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/* $Id$ */

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/** @file slope.h Definitions of a slope.

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 * This file defines the enumeration and helper functions for handling

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 * the slope info of a tile.

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 */

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#ifndef SLOPE_H

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#define SLOPE_H

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/**

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 * Enumeration of tile corners

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 */

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enum Corner {

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	CORNER_W = 0,

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	CORNER_S = 1,

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	CORNER_E = 2,

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	CORNER_N = 3,

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	CORNER_END

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};

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/**

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 * Enumeration for the slope-type.

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 *

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 * This enumeration use the chars N,E,S,W corresponding the

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 * direction north, east, south and west. The top corner of a tile

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 * is the north-part of the tile. The whole slope is encoded with

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 * 5 bits, 4 bits for each corner and 1 bit for a steep-flag.

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 *

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 * For halftile slopes an extra 3 bits are used to represent this

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 * properly; 1 bit for a halftile-flag and 2 bits to encode which

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 * extra side (corner) is leveled when the slope of the first 5

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 * bits is applied. This means that there can only be one leveled

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 * slope for steep slopes, which is logical because two leveled

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 * slopes would mean that it is not a steep slope as halftile

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 * slopes only span one height level.

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 */

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enum Slope {

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	SLOPE_FLAT     = 0x00,                                  ///< a flat tile

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	SLOPE_W        = 0x01,                                  ///< the west corner of the tile is raised

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	SLOPE_S        = 0x02,                                  ///< the south corner of the tile is raised

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	SLOPE_E        = 0x04,                                  ///< the east corner of the tile is raised

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	SLOPE_N        = 0x08,                                  ///< the north corner of the tile is raised

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	SLOPE_STEEP    = 0x10,                                  ///< indicates the slope is steep

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	SLOPE_NW       = SLOPE_N | SLOPE_W,                     ///< north and west corner are raised

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	SLOPE_SW       = SLOPE_S | SLOPE_W,                     ///< south and west corner are raised

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	SLOPE_SE       = SLOPE_S | SLOPE_E,                     ///< south and east corner are raised

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	SLOPE_NE       = SLOPE_N | SLOPE_E,                     ///< north and east corner are raised

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	SLOPE_EW       = SLOPE_E | SLOPE_W,                     ///< east and west corner are raised

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	SLOPE_NS       = SLOPE_N | SLOPE_S,                     ///< north and south corner are raised

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	SLOPE_ELEVATED = SLOPE_N | SLOPE_E | SLOPE_S | SLOPE_W, ///< all corner are raised, similar to SLOPE_FLAT

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	SLOPE_NWS      = SLOPE_N | SLOPE_W | SLOPE_S,           ///< north, west and south corner are raised

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	SLOPE_WSE      = SLOPE_W | SLOPE_S | SLOPE_E,           ///< west, south and east corner are raised

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	SLOPE_SEN      = SLOPE_S | SLOPE_E | SLOPE_N,           ///< south, east and north corner are raised

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	SLOPE_ENW      = SLOPE_E | SLOPE_N | SLOPE_W,           ///< east, north and west corner are raised

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	SLOPE_STEEP_W  = SLOPE_STEEP | SLOPE_NWS,               ///< a steep slope falling to east (from west)

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	SLOPE_STEEP_S  = SLOPE_STEEP | SLOPE_WSE,               ///< a steep slope falling to north (from south)

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	SLOPE_STEEP_E  = SLOPE_STEEP | SLOPE_SEN,               ///< a steep slope falling to west (from east)

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	SLOPE_STEEP_N  = SLOPE_STEEP | SLOPE_ENW,               ///< a steep slope falling to south (from north)

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	SLOPE_HALFTILE = 0x20,                                  ///< one halftile is leveled (non continuous slope)

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	SLOPE_HALFTILE_MASK = 0xE0,                             ///< three bits used for halftile slopes

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	SLOPE_HALFTILE_W = SLOPE_HALFTILE | (CORNER_W << 6),    ///< the west halftile is leveled (non continuous slope)

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	SLOPE_HALFTILE_S = SLOPE_HALFTILE | (CORNER_S << 6),    ///< the south halftile is leveled (non continuous slope)

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	SLOPE_HALFTILE_E = SLOPE_HALFTILE | (CORNER_E << 6),    ///< the east halftile is leveled (non continuous slope)

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	SLOPE_HALFTILE_N = SLOPE_HALFTILE | (CORNER_N << 6),    ///< the north halftile is leveled (non continuous slope)

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};

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/**

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 * Rangecheck for Corner enumeration.

