Implement <video controls> dodging for text track layout

Source/core/html/track/TextTrackContainer.cpp

 /*
  * Copyright (C) 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Google Inc. 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.
@@ skipping 35 matching lines @@
     RefPtrWillBeRawPtr<TextTrackContainer> element = adoptRefWillBeNoop(new TextTrackContainer(document));
     element->setShadowPseudoId(AtomicString("-webkit-media-text-track-container", AtomicString::ConstructFromLiteral));
     return element.release();
 }
 
 LayoutObject* TextTrackContainer::createLayoutObject(const LayoutStyle&)
 {
     return new LayoutTextTrackContainer(this);
 }
 
-void TextTrackContainer::updateDisplay(HTMLMediaElement& mediaElement)
+void TextTrackContainer::updateDisplay(HTMLMediaElement& mediaElement, ExposingControls exposingControls)
 {
     if (!mediaElement.closedCaptionsVisible()) {
         removeChildren();
         return;
     }
 
     // http://dev.w3.org/html5/webvtt/#dfn-rules-for-updating-the-display-of-webvtt-text-tracks
 
     // 1. If the media element is an audio element, or is another playback
     // mechanism with no rendering area, abort these steps. There is nothing to
     // render.
     if (isHTMLAudioElement(mediaElement))
         return;
 
     // 2. Let video be the media element or other playback mechanism.
     HTMLVideoElement& video = toHTMLVideoElement(mediaElement);
 
     // 3. Let output be an empty list of absolutely positioned CSS block boxes.
 
     // Note: This is a layout algorithm, expressed terms of appending CSS block
     // boxes to output, and the "apply WebVTT cue settings" part is implemented
     // in LayoutVTTCue. Here we merely create the DOM tree from which the layout
     // tree is built and append it to this TextTrackContainer.
 
     // 4. If the user agent is exposing a user interface for video, add to
     // output one or more completely transparent positioned CSS block boxes that
     // cover the same region as the user interface.
 
+    // Note: Overlap checking for the controls is implemented in LayoutVTTCue
+    // without a placeholder box (element or layout object).
+
     // 5. If the last time these rules were run, the user agent was not exposing
-    // a user interface for video, but now it is, let reset be true. Otherwise,
-    // let reset be false.
-
-    // TODO(philipj): Implement step 4 and 5.
+    // a user interface for video, but now it is, optionally let reset be true.
+    // Otherwise, let reset be false.
+    bool reset = exposingControls == DidStartExposingControls;
 
     // 6. Let tracks be the subset of video's list of text tracks that have as
     // their rules for updating the text track rendering these rules for
     // updating the display of WebVTT text tracks, and whose text track mode is
     // showing or showing by default.
     // 7. Let cues be an empty list of text track cues.
     // 8. For each track track in tracks, append to cues all the cues from
     // track's list of cues that have their text track cue active flag set.
     const CueList& activeCues = video.cueTimeline().currentlyActiveCues();
 
     // 9. If reset is false, then, for each text track cue cue in cues: if cue's
     // text track cue display state has a set of CSS boxes, then add those boxes
     // to output, and remove cue from cues.
 
-    // There is nothing explicitly to be done here, as all the caching occurs
-    // within the TextTrackCue instance itself. If parameters of the cue change,
-    // the display tree is cleared.
+    // Note: Removing all children will cause them to be re-inserted below,
+    // invalidating the layout.
+    // effect
+    if (reset)
+        removeChildren();
 
     // 10. For each text track cue cue in cues that has not yet had
     // corresponding CSS boxes added to output, in text track cue order, run the
     // following substeps:
     double movieTime = video.currentTime();
     for (size_t i = 0; i < activeCues.size(); ++i) {
         TextTrackCue* cue = activeCues[i].data();
 
         ASSERT(cue->isActive());
         if (!cue->track() || !cue->track()->isRendered() || !cue->isActive())
             continue;
 
         cue->updateDisplay(*this);
         cue->updatePastAndFutureNodes(movieTime);
     }
 
     // 11. Return output.
     // See the note for step 3 for why there is no output to return.
 }
 
 } // namespace blink