[2/3] Improve join point placement.

game/flightplan/__init__.py

@@ -1 +1,2 @@
 from .ipzonegeometry import IpZoneGeometry
+from .joinzonegeometry import JoinZoneGeometry

game/flightplan/joinzonegeometry.py

@@ -0,0 +1,84 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+import shapely.ops
+from dcs import Point
+from shapely.geometry import Point as ShapelyPoint, Polygon
+
+from game.theater import ConflictTheater
+from game.utils import nautical_miles
+
+if TYPE_CHECKING:
+    from game.coalition import Coalition
+
+
+class JoinZoneGeometry:
+    """Defines the zones used for finding optimal join point placement.
+
+    The zones themselves are stored in the class rather than just the resulting join
+    point so that the zones can be drawn in the map for debugging purposes.
+    """
+
+    def __init__(
+        self,
+        target: Point,
+        home: Point,
+        ip: Point,
+        coalition: Coalition,
+        theater: ConflictTheater,
+    ) -> None:
+        # Normal join placement is based on the path from home to the IP. If no path is
+        # found it means that the target is on a direct path. In that case we instead
+        # want to enforce that the join point is:
+        #
+        # * Not closer to the target than the IP.
+        # * Not too close to the home airfield.
+        # * Not threatened.
+        # * A minimum distance from the IP.
+        # * Not too sharp a turn at the ingress point.
+        self.ip = ShapelyPoint(ip.x, ip.y)
+        self.threat_zone = coalition.opponent.threat_zone.all
+        self.home = ShapelyPoint(home.x, home.y)
+
+        self.ip_bubble = self.ip.buffer(coalition.doctrine.join_distance.meters)
+
+        ip_distance = ip.distance_to_point(target)
+        self.target_bubble = ShapelyPoint(target.x, target.y).buffer(ip_distance)
+
+        # The minimum distance between the home location and the IP.
+        min_distance_from_home = nautical_miles(5)
+
+        self.home_bubble = self.home.buffer(min_distance_from_home.meters)
+
+        self.excluded_zone = shapely.ops.unary_union(
+            [self.home_bubble, self.ip_bubble, self.target_bubble, self.threat_zone]
+        )
+
+        ip_heading = target.heading_between_point(ip)
+
+        # Arbitrarily large since this is later constrained by the map boundary, and
+        # we'll be picking a location close to the IP anyway. Just used to avoid real
+        # distance calculations to project to the map edge.
+        large_distance = nautical_miles(400).meters
+        turn_limit = 40
+        ip_limit_ccw = ip.point_from_heading(ip_heading - turn_limit, large_distance)
+        ip_limit_cw = ip.point_from_heading(ip_heading + turn_limit, large_distance)
+
+        ip_direction_limit_wedge = Polygon(
+            [
+                (ip.x, ip.y),
+                (ip_limit_ccw.x, ip_limit_ccw.y),
+                (ip_limit_cw.x, ip_limit_cw.y),
+            ]
+        )
+
+        self.permissible_line = (
+            coalition.nav_mesh.map_bounds(theater)
+            .intersection(ip_direction_limit_wedge)
+            .intersection(self.excluded_zone.boundary)
+        )
+
+    def find_best_join_point(self) -> Point:
+        join, _ = shapely.ops.nearest_points(self.permissible_line, self.home)
+        return Point(join.x, join.y)