tts:direction special inheritance

sandflow · Nov 17, 2023 · 21f6762 · 21f6762
1 parent df085d8
commit 21f6762
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diff --git a/src/main/python/ttconv/isd.py b/src/main/python/ttconv/isd.py
@@ -505,6 +505,17 @@ def _process_element(
  styles_to_be_computed.add(spec_style_prop)
  isd_element.set_style(spec_style_prop, element.get_style(spec_style_prop))
 
+ # direction special semantics
+ # https://www.w3.org/TR/ttml2/#style-attribute-direction-special-semantics
+
+ if isinstance(element, model.Region) and \
+ (not element.has_style(styles.StyleProperties.Direction)) and \
+ element.get_style(styles.StyleProperties.WritingMode) in (styles.WritingModeType.lrtb, styles.WritingModeType.rltb):
+ styles_to_be_computed.add(styles.StyleProperties.Direction)
+ direction = styles.DirectionType.ltr if element.get_style(styles.StyleProperties.WritingMode) == styles.WritingModeType.lrtb \
+ else styles.DirectionType.rtl
+ isd_element.set_style(styles.StyleProperties.Direction, direction)
+
  # inherited styling
 
  if not isinstance(element, (model.Br, model.Text, model.Region)):

diff --git a/src/test/python/test_isd.py b/src/test/python/test_isd.py
@@ -519,6 +519,41 @@ def test_textEmphasis_auto(self):
  styles.TextEmphasisType.Position.outside
  )
 
+ def test_direction_special_semantics(self):
+ """https://github.com/sandflow/ttconv/issues/400"""
+ xml_str = """<?xml version="1.0" encoding="utf-8"?>
+<tt xmlns="http://www.w3.org/ns/ttml" xmlns:tts="http://www.w3.org/ns/ttml#styling" xml:lang="en">
+<head>
+<layout>
+<region xml:id="rl" tts:writingMode="rl"/>
+<region xml:id="lr" tts:writingMode="rl" tts:direction="ltr"/>
+</layout>
+</head>
+<body>
+<div>
+<p region="rl" begin="0s" end="1s">tts:direction should be "rtl".</p>
+<p region="lr" begin="0s" end="1s">tts:direction should be "ltr".</p>
+</div>
+</body>
+</tt>"""
+
+ tree = et.ElementTree(et.fromstring(xml_str))
+ doc = imsc_reader.to_model(tree)
+
+ p1 = (ISD.from_model(doc, 0).get_region("rl"))[0][0][0][0]
+
+ self.assertEqual(
+ p1.get_style(styles.StyleProperties.Direction),
+ styles.DirectionType.rtl
+ )
+
+ p2 = (ISD.from_model(doc, 0).get_region("lr"))[0][0][0][0]
+
+ self.assertEqual(
+ p2.get_style(styles.StyleProperties.Direction),
+ styles.DirectionType.ltr
+ )
+
 class ContentDocument1Test(unittest.TestCase):
 
  """