Round dimensions for images when scaling.

Add hook for validating image operations.

CHANGELOG.txt

@@ -9,6 +9,7 @@ Changelog
  * Rearranged SCSS folder structure to the client folder and split them approximately according to ITCSS. (Naomi Morduch Toubman, Jonny Scholes, Janneke Janssen, Hugo van den Berg)
  * Fix: ModelAdmin no longer fails when filtering over a foreign key relation (Jason Dilworth, Matt Westcott)
  * Fix: The Wagtail version number is now visible within the Settings menu (Kevin Howbrook)
+ * Fix: Scaling images now rounds values to an integer so that images render without errors (Adrian Brunyate)
 
 
 2.5 (24.04.2019)

docs/releases/2.6.rst

@@ -23,6 +23,7 @@ Bug fixes
 
  * ModelAdmin no longer fails when filtering over a foreign key relation (Jason Dilworth, Matt Westcott)
  * The Wagtail version number is now visible within the Settings menu (Kevin Howbrook)
+ * Scaling images now rounds values to an integer so that images render without errors (Adrian Brunyate)
 
 
 Upgrade considerations

wagtail/images/image_operations.py

@@ -225,8 +225,8 @@ class ScaleOperation(Operation):
         image_width, image_height = willow.get_size()
 
         scale = self.percent / 100
-        width = float(image_width * scale)
-        height = float(image_height * scale)
+        width = int(image_width * scale)
+        height = int(image_height * scale)
 
         return willow.resize((width, height))
 

wagtail/images/tests/test_image_operations.py

@@ -23,11 +23,20 @@ class WillowOperationRecorder:
 
     def __getattr__(self, attr):
         def operation(*args, **kwargs):
+            self.validate_operation(attr, args, kwargs)
             self.ran_operations.append((attr, args, kwargs))
             return self
 
         return operation
 
+    def validate_operation(self, operation, args, kwargs):
+        """Check if the requested operation is sane and raise an exception if not."""
+        # The Willow docs say resize must take integral dimensions.
+        if operation == "resize":
+            x, y = args[0]
+            if x != int(x) or y != int(y):
+                raise ValueError
+
     def get_size(self):
         size = self.start_size
 
@@ -46,6 +55,7 @@ class ImageOperationTestCase(TestCase):
     filter_spec_tests = []
     filter_spec_error_tests = []
     run_tests = []
+    norun_tests = []
 
     @classmethod
     def make_filter_spec_test(cls, filter_spec, expected_output):
@@ -88,6 +98,25 @@ class ImageOperationTestCase(TestCase):
         test_run.__name__ = str('test_run_%s' % filter_spec)
         return test_run
 
+    @classmethod
+    def make_norun_test(cls, filter_spec, image_kwargs):
+        def test_norun(self):
+            image = Image(**image_kwargs)
+
+            # Make operation
+            operation = self.operation_class(*filter_spec.split('-'))
+
+            # Make operation recorder
+            operation_recorder = WillowOperationRecorder((image.width, image.height))
+
+            # Attempt (and hopefully fail) to run
+            with self.assertRaises(ValueError):
+                operation.run(operation_recorder, image, {})
+
+        test_norun.__name__ = str('test_norun_%s' % filter_spec)
+        return test_norun
+
+
     @classmethod
     def setup_test_methods(cls):
         if cls.operation_class is None:
@@ -108,6 +137,11 @@ class ImageOperationTestCase(TestCase):
             run_test = cls.make_run_test(*args)
             setattr(cls, run_test.__name__, run_test)
 
+        # Runtime error tests
+        for args in cls.norun_tests:
+            norun_test = cls.make_norun_test(*args)
+            setattr(cls, norun_test.__name__, norun_test)
+
 
 class TestDoNothingOperation(ImageOperationTestCase):
     operation_class = image_operations.DoNothingOperation
@@ -388,7 +422,7 @@ class TestScaleOperation(ImageOperationTestCase):
         ]),
         # Rounded usage of scale
         ('scale-83.0322', dict(width=1000, height=500), [
-            ('resize', ((1000 * 0.830322, 500 * 0.830322), ), {}),
+            ('resize', ((int(1000 * 0.830322), int(500 * 0.830322)), ), {}),
         ]),
     ]