minecraft-src/net/minecraft/client/renderer/chunk/VisGraph.java

package net.minecraft.client.renderer.chunk;

import it.unimi.dsi.fastutil.ints.IntArrayFIFOQueue;
import it.unimi.dsi.fastutil.ints.IntPriorityQueue;
import java.util.BitSet;
import java.util.EnumSet;
import java.util.Set;
import net.fabricmc.api.EnvType;
import net.fabricmc.api.Environment;
import net.minecraft.Util;
import net.minecraft.core.BlockPos;
import net.minecraft.core.Direction;

@Environment(EnvType.CLIENT)
public class VisGraph {
	private static final int SIZE_IN_BITS = 4;
	private static final int LEN = 16;
	private static final int MASK = 15;
	private static final int SIZE = 4096;
	private static final int X_SHIFT = 0;
	private static final int Z_SHIFT = 4;
	private static final int Y_SHIFT = 8;
	private static final int DX = (int)Math.pow(16.0, 0.0);
	private static final int DZ = (int)Math.pow(16.0, 1.0);
	private static final int DY = (int)Math.pow(16.0, 2.0);
	private static final int INVALID_INDEX = -1;
	private static final Direction[] DIRECTIONS = Direction.values();
	private final BitSet bitSet = new BitSet(4096);
	private static final int[] INDEX_OF_EDGES = Util.make(new int[1352], is -> {
		int i = 0;
		int j = 15;
		int k = 0;

		for (int l = 0; l < 16; l++) {
			for (int m = 0; m < 16; m++) {
				for (int n = 0; n < 16; n++) {
					if (l == 0 || l == 15 || m == 0 || m == 15 || n == 0 || n == 15) {
						is[k++] = getIndex(l, m, n);
					}
				}
			}
		}
	});
	private int empty = 4096;

	public void setOpaque(BlockPos pos) {
		this.bitSet.set(getIndex(pos), true);
		this.empty--;
	}

	private static int getIndex(BlockPos pos) {
		return getIndex(pos.getX() & 15, pos.getY() & 15, pos.getZ() & 15);
	}

	private static int getIndex(int x, int y, int z) {
		return x << 0 | y << 8 | z << 4;
	}

	public VisibilitySet resolve() {
		VisibilitySet visibilitySet = new VisibilitySet();
		if (4096 - this.empty < 256) {
			visibilitySet.setAll(true);
		} else if (this.empty == 0) {
			visibilitySet.setAll(false);
		} else {
			for (int i : INDEX_OF_EDGES) {
				if (!this.bitSet.get(i)) {
					visibilitySet.add(this.floodFill(i));
				}
			}
		}

		return visibilitySet;
	}

	private Set<Direction> floodFill(int index) {
		Set<Direction> set = EnumSet.noneOf(Direction.class);
		IntPriorityQueue intPriorityQueue = new IntArrayFIFOQueue();
		intPriorityQueue.enqueue(index);
		this.bitSet.set(index, true);

		while (!intPriorityQueue.isEmpty()) {
			int i = intPriorityQueue.dequeueInt();
			this.addEdges(i, set);

			for (Direction direction : DIRECTIONS) {
				int j = this.getNeighborIndexAtFace(i, direction);
				if (j >= 0 && !this.bitSet.get(j)) {
					this.bitSet.set(j, true);
					intPriorityQueue.enqueue(j);
				}
			}
		}

		return set;
	}

	private void addEdges(int index, Set<Direction> faces) {
		int i = index >> 0 & 15;
		if (i == 0) {
			faces.add(Direction.WEST);
		} else if (i == 15) {
			faces.add(Direction.EAST);
		}

		int j = index >> 8 & 15;
		if (j == 0) {
			faces.add(Direction.DOWN);
		} else if (j == 15) {
			faces.add(Direction.UP);
		}

		int k = index >> 4 & 15;
		if (k == 0) {
			faces.add(Direction.NORTH);
		} else if (k == 15) {
			faces.add(Direction.SOUTH);
		}
	}

	private int getNeighborIndexAtFace(int index, Direction face) {
		switch (face) {
			case DOWN:
				if ((index >> 8 & 15) == 0) {
					return -1;
				}

				return index - DY;
			case UP:
				if ((index >> 8 & 15) == 15) {
					return -1;
				}

				return index + DY;
			case NORTH:
				if ((index >> 4 & 15) == 0) {
					return -1;
				}

				return index - DZ;
			case SOUTH:
				if ((index >> 4 & 15) == 15) {
					return -1;
				}

				return index + DZ;
			case WEST:
				if ((index >> 0 & 15) == 0) {
					return -1;
				}

				return index - DX;
			case EAST:
				if ((index >> 0 & 15) == 15) {
					return -1;
				}

				return index + DX;
			default:
				return -1;
		}
	}
}