Tweak WML and lua screen_fade interface

data/lua/wml-tags.lua

@@ -719,7 +719,8 @@ function wml_actions.color_adjust(cfg)
 end
 
 function wml_actions.screen_fade(cfg)
-	wesnoth.interface.screen_fade(cfg.red, cfg.green, cfg.blue, cfg.alpha, cfg.duration)
+	color = {cfg.red or 0, cfg.green or 0, cfg.blue or 0, cfg.alpha}
+	wesnoth.interface.screen_fade(color, cfg.duration)
 end
 
 function wml_actions.end_turn(cfg)

data/schema/core/actionwml.cfg

@@ -868,10 +868,8 @@
 	[tag]
 		name="screen_fade"
 		max=infinite
-		{REQUIRED_KEY red s_int}
-		{REQUIRED_KEY green s_int}
-		{REQUIRED_KEY blue s_int}
-		{REQUIRED_KEY alpha s_int}
+		{COLOR_KEYS s_unsigned}
+		{REQUIRED_KEY alpha s_unsigned}
 		{REQUIRED_KEY duration s_unsigned}
 	[/tag]
 	[tag]

src/scripting/game_lua_kernel.cpp

@@ -3727,12 +3727,12 @@ int game_lua_kernel::intf_get_color_adjust(lua_State *L)
 int game_lua_kernel::intf_screen_fade(lua_State *L)
 {
 	if(game_display_) {
-		color_t fade;
-		fade.r = luaL_checkinteger(L, 1);
-		fade.g = luaL_checkinteger(L, 2);
-		fade.b = luaL_checkinteger(L, 3);
-		fade.a = luaL_checkinteger(L, 4);
-		game_display_->fade_to(fade, luaL_checkinteger(L, 5));
+		auto vec = lua_check<std::vector<uint8_t>>(L, 1);
+		if(vec.size() != 4) {
+			return luaL_error(L, "screen fade colour must be an array of 4 integers");
+		}
+		color_t fade{vec[0], vec[1], vec[2], vec[3]};
+		game_display_->fade_to(fade, luaL_checkinteger(L, 2));
 	}
 	return 0;
 }

utils/emmylua/wesnoth/interface.lua

@@ -123,5 +123,10 @@ function wesnoth.interface.allow_end_turn(reason) end
 ---@param blue integer
 function wesnoth.interface.color_adjust(red, green, blue) end
 
+---Fade the screen to the given colour
+---@param color integer[] RGBA colour value to fade to; A=0 removes fade
+---@param duration integer How long the fade takes to apply, in milliseconds
+function wesnoth.interface.screen_fade(color, duration) end
+
 ---@type table<string, fun()>
 wesnoth.game_display = {}