C++ TextTrackCue::regionId方法代码示例

void MediaControlTextTrackContainerElement::updateDisplay()
{
    if (!mediaController()->closedCaptionsVisible()) {
        removeChildren();
        return;
    }

    HTMLMediaElement* mediaElement = toParentMediaElement(this);
    // 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 (!mediaElement || !mediaElement->isVideo())
        return;

    // 2. Let video be the media element or other playback mechanism.
    HTMLVideoElement* video = static_cast<HTMLVideoElement*>(mediaElement);

    // 3. Let output be an empty list of absolutely positioned CSS block boxes.
    Vector<RefPtr<HTMLDivElement> > output;

    // 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.

    // 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.

    // There is nothing to be done explicitly for 4th and 5th steps, as
    // everything is handled through CSS. The caption box is on top of the
    // controls box, in a container set with the -webkit-box display property.

    // 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.
    CueList activeCues = video->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.

    // 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:
    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;

        RefPtr<TextTrackCueBox> displayBox = cue->getDisplayTree(m_videoDisplaySize.size());

#if ENABLE(WEBVTT_REGIONS)
        String regionId = cue->regionId();
        TextTrackRegion* region = cue->track()->regions()->getRegionById(regionId);
        if (!region) {
            // If cue has an empty text track cue region identifier or there is no
            // WebVTT region whose region identifier is identical to cue's text
            // track cue region identifier, run the following substeps:
#endif
            if (displayBox->hasChildNodes() && !contains(static_cast<Node*>(displayBox.get())))
                // Note: the display tree of a cue is removed when the active flag of the cue is unset.
                appendChild(displayBox, ASSERT_NO_EXCEPTION, AttachNow);
#if ENABLE(WEBVTT_REGIONS)
        } else {
            // Let region be the WebVTT region whose region identifier
            // matches the text track cue region identifier of cue.
            RefPtr<HTMLDivElement> regionNode = region->getDisplayTree();

            // Append the region to the viewport, if it was not already.
            if (!contains(regionNode.get()))
                appendChild(region->getDisplayTree());

            region->appendTextTrackCueBox(displayBox);
        }
#endif
    }

    // 11. Return output.
    if (hasChildNodes())
        show();
    else
        hide();
}