Code/net/minecraft/world/level/lighting/ChunkSkyLightSources.java

package net.minecraft.world.level.lighting;

import net.minecraft.core.BlockPos;
import net.minecraft.core.Direction;
import net.minecraft.core.SectionPos;
import net.minecraft.util.BitStorage;
import net.minecraft.util.Mth;
import net.minecraft.util.SimpleBitStorage;
import net.minecraft.world.level.BlockGetter;
import net.minecraft.world.level.LevelHeightAccessor;
import net.minecraft.world.level.block.Blocks;
import net.minecraft.world.level.block.state.BlockState;
import net.minecraft.world.level.chunk.ChunkAccess;
import net.minecraft.world.level.chunk.LevelChunkSection;
import net.minecraft.world.phys.shapes.Shapes;
import net.minecraft.world.phys.shapes.VoxelShape;

public class ChunkSkyLightSources {
    private static final int SIZE = 16;
    public static final int NEGATIVE_INFINITY = Integer.MIN_VALUE;
    private final int minY;
    private final BitStorage heightmap;
    private final BlockPos.MutableBlockPos mutablePos1 = new BlockPos.MutableBlockPos();
    private final BlockPos.MutableBlockPos mutablePos2 = new BlockPos.MutableBlockPos();

    public ChunkSkyLightSources(LevelHeightAccessor p_285502_) {
        this.minY = p_285502_.getMinY() - 1;
        int i = p_285502_.getMaxY() + 1;
        int j = Mth.ceillog2(i - this.minY + 1);
        this.heightmap = new SimpleBitStorage(j, 256);
    }

    public void fillFrom(ChunkAccess p_285152_) {
        int i = p_285152_.getHighestFilledSectionIndex();
        if (i == -1) {
            this.fill(this.minY);
        } else {
            for (int j = 0; j < 16; j++) {
                for (int k = 0; k < 16; k++) {
                    int l = Math.max(this.findLowestSourceY(p_285152_, i, k, j), this.minY);
                    this.set(index(k, j), l);
                }
            }
        }
    }

    private int findLowestSourceY(ChunkAccess p_285214_, int p_285171_, int p_285021_, int p_285226_) {
        int i = SectionPos.sectionToBlockCoord(p_285214_.getSectionYFromSectionIndex(p_285171_) + 1);
        BlockPos.MutableBlockPos blockpos$mutableblockpos = this.mutablePos1.set(p_285021_, i, p_285226_);
        BlockPos.MutableBlockPos blockpos$mutableblockpos1 = this.mutablePos2.setWithOffset(blockpos$mutableblockpos, Direction.DOWN);
        BlockState blockstate = Blocks.AIR.defaultBlockState();

        for (int j = p_285171_; j >= 0; j--) {
            LevelChunkSection levelchunksection = p_285214_.getSection(j);
            if (levelchunksection.hasOnlyAir()) {
                blockstate = Blocks.AIR.defaultBlockState();
                int l = p_285214_.getSectionYFromSectionIndex(j);
                blockpos$mutableblockpos.setY(SectionPos.sectionToBlockCoord(l));
                blockpos$mutableblockpos1.setY(blockpos$mutableblockpos.getY() - 1);
            } else {
                for (int k = 15; k >= 0; k--) {
                    BlockState blockstate1 = levelchunksection.getBlockState(p_285021_, k, p_285226_);
                    if (isEdgeOccluded(blockstate, blockstate1)) {
                        return blockpos$mutableblockpos.getY();
                    }

                    blockstate = blockstate1;
                    blockpos$mutableblockpos.set(blockpos$mutableblockpos1);
                    blockpos$mutableblockpos1.move(Direction.DOWN);
                }
            }
        }

