Fix wrong working interpolation of labels in 3d (napari#6596)

# References and relevant issues

closes napari#6595

# Description

Set interpolation for rendering of 3D data for labels.

napari/_qt/_tests/test_qt_viewer.py

@@ -911,6 +911,22 @@ def test_background_color(qtbot, qt_viewer: QtViewer, dtype):
         )
 
 
+def test_rendering_interpolation(qtbot, qt_viewer):
+    data = np.zeros((20, 20, 20), dtype=np.uint8)
+    data[1:-1, 1:-1, 1:-1] = 5
+    layer = qt_viewer.viewer.add_labels(
+        data, opacity=1, rendering="translucent"
+    )
+    layer.selected_label = 5
+    qt_viewer.viewer.dims.ndisplay = 3
+    QApplication.processEvents()
+    canvas_screenshot = qt_viewer.screenshot(flash=False)
+    shape = np.array(canvas_screenshot.shape[:2])
+    pixel = canvas_screenshot[tuple((shape * 0.5).astype(int))]
+    color = layer.colormap.map(5)[0] * 255
+    npt.assert_array_equal(pixel, color)
+
+
 def test_shortcut_passing(make_napari_viewer):
     viewer = make_napari_viewer(ndisplay=3)
     layer = viewer.add_labels(

napari/_qt/qt_viewer.py

@@ -21,6 +21,7 @@
 )
 from weakref import WeakSet, ref
 
+import numpy as np
 from qtpy.QtCore import QCoreApplication, QObject, Qt, QUrl
 from qtpy.QtGui import QGuiApplication
 from qtpy.QtWidgets import QFileDialog, QSplitter, QVBoxLayout, QWidget
@@ -784,7 +785,7 @@ def _screenshot(self, flash=True):
             add_flash_animation(self._welcome_widget)
         return img
 
-    def screenshot(self, path=None, flash=True):
+    def screenshot(self, path=None, flash=True) -> np.ndarray:
         """Take currently displayed screen and convert to an image array.
 
         Parameters

napari/_vispy/layers/labels.py

@@ -337,6 +337,7 @@ def _setup_nodes(self, texture_format):
             ),
             clim=[0, 2**23 - 1],
             texture_format=texture_format,
+            interpolation='nearest',
         )
 
     def get_node(self, ndisplay: int, dtype=None) -> Node: