TrajectoryLens

TrajectoryLens — See where things are going, before they get there.

TrajectoryLens predicts and renders where dropped items, arrows, TNT, falling blocks and even whole explosion chains will end up, as translucent glass-like coloured segments you can see through terrain. No particles, no block changes, no world edits, and nothing is ever sent to the server: a client-side install works on any server, vanilla included.

FEATURES

- Item trajectories: per-tick faithful prediction for dropped items, rest markers with an ETA, per-item colours and a watch list.
- Projectiles: arrows, tridents, snowballs, eggs, ender pearls, potions and fireballs with the real 26.2 flight constants, impact labels (block or entity name) and a held-item aim preview. Ender pearls also show their teleport spot, self-damage and whether the landing is dangerous.
- Explosions: fuse countdown and blast rings for TNT, creepers and TNT minecarts, plus a causal-chain forecast: which TNT re-detonates and when, where launched items and mobs land (lava / cactus / void / water / fall damage), and which blocks are destroyed.
- Falling blocks: sand, gravel, anvils and dripstone show their landing spot and turn red when somebody is standing underneath.
- Mobs: a threat indicator (locked / alert / unaware) and a walk-range overlay showing the theoretical reachable area of a mob type over the next N seconds.
- Logistics: chokepoint counters with per-minute rate, backlog and a 3-minute trend; hopper jam detection (red = jammed, blue = redstone-locked); entity census; report export.
- Lost items: why an item disappeared (player, hopper, lava, fire, cactus, explosion, merge, despawn, void), a fading highlight on the hopper that ate it, and a despawn countdown.
- In-game panel: eight tabbed pages, key-chord binding by pressing the keys, search pickers for items and entity types, everything saved to config/trajectorylens.json.

INSTALL

1. Install Fabric Loader 0.19.3+ and Fabric API.
2. Put the jar into your client mods folder.
3. Press G for item paths, O+P for walk ranges, H+J for the panel, or type /trajectorylens (short alias /tl).

Client-side install is all you need; the server does not have to install anything, and the mod never sends a packet to the server.

KEY COMMANDS

/tl toggle — item trajectories (same as G)
/tl target <item id> — watch only some items (/tl target clear to watch everything again)
/tl color <item id> <RRGGBB> — per-item path colour
/tl projectiles / tnt / aim / chain / falling on|off|toggle — individual overlays
/tl chaindepth [layers] and /tl chainhorizon [seconds] — causal-chain depth and knock-back window
/tl threat / jam / despawn / losttrack on|off|toggle — threat / jam / despawn / provenance
/tl counter add <name>, /tl counter list, /tl flowcount — chokepoint counters
/tl range add <entity type>, /tl range time <s> — walk-range overlay
/tl export — write a statistics report to config/
/tl gui — open the control panel

ACCURACY

26.2 changed item physics a lot (water drag 0.99, lava 0.95, water flow push 0.014, ground friction from the block). This mod does not re-implement formulas: it creates a shadow ItemEntity, never added to the world, and calls the same engine methods every tick, so the prediction matches vanilla as long as nothing pushes, picks up or merges the item. Trajectories are cleared when an item is picked up and recomputed every 20 ticks or when the state drifts.

MULTIPLAYER

Everything is computed locally; only entities the server sends you are visible (tracking range / loaded chunks). Block, fluid and hopper enabled state is available client-side. Items taken by another player can only be reported as "unknown".

LANGUAGES

English and Chinese are shipped; the interface follows your game language.

REQUIREMENTS

Minecraft 26.2, Fabric Loader 0.19.3+, Fabric API, Java 25. License: MIT.