Add support for tts:position in IMSC reader (#36)

Author: palemieux

.gitmodules

@@ -1,3 +1,5 @@
 [submodule "src/test/resources/ttml/imsc-tests"]
 	path = src/test/resources/ttml/imsc-tests
 	url = https://github.com/w3c/imsc-tests
+[submodule "imsc-tests/"]
+	url = https://github.com/sandflow/imsc-tests.git

src/main/python/ttconv/imsc/elements.py

@@ -43,15 +43,13 @@ class TTMLElement:
   '''Static information about a TTML element
   '''
 
-  class ParsingContext:
+  class ParsingContext(imsc_styles.StyleParsingContext):
     '''State information when parsing a TTML element'''
 
     def __init__(self, ttml_class: TTMLElement, parent_ctx: typing.Optional[TTMLElement.ParsingContext] = None):
 
       self.doc = parent_ctx.doc if parent_ctx is not None else model.Document()
 
-      self.style_context = parent_ctx.style_context if parent_ctx else imsc_styles.StyleParsingContext()
-
       self.style_elements: typing.Dict[str, StyleElement] = parent_ctx.style_elements if parent_ctx else {}
 
       self.temporal_context = parent_ctx.temporal_context if parent_ctx else imsc_attr.TemporalAttributeParsingContext()
@@ -463,7 +461,7 @@ def from_xml(parent_ctx: TTMLElement.ParsingContext, xml_elem) -> typing.Optiona
 
       try:
 
-        style_ctx.styles[prop.model_prop] = prop.extract(style_ctx.style_context, xml_elem.attrib.get(attr))
+        style_ctx.styles[prop.model_prop] = prop.extract(style_ctx, xml_elem.attrib.get(attr))
 
       except ValueError:
 
@@ -526,7 +524,7 @@ def from_xml(parent_ctx: TTMLElement.ParsingContext, xml_elem) -> typing.Optiona
 
         initial_ctx.doc.put_initial_value(
           prop.model_prop,
-          prop.extract(initial_ctx.style_context, xml_elem.attrib.get(attr))
+          prop.extract(initial_ctx, xml_elem.attrib.get(attr))
         )
 
       except (ValueError, TypeError):
@@ -608,7 +606,7 @@ def process_specified_styling(self, xml_elem):
         try:
           self.model_element.set_style(
             prop.model_prop,
-            prop.extract(self.style_context, xml_elem.attrib.get(attr))
+            prop.extract(self, xml_elem.attrib.get(attr))
             )
         except ValueError:
           LOGGER.error("Error reading style property: %s", prop.__name__)
@@ -633,7 +631,7 @@ def process_set_style_properties(self, parent_ctx: TTMLElement, xml_elem):
                 prop.model_prop,
                 self.desired_begin,
                 self.desired_end,
-                prop.extract(self.style_context, xml_elem.attrib.get(attr))
+                prop.extract(self, xml_elem.attrib.get(attr))
               )
             )
             break

src/main/python/ttconv/imsc/style_properties.py

@@ -31,9 +31,10 @@
 import ttconv.imsc.namespaces as xml_ns
 import ttconv.style_properties as styles
 import ttconv.imsc.utils as utils
+import ttconv.model as model
 
 class StyleParsingContext:
-  pass
+  doc: model.Document
 
 class StyleProperty:
   '''Base class for style properties'''
@@ -486,9 +487,27 @@ class Position(StyleProperty):
     @classmethod
     def extract(cls, context: StyleParsingContext, xml_attrib: str):
 
