Improve correctness of hotkeys at low framerates.

SDL queues up all the input events received in a frame. When the hotkey
system saw a key up/down event, it immediately updated its
HotkeyIsPressed state and then pushed a hotkey event onto the end of the
queue.

If the initial queue was e.g. [key-down shift, key-press Z, key-up
shift], the hotkey event triggered by Z would be processed after the
key-up shift had updated the HotkeyIsPressed state, so the handler of
the Z hotkey would not think the shift hotkey was pressed.

If the initial queue was e.g. [key-press Z, mouse-click], the hotkey
triggered by Z would be processed after the mouse-click event, so it
could apply to the wrong building selection.

Fix by pushing the hotkey events onto a special queue that gets
processed before any subsequent SDL input events.

Also update the HotkeyIsPressed status when the HOTKEYDOWN/HOTKEYUP
events are processed, not when they are generated, to guarantee they are
consistent with the DOWN/UP events.

Fixes #1869.

This was SVN commit r14057.

source/lib/input.cpp

@@ -36,6 +36,8 @@ const size_t MAX_HANDLERS = 8;
 static InHandler handler_stack[MAX_HANDLERS];
 static size_t handler_stack_top = 0;
 
+static std::list<SDL_Event_> priority_events;
+
 void in_add_handler(InHandler handler)
 {
 	ENSURE(handler);
@@ -69,3 +71,20 @@ void in_dispatch_event(const SDL_Event_* ev)
 			DEBUG_WARN_ERR(ERR::LOGIC);	// invalid handler return value
 	}
 }
+
+void in_push_priority_event(const SDL_Event_* event)
+{
+	priority_events.push_back(*event);
+}
+
+int in_poll_event(SDL_Event_* event)
+{
+	if (!priority_events.empty())
+	{
+		*event = priority_events.front();
+		priority_events.pop_front();
+		return 1;
+	}
+
+	return SDL_PollEvent(&event->ev);
+}

source/lib/input.h

@@ -55,4 +55,13 @@ extern void in_reset_handlers();
 // send event to each handler (newest first) until one returns true
 extern void in_dispatch_event(const SDL_Event_* event);
 
+// push an event onto the back of a high-priority queue - the new event will
+// be returned by in_poll_event before any standard SDL events
+extern void in_push_priority_event(const SDL_Event_* event);
+
+// reads events that were pushed by in_push_priority_event, or (if there are
+// no high-priority events) reads from the SDL event queue with SDL_PollEvent.
+// returns 1 if an event was read, 0 otherwise.
+extern int in_poll_event(SDL_Event_* event);
+
 #endif	// #ifndef INCLUDED_INPUT

source/main.cpp

@@ -180,7 +180,7 @@ static void PumpEvents()
 	PROFILE3("dispatch events");
 
 	SDL_Event_ ev;
-	while (SDL_PollEvent(&ev.ev))
+	while (in_poll_event(&ev))
 	{
 		PROFILE2("event");
 		if (g_GUI)

source/ps/Hotkey.cpp

@@ -213,6 +213,14 @@ InReaction HotkeyInputHandler( const SDL_Event_* ev )
 		return IN_PASS;
 #endif
 
+	case SDL_HOTKEYDOWN:
+		g_HotkeyStatus[static_cast<const char*>(ev->ev.user.data1)] = true;
+		return IN_PASS;
+
+	case SDL_HOTKEYUP:
+		g_HotkeyStatus[static_cast<const char*>(ev->ev.user.data1)] = false;
+		return IN_PASS;
+
 	default:
 		return IN_PASS;
 	}
@@ -321,10 +329,6 @@ InReaction HotkeyInputHandler( const SDL_Event_* ev )
 
 		if( accept && !( consoleCapture && it->name != "console.toggle" ) )
 		{
-			// Tentatively set status to un-pressed, since it may be overridden by
-			// a closer match. (The closest matches will be set to pressed later.)
-			g_HotkeyStatus[it->name] = false;
-
 			// Check if this is an equally precise or more precise match
 			if( it->requires.size() + 1 >= closestMapMatch )
 			{
@@ -343,12 +347,10 @@ InReaction HotkeyInputHandler( const SDL_Event_* ev )
 
 	for (size_t i = 0; i < closestMapNames.size(); ++i)
 	{
-		g_HotkeyStatus[closestMapNames[i]] = true;
-
-		SDL_Event hotkeyNotification;
-		hotkeyNotification.type = SDL_HOTKEYDOWN;
-		hotkeyNotification.user.data1 = const_cast<char*>(closestMapNames[i]);
-		SDL_PushEvent(&hotkeyNotification);
+		SDL_Event_ hotkeyNotification;
+		hotkeyNotification.ev.type = SDL_HOTKEYDOWN;
+		hotkeyNotification.ev.user.data1 = const_cast<char*>(closestMapNames[i]);
+		in_push_priority_event(&hotkeyNotification);
 	}
 
 	// -- KEYUP SECTION --
@@ -386,11 +388,10 @@ InReaction HotkeyInputHandler( const SDL_Event_* ev )
 
 		if( accept )
 		{
-			g_HotkeyStatus[it->name] = false;
-			SDL_Event hotkeyNotification;
-			hotkeyNotification.type = SDL_HOTKEYUP;
-			hotkeyNotification.user.data1 = const_cast<char*>(it->name.c_str());
-			SDL_PushEvent( &hotkeyNotification );
+			SDL_Event_ hotkeyNotification;
+			hotkeyNotification.ev.type = SDL_HOTKEYUP;
+			hotkeyNotification.ev.user.data1 = const_cast<char*>(it->name.c_str());
+			in_push_priority_event(&hotkeyNotification);
 		}
 	}
 

source/tools/atlas/GameInterface/GameLoop.cpp

@@ -219,7 +219,7 @@ static void* RunEngine(void* data)
 
 		// Pump SDL events (e.g. hotkeys)
 		SDL_Event_ ev;
-		while (SDL_PollEvent(&ev.ev))
+		while (in_poll_event(&ev))
 			in_dispatch_event(&ev);
 
 		if (g_GUI)