(svn r10765) -Documentation [FS#1100]: of rail.h. Based on a patch by Progman.

1 files changed, 343 insertions, 122 deletions

diff --git a/src/rail.h b/src/rail.h
index 0ffefdb8e..ab6ea3b9f 100644
--- a/src/rail.h
+++ b/src/rail.h
@@ -9,14 +9,19 @@
 #include "direction.h"
 #include "tile.h"
 
+/**
+ * Enumeration for all possible railtypes.
+ *
+ * This enumeration defines all 4 possible railtypes.
+ */
 enum RailType {
-	RAILTYPE_BEGIN    = 0,
-	RAILTYPE_RAIL     = 0,
-	RAILTYPE_ELECTRIC = 1,
-	RAILTYPE_MONO     = 2,
-	RAILTYPE_MAGLEV   = 3,
-	RAILTYPE_END,
-	INVALID_RAILTYPE  = 0xFF
+	RAILTYPE_BEGIN    = 0,          ///< Used for iterations
+	RAILTYPE_RAIL     = 0,          ///< Standard non-electric rails
+	RAILTYPE_ELECTRIC = 1,          ///< Electric rails
+	RAILTYPE_MONO     = 2,          ///< Monorail
+	RAILTYPE_MAGLEV   = 3,          ///< Maglev
+	RAILTYPE_END,                   ///< Used for iterations
+	INVALID_RAILTYPE  = 0xFF        ///< Flag for invalid railtype
 };
 
 typedef byte RailTypeMask;
@@ -28,18 +33,20 @@ template <> struct EnumPropsT<RailType> : MakeEnumPropsT<RailType, byte, RAILTYP
 typedef TinyEnumT<RailType> RailTypeByte;
 
 
-/** These are used to specify a single track.
- * Can be translated to a trackbit with TrackToTrackbit */
+/**
+ * These are used to specify a single track.
+ * Can be translated to a trackbit with TrackToTrackbit
+ */
 enum Track {
-	TRACK_BEGIN = 0,
-	TRACK_X     = 0,
-	TRACK_Y     = 1,
-	TRACK_UPPER = 2,
-	TRACK_LOWER = 3,
-	TRACK_LEFT  = 4,
-	TRACK_RIGHT = 5,
-	TRACK_END,
-	INVALID_TRACK = 0xFF
+	TRACK_BEGIN = 0,        ///< Used for iterations
+	TRACK_X     = 0,        ///< Track along the x-axis (north-east to south-west)
+	TRACK_Y     = 1,        ///< Track along the y-axis (north-west to south-east)
+	TRACK_UPPER = 2,        ///< Track in the upper corner of the tile (north)
+	TRACK_LOWER = 3,        ///< Track in the lower corner of the tile (south)
+	TRACK_LEFT  = 4,        ///< Track in the left corner of the tile (west)
+	TRACK_RIGHT = 5,        ///< Track in the right corner of the tile (east)
+	TRACK_END,              ///< Used for iterations
+	INVALID_TRACK = 0xFF    ///< Flag for an invalid track
 };
 
 /** Allow incrementing of Track variables */
@@ -49,10 +56,14 @@ template <> struct EnumPropsT<Track> : MakeEnumPropsT<Track, byte, TRACK_BEGIN,
 typedef TinyEnumT<Track> TrackByte;
 
 
-/** Convert an Axis to the corresponding Track
+/**
+ * Convert an Axis to the corresponding Track
  * AXIS_X -> TRACK_X
  * AXIS_Y -> TRACK_Y
  * Uses the fact that they share the same internal encoding
+ *
+ * @param a the axis to convert
+ * @return the track corresponding to the axis
  */
 static inline Track AxisToTrack(Axis a)
 {
@@ -62,25 +73,25 @@ static inline Track AxisToTrack(Axis a)
 
