Port of the programmable signals patch to recent trunk

Also add some additional changes from the SpringPP patch,
and make some other minor changes/fixes.

src/signal_func.h

@@ -12,10 +12,12 @@
 #ifndef SIGNAL_FUNC_H
 #define SIGNAL_FUNC_H
 
+#include "signal_type.h"
 #include "track_type.h"
 #include "tile_type.h"
 #include "direction_type.h"
 #include "company_type.h"
+#include "debug.h"
 
 /**
  * Maps a trackdir to the bit that stores its status in the map arrays, in the
@@ -47,6 +49,61 @@ static inline byte SignalOnTrack(Track track)
 	return _signal_on_track[track];
 }
 
+/// Is a given signal type a presignal entry signal?
+static inline bool IsEntrySignal(SignalType type)
+{
+	return type == SIGTYPE_ENTRY || type == SIGTYPE_COMBO || type == SIGTYPE_PROG;
+}
+
+/// Is a given signal type a presignal exit signal?
+static inline bool IsExitSignal(SignalType type)
+{
+	return type == SIGTYPE_EXIT || type == SIGTYPE_COMBO || type == SIGTYPE_PROG;
+}
+
+/// Is a given signal type a presignal combo signal?
+static inline bool IsComboSignal(SignalType type)
+{
+	return type == SIGTYPE_COMBO || type == SIGTYPE_PROG;
+}
+
+/// Is a given signal type a PBS signal?
+static inline bool IsPbsSignal(SignalType type)
+{
+	return type == SIGTYPE_PBS || type == SIGTYPE_PBS_ONEWAY;
+}
+
+/// Is this a programmable signal?
+static inline bool IsProgrammableSignal(SignalType type)
+{
+	return type == SIGTYPE_PROG;
+}
+
+/// Does a given signal have a PBS sprite?
+static inline bool IsSignalSpritePBS(SignalType type)
+{
+	return type >= SIGTYPE_FIRST_PBS_SPRITE;
+}
+
+static inline SignalType NextSignalType(SignalType cur, uint which_signals)
+{
+	bool pbs   = (which_signals != 0);
+	bool block = (which_signals != 1);
+
+	switch(cur) {
+		case SIGTYPE_NORMAL:     return block ? SIGTYPE_ENTRY      : SIGTYPE_PBS;
+		case SIGTYPE_ENTRY:      return block ? SIGTYPE_EXIT       : SIGTYPE_PBS;
+		case SIGTYPE_EXIT:       return block ? SIGTYPE_COMBO      : SIGTYPE_PBS;
+		case SIGTYPE_COMBO:      return block ? SIGTYPE_PROG       : SIGTYPE_PBS;
+		case SIGTYPE_PROG:       return pbs   ? SIGTYPE_PBS        : SIGTYPE_NORMAL;
+		case SIGTYPE_PBS:        return pbs   ? SIGTYPE_PBS_ONEWAY : SIGTYPE_NORMAL;
+		case SIGTYPE_PBS_ONEWAY: return block ? SIGTYPE_NORMAL     : SIGTYPE_PBS;
+		default:
+			DEBUG(map, 0, "Attempt to cycle from signal type %d", cur);
+			return SIGTYPE_NORMAL; // Fortunately mostly harmless
+	}
+}
+
 /** State of the signal segment */
 enum SigSegState {
 	SIGSEG_FREE,    ///< Free and has no pre-signal exits or at least one green exit
@@ -54,6 +111,30 @@ enum SigSegState {
 	SIGSEG_PBS,     ///< Segment is a PBS segment
 };
 
+/** Checks for any data attached to any signals, and removes it. Call when performing
+ * an action which may potentially remove signals from a tile, in order to avoid leaking
+ * data.
+ */
+void CheckRemoveSignalsFromTile(TileIndex tile);
+
+/** Checks for, and removes, any extra signal data. Call when removing a piece of track
+ * which is potentially signalled, in order to free any extra data that may be associated
+ * with said track.
+ */
+void CheckRemoveSignal(TileIndex tile, Track track);
+
+/** Adds a signal dependency
+ *  The signal identified by @p dep will be marked as dependend upon
+ *  the signal identified by @p on
+ */
+void AddSignalDependency(SignalReference on, SignalReference dep);
+
+/// Removes a signal dependency. Arguments same as AddSignalDependency
+void RemoveSignalDependency(SignalReference on, SignalReference dep);
+
+/// Frees signal dependencies (for newgame/load)
+void FreeSignalDependencies();
+
 SigSegState UpdateSignalsOnSegment(TileIndex tile, DiagDirection side, Owner owner);
 void SetSignalsOnBothDir(TileIndex tile, Track track, Owner owner);
 void AddTrackToSignalBuffer(TileIndex tile, Track track, Owner owner);