Fix ISD cache ignoring regions with showBackground="always"

#420

src/main/python/ttconv/isd.py

@@ -184,6 +184,30 @@ def _make_absolute(
 
     return (begin_time, end_time)
 
+  def _region_always_has_background(region: typing.Type[model.Region]) -> bool:
+
+    if region.get_style(styles.StyleProperties.Opacity) == 0:
+      return False
+
+    if region.get_style(styles.StyleProperties.Display) is styles.DisplayType.none:
+      return False
+
+    if region.get_style(styles.StyleProperties.Visibility) is styles.VisibilityType.hidden:
+      return False
+
+    if region.get_style(styles.StyleProperties.ShowBackground) is styles.ShowBackgroundType.whenActive:
+      return False
+
+    bg_color: styles.ColorType = region.get_style(styles.StyleProperties.BackgroundColor)
+    if bg_color is not None:
+      if bg_color.ident is not styles.ColorType.Colorimetry.RGBA8:
+        raise RuntimeError(f"Unsupported colorimetry system: {bg_color.ident}")
+
+      if bg_color.components[3] == 0:
+        return False
+
+    return True
+
   @staticmethod
   def significant_times(doc: model.ContentDocument) -> SignificantTimes:
     '''Returns a list of the temporal offsets at which the document `doc` changes, sorted in
@@ -204,7 +228,8 @@ def compute_sig_times(
 
       interval_cache[element] = (begin_time, end_time)
 
-      if isinstance(element, (model.Br, model.Span)):
+      if isinstance(element, (model.Br, model.Span)) or \
+          isinstance(element, (model.Region)) and ISD._region_always_has_background(element):
         content_interval[0] = begin_time if content_interval[0] is None else min(begin_time, content_interval[0])
         content_interval[1] = None if end_time is None or content_interval[1] is None else max(end_time, content_interval[1])
 
@@ -249,15 +274,15 @@ def compute_sig_times(
 
       interval_cache = {}
 
+      content_interval = [None, 0]
+
       # add significant times for regions
 
       for region in cached_doc.iter_regions():
-        compute_sig_times(interval_cache, None, s_times, region, 0, None)
+        compute_sig_times(interval_cache, content_interval, s_times, region, 0, None)
 
       # add significant times for body and its descendents
 
-      content_interval = [None, 0]
-
       if cached_doc.get_body() is not None:
         compute_sig_times(interval_cache, content_interval, s_times, cached_doc.get_body(), 0, None)
 

src/test/python/test_isd_cache.py

@@ -0,0 +1,77 @@
+#!/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 ISD generation using caching'''
+
+# pylint: disable=R0201,C0115,C0116
+
+import unittest
+from ttconv.isd import ISD
+import ttconv.model as model
+import ttconv.style_properties as styles
+import xml.etree.ElementTree as et
+import ttconv.imsc.reader as imsc_reader
+
+
+class ISDCacheTests(unittest.TestCase):
+
+  def test_show_background(self):
+    ttml_doc = """<tt xml:lang="en"
+    xmlns="http://www.w3.org/ns/ttml"
+    xmlns:tts="http://www.w3.org/ns/ttml#styling"
+    xmlns:ttp="http://www.w3.org/ns/ttml#parameter"
+    ttp:timeBase="media">
+  <head>
+    <styling>
+      <style xml:id="s1" tts:backgroundColor="#ff0000" />
+    </styling>
+    <layout>
+      <region xml:id="r1" style="s1" tts:extent="50% 50%" tts:origin="0% 0%"/>
+      <region xml:id="r2" style="s1" tts:extent="50% 50%" tts:origin="0% 50%"/>
+      <region xml:id="r3" style="s1" tts:extent="50% 50%" tts:origin="50% 50%"/>
+      <region xml:id="r4" tts:extent="50% 50%" tts:origin="50% 0%"/>
+    </layout>
+  </head>
+  <body>
+    <div>
+      <p region="r4" begin="00:00:00" end="00:00:00.2" xml:id="p0">ABCDEF</p>
+      <p region="r1" begin="00:00:00.25" end="00:00:04" xml:id="p1"><span style="s1">a</span></p>
+      <p region="r2" begin="00:00:00.25" end="00:00:04" xml:id="p2"><span style="s1">g</span></p>
+      <p region="r3" begin="00:00:00.25" end="00:00:04" xml:id="p3"><span style="s1">m</span></p>
+      <p region="r4" begin="00:00:00.25" end="00:00:04" xml:id="p4"><span style="s1">s</span></p>
+    </div>
+  </body>
+</tt>"""
+
+    doc = imsc_reader.to_model(et.ElementTree(et.fromstring(ttml_doc)))
+
+    sig_times = ISD.significant_times(doc)
+
+    isd = ISD.from_model(doc, 0.2, sig_times)
+
+    self.assertEqual(len(list(isd.iter_regions())), 4)
+
+if __name__ == '__main__':
+  unittest.main()