 /** Bitfield corresponding to Track */
 enum TrackBits {
-	TRACK_BIT_NONE    = 0U,
-	TRACK_BIT_X       = 1U << TRACK_X,
-	TRACK_BIT_Y       = 1U << TRACK_Y,
-	TRACK_BIT_UPPER   = 1U << TRACK_UPPER,
-	TRACK_BIT_LOWER   = 1U << TRACK_LOWER,
-	TRACK_BIT_LEFT    = 1U << TRACK_LEFT,
-	TRACK_BIT_RIGHT   = 1U << TRACK_RIGHT,
-	TRACK_BIT_CROSS   = TRACK_BIT_X     | TRACK_BIT_Y,
-	TRACK_BIT_HORZ    = TRACK_BIT_UPPER | TRACK_BIT_LOWER,
-	TRACK_BIT_VERT    = TRACK_BIT_LEFT  | TRACK_BIT_RIGHT,
-	TRACK_BIT_3WAY_NE = TRACK_BIT_X     | TRACK_BIT_UPPER | TRACK_BIT_RIGHT,
-	TRACK_BIT_3WAY_SE = TRACK_BIT_Y     | TRACK_BIT_LOWER | TRACK_BIT_RIGHT,
-	TRACK_BIT_3WAY_SW = TRACK_BIT_X     | TRACK_BIT_LOWER | TRACK_BIT_LEFT,
-	TRACK_BIT_3WAY_NW = TRACK_BIT_Y     | TRACK_BIT_UPPER | TRACK_BIT_LEFT,
-	TRACK_BIT_ALL     = TRACK_BIT_CROSS | TRACK_BIT_HORZ  | TRACK_BIT_VERT,
-	TRACK_BIT_MASK    = 0x3FU,
-	TRACK_BIT_WORMHOLE = 0x40U,
-	TRACK_BIT_DEPOT   = 0x80U,
-	INVALID_TRACK_BIT = 0xFF
+	TRACK_BIT_NONE    = 0U,                                                 ///< No track
+	TRACK_BIT_X       = 1U << TRACK_X,                                      ///< X-axis track
+	TRACK_BIT_Y       = 1U << TRACK_Y,                                      ///< Y-axis track
+	TRACK_BIT_UPPER   = 1U << TRACK_UPPER,                                  ///< Upper track
+	TRACK_BIT_LOWER   = 1U << TRACK_LOWER,                                  ///< Lower track
+	TRACK_BIT_LEFT    = 1U << TRACK_LEFT,                                   ///< Left track
+	TRACK_BIT_RIGHT   = 1U << TRACK_RIGHT,                                  ///< Right track
+	TRACK_BIT_CROSS   = TRACK_BIT_X     | TRACK_BIT_Y,                      ///< X-Y-axis cross
+	TRACK_BIT_HORZ    = TRACK_BIT_UPPER | TRACK_BIT_LOWER,                  ///< Upper and lower track
+	TRACK_BIT_VERT    = TRACK_BIT_LEFT  | TRACK_BIT_RIGHT,                  ///< Left and right track
+	TRACK_BIT_3WAY_NE = TRACK_BIT_X     | TRACK_BIT_UPPER | TRACK_BIT_RIGHT,///< "Arrow" to the north-east
+	TRACK_BIT_3WAY_SE = TRACK_BIT_Y     | TRACK_BIT_LOWER | TRACK_BIT_RIGHT,///< "Arrow" to the south-east
+	TRACK_BIT_3WAY_SW = TRACK_BIT_X     | TRACK_BIT_LOWER | TRACK_BIT_LEFT, ///< "Arrow" to the south-west
+	TRACK_BIT_3WAY_NW = TRACK_BIT_Y     | TRACK_BIT_UPPER | TRACK_BIT_LEFT, ///< "Arrow" to the north-west
+	TRACK_BIT_ALL     = TRACK_BIT_CROSS | TRACK_BIT_HORZ  | TRACK_BIT_VERT, ///< All possible tracks
+	TRACK_BIT_MASK    = 0x3FU,                                              ///< Bitmask for the first 6 bits
+	TRACK_BIT_WORMHOLE = 0x40U,                                             ///< Bitflag for a wormhole (used for tunnels)
+	TRACK_BIT_DEPOT   = 0x80U,                                              ///< Bitflag for a depot
+	INVALID_TRACK_BIT = 0xFF                                                ///< Flag for an invalid trackbits value
 };
 
 /** Define basic enum properties */
@@ -91,70 +102,83 @@ DECLARE_ENUM_AS_BIT_SET(TrackBits);
 
 /**
  * Maps a Track to the corresponding TrackBits value
+ * @param track the track to convert
+ * @return the converted TrackBits value of the track
  */
 static inline TrackBits TrackToTrackBits(Track track)
 {
 	return (TrackBits)(1 << track);
 }
 
-
+/**
+ * Maps an Axis to the corresponding TrackBits value
+ * @param a the axis to convert
+ * @return the converted TrackBits value of the axis
+ */
 static inline TrackBits AxisToTrackBits(Axis a)
 {
 	return TrackToTrackBits(AxisToTrack(a));
 }
 
