Stop bar playback before the bar line, not on it

Playing a single bar still triggered notes placed exactly on the next bar
line. Two delays stack: the daemon polls at roughly frame rate, so it can
notice up to ~33ms late, and REAPER renders audio ahead of the play position
it reports, so the note has already reached the instrument before the stop
lands.

Stopping 60ms early clears both. The cost is a few milliseconds off the tail
of the bar, which is inaudible, and the benefit is that the downbeat you were
trying to exclude stays excluded. Tunable via the stoplead ExtState for setups
with large audio buffers.

MidiGrid_Daemon.lua

@@ -53,7 +53,14 @@ local function loop()
   local stopAt = tonumber(G.getTemp("stopat", ""))
   if stopAt then
     local playing = (reaper.GetPlayState() % 2) == 1
-    if playing and reaper.GetPlayPosition() >= stopAt then
+    -- Stop a little BEFORE the bar line, not on it. Two delays stack up
+    -- otherwise: this loop only runs at about frame rate, and REAPER renders
+    -- audio ahead of the play position it reports -- so a note sitting exactly
+    -- on the next bar line has already been sent to the instrument by the time
+    -- we notice. Leading by more than both delays keeps that note silent.
+    -- Costs a few ms off the tail of the bar, which is inaudible.
+    local lead = G.getNum("stoplead", 0.06)
+    if playing and reaper.GetPlayPosition() >= stopAt - lead then
       -- Stopping can move the edit cursor depending on preferences, and the
       -- edit cursor is the grid cursor, so put it back.
       local cur = reaper.GetCursorPosition()

README.md

@@ -177,6 +177,16 @@ script — a script that stayed alive waiting for the bar to end would trigger
 REAPER's "already running" prompt on the next press. Stopping can move the
 edit cursor depending on your preferences, so the daemon puts it back.
 
+It stops **60 ms before** the bar line rather than on it. Two delays stack up
+otherwise: the daemon runs at about frame rate, and REAPER renders audio ahead
+of the play position it reports, so a note sitting exactly on the next bar line
+has already reached the instrument by the time the stop lands — and you hear
+the downbeat you were trying to exclude. Leading by more than both delays keeps
+it silent, at the cost of a few inaudible milliseconds off the tail.
+
+If a next-bar note still sneaks through — a large audio buffer will do it —
+raise `stoplead` in `ExtState`.
+
 ## Shifting notes in time
 
 If a whole clip landed a couple of cells off the beat, `Ctrl+Shift+Left` and
@@ -268,6 +278,7 @@ In `ExtState` section `midigrid`:
 |---|---|---|
 | `vel` | 96 | Velocity of inserted notes |
 | `velstep` | 8 | Velocity change per keypress |
+| `stoplead` | 0.06 | How early to stop, in seconds, when playing one bar |
 | `chan` | 0 | MIDI channel (0-based) |
 | `previewdur` | 0.4 | Preview note length, seconds |