public Hex Step(
HexAdjacencyGraph adjacencyGraph,
ref RiverDigraph riverDigraph,
float extraLakeProbability,
float hexOuterRadius,
int waterLevel
)
{
if (RiverHead.IsUnderwater)
{
return(null);
}
int minNeighborElevation = int.MaxValue;
int minNeighborWaterLevel = int.MaxValue;
List <HexDirections> flowDirections = new List <HexDirections>();
HexDirections direction = HexDirections.Northeast;
for (
HexDirections directionCandidate = HexDirections.Northeast;
directionCandidate <= HexDirections.Northwest;
directionCandidate++
)
{
Hex neighborInDirection =
adjacencyGraph.TryGetNeighborInDirection(
RiverHead,
directionCandidate
);
if (!neighborInDirection || River.Contains(neighborInDirection))
{
continue;
}
if (neighborInDirection.elevation < minNeighborElevation)
{
minNeighborElevation = neighborInDirection.elevation;
minNeighborWaterLevel = neighborInDirection.WaterLevel;
}
// If the direction points to the river origin, or to a
// neighbor which already has an incoming river, continue.
if (
neighborInDirection == RiverHead ||
riverDigraph.HasIncomingRiver(neighborInDirection)
)
{
continue;
}
int delta =
neighborInDirection.elevation - RiverHead.elevation;
// If the elevation in the given direction is positive,
// continue.
if (delta > 0)
{
continue;
}
// If the direction points away from the river origin and
// any neighbors which already have an incoming river, and
// the elevation in the given direction is negative or
// zero, and the neighbor has an outgoing river, branch
// river in this direction.
if (
riverDigraph.HasOutgoingRiver(neighborInDirection)
)
{
SetOutgoingRiver(
RiverHead,
neighborInDirection,
directionCandidate,
ref riverDigraph
);
River.Add(neighborInDirection);
return(neighborInDirection);
}
// If the direction points away from the river origin and
// any neighbors which already have an incoming river, and
// the elevation in the given direction is not positive,
// and the neighbor does not have an outgoing river in the
// given direction...
// If the direction is a decline, make the probability for
// the branch 4 / 5.
if (delta < 0)
{
flowDirections.Add(directionCandidate);
flowDirections.Add(directionCandidate);
flowDirections.Add(directionCandidate);
}
// If the rivers local length is 1, and the direction does
// not result in a slight river bend, but rather a straight
// river or a corner river, make the probability of the
// branch 2 / 5
if (
River.Count == 1 ||
(directionCandidate != direction.NextClockwise2() &&
directionCandidate != direction.PreviousClockwise2())
)
{
flowDirections.Add(directionCandidate);
}
flowDirections.Add(directionCandidate);
}
// If there are no candidates for branching the river...
if (flowDirections.Count == 0)
{
// If the river contains only the river origin...
if (River.Count == 1)
{
// Do nothing and return null
return(null);
}
// If the hex is surrounded by hexes at a higher elevation,
// set the water level of the hex to the minium elevation
// of all neighbors.
if (minNeighborElevation >= RiverHead.elevation)
{
RiverHead.WaterLevel = RiverHead.elevation;
// If the hex is of equal elevation to a neighbor with
// a minimum elevation, lower the current hexes
// elevation to one below the minimum elevation of all
// of its neighbors so that it becomes a small lake
// that the river feeds into, and then break out of the
// while statement terminating the river in a lake
// rather than into the ocean.
if (minNeighborElevation == RiverHead.elevation)
{
RiverHead.SetElevation(
minNeighborElevation - 1,
hexOuterRadius,
_hexMap.WrapSize
);
}
}
return(null);
}
direction = flowDirections[
Random.Range(0, flowDirections.Count)
];
Hex neighborInRandomDirection =
adjacencyGraph.TryGetNeighborInDirection(
RiverHead,
direction
);
SetOutgoingRiver(
RiverHead,
neighborInRandomDirection,
direction,
ref riverDigraph
);
// If the hex is lower than the minimum elevation of its
// neighbors assign a lake based on a specified probability.
if (
minNeighborElevation >= RiverHead.elevation &&
Random.value < extraLakeProbability
)
{
RiverHead.WaterLevel = RiverHead.elevation;
RiverHead.SetElevation(
minNeighborElevation - 1,
hexOuterRadius,
_hexMap.WrapSize
);
}
River.Add(neighborInRandomDirection);
return(neighborInRandomDirection);
}