 
-/** These are a combination of tracks and directions. Values are 0-5 in one
+/**
+ * Enumeration for tracks and directions.
+ *
+ * These are a combination of tracks and directions. Values are 0-5 in one
  * direction (corresponding to the Track enum) and 8-13 in the other direction.
  * 6, 7, 14 and 15 are used to encode the reversing of road vehicles. Those
  * reversing track dirs are not considered to be 'valid' except in a small
  * corner in the road vehicle controller.
  */
 enum Trackdir {
-	TRACKDIR_BEGIN    =  0,
-	TRACKDIR_X_NE     =  0,
-	TRACKDIR_Y_SE     =  1,
-	TRACKDIR_UPPER_E  =  2,
-	TRACKDIR_LOWER_E  =  3,
-	TRACKDIR_LEFT_S   =  4,
-	TRACKDIR_RIGHT_S  =  5,
-	TRACKDIR_RVREV_NE =  6,
-	TRACKDIR_RVREV_SE =  7,
-	TRACKDIR_X_SW     =  8,
-	TRACKDIR_Y_NW     =  9,
-	TRACKDIR_UPPER_W  = 10,
-	TRACKDIR_LOWER_W  = 11,
-	TRACKDIR_LEFT_N   = 12,
-	TRACKDIR_RIGHT_N  = 13,
-	TRACKDIR_RVREV_SW = 14,
-	TRACKDIR_RVREV_NW = 15,
-	TRACKDIR_END,
-	INVALID_TRACKDIR  = 0xFF,
+	TRACKDIR_BEGIN    =  0,         ///< Used for iterations
+	TRACKDIR_X_NE     =  0,         ///< X-axis and direction to north-east
+	TRACKDIR_Y_SE     =  1,         ///< Y-axis and direction to south-east
+	TRACKDIR_UPPER_E  =  2,         ///< Upper track and direction to east
+	TRACKDIR_LOWER_E  =  3,         ///< Lower track and direction to east
+	TRACKDIR_LEFT_S   =  4,         ///< Left track and direction to south
+	TRACKDIR_RIGHT_S  =  5,         ///< Right track and direction to south
+	TRACKDIR_RVREV_NE =  6,         ///< (Road vehicle) reverse direction north-east
+	TRACKDIR_RVREV_SE =  7,         ///< (Road vehicle) reverse direction south-east
+	TRACKDIR_X_SW     =  8,         ///< X-axis and direction to south-west
+	TRACKDIR_Y_NW     =  9,         ///< Y-axis and direction to north-west
+	TRACKDIR_UPPER_W  = 10,         ///< Upper track and direction to west
+	TRACKDIR_LOWER_W  = 11,         ///< Lower track and direction to west
+	TRACKDIR_LEFT_N   = 12,         ///< Left track and direction to north
+	TRACKDIR_RIGHT_N  = 13,         ///< Right track and direction to north
+	TRACKDIR_RVREV_SW = 14,         ///< (Road vehicle) reverse direction south-west
+	TRACKDIR_RVREV_NW = 15,         ///< (Road vehicle) reverse direction north-west
+	TRACKDIR_END,                   ///< Used for iterations
+	INVALID_TRACKDIR  = 0xFF,       ///< Flag for an invalid trackdir
 };
 
 /** Define basic enum properties */
 template <> struct EnumPropsT<Trackdir> : MakeEnumPropsT<Trackdir, byte, TRACKDIR_BEGIN, TRACKDIR_END, INVALID_TRACKDIR> {};
 typedef TinyEnumT<Trackdir> TrackdirByte;
 
