minecraft-src/net/minecraft/server/level/ChunkTrackingView.java

package net.minecraft.server.level;

import com.google.common.annotations.VisibleForTesting;
import java.util.function.Consumer;
import net.minecraft.world.level.ChunkPos;

public interface ChunkTrackingView {
	ChunkTrackingView EMPTY = new ChunkTrackingView() {
		@Override
		public boolean contains(int x, int z, boolean includeOuterChunksAdjacentToViewBorder) {
			return false;
		}

		@Override
		public void forEach(Consumer<ChunkPos> action) {
		}
	};

	static ChunkTrackingView of(ChunkPos center, int viewDistance) {
		return new ChunkTrackingView.Positioned(center, viewDistance);
	}

	/**
	 * Calculates the chunks that the player needs to drop in the {@code oldChunkTrackingView} and the chunks that need to be sent for the {@code newChunkTrackingView}. The chunks that overlap in both views can be kept.
	 */
	static void difference(
		ChunkTrackingView oldChunkTrackingView, ChunkTrackingView newChunkTrackingView, Consumer<ChunkPos> chunkMarker, Consumer<ChunkPos> chunkDropper
	) {
		if (!oldChunkTrackingView.equals(newChunkTrackingView)) {
			if (oldChunkTrackingView instanceof ChunkTrackingView.Positioned positioned
				&& newChunkTrackingView instanceof ChunkTrackingView.Positioned positioned2
				&& positioned.squareIntersects(positioned2)) {
				int i = Math.min(positioned.minX(), positioned2.minX());
				int j = Math.min(positioned.minZ(), positioned2.minZ());
				int k = Math.max(positioned.maxX(), positioned2.maxX());
				int l = Math.max(positioned.maxZ(), positioned2.maxZ());

				for (int m = i; m <= k; m++) {
					for (int n = j; n <= l; n++) {
						boolean bl = positioned.contains(m, n);
						boolean bl2 = positioned2.contains(m, n);
						if (bl != bl2) {
							if (bl2) {
								chunkMarker.accept(new ChunkPos(m, n));
							} else {
								chunkDropper.accept(new ChunkPos(m, n));
							}
						}
					}
				}
			} else {
				oldChunkTrackingView.forEach(chunkDropper);
				newChunkTrackingView.forEach(chunkMarker);
			}
		}
	}

	default boolean contains(ChunkPos chunkPos) {
		return this.contains(chunkPos.x, chunkPos.z);
	}

	default boolean contains(int x, int z) {
		return this.contains(x, z, true);
	}

	boolean contains(int x, int z, boolean includeOuterChunksAdjacentToViewBorder);

	void forEach(Consumer<ChunkPos> action);

	default boolean isInViewDistance(int x, int z) {
		return this.contains(x, z, false);
	}

	static boolean isInViewDistance(int centerX, int centerZ, int viewDistance, int x, int z) {
		return isWithinDistance(centerX, centerZ, viewDistance, x, z, false);
	}

	/**
	 * Check if a chunk {@code (x,z)} is within a {@code viewDistance} which is centered on {@code (centerX, centerZ)}
	 */
	static boolean isWithinDistance(int centerX, int centerZ, int viewDistance, int x, int z, boolean includeOuterChunksAdjacentToViewBorder) {
		int i = includeOuterChunksAdjacentToViewBorder ? 2 : 1;
		long l = Math.max(0, Math.abs(x - centerX) - i);
		long m = Math.max(0, Math.abs(z - centerZ) - i);
		long n = l * l + m * m;
		int j = viewDistance * viewDistance;
		return n < j;
	}

	public record Positioned(ChunkPos center, int viewDistance) implements ChunkTrackingView {
		int minX() {
			return this.center.x - this.viewDistance - 1;
		}

		int minZ() {
			return this.center.z - this.viewDistance - 1;
		}

		int maxX() {
			return this.center.x + this.viewDistance + 1;
		}

		int maxZ() {
			return this.center.z + this.viewDistance + 1;
		}

		/**
		 * Determines if another {@link ChunkTrackingView}'s bounds intersects with its own
		 */
		@VisibleForTesting
		protected boolean squareIntersects(ChunkTrackingView.Positioned other) {
			return this.minX() <= other.maxX() && this.maxX() >= other.minX() && this.minZ() <= other.maxZ() && this.maxZ() >= other.minZ();
		}

		@Override
		public boolean contains(int x, int z, boolean includeOuterChunksAdjacentToViewBorder) {
			return ChunkTrackingView.isWithinDistance(this.center.x, this.center.z, this.viewDistance, x, z, includeOuterChunksAdjacentToViewBorder);
		}

		@Override
		public void forEach(Consumer<ChunkPos> action) {
			for (int i = this.minX(); i <= this.maxX(); i++) {
				for (int j = this.minZ(); j <= this.maxZ(); j++) {
					if (this.contains(i, j)) {
						action.accept(new ChunkPos(i, j));
					}
				}
			}
		}
	}
}