Add octile distance for tripoints.

Part of #74945. This will allow for better vertical pathfinding calculations,
allowing flying monsters to actually fly.

src/coordinates.h

@@ -840,6 +840,14 @@ inline int octile_dist( const coords::coord_point_ob<Point, Origin, Scale> &loc1
     return octile_dist( loc1.raw(), loc2.raw(), multiplier );
 }
 
+
+template<typename Point, coords::origin Origin, coords::scale Scale>
+inline float octile_dist_exact( const coords::coord_point<Point, Origin, Scale> &loc1,
+                                const coords::coord_point<Point, Origin, Scale> &loc2 )
+{
+    return octile_dist_exact( loc1.raw(), loc2.raw() );
+}
+
 template<typename Point, coords::origin Origin, coords::scale Scale>
 direction direction_from( const coords::coord_point_ob<Point, Origin, Scale> &loc1,
                           const coords::coord_point_ob<Point, Origin, Scale> &loc2 )

src/line.cpp

@@ -284,6 +284,19 @@ float octile_dist_exact( const point &loc1, const point &loc2 )
     return d.x + d.y - 2 * mind + mind * M_SQRT2;
 }
 
+float octile_dist_exact( const tripoint &from, const tripoint &to )
+{
+    const tripoint d = ( from - to ).abs();
+    const int min = std::min( d.x, std::min( d.y, d.z ) );
+    const int max = std::max( d.x, std::max( d.y, d.z ) );
+    const int mid = d.x + d.y + d.z - min - max;
+
+    constexpr int one_axis = 1;
+    constexpr float two_axis = M_SQRT2;
+    constexpr float three_axis = 1.73205f;
+    return ( three_axis - two_axis ) * min + ( two_axis - one_axis ) * mid + one_axis * max;
+}
+
 units::angle atan2( const point &p )
 {
     return units::atan2( p.y, p.x );

src/line.h

@@ -254,9 +254,10 @@ float rl_dist_exact( const tripoint &loc1, const tripoint &loc2 );
 int manhattan_dist( const point &loc1, const point &loc2 );
 
 // Travel distance between 2 points on a square grid, assuming diagonal moves
-// cost sqrt(2) and cardinal moves cost 1.
+// cost sqrt(2) or sqrt(3) and cardinal moves cost 1.
 int octile_dist( const point &loc1, const point &loc2, int multiplier = 1 );
 float octile_dist_exact( const point &loc1, const point &loc2 );
+float octile_dist_exact( const tripoint &from, const tripoint &to );
 
 // get angle of direction represented by point
 units::angle atan2( const point & );