+      (h_edge, h_offset, v_edge, v_offset) = utils.parse_position(xml_attrib)
+
+      if h_edge == "right":
+        if h_offset.units is styles.LengthType.Units.px:
+          h_offset = styles.LengthType(context.doc.get_px_resolution().width - h_offset.value, h_offset.units)
+        elif h_offset.units is styles.LengthType.Units.pct or h_offset.units is styles.LengthType.Units.rw:
+          h_offset = styles.LengthType(100 - h_offset.value, h_offset.units)
+        else:
+          raise ValueError("Units other than px, pct, rh, rw used in tts:position")
+
+      if v_edge == "bottom":
+        if v_offset.units is styles.LengthType.Units.px:
+          v_offset = styles.LengthType(context.doc.get_px_resolution().height - v_offset.value, v_offset.units)
+        elif v_offset.units is styles.LengthType.Units.pct or v_offset.units is styles.LengthType.Units.rh:
+          v_offset = styles.LengthType(100 - v_offset.value, v_offset.units)
+        else:
+          raise ValueError("Units other than px, pct, rh, rw used in tts:position")
+
       return styles.PositionType(
-        x=styles.LengthType(),
-        y=styles.LengthType()
+        x=h_offset,
+        y=v_offset
       )
 
     @classmethod

src/main/python/ttconv/imsc/utils.py

@@ -186,3 +186,128 @@ def parse_time_expression(tick_rate: int, frame_rate: Fraction, time_expr: str)
             frames / frame_rate
 
   raise ValueError("Syntax error")
+
+def parse_position(attr_value: str) -> typing.Tuple[str, styles.LengthType, str, styles.LengthType]:
+  '''Parse a TTML \\<position\\> value into offsets from a horizontal and vertical edge
+  '''
+
+  length_50pct = styles.LengthType(value=50, units=styles.LengthType.Units.pct)
+  length_0pct = styles.LengthType(value=0, units=styles.LengthType.Units.pct)
+
+  h_edges = {"left", "right"}
+  v_edges = {"top", "bottom"}
+
+  h_edge: str = None
+  h_offset: styles.LengthType = None
+  v_edge: str = None
+  v_offset: styles.LengthType = None
+
+  items = attr_value.split()
+
+  if len(items) in (1, 2):
+
+    # begin processing 1 and 2 components
+
+    while len(items) > 0:
+
+      cur_item = items.pop(0)
+
+      if cur_item in h_edges:
+
+        h_edge = cur_item
+        h_offset = length_0pct
+
+      elif cur_item in v_edges:
+
+        v_edge = cur_item
+        v_offset = length_0pct
+
+      elif cur_item == "center":
+
+        if h_edge is None:
+
+          h_edge = "left"
+          h_offset = length_50pct
+
+        elif v_edge is None:
+
+          v_edge = "top"
+          v_offset = length_50pct
+
+      else:
+
+        (value, units) = parse_length(cur_item)
+
+        if h_edge is None:
+
+          h_edge = "left"
+          h_offset = styles.LengthType(value, styles.LengthType.Units(units))
+
+        elif v_edge is None:
+
+          v_edge = "top"
+          v_offset = styles.LengthType(value, styles.LengthType.Units(units))
+    
+    # end processing 1 and 2 components
+
+  else:
+
+    # begin processing 3 and 4 components
+
+    while len(items) > 0:
+
+      cur_item = items.pop(0)
+
+      if cur_item in h_edges:
+
+        h_edge = cur_item
+
+        if v_edge is not None and v_offset is None:
+          v_offset = length_0pct
+
+      elif cur_item in v_edges:
+
+        v_edge = cur_item
+
+        if h_edge is not None and h_offset is None:
+          h_offset = length_0pct
+
+      elif cur_item == "center":
+
+        pass
+
+      else:
+
+        (value, units) = parse_length(cur_item)
+
+        if h_edge is not None and h_offset is None:
+
+          h_offset = styles.LengthType(value, styles.LengthType.Units(units))
+
+        if v_edge is not None and v_offset is None:
+
+          v_offset = styles.LengthType(value, styles.LengthType.Units(units))
+    
+    # end processing 3 and 4 components
+
+  # fill-in missing components, if any
+
+  if h_offset is None:
+
+    if h_edge is None:
+      h_edge = "left"
+      h_offset = length_50pct
+    else:
+      h_offset = length_0pct
+
+  if v_offset is None:
+
+    if v_edge is None:
+      v_edge = "top"
+      v_offset = length_50pct
+    else:
+      v_offset = length_0pct
+
+
+  return (h_edge, h_offset, v_edge, v_offset)
+  

src/main/python/ttconv/style_properties.py

@@ -317,11 +317,11 @@ class WritingModeType(Enum):
 