-/** These are a combination of tracks and directions. Values are 0-5 in one
- * direction (corresponding to the Track enum) and 8-13 in the other direction. */
+/**
+ * Enumeration of bitmasks for the TrackDirs
+ *
+ * These are a combination of tracks and directions. Values are 0-5 in one
+ * direction (corresponding to the Track enum) and 8-13 in the other direction.
+ */
 enum TrackdirBits {
-	TRACKDIR_BIT_NONE     = 0x0000,
-	TRACKDIR_BIT_X_NE     = 0x0001,
-	TRACKDIR_BIT_Y_SE     = 0x0002,
-	TRACKDIR_BIT_UPPER_E  = 0x0004,
-	TRACKDIR_BIT_LOWER_E  = 0x0008,
-	TRACKDIR_BIT_LEFT_S   = 0x0010,
-	TRACKDIR_BIT_RIGHT_S  = 0x0020,
+	TRACKDIR_BIT_NONE     = 0x0000, ///< No track build
+	TRACKDIR_BIT_X_NE     = 0x0001, ///< Track x-axis, direction north-east
+	TRACKDIR_BIT_Y_SE     = 0x0002, ///< Track y-axis, direction south-east
+	TRACKDIR_BIT_UPPER_E  = 0x0004, ///< Track upper, direction east
+	TRACKDIR_BIT_LOWER_E  = 0x0008, ///< Track lower, direction east
+	TRACKDIR_BIT_LEFT_S   = 0x0010, ///< Track left, direction south
+	TRACKDIR_BIT_RIGHT_S  = 0x0020, ///< Track right, direction south
 	/* Again, note the two missing values here. This enables trackdir -> track conversion by doing (trackdir & 0xFF) */
-	TRACKDIR_BIT_X_SW     = 0x0100,
-	TRACKDIR_BIT_Y_NW     = 0x0200,
-	TRACKDIR_BIT_UPPER_W  = 0x0400,
-	TRACKDIR_BIT_LOWER_W  = 0x0800,
-	TRACKDIR_BIT_LEFT_N   = 0x1000,
-	TRACKDIR_BIT_RIGHT_N  = 0x2000,
-	TRACKDIR_BIT_MASK     = 0x3F3F,
-	INVALID_TRACKDIR_BIT  = 0xFFFF,
+	TRACKDIR_BIT_X_SW     = 0x0100, ///< Track x-axis, direction south-west
+	TRACKDIR_BIT_Y_NW     = 0x0200, ///< Track y-axis, direction north-west
+	TRACKDIR_BIT_UPPER_W  = 0x0400, ///< Track upper, direction west
+	TRACKDIR_BIT_LOWER_W  = 0x0800, ///< Track lower, direction west
+	TRACKDIR_BIT_LEFT_N   = 0x1000, ///< Track left, direction north
+	TRACKDIR_BIT_RIGHT_N  = 0x2000, ///< Track right, direction north
+	TRACKDIR_BIT_MASK     = 0x3F3F, ///< Bitmask for bit-operations
+	INVALID_TRACKDIR_BIT  = 0xFFFF, ///< Flag for an invalid trackdirbit value
 };
 
 /** Define basic enum properties */
@@ -195,14 +219,14 @@ struct RailtypeInfo {
 	} gui_sprites;
 
 	struct {
-		CursorID rail_ns;
-		CursorID rail_swne;
-		CursorID rail_ew;
-		CursorID rail_nwse;
-		CursorID autorail;
-		CursorID depot;
-		CursorID tunnel;
-		CursorID convert;
+		CursorID rail_ns;    ///< Cursor for building rail in N-S direction
+		CursorID rail_swne;  ///< Cursor for building rail in X direction
+		CursorID rail_ew;    ///< Cursor for building rail in E-W direction
+		CursorID rail_nwse;  ///< Cursor for building rail in Y direction
+		CursorID autorail;   ///< Cursor for autorail tool
+		CursorID depot;      ///< Cursor for building a depot
+		CursorID tunnel;     ///< Cursor for building a tunnel
+		CursorID convert;    ///< Cursor for converting track
 	} cursor;
 
 	struct {
@@ -248,12 +272,28 @@ enum {
 
 /**
  * Maps a Trackdir to the corresponding TrackdirBits value
+ * @param trackdir the track direction to convert
+ * @return the converted TrackdirBits value
  */
-static inline TrackdirBits TrackdirToTrackdirBits(Trackdir trackdir) { return (TrackdirBits)(1 << trackdir); }
+static inline TrackdirBits TrackdirToTrackdirBits(Trackdir trackdir)
+{
+	return (TrackdirBits)(1 << trackdir);
+}
 
 /**
-* Removes first Track from TrackBits and returns it
-*/
+ * Removes first Track from TrackBits and returns it
+ *
+ * This function searchs for the first bit in the TrackBits,
+ * remove this bit from the parameter and returns the found
+ * bit as Track value. It returns INVALID_TRACK if the
+ * parameter was TRACK_BIT_NONE or INVALID_TRACK_BIT. This
+ * is basically used in while-loops to get up to 6 possible
+ * tracks on a tile until the parameter becomes TRACK_BIT_NONE.
+ *
+ * @param tracks The value with the TrackBits
+ * @return The first Track from the TrackBits value
+ * @see FindFirstTrack
+ */
 static inline Track RemoveFirstTrack(TrackBits *tracks)
 {
 	if (*tracks != TRACK_BIT_NONE && *tracks != INVALID_TRACK_BIT) {
@@ -265,8 +305,19 @@ static inline Track RemoveFirstTrack(TrackBits *tracks)
 }
 
