Added a simple scale filter to image_operations.

CHANGELOG.txt

@@ -5,6 +5,7 @@ Changelog
 ~~~~~~~~~~~~~~~~~~~~
 
  * Added support for Django 2.1 (Ryan Verner, Matt Westcott)
+ * Added 'scale' image filter (Oliver Wilkerson)
 
 
 2.2 (xx.xx.xxx) - IN DEVELOPMENT

CONTRIBUTORS.rst

@@ -312,6 +312,7 @@ Contributors
 * Aram Dulyan
 * Kevin Howbrook
 * Ryan Verner
+* Oliver Wilkerson
 
 Translators
 ===========

docs/releases/2.3.rst

@@ -22,6 +22,9 @@ Wagtail is now compatible with Django 2.1. Compatibility fixes were contributed
 Other features
 ~~~~~~~~~~~~~~
 
+ * Added 'scale' image filter (Oliver Wilkerson)
+
+
 Bug fixes
 ~~~~~~~~~
 

docs/topics/images.rst

@@ -88,6 +88,15 @@ The available resizing methods are as follows:
 
         Resize the height of the image to the dimension specified.
 
+    ``scale``
+        (takes percentage)
+
+        .. code-block:: html+django
+
+            {% image page.photo scale-50 %}
+
+        Resize the image to the percentage specified.
+
     ``fill``
         (takes two dimensions and an optional ``-c`` parameter)
 

wagtail/images/image_operations.py

@@ -217,6 +217,20 @@ class WidthHeightOperation(Operation):
         return willow.resize((width, height))
 
 
+class ScaleOperation(Operation):
+    def construct(self, percent):
+        self.percent = float(percent)
+
+    def run(self, willow, image, env):
+        image_width, image_height = willow.get_size()
+
+        scale = self.percent / 100
+        width = float(image_width * scale)
+        height = float(image_height * scale)
+
+        return willow.resize((width, height))
+
+
 class JPEGQualityOperation(Operation):
     def construct(self, quality):
         self.quality = int(quality)

wagtail/images/tests/test_image_operations.py

@@ -362,6 +362,40 @@ class TestWidthHeightOperation(ImageOperationTestCase):
 TestWidthHeightOperation.setup_test_methods()
 
 
+class TestScaleOperation(ImageOperationTestCase):
+    operation_class = image_operations.ScaleOperation
+
+    filter_spec_tests = [
+        ('scale-100', dict(method='scale', percent=100)),
+        ('scale-50', dict(method='scale', percent=50)),
+    ]
+
+    filter_spec_error_tests = [
+        'scale',
+        'scale-800x600',
+        'scale-abc',
+        'scale-800-c100',
+    ]
+
+    run_tests = [
+        # Basic almost a no-op of scale
+        ('scale-100', dict(width=1000, height=500), [
+            ('resize', ((1000, 500), ), {}),
+        ]),
+        # Basic usage of scale
+        ('scale-50', dict(width=1000, height=500), [
+            ('resize', ((500, 250), ), {}),
+        ]),
+        # Rounded usage of scale
+        ('scale-83.0322', dict(width=1000, height=500), [
+            ('resize', ((1000 * 0.830322, 500 * 0.830322), ), {}),
+        ]),
+    ]
+
+
+TestScaleOperation.setup_test_methods()
+
+
 class TestCacheKey(TestCase):
     def test_cache_key(self):
         image = Image(width=1000, height=1000)

wagtail/images/wagtail_hooks.py

@@ -113,6 +113,7 @@ def register_image_operations():
         ('max', image_operations.MinMaxOperation),
         ('width', image_operations.WidthHeightOperation),
         ('height', image_operations.WidthHeightOperation),
+        ('scale', image_operations.ScaleOperation),
         ('jpegquality', image_operations.JPEGQualityOperation),
         ('format', image_operations.FormatOperation),
         ('bgcolor', image_operations.BackgroundColorOperation),