replace custom padding code with np.pad

gunpowder/nodes/pad.py

@@ -127,43 +127,11 @@ def __expand(self, a, from_roi, to_roi, value):
         )
 
         num_channels = len(a.shape) - from_roi.dims
-        channel_shapes = a.shape[:num_channels]
-        b = np.zeros(channel_shapes + to_roi.shape, dtype=a.dtype)
-        shift = -to_roi.offset
+        lower_pad = from_roi.begin - to_roi.begin
+        upper_pad = to_roi.end - from_roi.end
+        pad_width = [(0, 0)] * num_channels + list(zip(lower_pad, upper_pad))
         if self.mode == "constant":
-            if value != 0:
-                b[:] = value
+            padded = np.pad(a, pad_width, "constant", constant_values=value)
         elif self.mode == "reflect":
-            if a.shape == b.shape:
-                pass  # handled later
-            else:
-                diff = Coordinate(b.shape) - Coordinate(a.shape)
-                slices = [
-                    (
-                        (slice(None),) * num_channels
-                        + tuple(
-                            slice(diff[i], None) if d == 1 else slice(None, diff[i])
-                            for i, d in enumerate(selected_dims)
-                        ),
-                        (slice(None),) * num_channels
-                        + tuple(
-                            slice(None, diff[i]) if d == 1 else slice(None)
-                            for i, d in enumerate(selected_dims)
-                        ),
-                        (slice(None),) * num_channels
-                        + tuple(
-                            slice(None, None, -1) if d == 1 else slice(None)
-                            for i, d in enumerate(selected_dims)
-                        ),
-                    )
-                    for selected_dims in product((0, 1), repeat=from_roi.dims)
-                ]
-                for output_slices, input_slices, rev_slices in slices:
-                    b[output_slices] = a[input_slices][rev_slices]
-
-        logger.debug("shifting 'from' by " + str(shift))
-        a_in_b = from_roi.shift(shift).to_slices()
-        logger.debug("target shape is " + str(b.shape))
-        logger.debug("target slice is " + str(a_in_b))
-        b[(slice(None),) * num_channels + a_in_b] = a
-        return b
+            padded = np.pad(a, pad_width, "reflect")
+        return padded