How can I make a dropper with a specific pattern of items inside turn into a building?

Question

So I am trying to make a dropper pointing upwards with a specific pattern of blocks inside turn into a building. I have made something that kind of works, but it doesn't completely work. Right now I have a repeating command block, always active pointing into a conditional chain command block, always active. The repeating command block has /execute @a ~ ~-1 ~ testforblock ~ ~ ~ dropper 1 {data tag} and the chain command block has /execute @a ~ ~-1 ~ clone x1 y1 z1 x2 y2 z2 ~ ~ ~ Now the issue I am having is when I go over the dropper the building appears, however the building also appears by my friend who is also playing on the world. So how could I modify the commands and/or add more commands to make it single only the person on the dropper?

Answer 1

New answer for 1.13, it's actually surprisingly easy in the new command system:

/execute as @a at @s if block ~ ~-1 ~ dropper{Items:[{Slot:4b,id:"minecraft:stone",Count:1b}]} run say spawn stuff, this gets executed at the player's location

This is what the parts do:

• /execute as @a at @s shifts the command execution to every player. I'm not sure why as is needed, maybe the if requires it.
• if block ~ ~-1 ~ tests the block under the player for being…
• dropper{Items:[{Slot:4b,id:"minecraft:stone",Count:1b}]} is whatever block and data you want. You can also specify block states in [] between the name and the NBT.
• run: All the execute stuff is over, now perform the real command.
• You can replace say spawn stuff, this gets executed at the player's location with your structure spawning command, of course.

You'll also have to make sure that the structure doesn't get spawned repeatedly of course, but that's a different question. Depending on your system, you either don't care or you tag the player or you put a marker armour stand there or whatever.

Answer 2

If the command blocks are near the dropper, you can use @p instead of @a.

If you know the coordinates of the dropper, you can just use /clone x1 y1 z1 x2 y2 z2 x3 y3 z3, where x3 y3 z3 are the coordinates of the dropper (or whatever nearby coordinates you need), and get rid of execute.

If you want this for multiple droppers in arbitrary locations, you have to give every player on top of a dropper a tag or whatever trigger your system has, then base the remaining commands on that.

If you need a completely perfect system, one that works for multiple players in the same tick, spawning different structures at arbitrary locations all at once… Then you probably need an ID system for players, then base your other commands on the currently structure spawning player IDs and it all gets pretty complicated. But usually one of the other solutions should work.