Support larger and smaller values for font-size

weasyprint/css/computed_values.py

@@ -10,6 +10,7 @@
 
 """
 
+from collections import OrderedDict
 from urllib.parse import unquote
 
 from tinycss2.color3 import parse_color
@@ -28,8 +29,7 @@
 # Value in pixels of font-size for <absolute-size> keywords: 12pt (16px) for
 # medium, and scaling factors given in CSS3 for others:
 # http://www.w3.org/TR/css3-fonts/#font-size-prop
-# TODO: this will need to be ordered to implement 'smaller' and 'larger'
-FONT_SIZE_KEYWORDS = dict(
+FONT_SIZE_KEYWORDS = OrderedDict(
     # medium is 16px, others are a ratio of medium
     (name, INITIAL_VALUES['font_size'] * a / b)
     for name, a, b in (
@@ -592,14 +592,29 @@ def font_size(computer, name, value):
     """Compute the ``font-size`` property."""
     if value in FONT_SIZE_KEYWORDS:
         return FONT_SIZE_KEYWORDS[value]
-    # TODO: support 'larger' and 'smaller'
 
+    keyword_values = list(FONT_SIZE_KEYWORDS.values())
     parent_font_size = computer['parent_style']['font_size']
+
+    if value == 'larger':
+        if parent_font_size >= keyword_values[-1]:
+            return parent_font_size * 1.2
+        for i, keyword_value in enumerate(keyword_values):
+            if keyword_value > parent_font_size:
+                return keyword_values[i]
+    elif value == 'smaller':
+        if parent_font_size <= keyword_values[0]:
+            return parent_font_size * 0.8
+        for i, keyword_value in enumerate(keyword_values[::-1]):
+            if keyword_value < parent_font_size:
+                return keyword_values[-i - 1]
+
     if value.unit == '%':
         return value.value * parent_font_size / 100.
     else:
-        return length(computer, name, value, pixels_only=True,
-                      font_size=parent_font_size)
+        return length(
+            computer, name, value, pixels_only=True,
+            font_size=parent_font_size)
 
 
 @register_computer('font-weight')

weasyprint/css/validation/properties.py

@@ -784,9 +784,8 @@ def font_size(token):
         return length
     font_size_keyword = get_keyword(token)
     if font_size_keyword in ('smaller', 'larger'):
-        raise InvalidValues('value not supported yet')
+        return font_size_keyword
     if font_size_keyword in computed_values.FONT_SIZE_KEYWORDS:
-        # or keyword in ('smaller', 'larger')
         return font_size_keyword
 
 

weasyprint/tests/test_css.py

@@ -9,6 +9,8 @@
 
 """
 
+from math import isclose
+
 import pytest
 import tinycss2
 
@@ -83,7 +85,7 @@ def test_annotate_document():
     style_for = get_all_computed_styles(
         document, user_stylesheets=[CSS(resource_filename('user.css'))])
 
-    # Element objects behave a lists of their children
+    # Element objects behave as lists of their children
     _head, body = document.etree_element
     h1, p, ul, div = body
     li_0, _li_1 = ul
@@ -451,3 +453,38 @@ def test_units(value, width):
     body, = html.children
     p, = body.children
     assert p.margin_left == width
+
+
+@assert_no_logs
+@pytest.mark.parametrize('parent_css, parent_size, child_css, child_size', (
+    ('10px', 10, '10px', 10),
+    ('x-small', 12, 'xx-large', 32),
+    ('x-large', 24, '2em', 48),
+    ('1em', 16, '1em', 16),
+    ('1em', 16, 'larger', 6 / 5 * 16),
+    ('medium', 16, 'larger', 6 / 5 * 16),
+    ('x-large', 24, 'larger', 32),
+    ('xx-large', 32, 'larger', 1.2 * 32),
+    ('1px', 1, 'larger', 3 / 5 * 16),
+    ('28px', 28, 'larger', 32),
+    ('100px', 100, 'larger', 120),
+    ('xx-small', 3 / 5 * 16, 'larger', 12),
+    ('1em', 16, 'smaller', 8 / 9 * 16),
+    ('medium', 16, 'smaller', 8 / 9 * 16),
+    ('x-large', 24, 'smaller', 6 / 5 * 16),
+    ('xx-large', 32, 'smaller', 24),
+    ('xx-small', 3 / 5 * 16, 'smaller', 0.8 * 3 / 5 * 16),
+    ('1px', 1, 'smaller', 0.8),
+    ('28px', 28, 'smaller', 24),
+    ('100px', 100, 'smaller', 32),
+))
+def test_font_size(parent_css, parent_size, child_css, child_size):
+    document = FakeHTML(string='<p>a<span>b')
+    style_for = get_all_computed_styles(document, user_stylesheets=[CSS(
+        string='p{font-size:%s}span{font-size:%s}' % (parent_css, child_css))])
+
+    _head, body = document.etree_element
+    p, = body
+    span, = p
+    assert isclose(style_for(p)['font_size'], parent_size)
+    assert isclose(style_for(span)['font_size'], child_size)