Iris Raycasting

Iris is a utility data pack for Minecraft: Java Edition 1.20.3+ designed to determine what block or entity a player is looking at, with micrometric precision and taking into account individual block geometries.

Building

The data pack comprises the files already present in this repository, along with the files generated by the gen_files.py script in the build folder, which should be executed directly in the root directory of this repository.

To build Iris on Unix-like systems, the following commands can be used:

git clone https://github.com/Aeldrion/Iris
cd Iris
./build/gen_files.py

Working versions of Iris (with everything built) are made available in GitHub releases.

Documentation

iris:get_target

Casts a ray from the current position, oriented with the current rotation, and returns data on the block or entity that is found. To tell where a player is facing, starting at the eye position is needed. Entities with the iris.ignore tag are ignored.

execute as <player> at @s anchored eyes positioned ^ ^ ^ run function iris:get_target

Output

The result of this function is the distance (in blocks, rounded up) before an obstacle is hit, or 0 if no block or entity is found before the maximum recursion depth is reached.

The success is 1 if a block or entity was hit, 0 otherwise.

Available information about the targeted position is saved to the iris:output storage. The exact storage output of the function is further documented in the header of the function itself (data/iris/functions/get_target.mcfunction).

If a block was hit, a marker with the iris.targeted_block tag is summoned in the middle of the targeted tile. If an entity was hit, it gets the iris.targeted_entity tag. When running the function again, iris.targeted_block markers are killed and iris.targeted_entity entities get the tag removed, and so there can only be one such entity in the world at any given moment.

Settings

Settings of the function can be modified in the iris:settings storage:

Tag	Description	Default value
MaxRecursionDepth	How many blocks to traverse before giving up	16
TargetEntities	Whether or not to look for collisions with entities	false
Callback	A function or function tag to run where the raycast ends	Unset
Blacklist	Which blocks to ignore during block traversal	"#iris:air"
Whitelist	The only blocks to look for during traversal	Unset

If both Blacklist and Whitelist are set, all blocks outside of the whitelist or in the blacklist will be ignored. If both Blacklist and Whitelist are unset, collisions will be tested for all tiles traversed. It is recommended that blocks with no outline (e.g. air) be blacklisted, or that a whitelist be set up to ignore them.

Examples

Detecting when the player is looking at a block that is within reach

In the following example, it is assumed that the function is executed as each player. A message is displayed in the actionbar of players targeting a block. The block reach is 5 blocks in creative mode, 4.5 blocks in survival mode.

# Detect when the player is looking at a block that is within reach
execute if entity @s[gamemode=survival] run scoreboard players set $max_distance mypack 4500000
execute if entity @s[gamemode=creative] run scoreboard players set $max_distance mypack 5000000
execute at @s anchored eyes positioned ^ ^ ^ store result score $distance mypack run function iris:get_target
title @s actionbar ""
execute if score $distance mypack <= $max_distance mypack at @e[type=minecraft:marker, tag=iris.targeted_block] run title @s actionbar "Looking at a block"

Targeting entities that the player looks at

In the following example, levitation is given to cows that the player looks at within a 10 block radius. It is assumed that TargetEntities has been set to true, and that MaxRecursionDepth has been set to a high enough value to catch everything within ten blocks; 20 is enough.

# Give levitation to cows the player is looking at
execute as <player> at @s anchored eyes positioned ^ ^ ^ run function iris:get_target
execute at <player> run effect give @e[type=minecraft:cow, tag=iris.targeted_entity, distance=..10] minecraft:levitation 1 0

Targeting hidden blocks

In the following example, a sound is played at the location of diamond ores that the player looks at, including through other blocks.

# Play a sound at diamond ores the player looks at, including through other blocks
data modify storage iris:settings Whitelist set value "#mypack:diamond_ores"
execute at @s anchored eyes positioned ^ ^ ^ run function iris:get_target
execute if data storage iris:output {TargetType: "BLOCK"} at @e[type=minecraft:marker, tag=iris.targeted_block] run playsound minecraft:block.note_block.bell block

// data/mypack/tags/blocks/diamond_ores.json
{
    "values": [
        "minecraft:diamond_ore",
        "minecraft:deepslate_diamond_ore"
    ]
}

Predicting where a block will be placed

In the following example, the direction of the targeted face (TargetedFace.Direction in storage iris:output) and the direction of the player (scores $dx, $dy, $dz on objective iris) is used to predict where a block would be placed if the player attempted to place one. If no block is targeted, the function fails early; otherwise, the iris.targeted_block marker that is summoned by iris:get_target is teleported, and a block is placed at its new position.

