Move backgroun-position parsing from draw to validation

weasy/css/validation.py

@@ -29,7 +29,8 @@ import functools
 import logging
 
 from ..formatting_structure import counters
-from .values import get_keyword, get_single_keyword, as_css
+from .values import (get_keyword, get_single_keyword, as_css,
+                     make_percentage_value)
 from .properties import INITIAL_VALUES, NOT_PRINT_MEDIA
 from . import computed_values
 
@@ -42,6 +43,14 @@ CONTENT_QUOTE_KEYWORDS = {
     'no-close-quote': (False, False),
 }
 
+BACKGROUND_POSITION_PERCENTAGES = {
+    'top': make_percentage_value(0),
+    'left': make_percentage_value(0),
+    'center': make_percentage_value(50),
+    'bottom': make_percentage_value(100),
+    'right': make_percentage_value(100),
+}
+
 LOGGER = logging.getLogger('WEASYPRINT')
 
 # yes/no validators for non-shorthand properties
@@ -176,25 +185,27 @@ def background_position(values):
     See http://www.w3.org/TR/CSS21/colors.html#propdef-background-position
 
     """
+    kw_to_percentage = dict(top=0, left=0, center=50, bottom=100, right=100)
     if len(values) == 1:
+        center = BACKGROUND_POSITION_PERCENTAGES['center']
         value = values[0]
         keyword = get_keyword(value)
-        if keyword in ('left', 'right', 'top', 'bottom', 'center'):
-            return keyword, 'center'
+        if keyword in BACKGROUND_POSITION_PERCENTAGES:
+            return BACKGROUND_POSITION_PERCENTAGES[keyword], center
         elif is_dimension_or_percentage(value):
-            return value, 'center'
+            return value, center
 
     elif len(values) == 2:
         value_1, value_2 = values
         keyword_1, keyword_2 = map(get_keyword, values)
         if is_dimension_or_percentage(value_1):
             if keyword_2 in ('top', 'center', 'bottom'):
-                return value_1, keyword_2
+                return value_1, BACKGROUND_POSITION_PERCENTAGES[keyword_2]
             elif is_dimension_or_percentage(value_2):
                 return value_1, value_2
         elif is_dimension_or_percentage(value_2):
             if keyword_1 in ('left', 'center', 'right'):
-                return keyword_1, value_2
+                return BACKGROUND_POSITION_PERCENTAGES[keyword_1], value_2
         elif (
                     keyword_1 in ('left', 'center', 'right') and
                     keyword_2 in ('top', 'center', 'bottom')
@@ -202,7 +213,8 @@ def background_position(values):
                     keyword_1 in ('top', 'center', 'bottom') and
                     keyword_2 in ('left', 'center', 'right')
                 ):
-            return keyword_1, keyword_2
+            return (BACKGROUND_POSITION_PERCENTAGES[keyword_1],
+                    BACKGROUND_POSITION_PERCENTAGES[keyword_2])
     #else: invalid
 
 

weasy/css/values.py

@@ -22,6 +22,9 @@ Utility functions and methods used by various modules in the css package.
 """
 
 
+import collections
+
+
 def get_keyword(value):
     """If ``value`` is a keyword, return its name.
 
@@ -63,3 +66,11 @@ def get_percentage_value(value):
 def as_css(values):
     """Return the string reperesentation of the ``values`` list."""
     return ' '.join(getattr(value, 'cssText', value) for value in values)
+
+
+FakeValue = collections.namedtuple('FakeValue', ('type', 'value', 'cssText'))
+
+
+def make_percentage_value(value):
+    """Return an object that ``get_percentage_value()`` will accept."""
+    return FakeValue('PERCENTAGE', value, '{}%'.format(value))

weasy/draw.py

@@ -177,9 +177,16 @@ def draw_background(document, context, box, clip=True):
 
         surface, image_width, image_height = image
 
-        bg_position = box.style.background_position
-        bg_position_x, bg_position_y = absolute_background_position(
-            bg_position, (bg_width, bg_height), (image_width, image_height))
+        bg_position_x, bg_position_y = box.style.background_position
+
+        percentage = get_percentage_value(bg_position_x)
+        if percentage is not None:
+            bg_position_x = (bg_width - image_width) * percentage / 100.
+
+        percentage = get_percentage_value(bg_position_y)
+        if percentage is not None:
+            bg_position_y = (bg_height - image_height) * percentage / 100.
+
         context.translate(bg_position_x, bg_position_y)
 
         bg_repeat = box.style.background_repeat
@@ -208,38 +215,6 @@ def draw_background(document, context, box, clip=True):
         context.paint()
 
 
-def absolute_background_position(css_values, bg_dimensions, image_dimensions):
-    """Return the background's ``position_x, position_y`` in pixels.
-
-    http://www.w3.org/TR/CSS21/colors.html#propdef-background-position
-
-    :param css_values: a list of one or two cssutils Value objects.
-    :param bg_dimensions: ``width, height`` of the background positionning area
-    :param image_dimensions: ``width, height`` of the background image
-
-    """
-    values = list(css_values)
-
-    if len(css_values) == 1:
-        values.append('center')
-    else:
-        assert len(css_values) == 2
-
-    if values[1] in ('left', 'right') or values[0] in ('top', 'bottom'):
-        values.reverse()
-    # Order is now [horizontal, vertical]
-
-    kw_to_percentage = dict(top=0, left=0, center=50, bottom=100, right=100)
-
-    for value, bg_dimension, image_dimension in zip(
-            values, bg_dimensions, image_dimensions):
-        percentage = kw_to_percentage.get(value, get_percentage_value(value))
-        if percentage is not None:
-            yield (bg_dimension - image_dimension) * percentage / 100.
-        else:
-            yield value
-
-
 def get_rectangle_edges(x, y, width, height):
     """Return the 4 edges of a rectangle as a list.
 

weasy/tests/test_css_properties.py

@@ -199,7 +199,7 @@ def test_expand_background():
         image='none',
         repeat='repeat',
         attachment='scroll',
-        position='top right' ##
+        position='0% 100%' ##
     )
     assert_background(
         'url(bar) #f00 repeat-y center left fixed',
@@ -207,7 +207,7 @@ def test_expand_background():
         image='bar', ##
         repeat='repeat-y', ##
         attachment='fixed', ##
-        position='center left' ##
+        position='50% 0%' ##
     )
     assert_background(
         '#00f 10% 200px',
@@ -223,7 +223,7 @@ def test_expand_background():
         image='none',
         repeat='repeat',
         attachment='fixed', ##
-        position='right 78px' ##
+        position='100% 78px' ##
     )