VTTCue: Simplify computation of direction-aware text position

Source/core/html/track/vtt/VTTCue.cpp

 /*
  * Copyright (c) 2013, Opera Software ASA. All rights reserved.
  *
  * 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
@@ skipping 536 matching lines @@
                 node = NodeTraversal::nextSkippingChildren(*node);
                 continue;
             }
         }
 
         node = NodeTraversal::next(*node);
     }
     return isLeftToRightDirection(textDirection) ? CSSValueLtr : CSSValueRtl;
 }
 
+static inline VTTCue::CueAlignment resolveCueAlignment(VTTCue::CueAlignment specifiedCueAlignment, CSSValueID direction)
+{
+    ASSERT(direction == CSSValueLtr || direction == CSSValueRtl);
+    switch (specifiedCueAlignment) {
+    case VTTCue::Start:
+        return direction == CSSValueLtr ? VTTCue::Left : VTTCue::Right;
+    case VTTCue::End:
+        return direction == CSSValueLtr ? VTTCue::Right : VTTCue::Left;
+    default:
+        return specifiedCueAlignment;
+    }
+}
+
 void VTTCue::calculateDisplayParameters()
 {
     createVTTNodeTree();
 
     // Steps 10.2, 10.3
     m_displayDirection = determineTextDirection(m_vttNodeTree.get());
 
     if (m_displayDirection == CSSValueRtl)
         UseCounter::count(document(), UseCounter::VTTCueRenderRtl);
 
@@ skipping 30 matching lines @@
     // 10.6 If the text track cue size is less than maximum size, then let size
     // be text track cue size. Otherwise, let size be maximum size.
     m_displaySize = std::min(m_cueSize, maximumSize);
 
     // FIXME: Understand why step 10.7 is missing (just a copy/paste error?)
     // Could be done within a spec implementation check - http://crbug.com/301580
 
     // 10.8 Determine the value of x-position or y-position for cue as per the
     // appropriate rules from the following list:
     if (m_writingDirection == Horizontal) {
-        switch (m_cueAlignment) {
-        case Start:
-            if (m_displayDirection == CSSValueLtr)
-                m_displayPosition.first = m_textPosition;
-            else
-                m_displayPosition.first = 100 - m_textPosition - m_displaySize;
-            break;
-        case End:
-            if (m_displayDirection == CSSValueRtl)
-                m_displayPosition.first = 100 - m_textPosition;
-            else
-                m_displayPosition.first = m_textPosition - m_displaySize;
-            break;
+        int visualTextPosition = m_displayDirection == CSSValueLtr ? m_textPosition : 100 - m_textPosition;
+
+        switch (resolveCueAlignment(m_cueAlignment, m_displayDirection)) {
         case Left:
-            if (m_displayDirection == CSSValueLtr)
-                m_displayPosition.first = m_textPosition;
-            else
-                m_displayPosition.first = 100 - m_textPosition;
+            m_displayPosition.first = visualTextPosition;
             break;
         case Right:
-            if (m_displayDirection == CSSValueLtr)
-                m_displayPosition.first = m_textPosition - m_displaySize;
-            else
-                m_displayPosition.first = 100 - m_textPosition - m_displaySize;
+            m_displayPosition.first = visualTextPosition - m_displaySize;
             break;
         case Middle:
-            if (m_displayDirection == CSSValueLtr)
-                m_displayPosition.first = m_textPosition - m_displaySize / 2;
-            else
-                m_displayPosition.first = 100 - m_textPosition - m_displaySize / 2;
+            m_displayPosition.first = visualTextPosition - m_displaySize / 2;
             break;
         default:
             ASSERT_NOT_REACHED();
         }
     } else {
         // Cases for m_writingDirection being VerticalGrowing{Left|Right}
         switch (m_cueAlignment) {
         case Start:
         case Left:
             m_displayPosition.second = m_textPosition;
@@ skipping 457 matching lines @@
 
 void VTTCue::trace(Visitor* visitor)
 {
     visitor->trace(m_vttNodeTree);
     visitor->trace(m_cueBackgroundBox);
     visitor->trace(m_displayTree);
     TextTrackCue::trace(visitor);
 }
 
 } // namespace blink