fix

rfg_adc_plotter/state/ring_buffer.py

@@ -10,6 +10,13 @@ import numpy as np
 from rfg_adc_plotter.constants import FFT_LEN, SWEEP_FREQ_MAX_GHZ, SWEEP_FREQ_MIN_GHZ
 from rfg_adc_plotter.processing.fft import compute_distance_axis, compute_fft_mag_row, fft_mag_to_db
 
+# The device sweep length jitters by a few percent (e.g. 896..920). Only treat a
+# shrink as real when the new width drops below this fraction of the current width;
+# genuine format changes (e.g. 2048 -> 256, or halving) fall well below it. This
+# stops the ring from reallocating every frame — which churned the buffer and made
+# the B-scan flicker.
+RING_WIDTH_SHRINK_FRACTION = 0.8
+
 
 class RingBuffer:
     """Store raw sweeps, FFT rows, and matching time markers."""
@@ -103,7 +110,12 @@ class RingBuffer:
             self.ring_fft_input = np.full((self.max_sweeps, self.width), np.nan + 0j, dtype=np.complex64)
             self.head = 0
             changed = True
-        elif target_width != self.width:
+        elif target_width > self.width or target_width < int(self.width * RING_WIDTH_SHRINK_FRACTION):
+            # Resize when the sweep grows, or shrinks by a meaningful fraction (a real
+            # format change). Ignore small shrinks: the device sweep length jitters by
+            # a few percent (e.g. 896 vs 920). Resizing on every such shrink churned
+            # the ring every frame and made the B-scan flicker. A shorter sweep just
+            # fills fewer columns (the rest stays NaN); the width converges to the max.
             new_ring = np.full((self.max_sweeps, target_width), np.nan, dtype=np.float32)
             new_fft_input = np.full((self.max_sweeps, target_width), np.nan + 0j, dtype=np.complex64)
             take = min(self.width, target_width)