Fix rounding errors when resizing 1x1 images (backport 217e9628c7 to 0.8.x)

wagtail/wagtailimages/backends/base.py

@@ -1,5 +1,7 @@
 from __future__ import division
 
+import math
+
 from django.conf import settings
 
 from wagtail.wagtailimages.rect import Rect
@@ -242,7 +244,9 @@ class BaseImageBackend(object):
             bottom = im_height
 
         # Crop!
-        return self.resize_to_min(self.crop(image, Rect(left, top, right, bottom)), size)
+        return self.resize_to_min(self.crop(image,
+            Rect(math.floor(left), math.floor(top), math.ceil(right), math.ceil(bottom))
+        ), size)
 
     def no_operation(self, image, param, focal_point=None):
         """Return the image unchanged"""

wagtail/wagtailimages/tests/test_models.py

@@ -164,6 +164,28 @@ class TestRenditions(TestCase):
         self.assertEqual(first_rendition, second_rendition)
 
 
+class TestSinglePixelRenditions(TestCase):
+    def setUp(self):
+        # Create an image for running tests on
+        self.image = Image.objects.create(
+            title="Test image",
+            file=get_test_image_file(width=1, height=1),
+        )
+
+    def test_resize(self):
+        rendition = self.image.get_rendition('fill-100x100')
+        self.assertEqual(rendition.width, 1)
+        self.assertEqual(rendition.height, 1)
+
+        rendition = self.image.get_rendition('fill-100x150')
+        self.assertEqual(rendition.width, 1)
+        self.assertEqual(rendition.height, 1)
+
+        rendition = self.image.get_rendition('fill-150x100')
+        self.assertEqual(rendition.width, 1)
+        self.assertEqual(rendition.height, 1)
+
+
 class TestRenditionsWand(TestCase):
     def setUp(self):
         try:

wagtail/wagtailimages/tests/utils.py

@@ -9,8 +9,8 @@ from wagtail.wagtailimages.models import get_image_model
 Image = get_image_model()
 
 
-def get_test_image_file(filename='test.png'):
+def get_test_image_file(filename='test.png', width=640, height=480):
     f = BytesIO()
-    image = PIL.Image.new('RGB', (640, 480), 'white')
+    image = PIL.Image.new('RGB', (width, height), 'white')
     image.save(f, 'PNG')
     return ImageFile(f, name=filename)