Try reusing one pick-spell dialog

src/game/boe.main.cpp

@@ -35,6 +35,7 @@
 #include "mathutil.hpp"
 #include "fileio/fileio.hpp"
 #include "fileio/resmgr/res_font.hpp"
+#include "fileio/resmgr/res_dialog.hpp"
 #include "dialogxml/dialogs/strdlog.hpp"
 #include "dialogxml/dialogs/choicedlog.hpp"
 #include "dialogxml/widgets/scrollbar.hpp"
@@ -351,11 +352,16 @@ static void init_buttons() {
 	init_btn(help_btn, BTN_HELP, {273,12});
 }
 
+// Spell dialog is slow to open on Windows, so keep it prepared and reuse it.
+std::unique_ptr<cDialog> storeCastSpell;
+
 // NOTE: this should possibly be moved to boe.ui.cpp at some point
 static void init_ui() {
 	cDialog::init();
 	init_scrollbars();
 	init_buttons();
+
+	storeCastSpell.reset(new cDialog(*ResMgr::dialogs.get("cast-spell")));
 }
 
 extern bool record_verbose;
@@ -1270,6 +1276,7 @@ void handle_events() {
 			ResMgr::fonts.drain();
 
 			adjust_window_mode();
+			storeCastSpell.reset(new cDialog(*ResMgr::dialogs.get("cast-spell")));
 			init_mini_map();
 		}
 

src/game/boe.party.cpp

@@ -2060,8 +2060,8 @@ eSpell pick_spell(short pc_num,eSkill type) { // 70 - no spell OW spell num
 	
 	set_cursor(sword_curs);
 	
-	cDialog castSpell(*ResMgr::dialogs.get("cast-spell"));
-	
+	extern std::unique_ptr<cDialog> storeCastSpell;
+	cDialog& castSpell = *storeCastSpell;
 	castSpell.attachClickHandlers(std::bind(pick_spell_caster, _1, _2, type, std::ref(dark), std::ref(former_spell)), {"caster1","caster2","caster3","caster4","caster5","caster6"});
 	castSpell.attachClickHandlers(std::bind(pick_spell_target,_1,_2, type, std::ref(dark), std::ref(former_spell)), {"target1","target2","target3","target4","target5","target6"});
 	castSpell.attachClickHandlers(std::bind(pick_spell_event_filter, _1, _2, type,std::ref(former_spell)), {"other", "help"});