Towards 1.13

[xoft]

More complications. PBA stores neither blocklight nor skylight, yet those need to be stored within the chunks. So chunks cannot be based just on PBAs. How should I combine these together?

This seems like the most reasonable skeleton:

class Chunk
{
  struct Section
  {
    PalettedBlockArea mBlocks;
    NIBBLETYPE mBlockLight[16 * 16 * 16];
    NIBBLETYPE mSkyLight[16 * 16 * 16];
  };
  using SectionPtr = std::unique_ptr<Section>;

  SectionPtr mSections[16];
};

The question is whether to make the entire sections optional like in the code above. If a section isn't present and a query comes for blocklight or skylight, what should the query return? Another option would be to make all 16 sections necessary, but each member of the section is optional. Now, looking at some 1.14 saves, I see that Vanilla sometimes doesn't store the BlockLight, sometimes doesn't store SkyLight, and sometimes neither. So it might be beneficial to wrap each of the light arrays into a structure that supports two states - either individual 16*16*16 values, or a single value for the entire section. That could produce some memory savings. However, it could be postponed as a later optimization.