 /**
-* Removes first Trackdir from TrackdirBits and returns it
-*/
+ * Removes first Trackdir from TrackdirBits and returns it
+ *
+ * This function searchs for the first bit in the TrackdirBits parameter,
+ * remove this bit from the parameter and returns the fnound bit as
+ * Trackdir value. It returns INVALID_TRACKDIR if the trackdirs is
+ * TRACKDIR_BIT_NONE or INVALID_TRACKDIR_BIT. This is basically used in a
+ * while-loop to get all track-directions step by step until the value
+ * reaches TRACKDIR_BIT_NONE.
+ *
+ * @param trackdirs The value with the TrackdirBits
+ * @return The first Trackdir from the TrackdirBits value
+ * @see FindFirstTrackdir
+ */
 static inline Trackdir RemoveFirstTrackdir(TrackdirBits *trackdirs)
 {
 	if (*trackdirs != TRACKDIR_BIT_NONE && *trackdirs != INVALID_TRACKDIR_BIT) {
@@ -278,16 +329,31 @@ static inline Trackdir RemoveFirstTrackdir(TrackdirBits *trackdirs)
 }
 
 /**
-* Returns first Track from TrackBits or INVALID_TRACK
-*/
+ * Returns first Track from TrackBits or INVALID_TRACK
+ *
+ * This function returns the first Track found in the TrackBits value as Track-value.
+ * It returns INVALID_TRACK if the parameter is TRACK_BIT_NONE or INVALID_TRACK_BIT.
+ *
+ * @param tracks The TrackBits value
+ * @return The first Track found or INVALID_TRACK
+ * @see RemoveFirstTrack
+ */
 static inline Track FindFirstTrack(TrackBits tracks)
 {
 	return (tracks != TRACK_BIT_NONE && tracks != INVALID_TRACK_BIT) ? (Track)FIND_FIRST_BIT(tracks) : INVALID_TRACK;
 }
 
 /**
-* Converts TrackBits to Track. TrackBits must contain just one Track or INVALID_TRACK_BIT!
-*/
+ * Converts TrackBits to Track.
+ *
+ * This function converts a TrackBits value to a Track value. As it
+ * is not possible to convert two or more tracks to one track the
+ * parameter must contain only one track or be the INVALID_TRACK_BIT value.
+ *
+ * @param tracks The TrackBits value to convert
+ * @return The Track from the value or INVALID_TRACK
+ * @pre tracks must contains only one Track or be INVALID_TRACK_BIT
+ */
 static inline Track TrackBitsToTrack(TrackBits tracks)
 {
 	assert(tracks == INVALID_TRACK_BIT || (tracks != TRACK_BIT_NONE && KILL_FIRST_BIT(tracks & TRACK_BIT_MASK) == 0));
@@ -295,8 +361,17 @@ static inline Track TrackBitsToTrack(TrackBits tracks)
 }
 
 /**
-* Returns first Trackdir from TrackdirBits or INVALID_TRACKDIR
-*/
+ * Returns first Trackdir from TrackdirBits or INVALID_TRACKDIR
+ *
+ * This function returns the first Trackdir in the given TrackdirBits value or
+ * INVALID_TRACKDIR if the value is TRACKDIR_BIT_NONE. The TrackdirBits must
+ * not be INVALID_TRACKDIR_BIT.
+ *
+ * @param trackdirs The TrackdirBits value
+ * @return The first Trackdir from the TrackdirBits or INVALID_TRACKDIR on TRACKDIR_BIT_NONE.
+ * @pre trackdirs must not be INVALID_TRACKDIR_BIT
+ * @see RemoveFirstTrackdir
+ */
 static inline Trackdir FindFirstTrackdir(TrackdirBits trackdirs)
 {
 	assert((trackdirs & ~TRACKDIR_BIT_MASK) == TRACKDIR_BIT_NONE);
@@ -304,13 +379,30 @@ static inline Trackdir FindFirstTrackdir(TrackdirBits trackdirs)
 }
 