 @dataclass(frozen=True)
 class PositionType:
-  '''Coordinates in the root container region
+  '''Coordinates (`x`, `y`) in the root container region, as measure from the left and top edges, respectively.
   '''
+  x: LengthType
+  y: LengthType
 
-  x: LengthType = None
-  y: LengthType = None
 
 #
 # Style properties
@@ -618,8 +618,8 @@ def make_initial_value():
     @staticmethod
     def validate(value: PositionType):
       return isinstance(value, PositionType) \
-        and value.x.units in (LengthType.Units.pct, LengthType.Units.px, LengthType.Units.c)  \
-        and value.y.units in (LengthType.Units.pct, LengthType.Units.px, LengthType.Units.c)
+        and value.x.units in (LengthType.Units.pct, LengthType.Units.px, LengthType.Units.c, LengthType.Units.rw)  \
+        and value.y.units in (LengthType.Units.pct, LengthType.Units.px, LengthType.Units.c, LengthType.Units.rh)
 
 
   class Overflow(StyleProperty):

src/test/python/test_imsc_position_parser.py

@@ -0,0 +1,120 @@
+#!/usr/bin/env python
+# -*- coding: UTF-8 -*-
+
+# Copyright (c) 2020, Sandflow Consulting LLC
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright notice, this
+#    list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright notice,
+#    this list of conditions and the following disclaimer in the documentation
+#    and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+'''Unit tests for the IMSC \\<position\\> parser'''
+
+# pylint: disable=R0201,C0115,C0116
+
+import unittest
+from ttconv.imsc.utils import parse_position
+import ttconv.style_properties as styles
+
+def position(h_edge, h_offval, h_offunit, v_edge, v_offval, v_offunit):
+  return (
+    h_edge,
+    styles.LengthType(value=h_offval, units=styles.LengthType.Units(h_offunit)),
+    v_edge,
+    styles.LengthType(value=v_offval, units=styles.LengthType.Units(v_offunit))
+  )
+
+class IMSCPositionTest(unittest.TestCase):
+
+  tests = [
+    # one component
+    ["center", position("left", 50, "%", "top", 50, "%")],
+    ["left", position("left", 0, "%", "top", 50, "%")],
+    ["right", position("right", 0, "%", "top", 50, "%")],
+    ["top", position("left", 50, "%", "top", 0, "%")],
+    ["bottom", position("left", 50, "%", "bottom", 0, "%")],
+    ["25%", position("left", 25, "%", "top", 50, "%")],
+    # two components
+    ["bottom center", position("left", 50, "%", "bottom", 0, "%")],
+    ["bottom left", position("left", 0, "%", "bottom", 0, "%")],
+    ["bottom right", position("right", 0, "%", "bottom", 0, "%")],
+    ["center center", position("left", 50, "%", "top", 50, "%")],
+    ["center top", position("left", 50, "%", "top", 0, "%")],
+    ["center bottom", position("left", 50, "%", "bottom", 0, "%")],
+    ["center left", position("left", 0, "%", "top", 50, "%")],
+    ["center right", position("right", 0, "%", "top", 50, "%")],
+    ["center 33%", position("left", 50, "%", "top", 33, "%")],
+    ["left center", position("left", 0, "%", "top", 50, "%")],
+    ["left top", position("left", 0, "%", "top", 0, "%")],
+    ["left bottom", position("left", 0, "%", "bottom", 0, "%")],
+    ["left 45%", position("left", 0, "%", "top", 45, "%")],
