[Grid] enable negative shifts

gridlock/base.py

@@ -76,6 +76,21 @@ class GridBase(Protocol):
         el = [0 if p else -1 for p in self.periodic]
         return [numpy.hstack((self.dxyz[a], self.dxyz[a][e])) for a, e in zip(range(3), el, strict=True)]
 
+    def _shifted_edge_dxyz(self, which_shifts: int | None) -> list[NDArray[numpy.float64]]:
+        if which_shifts is None:
+            return self.dxyz_with_ghost
+
+        shifts = self.shifts[which_shifts, :]
+        edge_dxyz = []
+        for a in range(3):
+            if shifts[a] < 0:
+                ghost = self.dxyz[a][-1] if self.periodic[a] else self.dxyz[a][0]
+                edge_dxyz.append(numpy.hstack((ghost, self.dxyz[a])))
+            else:
+                ghost = self.dxyz[a][0] if self.periodic[a] else self.dxyz[a][-1]
+                edge_dxyz.append(numpy.hstack((self.dxyz[a], ghost)))
+        return edge_dxyz
+
     @property
     def center(self) -> NDArray[numpy.float64]:
         """
@@ -115,15 +130,9 @@ class GridBase(Protocol):
         """
         if which_shifts is None:
             return self.exyz
-        dxyz = self.dxyz_with_ghost
+        edge_dxyz = self._shifted_edge_dxyz(which_shifts)
         shifts = self.shifts[which_shifts, :]
-
-        # If shift is negative, use left cell's dx to determine shift
-        for a in range(3):
-            if shifts[a] < 0:
-                dxyz[a] = numpy.roll(dxyz[a], 1)
-
-        return [self.exyz[a] + dxyz[a] * shifts[a] for a in range(3)]
+        return [self.exyz[a] + edge_dxyz[a] * shifts[a] for a in range(3)]
 
     def shifted_dxyz(self, which_shifts: int | None) -> list[NDArray]:
         """
@@ -137,20 +146,7 @@ class GridBase(Protocol):
         """
         if which_shifts is None:
             return self.dxyz
-        shifts = self.shifts[which_shifts, :]
-        dxyz = self.dxyz_with_ghost
-
-        # If shift is negative, use left cell's dx to determine size
-        sdxyz = []
-        for a in range(3):
-            if shifts[a] < 0:
-                roll_dxyz = numpy.roll(dxyz[a], 1)
-                abs_shift = numpy.abs(shifts[a])
-                sdxyz.append(roll_dxyz[:-1] * abs_shift + roll_dxyz[1:] * (1 - abs_shift))
-            else:
-                sdxyz.append(dxyz[a][:-1] * (1 - shifts[a]) + dxyz[a][1:] * shifts[a])
-
-        return sdxyz
+        return [numpy.diff(exyz) for exyz in self.shifted_exyz(which_shifts)]
 
     def shifted_xyz(self, which_shifts: int | None) -> list[NDArray[numpy.float64]]:
         """

gridlock/read.py

@@ -73,7 +73,7 @@ class GridReadMixin(GridPosMixin):
         surface = numpy.delete(range(3), plane.axis)
 
         # Extract indices and weights of planes
-        center3 = numpy.insert([0, 0], plane.axis, (plane.pos,))
+        center3 = numpy.insert([0.0, 0.0], plane.axis, (plane.pos,))
         center_index = self.pos2ind(center3, which_shifts,
                                     round_ind=False, check_bounds=False)[plane.axis]
         centers = numpy.unique([numpy.floor(center_index), numpy.ceil(center_index)]).astype(int)

gridlock/test/test_grid.py

@@ -309,3 +309,58 @@ def test_visualize_isosurface_sampling_uses_preview_lattice(monkeypatch: pytest.
     assert_allclose(captured['zs'], [1.5, 1.5, 1.5])
 
     pyplot.close(fig)
+
+
+
+
+def test_negative_shift_nonperiodic_edges_and_widths() -> None:
+    grid = Grid([[0, 1, 3], [0, 2], [0, 1]], shifts=[[-0.5, 0, 0]], periodic=[False, False, False])
+
+    assert_allclose(grid.shifted_exyz(0)[0], [-0.5, 0.5, 2.0])
+    assert_allclose(grid.shifted_dxyz(0)[0], [1.0, 1.5])
+    assert_allclose(grid.shifted_xyz(0)[0], [0.0, 1.25])
+
+
+def test_negative_shift_periodic_edges_and_widths() -> None:
+    grid = Grid([[0, 1, 3], [0, 2], [0, 1]], shifts=[[-0.5, 0, 0]], periodic=[True, False, False])
+
+    assert_allclose(grid.shifted_exyz(0)[0], [-1.0, 0.5, 2.0])
+    assert_allclose(grid.shifted_dxyz(0)[0], [1.5, 1.5])
+
+
+def test_negative_shift_coordinate_round_trip() -> None:
+    grid = Grid([[0, 1, 3], [0, 2], [0, 1]], shifts=[[-0.5, 0, 0]], periodic=[False, False, False])
+
+    ind = grid.pos2ind([1.25, 1.0, 0.5], 0, round_ind=False)
+    pos = grid.ind2pos(ind, 0, round_ind=False)
+
+    assert_allclose(ind, [1.0, 0.0, 0.0])
+    assert_allclose(pos, [1.25, 1.0, 0.5])
+
+
+def test_negative_shift_draw_cuboid_fractional_fill() -> None:
+    grid = Grid([[0, 1, 3], [0, 1], [0, 1]], shifts=[[-0.5, 0, 0]], periodic=[False, False, False])
+    arr = grid.allocate(0)
+
+    grid.draw_cuboid(
+        arr,
+        x=dict(min=0, max=1),
+        y=dict(min=0, max=1),
+        z=dict(min=0, max=1),
+        foreground=1,
+    )
+
+    assert_allclose(arr[0, :, 0, 0], [0.5, 1 / 3])
+
+
+def test_negative_shift_get_slice_uses_shifted_centers() -> None:
+    grid = Grid([[0, 1, 3], [0, 1, 2], [0, 1]], shifts=[[-0.5, 0, 0]], periodic=[False, False, False])
+    cell_data = numpy.zeros(grid.cell_data_shape)
+    cell_data[0, 1, :, 0] = [7, 9]
+    x_center = float(grid.shifted_xyz(0)[0][1])
+
+    grid_slice = grid.get_slice(cell_data, Plane(x=x_center), which_shifts=0)
+
+    assert_allclose(grid_slice, [7, 9])
+
+