Expose a `force_reformat: bool` up through graphics stack

piker/data/_formatters.py

@@ -222,6 +222,7 @@ class IncrementalFormatter(msgspec.Struct):
         profiler: Profiler,
 
         slice_to_inview: bool = True,
+        force_full_realloc: bool = False,
 
     ) -> tuple[
         np.ndarray,
@@ -248,7 +249,10 @@ class IncrementalFormatter(msgspec.Struct):
 
         # we first need to allocate xy data arrays
         # from the source data.
-        if self.y_nd is None:
+        if (
+            self.y_nd is None
+            or force_full_realloc
+        ):
             self.xy_nd_start = shm._first.value
             self.xy_nd_stop = shm._last.value
             self.x_nd, self.y_nd = self.allocate_xy_nd(

piker/ui/_dataviz.py

@@ -752,6 +752,7 @@ class Viz(Struct):
 
         profiler: Profiler | None = None,
         do_append: bool = True,
+        force_redraw: bool = False,
 
         **kwargs,
 
@@ -796,7 +797,7 @@ class Viz(Struct):
                 graphics,
             )
 
-        should_redraw: bool = False
+        should_redraw: bool = force_redraw or False
         ds_allowed: bool = True  # guard for m4 activation
 
         # TODO: probably specialize ``Renderer`` types instead of
@@ -906,6 +907,11 @@ class Viz(Struct):
             should_ds=should_ds,
             showing_src_data=showing_src_data,
 
+            # XXX: reallocate entire underlying "format graphics array"
+            # whenever the caller insists, such as on history
+            # backfills.
+            force_reformat=force_redraw,
+
             do_append=do_append,
         )
 
@@ -925,6 +931,7 @@ class Viz(Struct):
         reset_cache = False
         if (
             reset_cache
+            or should_redraw
         ):
             # assign output paths to graphicis obj but
             # after a coords-cache reset.

piker/ui/_render.py

@@ -136,6 +136,7 @@ class Renderer(msgspec.Struct):
 
         do_append: bool = True,
         use_fpath: bool = True,
+        force_reformat: bool = False,
 
         # only render datums "in view" of the ``ChartView``
         use_vr: bool = True,
@@ -174,6 +175,7 @@ class Renderer(msgspec.Struct):
             profiler,
 
             slice_to_inview=use_vr,
+            force_full_realloc=force_reformat,
         )
 
         # no history in view case
@@ -222,7 +224,10 @@ class Renderer(msgspec.Struct):
             or should_redraw
         ):
             # print(f"{self.viz.name} -> REDRAWING BRUH")
-            if new_sample_rate and showing_src_data:
+            if (
+                new_sample_rate
+                and showing_src_data
+            ):
                 log.info(f'DE-downsampling -> {array_key}')
                 self._in_ds = False