midiviz: the column glow lives 30% longer than the cells

tools/bridge/midiviz.py

@@ -426,6 +426,10 @@ THEME_MENU: dict[str, str] = {
 }
 
 TAU = 0.85                          # seconds; brightness e-folding time
+# PLN, 2026-09-24: the column glow dies noticeably faster than the cells do —
+# at 0.85 s it is gone while the last-moved cell is still lit. The column is
+# the "this orbit is live" signal, so it keeps its own, 30 % slower curve.
+TAU_COL = TAU * 1.3
 IDLE_AFTER = 2.0                    # seconds of silence before the slow pulse
 # 40 ms = 25 fps. Profiling a frame (see MAX_DROPS) put the cost squarely in the
 # number of drawText calls, and at this size 25 fps is indistinguishable from 33
@@ -1676,11 +1680,12 @@ def build_widget(port_label: str, reader: "Reader | None", scale: float = 1.0,
             if max(frame) > 0.04:
                 self._spec_hot_t = now
 
-        def _lv(self, age: float, floor: int = 0) -> int:
-            """Age in seconds → LUT level. The only decay curve in the file."""
+        def _lv(self, age: float, floor: int = 0, tau: float = TAU) -> int:
+            """Age in seconds → LUT level. The only decay shape in the file;
+            the time constant is a parameter so the column can outlive the cells."""
             if age < 0:
                 return LEVELS - 1
-            lv = int((LEVELS - 1) * math.exp(-age / TAU))
+            lv = int((LEVELS - 1) * math.exp(-age / tau))
             return max(floor, min(LEVELS - 1, lv))
 
         # ── paint ──────────────────────────────────────────────────────────
@@ -1880,7 +1885,7 @@ def build_widget(port_label: str, reader: "Reader | None", scale: float = 1.0,
             for col in range(1, 9):
                 if not self.col_t[col]:
                     continue
-                lv = self._lv(now - self.col_t[col])
+                lv = self._lv(now - self.col_t[col], tau=TAU_COL)
                 if lv > 1:
                     # A SURFACE, not ink: this is the slab a live column stands
                     # on. Sampled from the ink ramp it would paint a dark bar
@@ -1893,7 +1898,8 @@ def build_widget(port_label: str, reader: "Reader | None", scale: float = 1.0,
             # column digits = orbit numbers, brightening with that orbit's activity
             col_base = self.col_y + self.u_asc
             for col in range(1, 9):
-                lv = self._lv(now - self.col_t[col], floor=4) if self.col_t[col] \
+                lv = self._lv(now - self.col_t[col], floor=4, tau=TAU_COL) \
+                    if self.col_t[col] \
                     else 4 + int(2 * pulse)
                 p.setPen(self.lut[FAM_LEVEL][min(LEVELS - 1, lv)])
                 p.drawText(round(mx + (col - 1) * cw + (cw - self.uw) / 2),