemapCel = app.layer:cel(1)
+  assert(tilemapCel.bounds == Rectangle(2, 0, 4, 2))
+  assert(#spr.layers[2].tileset == 3)
+
+  app.fgTile = 1
+  app.useTool{
+    tool='pencil',
+    tilemapMode=TilemapMode.TILES,
+    points={ Point(0, 0), Point(5, 0)}
+  }
+
+  app.fgTile = 2
+  app.useTool{
+    tool='pencil',
+    tilemapMode=TilemapMode.TILES,
+    points={ Point(0, 2), Point(5, 2)}
+  }
+
+  local cel = spr.layers[2].cels[1]
+  expect_img(cel.image, { 1,1,1,
+                          2,2,2 })
+
+  app.fgTile = 0
+  app.useTool{
+    tool='pencil',
+    tilemapMode=TilemapMode.TILES,
+    points={ Point(0, 0), Point(4, 0),
+             Point(4, 2), Point(0, 2)}
+  }
+
+  local cel = spr.layers[2].cels[1]
+  assert(cel == nil)
+  local tileImg1 = spr.layers[2].tileset:tile(1).image
+  expect_img(tileImg1, { 1,1,
+                         0,0 })
+  local tileImg2 = spr.layers[2].tileset:tile(2).image
+  expect_img(tileImg2, { 1,0,
+                         0,1 })
+end
+
 ----------------------------------------------------------------------
 -- Tests drawing in the tilemap with tiles
 ----------------------------------------------------------------------