Fix iterating tiles where the overlap larger than the tile size

CHANGELOG.md

@@ -6,6 +6,9 @@
 - Add a general filter control to item lists ([938](../../pull/938))
 - Item list modal dialogs are wider ([939](../../pull/939))
 
+### Bug Fixes
+- Fix iterating tiles where the overlap larger than the tile size ([940](../../pull/940))
+
 ## 1.16.1
 
 ### Improvements

large_image/tilesource/base.py

@@ -534,7 +534,7 @@ def _tileIteratorInfo(self, **kwargs):
         outWidth, outHeight, calcScale = self._calculateWidthHeight(
             maxWidth, maxHeight, regionWidth, regionHeight)
         requestedScale = calcScale if requestedScale is None else requestedScale
-        if (regionWidth == 0 or regionHeight == 0 or outWidth == 0 or
+        if (regionWidth < 0 or regionHeight < 0 or outWidth == 0 or
                 outHeight == 0):
             return None
 
@@ -609,11 +609,11 @@ def _tileIteratorInfo(self, **kwargs):
         # size of the region is reduced by the overlap.  This factor is stored
         # in the overlap offset_*.
         xmin = int(left / tile_size['width'])
-        xmax = int(math.ceil((float(right) - tile_overlap['range_x']) /
-                             tile_size['width']))
+        xmax = max(int(math.ceil((float(right) - tile_overlap['range_x']) /
+                                 tile_size['width'])), xmin + 1)
         ymin = int(top / tile_size['height'])
-        ymax = int(math.ceil((float(bottom) - tile_overlap['range_y']) /
-                             tile_size['height']))
+        ymax = max(int(math.ceil((float(bottom) - tile_overlap['range_y']) /
+                                 tile_size['height'])), ymin + 1)
         tile_overlap.update({'xmin': xmin, 'xmax': xmax,
                              'ymin': ymin, 'ymax': ymax})
 

test/test_source_base.py

@@ -285,6 +285,15 @@ def testTileOverlap():
         (60, 120, 60, 30, 15),
         (75, 120, 45, 30, 0),
     ]
+    assert [(
+        tiles['x'], tiles['x'] + tiles['width'], tiles['width'],
+        tiles['tile_overlap']['left'], tiles['tile_overlap']['right']
+    ) for tiles in ts.tileIterator(
+        tile_size=dict(width=60, height=60), tile_overlap=dict(x=40, y=40),
+        region=dict(left=55, top=65, width=15, height=15))
+    ] == [
+        (55, 70, 15, 0, 0)
+    ]
 
 
 def testLazyTileRelease():