pre merge cleanup

sras_viewer/dialogs.py

@@ -48,7 +48,8 @@ class FftOptionsDialog(QDialog):
                  current_pad_factor: int,
                  samples_per_frame: int | None,
                  sample_rate_hz: float | None,
-                 grating_um: float):
+                 grating_um: float,
+                 cached_pad_factor: int | None = None):
         super().__init__(parent)
         self.setWindowTitle("FFT Options")
         self.setModal(True)
@@ -57,6 +58,10 @@ class FftOptionsDialog(QDialog):
         self._samples_per_frame = samples_per_frame
         self._sample_rate_hz = sample_rate_hz
         self._grating_um = grating_um
+        # The pad the open file's stored FFT cache was computed at, if it has
+        # one — picking anything else here makes that cache unreadable, which
+        # is worth saying before Apply rather than after.
+        self._cached_pad_factor = cached_pad_factor
 
         layout = QVBoxLayout(self)
 
@@ -109,6 +114,11 @@ class FftOptionsDialog(QDialog):
             lbl.setStyleSheet(_CSS_HINT)
             zl.addWidget(lbl)
 
+        self._lbl_cache = QLabel()
+        self._lbl_cache.setWordWrap(True)
+        self._lbl_cache.setStyleSheet(_CSS_WARN)
+        zl.addWidget(self._lbl_cache)
+
         layout.addWidget(grp_zp)
 
         # ---- Buttons ---------------------------------------------------
@@ -126,6 +136,13 @@ class FftOptionsDialog(QDialog):
         sr = self._sample_rate_hz
         pad = self._spin_pad.value()
 
+        self._lbl_cache.setText(
+            "" if self._cached_pad_factor in (None, pad) else
+            f"! This file's stored FFT cache was computed at pad "
+            f"{self._cached_pad_factor}x, so at {pad}x it can't be used and "
+            f"CH1/Velocity will recompute. Re-run Convert -> Batch Compute FFT "
+            f"to cache at {pad}x.")
+
         if spf is None or sr is None:
             self._lbl_nfft.setText("Load a file to preview FFT parameters.")
             self._lbl_freq_res.setText("")