Bedrock Line Placement

A small, client-side quality-of-life mod for Minecraft 1.21.1 (NeoForge) that recreates Bedrock Edition's straight-line block placement in Java Edition.

When you hold the use/place key and drag to place a row of blocks, the mod locks your placements to the first clear cardinal direction you move in and suppresses sideways drift — so floors, walls, bridges and rows come out perfectly straight.

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What it does

1. You place a block while holding the use/place key.
2. As you keep holding and move, the mod watches the next placement to detect a clear cardinal direction (+X / -X / +Z / -Z, or +Y / -Y if vertical locking is on).
3. Once a direction is established, the placement line is locked: only blocks that stay on that straight line (and progress in the locked direction) are allowed. Off-line attempts are silently cancelled.
4. Releasing the use/place key clears the lock, so your next drag can pick a new direction.

For every placement attempt it answers allow or suppress. On top of that, the optional Line Reacharound helper (below) lets an already-locked line keep going even when your crosshair narrowly misses the lead block.

Line Reacharound

When a line lock is active, the mod can infer the lead block (the front of the line) and continue the line from its forward face — even when Java's crosshair targeting is too picky to hit that face directly. This helps with elevated bridges, long rows, and other straight-line builds where you stand on the line and walk forward while holding the use key.

It is deliberately conservative and not a scaffold / printer / automation mod:

• It only ever runs while a line is already locked and you are holding the use key. Outside an active line it does nothing — it will not place blocks when you are looking at containers, buttons, levers, doors, or building normally.
• It uses the vanilla placement path (it synthesizes the same interaction you would make by aiming at the lead block's face) and respects vanilla reach, collision, inventory, and server validation. It never adds reach, sends no custom packets, and never sets blocks in the world directly.
• It is rate-limited to vanilla's normal held-use cadence — it never places faster than, or more than, holding right-click already would.
• If the lead block is missing, unloaded, replaced, or the next cell is occupied or out of reach, it simply does nothing and defers to vanilla.

Disable it with enableLineReacharound = false to require directly hitting the lead block face.

How it differs from scaffolding / printer / schematic mods

This is not a building automation mod. The difference is deliberate and important for server safety:

	Bedrock Line Placement	Scaffold / Printer / Schematic mods
Builds without you holding use	No	Yes
Places faster than vanilla right-click	No	Often
Adds reach / speed	No	Often
Sends non-vanilla actions	No	Often
Works by	Cancelling off-line attempts, or redirecting a held-use placement to the lead block (Line Reacharound)	Generating placements from schematics/automation
Needs server-side install	No	Sometimes

The mod only acts while you are holding the use key on an active line: it either cancels an off-line attempt, or (with Line Reacharound) redirects the placement you are already making to the lead block's forward face. It never places more than vanilla would per click/tick, never adds reach, sends no custom packets, and uses only the normal vanilla placement path — the server stays authoritative.

How to build

Requirements: JDK 21 (the Gradle toolchain will fetch one if missing).

From the project root:

# Windows (PowerShell / cmd)
.\gradlew.bat build

# Linux / macOS
./gradlew build

The finished, Modrinth-compatible jar is written to:

build/libs/bedrocklineplacement-1.2.0.jar

Run the unit tests on their own with:

.\gradlew.bat test

How to install (Modrinth App, NeoForge profile)

1. In the Modrinth App, create or open a profile using Minecraft 1.21.1 with the NeoForge loader.
2. Open the profile's content/mods folder (in the Modrinth App: profile → ⋯ → Open folder → mods).
3. Copy build/libs/bedrocklineplacement-1.2.0.jar into that mods folder.
4. Launch the profile. The mod is client-only — you do not install it on any server, and it works when connecting to vanilla servers.

(The same jar works in any standard NeoForge 1.21.1 instance — just drop it in mods.)

Config options

Config file: config/bedrocklineplacement-client.toml (created on first run).