 /**
- * These functions check the validity of Tracks and Trackdirs. assert against
- * them when convenient.
+ * Checks if a Track is valid.
+ *
+ * @param track The value to check
+ * @return true if the given value is a valid track.
+ * @note Use this in an assert()
  */
-static inline bool IsValidTrack(Track track) { return track < TRACK_END; }
-static inline bool IsValidTrackdir(Trackdir trackdir) { return (TrackdirToTrackdirBits(trackdir) & TRACKDIR_BIT_MASK) != 0; }
+static inline bool IsValidTrack(Track track)
+{
+	return track < TRACK_END;
+}
 
 /**
+ * Checks if a Trackdir is valid.
+ *
+ * @param trackdir The value to check
+ * @return true if the given valie is a valid Trackdir
+ * @note Use this in an assert()
+ */
+static inline bool IsValidTrackdir(Trackdir trackdir)
+{
+	return (TrackdirToTrackdirBits(trackdir) & TRACKDIR_BIT_MASK) != 0;
+}
+
+/*
  * Functions to map tracks to the corresponding bits in the signal
  * presence/status bytes in the map. You should not use these directly, but
  * wrapper functions below instead. XXX: Which are these?
@@ -354,6 +446,13 @@ static inline byte SignalOnTrack(Track track)
 
 /**
  * Maps a trackdir to the reverse trackdir.
+ *
+ * Returns the reverse trackdir of a Trackdir value. The reverse trackdir
+ * is the same track with the other direction on it.
+ *
+ * @param trackdir The Trackdir value
+ * @return The reverse trackdir
+ * @pre trackdir must not be INVALID_TRACKDIR
  */
 static inline Trackdir ReverseTrackdir(Trackdir trackdir)
 {
@@ -363,20 +462,42 @@ static inline Trackdir ReverseTrackdir(Trackdir trackdir)
 
 /**
  * Returns the Track that a given Trackdir represents
+ *
+ * This function filters the Track which is used in the Trackdir value and
+ * returns it as a Track value.
+ *
+ * @param trackdir The trackdir value
+ * @return The Track which is used in the value
  */
-static inline Track TrackdirToTrack(Trackdir trackdir) { return (Track)(trackdir & 0x7); }
+static inline Track TrackdirToTrack(Trackdir trackdir)
+{
+	return (Track)(trackdir & 0x7);
+}
 
 /**
- * Returns a Trackdir for the given Track. Since every Track corresponds to
- * two Trackdirs, we choose the one which points between NE and S.
- * Note that the actual implementation is quite futile, but this might change
+ * Returns a Trackdir for the given Track
+ *
+ * Since every Track corresponds to two Trackdirs, we choose the
+ * one which points between NE and S. Note that the actual
+ * implementation is quite futile, but this might change
  * in the future.
+ *
+ * @param track The given Track
+ * @return The Trackdir from the given Track
  */
-static inline Trackdir TrackToTrackdir(Track track) { return (Trackdir)track; }
+static inline Trackdir TrackToTrackdir(Track track)
+{
+	return (Trackdir)track;
+}
 
 /**
- * Returns a TrackdirBit mask that contains the two TrackdirBits that
+ * Returns a TrackdirBit mask from a given Track
+ *
+ * The TrackdirBit mask contains the two TrackdirBits that
  * correspond with the given Track (one for each direction).
+ *
+ * @param track The track to get the TrackdirBits from
+ * @return The TrackdirBits which the selected tracks
  */
 static inline TrackdirBits TrackToTrackdirBits(Track track)
 {
@@ -385,8 +506,12 @@ static inline TrackdirBits TrackToTrackdirBits(Track track)
 }
 
 /**
- * Discards all directional information from the given TrackdirBits. Any
- * Track which is present in either direction will be present in the result.
+ * Discards all directional information from a TrackdirBits value
+ *
+ * Any Track which is present in either direction will be present in the result.
+ *
+ * @param bits The TrackdirBits to get the TrackBits from
+ * @return The TrackBits
  */
 static inline TrackBits TrackdirBitsToTrackBits(TrackdirBits bits)
 {
@@ -395,8 +520,13 @@ static inline TrackBits TrackdirBitsToTrackBits(TrackdirBits bits)
 
