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/* $Id$ */

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#ifndef DIRECTION_H

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#define DIRECTION_H

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/* Direction as commonly used in v->direction, 8 way. */

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typedef enum Direction {

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	DIR_N   = 0,

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	DIR_NE  = 1,      /* Northeast, upper right on your monitor */

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	DIR_E   = 2,

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	DIR_SE  = 3,

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	DIR_S   = 4,

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	DIR_SW  = 5,

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	DIR_W   = 6,

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	DIR_NW  = 7,

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	DIR_END,

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	INVALID_DIR = 0xFF,

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} Direction;

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static inline Direction ReverseDir(Direction d)

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{

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	return (Direction)(4 ^ d);

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}

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typedef enum DirDiff {

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	DIRDIFF_SAME    = 0,

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	DIRDIFF_45RIGHT = 1,

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	DIRDIFF_90RIGHT = 2,

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	DIRDIFF_REVERSE = 4,

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	DIRDIFF_90LEFT  = 6,

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	DIRDIFF_45LEFT  = 7

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} DirDiff;

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static inline DirDiff DirDifference(Direction d0, Direction d1)

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{

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	return (DirDiff)((d0 + 8 - d1) % 8);

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}

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static inline DirDiff ChangeDirDiff(DirDiff d, DirDiff delta)

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{

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	return (DirDiff)((d + delta) % 8);

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}

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static inline Direction ChangeDir(Direction d, DirDiff delta)

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{

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	return (Direction)((d + delta) % 8);

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}

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/* Direction commonly used as the direction of entering and leaving tiles, 4-way */

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typedef enum DiagDirection {

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	DIAGDIR_NE  = 0,      /* Northeast, upper right on your monitor */

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	DIAGDIR_SE  = 1,

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	DIAGDIR_SW  = 2,

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	DIAGDIR_NW  = 3,

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	DIAGDIR_END,

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	INVALID_DIAGDIR = 0xFF,

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} DiagDirection;

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static inline DiagDirection ReverseDiagDir(DiagDirection d)

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{

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	return (DiagDirection)(2 ^ d);

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}

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typedef enum DiagDirDiff {

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	DIAGDIRDIFF_SAME    = 0,

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	DIAGDIRDIFF_90RIGHT = 1,

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	DIAGDIRDIFF_REVERSE = 2,

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	DIAGDIRDIFF_90LEFT  = 3

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} DiagDirDiff;

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static inline DiagDirection ChangeDiagDir(DiagDirection d, DiagDirDiff delta)

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{

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	return (DiagDirection)((d + delta) % 4);

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}

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static inline DiagDirection DirToDiagDir(Direction dir)

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{

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	return (DiagDirection)(dir >> 1);

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}

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static inline Direction DiagDirToDir(DiagDirection dir)

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{

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	return (Direction)(dir * 2 + 1);

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}

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/* the 2 axis */

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typedef enum Axis {

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	AXIS_X = 0,

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	AXIS_Y = 1,

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	AXIS_END

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} Axis;

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static inline Axis DiagDirToAxis(DiagDirection d)

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{

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	return (Axis)(d & 1);

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}

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/*

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 * Converts an Axis to a DiagDirection

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 * Points always in the positive direction, i.e. S[EW]

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 */

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static inline DiagDirection AxisToDiagDir(Axis a)

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{

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	return (DiagDirection)(2 - a);

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}

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static inline bool IsValidDiagDirection(DiagDirection d)

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{

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	return d < DIAGDIR_END;

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}

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static inline bool IsValidDirection(Direction d)

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{

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	return d < DIR_END;

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}

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static inline bool IsValidAxis(Axis d)

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{

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	return d < AXIS_END;

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}

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#endif