getStateFromMeta, getMetaFromState in BlockSapling algorithm

[WaffleMan0310]

I was working on implementing my own trees, wood and whatnot and while l was looking at the BlockSapling class I noticed it has two properties, and the algorithms for converting the two properties into one meta data value and back is as follows:

 

To convert to meta:

int i = 0;
i = i | ((BlockPlanks.EnumType)state.getValue(TYPE)).getMetadata();
i = i | ((Integer)state.getValue(STAGE)).intValue() << 3;
return i;

To convert back:

this.getDefaultState().withProperty(TYPE, BlockPlanks.EnumType.byMetadata(meta & 7)).withProperty(STAGE, Integer.valueOf((meta &  >> 3));

 

When I first saw this I was a bit perplexed, but then I did the bit-wise operations on paper with some random meta and state values and it worked. So I understand that it works, but I am still curious about how it works. I imagine this did not just pop out of someones head when they needed one meta value to represent multiple pieces of data, or maybe it did? The values being compared against are seemingly arbitrary?. Is there a name for operations that give the operands from the base operation? Is there an algorithm being followed here, if so what algorithm? I am very curious about the thought process behind this code, any information would be wonderful. Again, I am asking about the logic within these functions, not the functions themselves.

 

 

[Draco18s]

http://minecraft.gamepedia.com/Sapling#Block_state

 

The 4th bit of the metadata component number is the "stage."  Saplings need to receive two block updates in order to turn into trees, rather than 1.  That bit stores whether or not its already "grown" once (it's similar to crop's AGE state value).

 

The bitwise operators are just a fast way of composing and decomposing the state into/outof metadata integers.

[WaffleMan0310]

I see now, thanks!

[trollworkout]

Feel free to also have a look over my project on github as I have created a fully working wood set: log, leaves, sapling with tree gen, plank, door, slab and stairs.

https://github.com/trollworkout/technorcery

 

Well almost fully the only missing piece of the puzzle is fence and gate.

 

I understand my methods are different from what most people do. I like to reduce the amount of clutter by using  multipurpose classes and avoid using sub blocks or packing sub blocks into one block like for ex Log or NewLog does this. I use a custom WoodType enum found in my custom plank class and is used by everything wood including doors. 

 

For ex my Sapling block class

https://github.com/trollworkout/technorcery/blob/master/src/main/java/com/technorcery/common/blocks/SaplingBlock.java

 

I think I could not extend original Sapling class because it had a constructor for VARIANT or TYPE meta in the sapling which contractor cannot be overriden so I had to make my own. is been a few weeks so I don't fully remember now. but it works!