minecraft-src/net/minecraft/world/level/levelgen/Column.java

package net.minecraft.world.level.levelgen;

import java.util.Optional;
import java.util.OptionalInt;
import java.util.function.Predicate;
import net.minecraft.core.BlockPos;
import net.minecraft.core.Direction;
import net.minecraft.world.level.LevelSimulatedReader;
import net.minecraft.world.level.block.state.BlockState;

/**
 * A representation of an integer valued interval, either bounded or unbounded.
 * While the class itself does not imply any coordinate in particular, this is practically used to represent a column in the Y direction.
 */
public abstract class Column {
	/**
	 * @return A column of the closed interval [floor, ceiling].
	 */
	public static Column.Range around(int floor, int ceiling) {
		return new Column.Range(floor - 1, ceiling + 1);
	}

	/**
	 * @return A column of the open interval (floor, ceiling).
	 */
	public static Column.Range inside(int floor, int ceiling) {
		return new Column.Range(floor, ceiling);
	}

	/**
	 * @return A column of the unbounded interval (-infinity, ceiling).
	 */
	public static Column below(int ceiling) {
		return new Column.Ray(ceiling, false);
	}

	/**
	 * @return A column of the unbounded interval (-infinity, ceiling].
	 */
	public static Column fromHighest(int ceiling) {
		return new Column.Ray(ceiling + 1, false);
	}

	/**
	 * @return A column of the unbounded interval (floor, infinity).
	 */
	public static Column above(int floor) {
		return new Column.Ray(floor, true);
	}

	/**
	 * @return A column of the unbounded interval [floor, infinity).
	 */
	public static Column fromLowest(int floor) {
		return new Column.Ray(floor - 1, true);
	}

	/**
	 * @return A column of the unbounded interval (-infinity, infinity).
	 */
	public static Column line() {
		return Column.Line.INSTANCE;
	}

	public static Column create(OptionalInt floor, OptionalInt ceiling) {
		if (floor.isPresent() && ceiling.isPresent()) {
			return inside(floor.getAsInt(), ceiling.getAsInt());
		} else if (floor.isPresent()) {
			return above(floor.getAsInt());
		} else {
			return ceiling.isPresent() ? below(ceiling.getAsInt()) : line();
		}
	}

	public abstract OptionalInt getCeiling();

	public abstract OptionalInt getFloor();

	public abstract OptionalInt getHeight();

	public Column withFloor(OptionalInt floor) {
		return create(floor, this.getCeiling());
	}

	public Column withCeiling(OptionalInt ceiling) {
		return create(this.getFloor(), ceiling);
	}

	/**
	 * Scans for a column of states satisfying {@code columnPredicate}, up to a length of {@code maxDistance} from the origin, and ending with a state which satisfies {@code tipPredicate}.
	 * @return A column representing the tips found. The column will be bounded if a tip was reached in the given direction, unbounded otherwise.
	 */
	public static Optional<Column> scan(
		LevelSimulatedReader level, BlockPos pos, int maxDistance, Predicate<BlockState> columnPredicate, Predicate<BlockState> tipPredicate
	) {
		BlockPos.MutableBlockPos mutableBlockPos = pos.mutable();
		if (!level.isStateAtPosition(pos, columnPredicate)) {
			return Optional.empty();
		} else {
			int i = pos.getY();
			OptionalInt optionalInt = scanDirection(level, maxDistance, columnPredicate, tipPredicate, mutableBlockPos, i, Direction.UP);
			OptionalInt optionalInt2 = scanDirection(level, maxDistance, columnPredicate, tipPredicate, mutableBlockPos, i, Direction.DOWN);
			return Optional.of(create(optionalInt2, optionalInt));
		}
	}

	/**
	 * Scans for a sequence of states in a given {@code direction}, up to a length of {@code maxDistance} which satisfy {@code columnPredicate}, and ending with a state which satisfies {@code tipPredicate}.
	 * @return The y position of the tip, if found.
	 */
	private static OptionalInt scanDirection(
		LevelSimulatedReader level,
		int maxDistance,
		Predicate<BlockState> columnPredicate,
		Predicate<BlockState> tipPredicate,
		BlockPos.MutableBlockPos mutablePos,
		int startY,
		Direction direction
	) {
		mutablePos.setY(startY);

		for (int i = 1; i < maxDistance && level.isStateAtPosition(mutablePos, columnPredicate); i++) {
			mutablePos.move(direction);
		}

		return level.isStateAtPosition(mutablePos, tipPredicate) ? OptionalInt.of(mutablePos.getY()) : OptionalInt.empty();
	}

	public static final class Line extends Column {
		static final Column.Line INSTANCE = new Column.Line();

		private Line() {
		}

		@Override
		public OptionalInt getCeiling() {
			return OptionalInt.empty();
		}

		@Override
		public OptionalInt getFloor() {
			return OptionalInt.empty();
		}

		@Override
		public OptionalInt getHeight() {
			return OptionalInt.empty();
		}

		public String toString() {
			return "C(-)";
		}
	}

	public static final class Range extends Column {
		private final int floor;
		private final int ceiling;

		protected Range(int floor, int ceiling) {
			this.floor = floor;
			this.ceiling = ceiling;
			if (this.height() < 0) {
				throw new IllegalArgumentException("Column of negative height: " + this);
			}
		}

		@Override
		public OptionalInt getCeiling() {
			return OptionalInt.of(this.ceiling);
		}

		@Override
		public OptionalInt getFloor() {
			return OptionalInt.of(this.floor);
		}

		@Override
		public OptionalInt getHeight() {
			return OptionalInt.of(this.height());
		}

		public int ceiling() {
			return this.ceiling;
		}

		public int floor() {
			return this.floor;
		}

		public int height() {
			return this.ceiling - this.floor - 1;
		}

		public String toString() {
			return "C(" + this.ceiling + "-" + this.floor + ")";
		}
	}

	public static final class Ray extends Column {
		private final int edge;
		private final boolean pointingUp;

		public Ray(int edge, boolean pointingUp) {
			this.edge = edge;
			this.pointingUp = pointingUp;
		}

		@Override
		public OptionalInt getCeiling() {
			return this.pointingUp ? OptionalInt.empty() : OptionalInt.of(this.edge);
		}

		@Override
		public OptionalInt getFloor() {
			return this.pointingUp ? OptionalInt.of(this.edge) : OptionalInt.empty();
		}

		@Override
		public OptionalInt getHeight() {
			return OptionalInt.empty();
		}

		public String toString() {
			return this.pointingUp ? "C(" + this.edge + "-)" : "C(-" + this.edge + ")";
		}
	}
}