Option	Default	Meaning
enableLinePlacement	true	Master switch. When false, vanilla placement is untouched.
enableForBlocksOnly	true	Only constrain placement when the held item is a block.
requireContinuousUseKey	true	Only lock while the use/place key is held; releasing clears the lock.
allowVerticalLocking	true	Allow locking onto the vertical (Y) axis for towers/pillars.
enableLineReacharound	true	Line Reacharound: while a line is locked, continue it from the lead block's forward face even when your crosshair narrowly misses it (see above). Vanilla placement/reach/server rules still apply.
firstPlacementPauseTicks	6	Bedrock-style pause (in ticks; 20 = 1s) after the first block before the second is allowed, giving you time to aim. 0 disables.
resetOnItemChange	true	Clear the lock when the selected slot or held item changes.
resetOnSneak	false	Clear the lock when you start/stop sneaking.
debugLogging	false	Log lock/suppress decisions to the client log (troubleshooting).

How the lock is decided (brief)

• The first placement is the anchor. A short pause (firstPlacementPauseTicks) follows so you can start moving before the direction is committed.
• The vector to the next placement establishes the axis and direction, but only if it is a clean single-block cardinal step — a diagonal or gapped step is not locked (vanilla fallback).
• Once locked, placement is contiguous: only the single block immediately past the last one you placed is allowed. If your cursor drifts and you aim further down the line, those attempts are suppressed — you must come back to the block right after the last placed one to keep going (exactly like Bedrock). The axis cannot change until the lock is reset.

This logic lives in LinePolicy and is covered by unit tests.

Resets

The lock clears when any of these happen:

• The use/place key is released (when requireContinuousUseKey is on).
• The selected hotbar slot or held item changes (when resetOnItemChange is on).
• A screen/GUI opens (inventory, container, sign, etc.).
• You change dimension or leave the world.
• You start/stop sneaking (only when resetOnSneak is on).
• The held item is no longer a block (when enableForBlocksOnly is on).

Manual testing checklist

The decision/geometry logic is unit-tested, but the live placement behaviour must be verified in a running client. After building, drop the jar into a NeoForge 1.21.1 client and confirm:

Line placement / locking

• Hold use and drag a row: it stays perfectly straight and sideways drift does not branch the line.
• Releasing the use key resets the line (the next drag can pick a new direction).
• Changing the hotbar item resets the line (when resetOnItemChange is on).

Line Reacharound — ✅ verified in-game (2026-06-05)

• Build a straight elevated bridge while standing on top of the line and walking forward — blocks place in front of the lead block while you hold right-click.
• Verify it respects normal reach distance (it stops when the lead block gets too far away; it does not extend reach).
• Verify it does not place blocks when you look at containers / buttons / levers / doors, or when building outside an active line lock.
• Verify it does not place faster than holding right-click normally would, and does not run after the line resets.
• Verify it works on a vanilla server without installing the mod server-side.

Known limitations

Line Reacharound is verified in-game (elevated-bridge build, reach respected). The remaining line-placement edge cases (complex/multi-state blocks, off-hand placement, exact suppression feel) are unit-tested at the policy level and exercised in normal play, but have not each been individually checked — see the checklist above.

• Complex / multi-state blocks (slabs, stairs, doors, trapdoors, beds, etc.) are placed by vanilla rules. The mod only reasons about the target position, not the block's orientation/half, so these will not crash but the straight-line constraint is purely positional.
• Off-hand placement is handled best-effort (the same hook fires per hand). If you hit problems, place from the main hand.
• Interactions while locked: the mod only suppresses once a line is locked. In that state, an off-line right-click (e.g. opening a chest that isn't on the line) could be suppressed — release the use key (or it auto-resets) and try again.
• Replaceable-target prediction uses vanilla's own BlockPlaceContext, so it matches vanilla for grass/snow-layer style replacements, but unusual modded placement contexts fall back to vanilla rather than guess.
• Line Reacharound is intentionally conservative. It only continues a line whose lead block the client can still see as solid and in reach; if the lead block is missing, unloaded, replaced, or the next cell is occupied, it does nothing and defers to vanilla. It tracks the lead from confirmed placements only — it never assumes a failed attempt succeeded.

License

Apache License 2.0.