A datapack that allows the user to smelt items using input and output NBT data and item count, without altering the behaviour of normal Funaces, Blasting Furnaces and Smokers.

In vanilla minecraft, there is no way to use NBT on items as input or output using custom recipes in a datapack.

This datapack allows the user to do just that, using the vanilla smelters (Furnace, Blast Furnace, Smoker).

When the player places a smelter, it is marked by a marker entity.

• Smelters that are IDLE check their block every 10 ticks (0.5s at 20tps).
• If the block that they are marking is destroyed, they will kill themselves.

• The checking is divided over 4 loops that are offset by 1 tick, which divides the load of all IDLE smelters over 4 ticks instead of just one.
• This means that smelters that do nothing are very efficient: you can have hundreds of them and this datapack will not significantly affect overall performance.
• In a test with 1331 IDLE smelters, the average tick speed was 6ms (9ms max) without a nearby player or 7ms (12ms max) if a player is nearby, in an otherwise empty world.

• Smelters that are CHECKING check if they can smelt every tick.
• Smelters can only be CHECKING if:
  • A player is within 9 blocks AND a player interacted with a nearby smelter --> a player may have opened the smelter GUI.
    • Possible optimisation: only go to CHECKING if the player has a smeltable item or a fuel in inventory. Requires extra tag on markers and inventory_changed advancement to check items picked up while in GUI.
    • Possible optimisation: only go to CHECKING if a player changes their inventory in addition to having opened the GUI --> only then do they move an item to a smelter slot. Requires CHECKING and SMELTING states to be processed in the same tick for the same marker entity + extra tag on markers + inventory_changed advancement.
  • The smelter is adjacent to a dropper or hopper that can input items --> the smelter may be able to smelt items provided by these blocks.
    • Possible optimisation: only go to CHECKING if the hopper can make the smelter actually smelt. I.e. if there is a hopper for input and none for fuel and there is no fuel in the fuel slot, then it is impossible for the smelter to start smelting without player interaction.

• When in the CHECKING state, we cannot:
  • Assume the player is out of the GUI when moving: they may be pushed by a mob or in water, or they may be falling.
  • Use raycasting for player interaction: the ray may miss if the player is falling or otherwise moving quickly while interacting with the smelter.

• When a ray is cast after placing a block, this ray can miss the block if the player moves the screen too quickly while placing that block.
• Therefore, we need to check every coordinate around the player for the placed block.
• More information in data/peerheer.nbtsmelting/functions/mark_block/find_block.

• When a player opens the GUI, the inventory_changed advancement is triggered once for every occupied slot.
• I only want the marker to check the slots of its block when the player's inventory changes after the player opened the GUI.
• To solve this, we need to ignore the inventory_changed advancement if it triggered in the same tick as the item_used_on_block advancement.