 /**
  * Maps a trackdir to the trackdir that you will end up on if you go straight
- * ahead. This will be the same trackdir for diagonal trackdirs, but a
+ * ahead.
+ *
+ * This will be the same trackdir for diagonal trackdirs, but a
  * different (alternating) one for straight trackdirs
+ *
+ * @param trackdir The given trackdir
+ * @return The next Trackdir value of the next tile.
  */
 static inline Trackdir NextTrackdir(Trackdir trackdir)
 {
@@ -406,6 +536,13 @@ static inline Trackdir NextTrackdir(Trackdir trackdir)
 
 /**
  * Maps a track to all tracks that make 90 deg turns with it.
+ *
+ * For the diagonal directions these are the complement of the
+ * direction, for the straight directions these are the
+ * two vertical or horizontal tracks, depend on the given direction
+ *
+ * @param track The given track
+ * @return The TrackBits with the tracks marked which cross the given track by 90 deg.
  */
 static inline TrackBits TrackCrossesTracks(Track track)
 {
@@ -416,6 +553,14 @@ static inline TrackBits TrackCrossesTracks(Track track)
 /**
  * Maps a trackdir to the (4-way) direction the tile is exited when following
  * that trackdir.
+ *
+ * For the diagonal directions these are the same directions. For
+ * the straight directions these are the directions from the imagined
+ * base-tile to the bordering tile which will be joined if the given
+ * straight direction is leaved from the base-tile.
+ *
+ * @param trackdir The given track direction
+ * @return The direction which points to the resulting tile if following the Trackdir
  */
 static inline DiagDirection TrackdirToExitdir(Trackdir trackdir)
 {
@@ -426,6 +571,17 @@ static inline DiagDirection TrackdirToExitdir(Trackdir trackdir)
 /**
  * Maps a track and an (4-way) dir to the trackdir that represents the track
  * with the exit in the given direction.
+ *
+ * For the diagonal tracks the resulting track direction are clear for a given
+ * DiagDirection. It either matches the direction or it returns INVALID_TRACKDIR,
+ * as a TRACK_X cannot be applied with DIAG_SE.
+ * For the straight tracks the resulting track direction will be the
+ * direction which the DiagDirection is pointing. But this will be INVALID_TRACKDIR
+ * if the DiagDirection is pointing 'away' the track.
+ *
+ * @param track The track to applie an direction on
+ * @param diagdir The DiagDirection to applie on
+ * @return The resulting track direction or INVALID_TRACKDIR if not possible.
  */
 static inline Trackdir TrackExitdirToTrackdir(Track track, DiagDirection diagdir)
 {
@@ -435,7 +591,20 @@ static inline Trackdir TrackExitdirToTrackdir(Track track, DiagDirection diagdir
 
 /**
  * Maps a track and an (4-way) dir to the trackdir that represents the track
- * with the exit in the given direction.
+ * with the entry in the given direction.
+ *
+ * For the diagonal tracks the return value is clear, its either the matching
+ * track direction or INVALID_TRACKDIR.
+ * For the straight tracks this returns the track direction which results if
+ * you follow the DiagDirection and then turn by 45 deg left or right on the
+ * next tile. The new direction on the new track will be the returning Trackdir
+ * value. If the parameters makes no sense like the track TRACK_UPPER and the
+ * diraction DIAGDIR_NE (target track cannot be reached) this function returns
+ * INVALID_TRACKDIR.
+ *
+ * @param track The target track
+ * @param diagdir The direction to "come from"
+ * @return the resulting Trackdir or INVALID_TRACKDIR if not possible.
  */
 static inline Trackdir TrackEnterdirToTrackdir(Track track, DiagDirection diagdir)
 {
@@ -456,6 +625,9 @@ static inline Trackdir TrackDirectionToTrackdir(Track track, Direction dir)
 /**
  * Maps a (4-way) direction to the diagonal trackdir that runs in that
  * direction.
+ *
+ * @param diagdir The direction
+ * @return The resulting Trackdir direction
  */
 static inline Trackdir DiagdirToDiagTrackdir(DiagDirection diagdir)
 {
@@ -465,8 +637,15 @@ static inline Trackdir DiagdirToDiagTrackdir(DiagDirection diagdir)
 
 /**
  * Returns all trackdirs that can be reached when entering a tile from a given
- * (diagonal) direction. This will obviously include 90 degree turns, since no
- * information is available about the exact angle of entering */
+ * (diagonal) direction.
+ *
+ * This will obviously include 90 degree turns, since no information is available
+ * about the exact angle of entering
+ *
+ * @param diagdir The joining direction
+ * @return The TrackdirBits which can be used from the given direction
+ * @see DiagdirReachesTracks
+ */
 static inline TrackdirBits DiagdirReachesTrackdirs(DiagDirection diagdir)
 {
 	extern const TrackdirBits _exitdir_reaches_trackdirs[DIAGDIR_END];
@@ -475,26 +654,46 @@ static inline TrackdirBits DiagdirReachesTrackdirs(DiagDirection diagdir)
 