execute at @s anchored eyes positioned ^ ^ ^ run function iris:get_target
execute unless data storage iris:output {TargetType: "BLOCK"} run return fail
execute if data storage iris:output TargetedFace{Direction: "WEST"} as @e[type=minecraft:marker, tag=iris.targeted_block] at @s run teleport @s ~-1 ~ ~
execute if data storage iris:output TargetedFace{Direction: "EAST"} as @e[type=minecraft:marker, tag=iris.targeted_block] at @s run teleport @s ~1 ~ ~
execute if data storage iris:output TargetedFace{Direction: "DOWN"} as @e[type=minecraft:marker, tag=iris.targeted_block] at @s run teleport @s ~ ~-1 ~
execute if data storage iris:output TargetedFace{Direction: "UP"} as @e[type=minecraft:marker, tag=iris.targeted_block] at @s run teleport @s ~ ~1 ~
execute if data storage iris:output TargetedFace{Direction: "NORTH"} as @e[type=minecraft:marker, tag=iris.targeted_block] at @s run teleport @s ~ ~ ~-1
execute if data storage iris:output TargetedFace{Direction: "SOUTH"} as @e[type=minecraft:marker, tag=iris.targeted_block] at @s run teleport @s ~ ~ ~1
execute at @e[type=minecraft:marker, tag=iris.targeted_block] if block ~ ~ ~ minecraft:air run playsound minecraft:block.stone.place block @a ~ ~ ~
execute at @e[type=minecraft:marker, tag=iris.targeted_block] if block ~ ~ ~ minecraft:air run setblock ~ ~ ~ minecraft:cobblestone

Note: Here, we check that the placing position is not occupied (if block ~ ~ ~ minecraft:air). A better approach would be to test for any replaceable block (including water, tall gras...) with a block tag check.

iris:set_coordinates

Teleports the executing entity to a position provided by six scores on the iris objective: $[x], $[y], $[z] for integer coordinates, ${x}, ${y}, ${z} for fractional coordinates (with a scale of 1,000,000). After running iris:get_target, the six scores are set to the exact position where the ray lands and so iris:get_target and iris:set_coordinates can easily be used in conjunction:

# Teleport the player where they are looking
execute as <player> at @s anchored eyes positioned ^ ^ ^ run function iris:get_target
execute as <player> run function iris:set_coordinates

Output

The result and success of this function is 1 if executed by an entity, 0 otherwise.

Including Iris in your data pack

To include Iris in your own data pack:

• Copy the iris folder and its contents in the data folder of your data pack
• Make sure the #minecraft:load function tag includes iris:setup/load

If you are redistributing modified versions of Iris as a part of your own data packs, it is recommended to change the iris namespace to avoid conflicts with other data packs using Iris. To do so, you may simply rename the iris folder to e.g. iris_mypack and every instance of iris in the contents of data pack files to iris_mypack (including storage names, objectives, entity tags...)

How it works

Since this will most likely be used mostly by other data pack nerds, here is a summary of how Iris operates.

Getting the coordinates/rotation

execute store can be used to get an entity's position, however any scale over 70 is unusable for X and Z coordinates due to overflowing. To get the current position with enough detail, string manipulation is done with macro functions to cut and read everything past the decimal point in any position coordinate. From then on, the starting position is saved as six scores: the integer part ($[x], $[y], $[z]) and the fractional part (${x}, ${y}, ${z}).

To get the rotation, a marker is summoned 1,000,000 blocks forward starting from 0.0, 0.0, 0.0 using the executing rotation. The marker's position describes the rotation as a steering vector that can be used in later calculations.

Raycasting

The data pack solves simple linear equations to figure out which tile it hits next (ray/plane intersections), instead of progressing by a fixed length at every iteration like most raycasting functions do. Upon hitting a block other than air (or an entity, if TargetEntities is true), it gets its shape as a list of axis-aligned bounding boxes (AABB) and checks which faces it hits. For every AABB, there are three faces to check, and the three others (back-faces) are culled.

Getting the hitbox of a block

Block hitbox information is pulled from ArticData. Blocks with the same set of block state properties and corresponding hitboxes are grouped together in block tags. Iris also accounts for the random horizontal offset on the hitbox of a few blocks, namely flowers, bamboo, pointed dripstone, and mangrove propagules.