UI: Highlight enemy units in "Show Enemy Moves" mode (#3961)

Fixes #1989

src/game_display.cpp

@@ -556,17 +556,25 @@ void game_display::highlight_reach(const pathfind::paths &paths_list)
 	highlight_another_reach(paths_list);
 }
 
-void game_display::highlight_another_reach(const pathfind::paths &paths_list)
+void game_display::highlight_another_reach(const pathfind::paths &paths_list,
+			const map_location& goal)
 {
 	// Fold endpoints of routes into reachability map.
 	for (const pathfind::paths::step &dest : paths_list.destinations) {
 		reach_map_[dest.curr]++;
 	}
 	reach_map_changed_ = true;
+
+	if(goal != map_location::null_location() && paths_list.destinations.contains(goal)) {
+		const auto& path_to_goal = paths_list.destinations.get_path(paths_list.destinations.find(goal));
+		const map_location enemy_unit_location = path_to_goal[0];
+		units_that_can_reach_goal_.insert(enemy_unit_location);
+	}
 }
 
 bool game_display::unhighlight_reach()
 {
+	units_that_can_reach_goal_.clear();
 	if(!reach_map_.empty()) {
 		reach_map_.clear();
 		reach_map_changed_ = true;

src/game_display.hpp

@@ -95,9 +95,15 @@ public:
 
 	/**
 	 * Add more paths to highlight.  Print numbers where they overlap.
-	 * Used only by Show Enemy Moves.
+	 * Used by Show Enemy Moves.  If @a goal is not @c null_location, highlight
+	 * enemy units that can reach @a goal.
 	 */
-	void highlight_another_reach(const pathfind::paths &paths_list);
+	void highlight_another_reach(const pathfind::paths &paths_list,
+			const map_location& goal = map_location::null_location());
+	/**
+	 * Return the locations of units that can reach @a goal (@see highlight_another_reach()).
+	 */
+	const std::set<map_location>& units_that_can_reach_goal() const { return units_that_can_reach_goal_; }
 
 	/** Reset highlighting of paths. */
 	bool unhighlight_reach();
@@ -142,6 +148,8 @@ protected:
 
 	virtual void draw_hex(const map_location& loc) override;
 
+	std::set<map_location> units_that_can_reach_goal_;
+
 public:
 	/** Set the attack direction indicator. */
 	void set_attack_indicator(const map_location& src, const map_location& dst);

src/menu_events.cpp

@@ -439,6 +439,9 @@ void menu_handler::show_enemy_moves(bool ignore_units, int side_num)
 {
 	wb::future_map future; // use unit positions as if all planned actions were executed
 
+	mouse_handler& mh = pc_.get_mouse_handler_base();
+	const map_location& hex_under_mouse = mh.hovered_hex();
+
 	gui_->unhighlight_reach();
 
 	// Compute enemy movement positions
@@ -451,14 +454,12 @@ void menu_handler::show_enemy_moves(bool ignore_units, int side_num)
 			const pathfind::paths& path
 					= pathfind::paths(u, false, true, teams()[gui_->viewing_team()], 0, false, ignore_units);
 
-			gui_->highlight_another_reach(path);
+			gui_->highlight_another_reach(path, hex_under_mouse);
 		}
 	}
 
 	// Find possible unit (no matter whether friend or foe) under the
 	// mouse cursor.
-	mouse_handler& mh = pc_.get_mouse_handler_base();
-	const map_location& hex_under_mouse = mh.hovered_hex();
 	const bool selected_hex_has_unit = mh.hex_hosts_unit(hex_under_mouse);
 
 	if(selected_hex_has_unit) {

src/units/drawer.cpp

@@ -17,6 +17,7 @@
 #include "display.hpp"
 #include "display_context.hpp"
 #include "formatter.hpp"
+#include "game_display.hpp"
 #include "preferences/game.hpp"
 #include "halo.hpp"
 #include "map/map.hpp"
@@ -49,7 +50,11 @@ unit_drawer::unit_drawer(display & thedisp) :
 	zoom_factor(disp.get_zoom_factor()),
 	hex_size(disp.hex_size()),
 	hex_size_by_2(disp.hex_size()/2)
-{}
+{
+	if(const game_display* game_display = dynamic_cast<class game_display*>(&disp)) {
+		units_that_can_reach_goal = game_display->units_that_can_reach_goal();
+	}
+}
 
 void unit_drawer::redraw_unit (const unit & u) const
 {
@@ -79,6 +84,9 @@ void unit_drawer::redraw_unit (const unit & u) const
 
 	std::string ellipse=u.image_ellipse();
 
+	const bool is_highlighted_enemy = units_that_can_reach_goal.count(loc) > 0;
+	const bool is_selected_hex = (loc == sel_hex || is_highlighted_enemy);
+
 	if ( hidden || is_blindfolded || !u.is_visible_to_team(viewing_team_ref, dc, show_everything) )
 	{
 		ac.clear_haloes();
@@ -109,7 +117,7 @@ void unit_drawer::redraw_unit (const unit & u) const
 			params.highlight_ratio > 0.6) {
 		params.highlight_ratio = 0.6;
 	}
-	if (loc == sel_hex && params.highlight_ratio == 1.0) {
+	if (is_selected_hex && params.highlight_ratio == 1.0) {
 		params.highlight_ratio = 1.5;
 	}
 
@@ -184,7 +192,7 @@ void unit_drawer::redraw_unit (const unit & u) const
 	surface ellipse_back(nullptr);
 	int ellipse_floating = 0;
 	// Always show the ellipse for selected units
-	if(draw_bars && (preferences::show_side_colors() || sel_hex == loc)) {
+	if(draw_bars && (preferences::show_side_colors() || is_selected_hex)) {
 		if(adjusted_params.submerge > 0.0) {
 			// The division by 2 seems to have no real meaning,
 			// It just works fine with the current center of ellipse
@@ -200,7 +208,7 @@ void unit_drawer::redraw_unit (const unit & u) const
 			// check if the unit has a ZoC or can recruit
 			const std::string nozoc    = !emit_zoc      ? "nozoc-"    : "";
 			const std::string leader   = can_recruit    ? "leader-"   : "";
-			const std::string selected = sel_hex == loc ? "selected-" : "";
+			const std::string selected = is_selected_hex? "selected-" : "";
 			const std::string tc       = team::get_side_color_id(side);
 
 			const std::string ellipse_top = formatter() << ellipse << "-" << leader << nozoc << selected << "top.png~RC(ellipse_red>" << tc << ")";
@@ -296,7 +304,7 @@ void unit_drawer::redraw_unit (const unit & u) const
 		const int bar_shift = static_cast<int>(-5*zoom_factor);
 		const int hp_bar_height = static_cast<int>(max_hitpoints * u.hp_bar_scaling());
 
-		const fixed_t bar_alpha = (loc == mouse_hex || loc == sel_hex) ? ftofxp(1.0): ftofxp(0.8);
+		const fixed_t bar_alpha = (loc == mouse_hex || is_selected_hex) ? ftofxp(1.0): ftofxp(0.8);
 
 		draw_bar(*energy_file, xsrc+xoff+bar_shift, ysrc+yoff+adjusted_params.y,
 			loc, hp_bar_height, unit_energy,hp_color, bar_alpha);

src/units/drawer.hpp

@@ -60,6 +60,7 @@ private:
 	map_location sel_hex;
 	map_location mouse_hex;
 	double zoom_factor;
+	std::set<map_location> units_that_can_reach_goal;
 
 	int hex_size;
 	int hex_size_by_2;