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 *

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 * @param corner A #Corner.

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 * @return true iff corner is in a valid range.

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 */

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static inline bool IsValidCorner(Corner corner)

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{

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	return IS_INT_INSIDE(corner, 0, CORNER_END);

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}

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/**

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 * Checks if a slope is steep.

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 *

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 * @param s The given #Slope.

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 * @return True if the slope is steep, else false.

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 */

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static inline bool IsSteepSlope(Slope s)

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{

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	return (s & SLOPE_STEEP) != 0;

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}

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/**

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 * Checks for non-continuous slope on halftile foundations.

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 *

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 * @param s The given #Slope.

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 * @return True if the slope is non-continuous, else false.

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 */

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static inline bool IsHalftileSlope(Slope s)

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{

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	return (s & SLOPE_HALFTILE) != 0;

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}

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/**

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 * Return the complement of a slope.

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 *

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 * This method returns the complement of a slope. The complement of a

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 * slope is a slope with raised corner which aren't raised in the given

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 * slope.

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 *

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 * @pre The slope must neither be steep nor a halftile slope.

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 * @param s The #Slope to get the complement.

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 * @return a complement Slope of the given slope.

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 */

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static inline Slope ComplementSlope(Slope s)

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{

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	assert(!IsSteepSlope(s) && !IsHalftileSlope(s));

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	return (Slope)(0xF ^ s);

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}

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/**

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 * Tests if a slope has a highest corner (i.e. one corner raised or a steep slope).

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 *

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 * Note: A halftile slope is ignored.

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 *

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 * @param s The #Slope.

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 * @return  true iff the slope has a highest corner.

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 */

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static inline bool HasSlopeHighestCorner(Slope s)

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{

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	s = (Slope)(s & ~SLOPE_HALFTILE_MASK);

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	return IsSteepSlope(s) || (s == SLOPE_W) || (s == SLOPE_S) || (s == SLOPE_E) || (s == SLOPE_N);

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}

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/**

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 * Returns the highest corner of a slope (one corner raised or a steep slope).

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 *

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 * @pre      The slope must be a slope with one corner raised or a steep slope. A halftile slope is ignored.

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 * @param s  The #Slope.

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 * @return   Highest corner.

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 */

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static inline Corner GetHighestSlopeCorner(Slope s)

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{

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	switch (s & ~SLOPE_HALFTILE_MASK) {

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		case SLOPE_W:

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		case SLOPE_STEEP_W: return CORNER_W;

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		case SLOPE_S:

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		case SLOPE_STEEP_S: return CORNER_S;

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		case SLOPE_E:

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		case SLOPE_STEEP_E: return CORNER_E;

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		case SLOPE_N:

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		case SLOPE_STEEP_N: return CORNER_N;

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		default: NOT_REACHED();

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	}

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}

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/**

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 * Returns the leveled halftile of a halftile slope.

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 *

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 * @pre     The slope must be a halftile slope.

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 * @param s The #Slope.

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 * @return  The corner of the leveled halftile.

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 */

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static inline Corner GetHalftileSlopeCorner(Slope s)

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{

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	assert(IsHalftileSlope(s));

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	return (Corner)((s >> 6) & 3);

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}

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/**

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 * Returns the height of the highest corner of a slope relative to TileZ (= minimal height)

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 *

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 * @param s The #Slope.

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 * @return Relative height of highest corner.

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 */

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static inline uint GetSlopeMaxZ(Slope s)

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{

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	if (s == SLOPE_FLAT) return 0;

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	if (IsSteepSlope(s)) return 2 * TILE_HEIGHT;

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	return TILE_HEIGHT;

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}

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/**

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 * Returns the opposite corner.

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 *

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 * @param corner A #Corner.

