69 lines
2.4 KiB
C#
69 lines
2.4 KiB
C#
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namespace Theriapolis.Core.Util;
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/// <summary>
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/// Direction encoding for tile-level features (rivers, rail, roads).
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/// Directions are stored as byte values 0–7, matching the 8 compass points.
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/// 255 = "no direction" / unset.
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/// </summary>
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public static class Dir
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{
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// Direction constants (0-based, CCW from North)
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public const byte None = 255;
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public const byte N = 0; // (dx= 0, dy=-1)
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public const byte NE = 1; // (dx= 1, dy=-1)
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public const byte E = 2; // (dx= 1, dy= 0)
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public const byte SE = 3; // (dx= 1, dy= 1)
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public const byte S = 4; // (dx= 0, dy= 1)
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public const byte SW = 5; // (dx=-1, dy= 1)
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public const byte W = 6; // (dx=-1, dy= 0)
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public const byte NW = 7; // (dx=-1, dy=-1)
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private static readonly (int dx, int dy)[] _deltas =
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{
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( 0,-1), ( 1,-1), ( 1, 0), ( 1, 1),
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( 0, 1), (-1, 1), (-1, 0), (-1,-1),
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};
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/// <summary>Convert a (dx, dy) delta to a direction byte. Both values must be in {-1,0,1}.</summary>
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public static byte FromDelta(int dx, int dy)
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{
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for (byte i = 0; i < 8; i++)
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if (_deltas[i].dx == dx && _deltas[i].dy == dy)
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return i;
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return None;
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}
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public static (int dx, int dy) ToDelta(byte dir)
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{
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if (dir == None) return (0, 0);
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return _deltas[dir & 7];
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}
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/// <summary>
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/// Two directions are parallel if their angular difference is ≤ 45° (including opposite directions).
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/// </summary>
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public static bool IsParallel(byte a, byte b)
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{
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if (a == None || b == None) return false;
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int diff = Math.Abs((int)(a & 7) - (int)(b & 7));
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diff = Math.Min(diff, 8 - diff);
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// diff 0 = same; diff 1 = 45°; diff 4 = 180° (opposite still parallel)
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return diff <= 1 || diff >= 3; // ≤45° or ≥135° (anti-parallel)
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}
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/// <summary>
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/// Two directions are perpendicular if their angular difference is in [60°, 120°].
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/// Using discrete 45° steps: diff 2 = 90°.
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/// </summary>
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public static bool IsPerpendicular(byte a, byte b)
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{
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if (a == None || b == None) return false;
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int diff = Math.Abs((int)(a & 7) - (int)(b & 7));
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diff = Math.Min(diff, 8 - diff);
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return diff == 2;
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}
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/// <summary>Opposite direction.</summary>
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public static byte Opposite(byte d) => d == None ? None : (byte)((d + 4) & 7);
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}
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