Support SavePanorama data

* saves and loads scrolling panorama x and y position.
* Only supported by rm2k3e, but we enable for all modes.

src/game_map.cpp

@@ -46,6 +46,7 @@
 namespace {
 	RPG::SaveMapInfo& map_info = Main_Data::game_data.map_info;
 	RPG::SavePartyLocation& location = Main_Data::game_data.party_location;
+	RPG::SavePanorama& panorama = Main_Data::game_data.panorama;
 
 	std::string chipset_name;
 	std::string battleback_name;
@@ -134,6 +135,8 @@ void Game_Map::Quit() {
 void Game_Map::Setup(int _id) {
 	SetupCommon(_id, false);
 	map_info.encounter_rate = GetMapInfo().encounter_steps;
+	panorama.pan_x = 0;
+	panorama.pan_y = 0;
 	ResetEncounterSteps();
 
 	Parallax::ClearChangedBG();
@@ -1423,11 +1426,11 @@ std::string Game_Map::Parallax::GetName() {
 }
 
 int Game_Map::Parallax::GetX() {
-	return parallax_x / TILE_SIZE;
+	return (parallax_x - panorama.pan_x / 2) / TILE_SIZE;
 }
 
 int Game_Map::Parallax::GetY() {
-	return parallax_y / TILE_SIZE;
+	return (parallax_y - panorama.pan_y / 2) / TILE_SIZE;
 }
 
 void Game_Map::Parallax::Initialize(int width, int height) {
@@ -1469,11 +1472,16 @@ void Game_Map::Parallax::Update() {
 		return 0;
 	};
 
+
 	if (params.scroll_horz && params.scroll_horz_auto) {
-		parallax_x += scroll_amt(params.scroll_horz_speed);
+		const auto w = parallax_width * TILE_SIZE * 2;
+		panorama.pan_x -= scroll_amt(params.scroll_horz_speed) * 2;
+		panorama.pan_x = (panorama.pan_x + w) % w;
 	}
 	if (params.scroll_vert && params.scroll_vert_auto) {
-		parallax_y += scroll_amt(params.scroll_vert_speed);
+		const auto h = parallax_height * TILE_SIZE * 2;
+		panorama.pan_y -= scroll_amt(params.scroll_vert_speed) * 2;
+		panorama.pan_y = (panorama.pan_y + h) % h;
 	}
 }