Fixed-BPM grid + piecewise fit + dual-mode support

app.py

@@ -15,7 +15,7 @@ import numpy as np
 import torch
 
 from softchart.generate import generate_song, generate_song_slot, load_hf
-from softchart.grid import debias_to_grid, fit_grid
+from softchart.grid import debias_to_grid, fit_grid_fixed_bpm, fit_grid_piecewise
 from softchart.hf import SoftChartPlanner
 from softchart.rhythm import snap_chart
 from softchart.tja import write_tja_slots
@@ -246,7 +246,7 @@ def generate(audio, course, level, bpm_override, auto_plan_on, use_beat, use_pla
     if use_beat and M["beat"] is not None:
         # global robust (period, phase) fit over the whole song — much more
         # precise than per-peak use (each raw peak carries ~±23 ms bin noise)
-        grid = fit_grid(M["beat"], mel, device=DEVICE)
+        grid = fit_grid_piecewise(M["beat"], mel, device=DEVICE)
         if grid is not None:
             # rigid synthesized barlines when the fit is trustworthy; raw peaks
             # (plan-block edges only, no anchoring) when it is not
@@ -255,8 +255,13 @@ def generate(audio, course, level, bpm_override, auto_plan_on, use_beat, use_pla
                 grid = None
     if bpm_override and bpm_override > 0:
         bpm = float(bpm_override)
-        if grid is not None and abs(grid["bpm"] - bpm) > 0.5:
-            grid = None  # user disagrees with the fit: don't anchor to it
+        if use_beat and M["beat"] is not None and (grid is None or abs(grid["bpm"] - bpm) > 0.5):
+            # the user KNOWS the tempo: phase-only fit with a trusted period —
+            # much easier than the free fit, often unlocks the slot-exact path
+            g2 = fit_grid_fixed_bpm(M["beat"], mel, bpm, device=DEVICE)
+            grid = g2 if (g2 is not None and g2["ok"]) else None
+            if grid is not None:
+                dbs = grid["downbeats"]
     elif grid is not None:
         bpm = grid["bpm"]  # already integer-snapped when the residual allows
     elif dbs is not None and len(dbs) > 4:
@@ -301,6 +306,7 @@ def generate(audio, course, level, bpm_override, auto_plan_on, use_beat, use_pla
     img = render(mel, g, title, course)
     if grid is not None:
         grid_info = (f" · grid: rms {grid['rms_ms']:.1f}ms ({grid['inlier_frac']:.0%} inlier)"
+                     + (f" · {grid['n_segments']} tempo segs" if grid.get("piecewise") else "")
                      + (" · slot-exact" if slot_used else ""))
     elif use_beat and M["beat"] is not None:
         grid_info = " · grid: unreliable, barline anchoring off"