        return this.minY;
    }

    public boolean update(BlockGetter p_285514_, int p_284999_, int p_285358_, int p_284944_) {
        int i = p_285358_ + 1;
        int j = index(p_284999_, p_284944_);
        int k = this.get(j);
        if (i < k) {
            return false;
        } else {
            BlockPos blockpos = this.mutablePos1.set(p_284999_, p_285358_ + 1, p_284944_);
            BlockState blockstate = p_285514_.getBlockState(blockpos);
            BlockPos blockpos1 = this.mutablePos2.set(p_284999_, p_285358_, p_284944_);
            BlockState blockstate1 = p_285514_.getBlockState(blockpos1);
            if (this.updateEdge(p_285514_, j, k, blockpos, blockstate, blockpos1, blockstate1)) {
                return true;
            } else {
                BlockPos blockpos2 = this.mutablePos1.set(p_284999_, p_285358_ - 1, p_284944_);
                BlockState blockstate2 = p_285514_.getBlockState(blockpos2);
                return this.updateEdge(p_285514_, j, k, blockpos1, blockstate1, blockpos2, blockstate2);
            }
        }
    }

    private boolean updateEdge(
        BlockGetter p_285066_, int p_285184_, int p_285101_, BlockPos p_285446_, BlockState p_285185_, BlockPos p_285103_, BlockState p_285009_
    ) {
        int i = p_285446_.getY();
        if (isEdgeOccluded(p_285185_, p_285009_)) {
            if (i > p_285101_) {
                this.set(p_285184_, i);
                return true;
            }
        } else if (i == p_285101_) {
            this.set(p_285184_, this.findLowestSourceBelow(p_285066_, p_285103_, p_285009_));
            return true;
        }

        return false;
    }

    private int findLowestSourceBelow(BlockGetter p_285279_, BlockPos p_285119_, BlockState p_285096_) {
        BlockPos.MutableBlockPos blockpos$mutableblockpos = this.mutablePos1.set(p_285119_);
        BlockPos.MutableBlockPos blockpos$mutableblockpos1 = this.mutablePos2.setWithOffset(p_285119_, Direction.DOWN);
        BlockState blockstate = p_285096_;

        while (blockpos$mutableblockpos1.getY() >= this.minY) {
            BlockState blockstate1 = p_285279_.getBlockState(blockpos$mutableblockpos1);
            if (isEdgeOccluded(blockstate, blockstate1)) {
                return blockpos$mutableblockpos.getY();
            }

            blockstate = blockstate1;
            blockpos$mutableblockpos.set(blockpos$mutableblockpos1);
            blockpos$mutableblockpos1.move(Direction.DOWN);
        }

        return this.minY;
    }

    private static boolean isEdgeOccluded(BlockState p_285219_, BlockState p_285512_) {
        if (p_285512_.getLightBlock() != 0) {
            return true;
        } else {
            VoxelShape voxelshape = LightEngine.getOcclusionShape(p_285219_, Direction.DOWN);
            VoxelShape voxelshape1 = LightEngine.getOcclusionShape(p_285512_, Direction.UP);
            return Shapes.faceShapeOccludes(voxelshape, voxelshape1);
        }
    }

    public int getLowestSourceY(int p_285247_, int p_285082_) {
        int i = this.get(index(p_285247_, p_285082_));
        return this.extendSourcesBelowWorld(i);
    }

    public int getHighestLowestSourceY() {
        int i = Integer.MIN_VALUE;

        for (int j = 0; j < this.heightmap.getSize(); j++) {
            int k = this.heightmap.get(j);
            if (k > i) {
                i = k;
            }
        }

        return this.extendSourcesBelowWorld(i + this.minY);
    }

    private void fill(int p_285311_) {
        int i = p_285311_ - this.minY;

        for (int j = 0; j < this.heightmap.getSize(); j++) {
            this.heightmap.set(j, i);
        }
    }

    private void set(int p_285323_, int p_285220_) {
        this.heightmap.set(p_285323_, p_285220_ - this.minY);
    }

    private int get(int p_284951_) {
        return this.heightmap.get(p_284951_) + this.minY;
    }

    private int extendSourcesBelowWorld(int p_284953_) {
        return p_284953_ == this.minY ? Integer.MIN_VALUE : p_284953_;
    }

    private static int index(int p_284980_, int p_285277_) {
        return p_284980_ + p_285277_ * 16;
    }
}