 /**
  * Returns all tracks that can be reached when entering a tile from a given
- * (diagonal) direction. This will obviously include 90 degree turns, since no
- * information is available about the exact angle of entering */
+ * (diagonal) direction.
+ *
+ * This will obviously include 90 degree turns, since no
+ * information is available about the exact angle of entering
+ *
+ * @param diagdir The joining irection
+ * @return The tracks which can be used
+ * @see DiagdirReachesTrackdirs
+ */
 static inline TrackBits DiagdirReachesTracks(DiagDirection diagdir) { return TrackdirBitsToTrackBits(DiagdirReachesTrackdirs(diagdir)); }
 
 /**
  * Maps a trackdir to the trackdirs that can be reached from it (ie, when
- * entering the next tile. This will include 90 degree turns!
+ * entering the next tile.
+ *
+ * This will include 90 degree turns!
+ *
+ * @param trackdir The track direction which will be leaved
+ * @return The track directions which can be used from this direction (in the next tile)
  */
 static inline TrackdirBits TrackdirReachesTrackdirs(Trackdir trackdir)
 {
 	extern const TrackdirBits _exitdir_reaches_trackdirs[DIAGDIR_END];
 	return _exitdir_reaches_trackdirs[TrackdirToExitdir(trackdir)];
 }
-
 /* Note that there is no direct table for this function (there used to be),
  * but it uses two simpeler tables to achieve the result */
 
-
 /**
  * Maps a trackdir to all trackdirs that make 90 deg turns with it.
+ *
+ * For the diagonal tracks this returns the track direction bits
+ * of the other axis in both directions, which cannot be joined by
+ * the given track direction.
+ * For the straight tracks this returns all possible 90 deg turns
+ * either on the current tile (which no train can joined) or on the
+ * bordering tiles.
+ *
+ * @param trackdir The track direction
+ * @return The TrackdirBits which are (more or less) 90 deg turns.
  */
 static inline TrackdirBits TrackdirCrossesTrackdirs(Trackdir trackdir)
 {
@@ -502,13 +701,27 @@ static inline TrackdirBits TrackdirCrossesTrackdirs(Trackdir trackdir)
 	return _track_crosses_trackdirs[TrackdirToTrack(trackdir)];
 }
 
+/**
+ * Checks if a given Track is diagonal
+ *
+ * @param track The given track to check
+ * @return true if diagonal, else false
+ */
+static inline bool IsDiagonalTrack(Track track)
+{
+	return (track == TRACK_X) || (track == TRACK_Y);
+}
 
-/* Checks if a given Track is diagonal */
-static inline bool IsDiagonalTrack(Track track) { return (track == TRACK_X) || (track == TRACK_Y); }
-
-/* Checks if a given Trackdir is diagonal. */
-static inline bool IsDiagonalTrackdir(Trackdir trackdir) { return IsDiagonalTrack(TrackdirToTrack(trackdir)); }
-
+/**
+ * Checks if a given Trackdir is diagonal.
+ *
+ * @param trackdir The given trackdir
+ * @return true if the trackdir use a diagonal track
+ */
+static inline bool IsDiagonalTrackdir(Trackdir trackdir)
+{
+	return IsDiagonalTrack(TrackdirToTrack(trackdir));
+}
 
 /**
  * Returns a pointer to the Railtype information for a given railtype
@@ -535,6 +748,14 @@ static inline bool IsCompatibleRail(RailType enginetype, RailType tiletype)
 	return HASBIT(GetRailTypeInfo(enginetype)->compatible_railtypes, tiletype);
 }
 
+/**
+ * Checks if an engine of the given RailType got power on a tile with a given
+ * RailType. This would normally just be an equality check, but for electric
+ * rails (which also support non-electric engines).
+ * @return Whether the engine got power on this tile.
+ * @param  enginetype The RailType of the engine we are considering.
+ * @param  tiletype   The RailType of the tile we are considering.
+ */
 static inline bool HasPowerOnRail(RailType enginetype, RailType tiletype)
 {
 	return HASBIT(GetRailTypeInfo(enginetype)->powered_railtypes, tiletype);