+    ["right center", position("right", 0, "%", "top", 50, "%")],
+    ["right top", position("right", 0, "%", "top", 0, "%")],
+    ["right bottom", position("right", 0, "%", "bottom", 0, "%")],
+    ["right 20%", position("right", 0, "%", "top", 20, "%")],
+    ["top center", position("left", 50, "%", "top", 0, "%")],
+    ["top left", position("left", 0, "%", "top", 0, "%")],
+    ["top right", position("right", 0, "%", "top", 0, "%")],
+    ["75% center", position("left", 75, "%", "top", 50, "%")],
+    ["75% top", position("left", 75, "%", "top", 0, "%")],
+    ["75% bottom", position("left", 75, "%", "bottom", 0, "%")],
+    ["75% 75%", position("left", 75, "%", "top", 75, "%")],
+    # three components
+    ["bottom left 1%", position("left", 1, "%", "bottom", 0, "%")],
+    ["bottom right 2%", position("right", 2, "%", "bottom", 0, "%")],
+    ["bottom 3% center", position("left", 50, "%", "bottom", 3, "%")],
+    ["bottom 4% left", position("left", 0, "%", "bottom", 4, "%")],
+    ["bottom 5% right", position("right", 0, "%", "bottom", 5, "%")],
+    ["center bottom 6%", position("left", 50, "%", "bottom", 6, "%")],
+    ["center left 7%", position("left", 7, "%", "top", 50, "%")],
+    ["center right 8%", position("right", 8, "%", "top", 50, "%")],
+    ["center top 9%", position("left", 50, "%", "top", 9, "%")],
+    ["left bottom 10%", position("left", 0, "%", "bottom", 10, "%")],
+    ["left top 11%", position("left", 0, "%", "top", 11, "%")],
+    ["left 12% bottom", position("left", 12, "%", "bottom", 0, "%")],
+    ["left 13% center", position("left", 13, "%", "top", 50, "%")],
+    ["left 14% top", position("left", 14, "%", "top", 0, "%")],
+    ["right bottom 15%", position("right", 0, "%", "bottom", 15, "%")],
+    ["right top 16%", position("right", 0, "%", "top", 16, "%")],
+    ["right 17% bottom", position("right", 17, "%", "bottom", 0, "%")],
+    ["right 18% center", position("right", 18, "%", "top", 50, "%")],
+    ["right 19% top", position("right", 19, "%", "top", 0, "%")],
+    ["top left 20%", position("left", 20, "%", "top", 0, "%")],
+    ["top right 21%", position("right", 21, "%", "top", 0, "%")],
+    ["top 22% center", position("left", 50, "%", "top", 22, "%")],
+    ["top 23% left", position("left", 0, "%", "top", 23, "%")],
+    ["top 24% right", position("right", 0, "%", "top", 24, "%")],
+    # four components
+    ["bottom 25% left 75%", position("left", 75, "%", "bottom", 25, "%")],
+    ["bottom 25% right 75%", position("right", 75, "%", "bottom", 25, "%")],
+    ["left 25% bottom 75%", position("left", 25, "%", "bottom", 75, "%")],
+    ["right 25% bottom 75%", position("right", 25, "%", "bottom", 75, "%")],
+    ["top 25% left 75%", position("left", 75, "%", "top", 25, "%")],
+    ["top 25% right 75%", position("right", 75, "%", "top", 25, "%")],
+    ["left 25% top 75%", position("left", 25, "%", "top", 75, "%")],
+    ["right 25% top 75%", position("right", 25, "%", "top", 75, "%")]
+  ]
+
+  def test_positions(self):
+    for test in self.tests:
+      with self.subTest(test[0]):
+        c = parse_position(test[0])
+        self.assertEqual(c, test[1])
+
+if __name__ == '__main__':
+  unittest.main()