Add a submerge value to items, to control submerge amount

It defaults to 0, which is no submersion.

data/lua/wml/items.lua

@@ -24,6 +24,7 @@ local function add_overlay(x, y, cfg)
 			team_name = cfg.team_name,
 			filter_team = cfg.filter_team,
 			visible_in_fog = cfg.visible_in_fog,
+			submerge = cfg.submerge,
 			redraw = cfg.redraw,
 			name = cfg.name,
 			z_order = cfg.z_order,
@@ -60,6 +61,7 @@ end
 ---@field team_name string
 ---@field filter_team WML
 ---@field visible_in_fog boolean
+---@field submerge number
 ---@field redraw boolean
 ---@field name string
 ---@field z_order integer
@@ -82,6 +84,7 @@ function wesnoth.interface.get_items(x, y)
 			team_name = cfg.team_name,
 			filter_team = cfg.filter_team,
 			visible_in_fog = cfg.visible_in_fog,
+			submerge = cfg.submerge,
 			redraw = cfg.redraw,
 			name = cfg.name,
 			z_order = cfg.z_order,

data/schema/core/actionwml.cfg

@@ -749,6 +749,7 @@
 		{SIMPLE_KEY name string}
 		# Override some supertag keys to allow variable substitutions
 		{DEFAULT_KEY visible_in_fog s_bool yes}
+		{SIMPLE_KEY submerge s_real}
 		{FILTER_TAG "filter_side" side ()}
 	[/tag]
 	[tag]

data/schema/core/addons.cfg

@@ -462,6 +462,7 @@
 		{SIMPLE_KEY halo string}
 		{SIMPLE_KEY team_name string}
 		{DEFAULT_KEY visible_in_fog bool yes}
+		{SIMPLE_KEY submerge real}
 	[/tag]
 	[tag]
 		name="time"

src/display.cpp

@@ -139,7 +139,7 @@ void display::parse_team_overlays()
 }
 
 
-void display::add_overlay(const map_location& loc, const std::string& img, const std::string& halo, const std::string& team_name, const std::string& item_id, bool visible_under_fog, float z_order)
+void display::add_overlay(const map_location& loc, const std::string& img, const std::string& halo, const std::string& team_name, const std::string& item_id, bool visible_under_fog, float submerge, float z_order)
 {
 	halo::handle halo_handle;
 	if(halo != "") {
@@ -149,7 +149,7 @@ void display::add_overlay(const map_location& loc, const std::string& img, const
 
 	std::vector<overlay>& overlays = get_overlays()[loc];
 	auto it = std::find_if(overlays.begin(), overlays.end(), [z_order](const overlay& ov) { return ov.z_order > z_order; });
-	overlays.emplace(it, img, halo, halo_handle, team_name, item_id, visible_under_fog, z_order);
+	overlays.emplace(it, img, halo, halo_handle, team_name, item_id, visible_under_fog, submerge, z_order);
 }
 
 void display::remove_overlay(const map_location& loc)
@@ -1516,8 +1516,16 @@ void display::draw_text_in_hex(const map_location& loc,
 static void add_submerge_ipf_mod(
 	std::string& image_path,
 	int image_height,
-	double submersion_amount)
+	double submersion_amount,
+	int shift = 0)
 {
+	// We may also want to shift the position so that the waterline matches.
+	// Note: This currently has blending problems (see the note on sdl_blit),
+	// but if that blending problem is fixed it should work.
+	if (shift) {
+		image_path = "misc/blank-hex.png~BLIT(" + image_path;
+	}
+
 	// general formula for submerge alpha:
 	//   if (y > WATERLINE)
 	//   then min(max(alpha_mod, 0), 1) * alpha
@@ -1542,6 +1550,13 @@ static void add_submerge_ipf_mod(
 	// but that's not available below SDL 2.0.18.
 	// Alternately it could also be done fairly easily using shaders,
 	// if a graphics system supporting them (such as openGL) is moved to.
+
+	if (shift) {
+		// Finish the shifting blit. This assumes a hex-sized image.
+		image_path += ",0,";
+		image_path += std::to_string(shift);
+		image_path += ')';
+	}
 }
 
