Use step size to determine bar gaps

piker/data/_formatters.py

@@ -99,6 +99,16 @@ class IncrementalFormatter(msgspec.Struct):
     _last_vr: tuple[float, float] | None = None
     _last_ivdr: tuple[float, float] | None = None
 
+    _index_step_size: float = None
+
+    @property
+    def index_step_size(self) -> float:
+        '''
+        Readonly value computed on first ``.diff()`` call.
+
+        '''
+        return self._index_step_size
+
     def __repr__(self) -> str:
         msg = (
             f'{type(self)}: ->\n\n'
@@ -172,6 +182,9 @@ class IncrementalFormatter(msgspec.Struct):
             # set us in a zero-to-append state
             nd_stop = self.xy_nd_stop = src_stop
 
+            align_index = array[self.index_field]
+            self._index_step_size = align_index[-1] - align_index[-2]
+
         # compute the length diffs between the first/last index entry in
         # the input data and the last indexes we have on record from the
         # last time we updated the curve index.
@@ -559,8 +572,7 @@ class OHLCBarsFmtr(IncrementalFormatter):
         x, y, c = path_arrays_from_ohlc(
             array,
             start,
-            # self.index_field,
-            bar_gap=w,
+            bar_gap=w * self.index_step_size,
         )
         return x, y, c