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 * @return The opposite corner to "corner".

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 */

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static inline Corner OppositeCorner(Corner corner)

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{

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	return (Corner)(corner ^ 2);

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}

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/**

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 * Returns the slope with a specific corner raised.

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 *

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 * @param corner The #Corner.

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 * @return The #Slope with corner "corner" raised.

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 */

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static inline Slope SlopeWithOneCornerRaised(Corner corner)

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{

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	assert(IsValidCorner(corner));

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	return (Slope)(1 << corner);

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}

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/**

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 * Returns the slope with all except one corner raised.

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 *

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 * @param corner The #Corner.

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 * @return The #Slope with all corners but "corner" raised.

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 */

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static inline Slope SlopeWithThreeCornersRaised(Corner corner)

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{

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	return ComplementSlope(SlopeWithOneCornerRaised(corner));

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}

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/**

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 * Adds a halftile slope to a slope.

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 *

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 * @param s #Slope without a halftile slope.

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 * @param corner The #Corner of the halftile.

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 * @return The #Slope s with the halftile slope added.

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 */

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static inline Slope HalftileSlope(Slope s, Corner corner)

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{

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	assert(IsValidCorner(corner));

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	return (Slope)(s | SLOPE_HALFTILE | (corner << 6));

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}

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/**

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 * Enumeration for Foundations.

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 */

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enum Foundation {

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	FOUNDATION_NONE,             ///< The tile has no foundation, the slope remains unchanged.

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	FOUNDATION_LEVELED,          ///< The tile is leveled up to a flat slope.

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	FOUNDATION_INCLINED_X,       ///< The tile has an along X-axis inclined foundation.

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	FOUNDATION_INCLINED_Y,       ///< The tile has an along Y-axis inclined foundation.

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	FOUNDATION_STEEP_LOWER,      ///< The tile has a steep slope. The lowerst corner is raised by a foundation to allow building railroad on the lower halftile.

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	FOUNDATION_STEEP_HIGHER,     ///< The tile has a steep slope. Three corners are raised by a foundation to allow building railroad on the higher halftile.

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	FOUNDATION_INVALID = 0xFF    ///< Used inside "rail_cmd.cpp" to indicate invalid slope/track combination.

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};

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/**

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 * Tests for FOUNDATION_NONE.

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 *

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 * @param f  Maybe a #Foundation.

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 * @return   true iff f is a foundation.

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 */

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static inline bool IsFoundation(Foundation f)

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{

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	return f != FOUNDATION_NONE;

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}

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/**

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 * Tests if the foundation is a leveled foundation.

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 *

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 * @param f  The #Foundation.

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 * @return   true iff f is a leveled foundation.

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 */

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static inline bool IsLeveledFoundation(Foundation f)

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{

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	return f == FOUNDATION_LEVELED;

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}

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/**

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 * Tests if the foundation is an inclined foundation.

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 *

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 * @param f  The #Foundation.

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 * @return   true iff f is an inclined foundation.

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 */

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static inline bool IsInclinedFoundation(Foundation f)

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{

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	return (f == FOUNDATION_INCLINED_X) || (f == FOUNDATION_INCLINED_Y);

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}

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/**

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 * Returns the foundation needed to flatten a slope.

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 * The returned foundation is either FOUNDATION_NONE if the tile was already flat, or FOUNDATION_LEVELED.

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 *

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 * @pre      The slope must not be steep.

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 * @param s  The current #Slope.

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 * @return   The needed #Foundation.

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 */

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static inline Foundation FlatteningFoundation(Slope s)

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{

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	assert(!IsSteepSlope(s));

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	return (s == SLOPE_FLAT ? FOUNDATION_NONE : FOUNDATION_LEVELED);

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}

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/**

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 * Returns the along a specific axis inclined foundation.

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 *

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 * @param axis  The #Axis.

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 * @return      The needed #Foundation.

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 */

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static inline Foundation InclinedFoundation(Axis axis)

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{

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	return (axis == AXIS_X ? FOUNDATION_INCLINED_X : FOUNDATION_INCLINED_Y);

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}

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#endif /* SLOPE_H */