 void display::render_image(int x, int y, const display::drawing_layer drawing_layer,
@@ -2814,10 +2829,17 @@ void display::draw_hex(const map_location& loc)
 					{
 						point isize = image::get_size(ov.image, image::HEXED);
 						std::string ipf = ov.image;
-						add_submerge_ipf_mod(ipf, isize.y, submerge);
-						const texture tex = ov.image.find("~NO_TOD_SHIFT()") == std::string::npos ?
-							image::get_lighted_texture(ipf, lt) :
-							image::get_texture(ipf, image::HEXED);
+						if(ov.submerge) {
+							// Adjust submerge appropriately
+							double sub = submerge * ov.submerge;
+							// Shift the image so the waterline remains static.
+							// This is so that units swimming there look okay.
+							int shift = isize.y * (sub - submerge);
+							add_submerge_ipf_mod(ipf, isize.y, sub, shift);
+						}
+						const texture tex = ov.image.find("~NO_TOD_SHIFT()") == std::string::npos
+							? image::get_lighted_texture(ipf, lt)
+							: image::get_texture(ipf, image::HEXED);
 						drawing_buffer_add(LAYER_TERRAIN_BG, loc, dest, tex);
 					}
 				}

src/display.hpp

@@ -158,7 +158,7 @@ public:
 	 */
 	void add_overlay(const map_location& loc, const std::string& image,
 		const std::string& halo="", const std::string& team_name="",const std::string& item_id="",
-		bool visible_under_fog = true, float z_order = 0);
+		bool visible_under_fog = true, float submerge = 0.0f, float z_order = 0);
 
 	/** remove_overlay will remove all overlays on a tile. */
 	void remove_overlay(const map_location& loc);

src/editor/action/mouse/mouse_action_item.cpp

@@ -52,7 +52,7 @@ std::unique_ptr<editor_action> mouse_action_item::click_left(editor_display& dis
 	}
 
 	const overlay& item = item_palette_.selected_fg_item();
-	disp.add_overlay(start_hex_, item.image, item.halo, "", "", true);
+	disp.add_overlay(start_hex_, item.image, item.halo, "", "", item.visible_in_fog, item.submerge);
 
 	click_ = true;
 	return nullptr;

src/editor/map/map_context.cpp

@@ -513,6 +513,9 @@ config map_context::to_config()
 			item["name"].write_if_not_empty(o.name);
 			item["team_name"].write_if_not_empty(o.team_name);
 			item["halo"].write_if_not_empty(o.halo);
+			if(o.submerge) {
+				item["submerge"] = o.submerge;
+			}
 		}
 	}
 

src/overlay.hpp

@@ -26,6 +26,7 @@ struct overlay
 			const std::string& overlay_team_name,
 			const std::string& item_id,
 			const bool fogged,
+			float submerge,
 			float item_z_order = 0)
 		: image(img)
 		, halo(halo_img)
@@ -33,6 +34,7 @@ struct overlay
 		, id(item_id)
 		, halo_handle(handle)
 		, visible_in_fog(fogged)
+		, submerge(submerge)
 		, z_order(item_z_order)
 	{}
 
@@ -45,6 +47,7 @@ struct overlay
 		, id(cfg["id"])
 		, halo_handle()
 		, visible_in_fog(cfg["visible_in_fog"].to_bool())
+		, submerge(cfg["submerge"].to_double(0))
 		, z_order(cfg["z_order"].to_double(0))
 	{
 	}
@@ -57,6 +60,7 @@ struct overlay
 
 	halo::handle halo_handle;
 	bool visible_in_fog;
+	float submerge;
 	float z_order;
 
 };

src/scripting/game_lua_kernel.cpp

@@ -3645,7 +3645,8 @@ int game_lua_kernel::intf_add_tile_overlay(lua_State *L)
 
 	if (game_display_) {
 		game_display_->add_overlay(loc, cfg["image"], cfg["halo"],
-			team_name, cfg["name"], cfg["visible_in_fog"].to_bool(true), cfg["z_order"].to_double(0));
+			team_name, cfg["name"], cfg["visible_in_fog"].to_bool(true),
+			cfg["submerge"].to_double(0), cfg["z_order"].to_double(0));
 	}
 	return 0;
 }