Image previews: smart crop down to 1:2 aspect ratio

Per request from the mobile team, image previews should be cropped down to a
1:2 width-to-height ratio as necessary.

r2/r2/lib/jsontemplates.py

@@ -581,6 +581,7 @@ class LinkJsonTemplate(ThingJsonTemplate):
     )
 
     PREVIEW_RESOLUTIONS = (108, 216, 320, 640, 960, 1080)
+    PREVIEW_MAX_RATIO = 2
 
     def __init__(self):
         super(LinkJsonTemplate, self).__init__()
@@ -650,7 +651,7 @@ class LinkJsonTemplate(ThingJsonTemplate):
                         continue
 
                     url = g.image_resizing_provider.resize_image(
-                        preview_object, w, censor_nsfw)
+                        preview_object, w, censor_nsfw, self.PREVIEW_MAX_RATIO)
                     h = int(w * source_ratio)
                     preview_resolutions.append({
                         "url": url,

r2/r2/lib/providers/image_resizing/__init__.py

@@ -24,7 +24,7 @@ class ImageResizingProvider(object):
     """Provider for generating resizable image urls.
 
     """
-    def resize_image(self, image, width=None, censor_nsfw=False):
+    def resize_image(self, image, width=None, censor_nsfw=False, max_ratio=None):
         """Turn a url of an image in storage into one that will produce a
         resized image.
 
@@ -39,6 +39,10 @@ class ImageResizingProvider(object):
         `censor_nsfw` is a boolean indicating whether the resizer should
         attempt to censor the image (e.g. by blurring it) due to it being NSFW.
 
+        `max_ratio` is the maximum value of the height of the resultant image
+        divided by the width; if not specified, the aspect ratio will be the
+        same as the source image.
+
         The return value should be an absolute URL with the `https` scheme if
         supported, but should also work if accessed with `http`.
 

r2/r2/lib/providers/image_resizing/imgix.py

@@ -39,12 +39,19 @@ class ImgixImageResizingProvider(ImageResizingProvider):
         ],
     }
 
-    def resize_image(self, image, width=None, censor_nsfw=False):
+    def resize_image(self, image, width=None, censor_nsfw=False, max_ratio=None):
         url = UrlParser(image['url'])
         url.hostname = g.imgix_domain
         # Let's encourage HTTPS; it's cool, works just fine on HTTP pages, and
         # will prevent insecure content warnings on HTTPS pages.
         url.scheme = 'https'
+
+        if max_ratio:
+            url.update_query(fit='crop')
+            # http://www.imgix.com/docs/reference/size#param-crop
+            url.update_query(crop='faces,entropy')
+            url.update_query(arh=max_ratio)
+
         if width:
             if width > image['width']:
                 raise NotLargeEnough()

r2/r2/lib/providers/image_resizing/no_op.py

@@ -28,6 +28,6 @@ class NoOpImageResizingProvider(ImageResizingProvider):
     Combines well with the filesystem media provider for an entirely local
     setup.
     """
-    def resize_image(self, image, width=None, censor_nsfw=False):
+    def resize_image(self, image, width=None, censor_nsfw=False, max_ratio=None):
         # The simplest solution: just pass it on through.
         return image['url']

r2/r2/lib/providers/image_resizing/unsplashit.py

@@ -28,7 +28,7 @@ class UnsplashitImageResizingProvider(ImageResizingProvider):
     Useful if you don't want the external dependencies of imgix, but need
     correctly-sized images for testing a UI.
     """
-    def resize_image(self, image, width=None, censor_nsfw=False):
+    def resize_image(self, image, width=None, censor_nsfw=False, max_ratio=None):
         if width is None:
             width = image['width']
         height = width * 2

r2/r2/tests/unit/lib/providers/image_resizing/imgix_test.py

@@ -33,6 +33,9 @@ from r2.lib.providers.image_resizing.imgix import ImgixImageResizingProvider
 from r2.lib.utils import UrlParser
 
 
+URLENCODED_COMMA = '%2C'
+
+
 class TestImgixResizer(unittest.TestCase):
     @classmethod
     def setUpClass(cls):
@@ -66,7 +69,21 @@ class TestImgixResizer(unittest.TestCase):
             url = self.provider.resize_image(image, width)
             self.assertEqual(url, 'https://example.com/a.jpg?w=%d' % width)
 
-        # TODO: test acceptable aspect ratios per spec!
+    def test_cropping(self):
+        image = dict(url='http://s3.amazonaws.com/a.jpg', width=1200,
+                      height=800)
+        max_ratio = 0.5
+        url = self.provider.resize_image(image, max_ratio=max_ratio)
+        crop = URLENCODED_COMMA.join(('faces', 'entropy'))
+        self.assertEqual(url,
+                ('https://example.com/a.jpg?fit=crop&crop=%s&arh=%s'
+                    % (crop, max_ratio)))
+
+        width = 108
+        url = self.provider.resize_image(image, width, max_ratio=max_ratio)
+        self.assertEqual(url,
+                ('https://example.com/a.jpg?fit=crop&crop=%s&arh=%s&w=%s'
+                    % (crop, max_ratio, width)))
 
     def test_sign_url(self):
         u = UrlParser('http://examples.imgix.net/frog.jpg?w=100')