fix: idisp() crashes when reuse=True with no title given

src/machinevisiontoolbox/base/imageio.py

@@ -882,10 +882,15 @@ def key_press(event: Any) -> None:
         ## display using OpenCV
         global __last_window_number
 
-        if not reuse and title is None:
-            # create a unique window name for each call
-            title = "idisp." + str(__last_window_number)
-            __last_window_number += 1
+        if title is None:
+            if reuse:
+                # fixed name (no counter) so repeated calls in an
+                # animation loop share the same window
+                title = "idisp"
+            else:
+                # create a unique window name for each call
+                title = "idisp." + str(__last_window_number)
+                __last_window_number += 1
 
         # At this point title is guaranteed to be a string
         assert title is not None

tests/base/test_io.py

@@ -369,6 +369,20 @@ def test_idisp_uint16_image(self):
         result = idisp(im, matplotlib=False)
         self.assertIsNone(result)
 
+    def test_idisp_reuse_no_title(self):
+        """reuse=True with no title must not crash -- regression test for
+        the OpenCV path's title fallback (previously asserted title is not
+        None even though reuse=True skipped generating one)"""
+        from machinevisiontoolbox.base.imageio import cv_destroy_window, idisp
+
+        im = np.random.randint(0, 256, (30, 30), dtype=np.uint8)
+
+        try:
+            idisp(im, matplotlib=False, reuse=True)
+            idisp(im, matplotlib=False, reuse=True)
+        finally:
+            cv_destroy_window("idisp", block=False)
+
     def test_idisp_float_image(self):
         """Test idisp with float image"""
         im = np.random.rand(30, 30).astype(np.float32)