How to calculate the area of a region of any shape (Minecraft Java Edition 1.18)

Question

There is an armorstand on one of the red regions. How to count blocks that are including to the region the armorstand stands on? The result has to be stored to a scoreboard. Red regions can have any shape and size, and also have some number of holes.

The illustration of it is below:

Answer 1

My idea is to use a flood fill algorithm

Before we start the loop, we do

1. Spawn a temporary armor stand (called "filled") on the start tile (if the starting point is allowed to be outside the red region, you need to add an if to the execute command

   execute as @e[tag=,type=minecraft:armor_stand] at @s run summon minecraft:armor_stand ~ ~ ~ {Tags:[filled]}
   

2. Start an loop executing every tick

   setblock ~ ~ ~1 minecraft:redstone_block
   

3. Reset scoreboard to 0

   /scoreboard players set count region 0
   

In the loop, do:

1. For each cardinal direction, try to spawn a new armor stand, if the location is not occupied and the new location is above a red wool block

   execute as @e[tag=filled,type=minecraft:armor_stand] at @s positioned ~-1 ~ ~ unless entity @e[type=minecraft:armor_stand,tag=filled,distance=...9] if block ~ ~-1 ~ minecraft:red_wool run summon minecraft:armor_stand ~ ~ ~ {Tags:[filled]}
   execute as @e[tag=filled,type=minecraft:armor_stand] at @s positioned ~1 ~ ~ unless entity @e[type=minecraft:armor_stand,tag=filled,distance=...9] if block ~ ~-1 ~ minecraft:red_wool run summon minecraft:armor_stand ~ ~ ~ {Tags:[filled]}
   execute as @e[tag=filled,type=minecraft:armor_stand] at @s positioned ~ ~ ~1 unless entity @e[type=minecraft:armor_stand,tag=filled,distance=...9] if block ~ ~-1 ~ minecraft:red_wool run summon minecraft:armor_stand ~ ~ ~ {Tags:[filled]}
   execute as @e[tag=filled,type=minecraft:armor_stand] at @s positioned ~ ~ ~-1 unless entity @e[type=minecraft:armor_stand,tag=filled,distance=...9] if block ~ ~-1 ~ minecraft:red_wool run summon minecraft:armor_stand ~ ~ ~ {Tags:[filled]}
   

2. Use comparators to monitor the spawning process, if no armorstands are spawned, we have filled the area

After the loop, we need to cleanup:

1. Update the scoreboard

   execute as @e[type=minecraft:armor_stand,tag=filled] run scoreboard players add count region 1
   

2. Cleanup the progress armorstands

   execute as @e[type=minecraft:armor_stand,tag=filled] run kill @s
   

3. Stop the repeating clock

   setblock ~ ~ ~-11 air
   

^{World download: https://files.ferrybig.me/s/HCd9mgKSB9jPSPJt (though the descriptions in the answer should be good enough to recreate this)}

Answer 2

I've created a datapack that solves this problem by the @Ferrybig's algorithm but with no redstone, functions only.

Setup

First of all, it creates a scoreboard that will be displayed at the sidebar.

setup.mcfunction

scoreboard objectives add area_counter dummy
scoreboard objectives setdisplay sidebar area_counter

Main

Next, we need to set the initial value of the main counter variable. The only way to loop a mcfunction code fragment I know is by recursion, so we create another function count_area.

NB. I replaced most armor_stand with area_effect_cloud for optimization.

main.mcfunction

scoreboard players set count area_counter 0

execute as @e[tag=,type=minecraft:armor_stand] at @s run summon minecraft:area_effect_cloud ~ ~ ~ {Tags:[filled], Duration:1000}

execute as @e[tag=filled,type=minecraft:area_effect_cloud] at @s if block ~ ~-1 ~ minecraft:red_wool run function ac:count_area

execute as @e[tag=filled,type=minecraft:area_effect_cloud] run scoreboard players add count area_counter 1

kill @e[tag=filled,type=minecraft:area_effect_cloud]

Count_area

This is the most difficult part of the solution. First, we set the initial values for following variables:

count_area.mcfunction. 1/3

scoreboard players set has_been_executed area_counter 0
scoreboard players set north area_counter 0
scoreboard players set south area_counter 0
scoreboard players set east area_counter 0
scoreboard players set west area_counter 0

Next, we check every cardinal direction for red wool block exactly like in @Ferrybig's answer.

count_area.mcfunction. 2/3

execute store success score north area_counter as @e[type=minecraft:area_effect_cloud,tag=filled] at @s positioned ~ ~ ~-1 unless entity @e[type=minecraft:area_effect_cloud,tag=filled,distance=...9] if block ~ ~-1 ~ minecraft:red_wool run summon minecraft:area_effect_cloud ~ ~ ~ {Tags:[filled], Duration:1000}
execute store success score south area_counter as @e[type=minecraft:area_effect_cloud,tag=filled] at @s positioned ~ ~ ~1 unless entity @e[type=minecraft:area_effect_cloud,tag=filled,distance=...9] if block ~ ~-1 ~ minecraft:red_wool run summon minecraft:area_effect_cloud ~ ~ ~ {Tags:[filled], Duration:1000}
execute store success score east area_counter as @e[type=minecraft:area_effect_cloud,tag=filled] at @s positioned ~1 ~ ~ unless entity @e[type=minecraft:area_effect_cloud,tag=filled,distance=...9] if block ~ ~-1 ~ minecraft:red_wool run summon minecraft:area_effect_cloud ~ ~ ~ {Tags:[filled], Duration:1000}
execute store success score west area_counter as @e[type=minecraft:area_effect_cloud,tag=filled] at @s positioned ~-1 ~ ~ unless entity @e[type=minecraft:area_effect_cloud,tag=filled,distance=...9] if block ~ ~-1 ~ minecraft:red_wool run summon minecraft:area_effect_cloud ~ ~ ~ {Tags:[filled], Duration:1000}

Finally, we sum every successful summoning to the has_been_executed and check for it actually has. If it has, the function runs itself.

count_area.mcfunction. 3/3

scoreboard players operation has_been_executed vars += north area_counter
scoreboard players operation has_been_executed vars += south area_counter
scoreboard players operation has_been_executed vars += east area_counter
scoreboard players operation has_been_executed vars += west area_counter

execute unless score has_been_executed area_counter matches 0 run function ac:count_area

You can download the complete datapack here: https://www.mediafire.com/file/2f4l67zem23jl09/area_counter.zip/file