AliasTrack v0.1.0 – linked item groups inside REAPER folders

One action (AliasTrack.lua) opens a ReaImGui window. Select items on tracks inside one folder and group them: an ALIAS lane appears as the folder's first track, holding one alias item that spans the selection. The alias behaves like a normal item whose "source" is the group:

• move it – its members move with it
• trim it – members are hidden or revealed, never destroyed (extend it again and they are back)
• split it, or split / razor-delete any member – the whole group is cut at that point
• copy it – a linked copy: edit a member in one copy and every linked copy follows
• put it on the COPIES lane – an independent copy with its own edits

Install

macOS (or --portable anywhere): close REAPER, then ./install_mac.sh from this folder (also finds dist/AliasTrack.lua). It copies the script to Scripts/AliasTrack/, removes the download quarantine flag and registers the action in reaper-kb.ini (backed up first; skipped if REAPER is running – use --no-register to skip it yourself). ./install_mac.sh --uninstall removes exactly that.

Manual: load dist/AliasTrack.lua as a ReaScript (Actions → Show action list → New action → Load ReaScript…) and run it. Needs ReaImGui (ReaPack → ReaTeam Extensions). Optional: js_ReaScriptAPI – syncing then waits until you release the mouse. Running the action again while the window is open closes it.

How it works

Drums (folder)
  ALIAS · Beat    [ Beat ][ Beat ]          <- linked aliases: all show the same group
  COPIES · Beat           [ Beat #2 ]       <- unique aliases: each its own variant (created on first use)
  Kick            [k   ]  [k   ]  [k   ]
  Snare              [s]     [s]     [s]
  HH              [hhhh]  [hhhh]  [hh--]    <- members are derived from alias + group

• The alias item is an empty MIDI item: REAPER itself keeps its start offset through trims and splits, and that offset is the window into the group.
• Member edits – move inside the alias, trim, volume, mute, pitch, rate, fades, move to another track in the folder – go into the group automatically (setting), so every linked alias follows.
• Edits that cannot be applied safely mark the alias MIXED: a member deleted, dragged past the alias edge, moved out of the folder, or trimmed at an edge the alias itself cut. Apply makes the group like this alias; Revert makes the alias like the group.
• FX, envelopes and take changes of a member: select it and press Push selected edits.
• Add selected to alias / Remove selected from group change the group's content.
• Flatten turns one alias back into plain items; Ungroup does it for all and removes the lanes; Detach all removes every tag and leaves everything else as it is.
• Identity comes from P_EXT tags, never from names: rename tracks and items freely.

Undo

• One step per edit (default): syncs add no undo points. Ctrl+Z undoes your edit and the aliases are derived again.
• Separate sync steps: each sync is an undo point "AliasTrack: sync"; after undoing one, syncing pauses until you undo again or edit something.
• Every button (Group, Make unique, Apply …) is one undo step.

Settings

Freeze / Go live · undo mode · apply member edits automatically · deleting an alias deletes its members · keep MIDI pooled between linked aliases · create the COPIES lane with every group · fade length on edges cut by an alias.

Development

./tools/run_tests.sh builds dist/AliasTrack.lua and runs the offline tests (Lua 5.3+) against a mock REAPER and an ImGui stub. DESIGN.md explains the model and the open questions; spikes/ lists what still has to be confirmed in real REAPER, with a probe script for the main assumptions.

MIT licence.