feat: pixel<->time geometry helpers for the waveform

core/waveform.py

@@ -5,6 +5,20 @@ import numpy as np
 from core.paths import _bin
 
 
+def x_to_t(x: float, width: float, view_start: float, view_dur: float) -> float:
+    """Map a pixel x in [0,width] to a time in [view_start, view_start+view_dur]."""
+    if width <= 0 or view_dur <= 0:
+        return view_start
+    return view_start + (x / width) * view_dur
+
+
+def t_to_x(t: float, width: float, view_start: float, view_dur: float) -> int:
+    """Map a time to a pixel x in [0,width] (rounded)."""
+    if width <= 0 or view_dur <= 0:
+        return 0
+    return int(round((t - view_start) / view_dur * width))
+
+
 def peaks(samples, buckets: int = 128) -> list[float]:
     """Reduce a 1-D sample array to *buckets* normalized peak magnitudes (0..1)."""
     if samples is None or len(samples) == 0: