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Item Comparator

Following is a unique redstone component that may open up design space. The Item Comparator allows you to calculate if a recipe is craftable by telling you how many multiples of particular set of items there are in an attached chest. That may sound complicated so please read on for clarification.

The Item Comparator is crafted with a chest on top of a comparator. It contains 3 slots for items. The Item Comparator compares the number and type of items in a connected container to the number and type of items in the Item Comparator. It outputs a redstone signal equal to the smallest multiple of those items in the connected container.

For example, with a comparator that contains 3 diamonds and 2 sticks, if the container has 10 diamonds and 10 sticks, the output will be 3 i.e. we have enough ingredients for 3 diamond pickaxes. If the container has 100 sticks and 2 diamonds, the signal strength will be zero because there is not enough ingredients to make any pickaxes.

I chose to have 3 slots because that is enough to calculate for most recipes. If performance is concerning, the Item Comparator may simply have one slot. In that case it may be made with a Comparator + Item Frame and we could employ the use of AND gates to calculate for recipes.

This block would assist in complex item transportation. It would open up design space for automatable blocks that require more than 1 item as input and blocks that determine the output based on specific quantities. 

Current use cases for the item comparator that the current comparator doesn't do include, checking if a furnace has coal without counting other items or checking if a hopper has exactly 1 diamond in it. Keep in mind that this component is breaking new ground; I believe the best use cases don't exist yet. I am looking forward to seeing new potentially automated blocks that encourage its use.

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    Registered User commented
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    Imagine an automatic crafting bench that determines the recipe using the quantity of items instead of where those items are placed.

    To build a fence I would insert a stack of 2 sticks and 4 planks.

    Activating with redstone gives me fences.

    The same crafting block can create gates as well so your redstone system has to calculate how many of each item is in the crafting block.

    The Item Comparator can do that. The regular Comparator cannot.

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    Registered User commented
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    I believe this is a feature that is not too difficult to program and is almost impossible to do using current materials.

    Below is pseudocode for implementing it:

    Int multiples = 0
    FOR stack1 in Comparator:
       IF stack1 != null:
          Int size = 0
          FOR stack2 in container:
             IF stack2 != null AND stack1.name == stack2.name:
                size += stack2.size
          IF multiples == 0:
             multiples = size / stack1.size
          ELSE:
             multiples = min(multiples, size / stack1.size)
    redstoneSignal = min(multiples, 15)

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    Registered User commented
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    There are some complications to work out. For instance, the recipes for wooden slabs require that all the planks be of the same species, but the recipe for a bookshelf doesn't, so how do you know whether you need to count all planks or specifically spruce planks, birch planks, etc.?

    I doubt that more slots would be a problem. A hopper has to do (nominally) 5 x 54 comparisons when used with a double chest, and while hoppers can be a source of lag, that's only if you have a lot of them. It doesn't seem likely you'd use very many of these in a given device; the absolute most you could use on a given container is 6, and if you have many containers you'd have complications with items need to be in more than one of them.

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    Registered User commented
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    @Auldrick Thanks for the excellent feedback! Basically items with different names should be considered unique. You would need multiple of these to detect different types of wool but I think it's more important to detect them separately than to detect them together.

    It is more efficient to compare IDs than to compare names but I'm not sure how the game handles damage values anymore. I would like damaged swords to be considered the same as non-damaged swords but pink wool to be different to blue wool.