Add WML tag to change the map zoom level

changelog

@@ -15,6 +15,7 @@ Version 1.13.7+dev:
    * Small change to animator API - facing parameter replaced with target and required to be
      a space adjacent to the unit.
    * New modifiable theme attribute in wesnoth.game_config
+   * New wesnoth.zoom() function allows changing the zoom level
  * Multiplayer:
    * Fixed statistics being lost when reloading an MP game.
  * Performance:
@@ -40,6 +41,7 @@ Version 1.13.7+dev:
        the color as a list of its components, eg "([r, g, b, a])"
    * Empty tags are no longer written to the configs of [unit]s and [side]s.
    * New [change_theme] tag to change the theme mid-scenario
+   * New [zoom] tag allows changing the zoom level from an event
 
 Version 1.13.7:
  * AI:

data/lua/wml-tags.lua

@@ -1417,6 +1417,10 @@ function wesnoth.wml_actions.change_theme(cfg)
 	wesnoth.game_config.theme = cfg.theme
 end
 
+function wesnoth.wml_actions.zoom(cfg)
+	wesnoth.zoom(cfg.factor, cfg.relative)
+end
+
 function wesnoth.wml_conditionals.proceed_to_next_scenario(cfg)
 	local endlevel_data = wesnoth.get_end_level_data()
 	if not endlevel_data then

src/display.cpp

@@ -2006,7 +2006,7 @@ bool display::set_zoom(bool increase)
 
 bool display::set_zoom(unsigned int amount, const bool validate_value_and_set_index)
 {
-	const unsigned int new_zoom = utils::clamp(amount, MinZoom, MaxZoom);
+	unsigned int new_zoom = utils::clamp(amount, MinZoom, MaxZoom);
 
 	LOG_DP << "new_zoom = " << new_zoom << std::endl;
 
@@ -2016,13 +2016,22 @@ bool display::set_zoom(unsigned int amount, const bool validate_value_and_set_in
 
 	// Confirm this is indeed a valid zoom level.
 	if(validate_value_and_set_index) {
-		auto iter = std::find(zoom_levels.begin(), zoom_levels.end(), new_zoom);
+		auto iter = std::lower_bound(zoom_levels.begin(), zoom_levels.end(), new_zoom);
 
-		// TODO: do we need an error?
 		if(iter == zoom_levels.end()) {
+			// This should never happen, since the value was already clamped earlier
 			return false;
+		} else if(iter != zoom_levels.begin()) {
+			float diff = *iter - *(iter - 1);
+			float lower = (new_zoom - *(iter - 1)) / diff;
+			float upper = (*iter - new_zoom) / diff;
+			if(lower < upper) {
+				// It's actually closer to the previous element.
+				iter--;
+			}
 		}
 
+		new_zoom = *iter;
 		zoom_index_ = iter - zoom_levels.begin();
 	}
 

src/scripting/game_lua_kernel.cpp

@@ -1394,6 +1394,23 @@ int game_lua_kernel::intf_open_help(lua_State *L)
 	return 0;
 }
 
+int game_lua_kernel::intf_zoom(lua_State* L)
+{
+	if(!game_display_) {
+		return 0;
+	}
+	double factor = luaL_checknumber(L, 1);
+	bool relative = luaW_toboolean(L, 2);
+	if(relative) {
+		factor *= game_display_->get_zoom_factor();
+	}
+	// Passing true explicitly to avoid casting to int.
+	// Without doing one of the two, the call is ambiguous.
+	game_display_->set_zoom(factor * game_config::tile_size, true);
+	lua_pushnumber(L, game_display_->get_zoom_factor());
+	return 1;
+}
+
 /**
  * Dumps a wml table or userdata wml object into a pretty string.
  * - Arg 1: wml table or vconfig userdata
@@ -4181,6 +4198,7 @@ game_lua_kernel::game_lua_kernel(game_state & gs, play_controller & pc, reports
 		{ "switch_ai",                 &intf_switch_ai                                                      },
 		{ "synchronize_choice",        &intf_synchronize_choice                                             },
 		{ "synchronize_choices",       &intf_synchronize_choices                                            },
+		{ "zoom",                      &dispatch<&game_lua_kernel::intf_zoom                       >        },
 		{ "teleport",                  &dispatch<&game_lua_kernel::intf_teleport                   >        },
 		{ "unit_ability",              &dispatch<&game_lua_kernel::intf_unit_ability               >        },
 		{ "view_locked",               &dispatch<&game_lua_kernel::intf_view_locked                >        },

src/scripting/game_lua_kernel.hpp

@@ -172,6 +172,7 @@ class game_lua_kernel : public lua_kernel_base
 	int intf_toggle_fog(lua_State *L, const bool clear);
 	int intf_get_fog_or_shroud(lua_State *L, bool fog);
 	int intf_log_replay(lua_State* L);
+	int intf_zoom(lua_State* L);
 
 	//private helpers
 	std::string synced_state();