pocketmine\level\generator\Void::generateChunk PHP Method

    public function generateChunk($chunkX, $chunkZ)
    {
        if ($this->emptyChunk !== null) {
            //Use the cached empty chunk instead of generating a new one
            $this->chunk = clone $this->emptyChunk;
        } else {
            $this->chunk = clone $this->level->getChunk($chunkX, $chunkZ);
            $this->chunk->setGenerated();
            $c = Biome::getBiome(1)->getColor();
            $R = $c >> 16;
            $G = $c >> 8 & 0xff;
            $B = $c & 0xff;
            for ($Z = 0; $Z < 16; ++$Z) {
                for ($X = 0; $X < 16; ++$X) {
                    $this->chunk->setBiomeId($X, $Z, 1);
                    $this->chunk->setBiomeColor($X, $Z, $R, $G, $B);
                    for ($y = 0; $y < 128; ++$y) {
                        $this->chunk->setBlockId($X, $y, $Z, Block::AIR);
                    }
                }
            }
            $spawn = $this->getSpawn();
            if ($spawn->getX() >> 4 === $chunkX and $spawn->getZ() >> 4 === $chunkZ) {
                $this->chunk->setBlockId(0, 64, 0, Block::GRASS);
            } else {
                $this->emptyChunk = $this->chunk;
            }
        }
        $chunk = clone $this->chunk;
        $chunk->setX($chunkX);
        $chunk->setZ($chunkZ);
        $this->level->setChunk($chunkX, $chunkZ, $chunk);
    }