core/rendering/RenderVTTCue.cpp

/*
 * Copyright (C) 2012 Victor Carbune (victor (at) rosedu.org)
 *
 * 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 APPLE COMPUTER, INC. ``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 APPLE COMPUTER, INC. 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.
 */

#include "config.h"
#include "core/rendering/RenderVTTCue.h"

#include "core/html/track/vtt/VTTCue.h"
#include "core/rendering/RenderView.h"

namespace WebCore {

RenderVTTCue::RenderVTTCue(VTTCueBox* element)
    : RenderBlockFlow(element)
    , m_cue(element->getCue())
{
}

void RenderVTTCue::layout()
{
    RenderBlockFlow::layout();

    // If WebVTT Regions are used, the regular WebVTT layout algorithm is no
    // longer necessary, since cues having the region parameter set do not have
    // any positioning parameters. Also, in this case, the regions themselves
    // have positioning information.
    if (!m_cue->regionId().isEmpty())
        return;

    LayoutState state(*this, locationOffset());

    if (m_cue->snapToLines())
        repositionCueSnapToLinesSet();
    else
        repositionCueSnapToLinesNotSet();
}

bool RenderVTTCue::findFirstLineBox(InlineFlowBox*& firstLineBox)
{
    if (firstChild()->isRenderInline())
        firstLineBox = toRenderInline(firstChild())->firstLineBox();
    else
        return false;

    return true;
}

bool RenderVTTCue::initializeLayoutParameters(InlineFlowBox* firstLineBox, LayoutUnit& step, LayoutUnit& position)
{
    ASSERT(firstChild());

    RenderBlock* parentBlock = containingBlock();

    // 1. Horizontal: Let step be the height of the first line box in boxes.
    //    Vertical: Let step be the width of the first line box in boxes.
    step = m_cue->getWritingDirection() == VTTCue::Horizontal ? firstLineBox->height() : firstLineBox->width();

    // 2. If step is zero, then jump to the step labeled done positioning below.
    if (!step)
        return false;

    // 3. Let line position be the text track cue computed line position.
    int linePosition = m_cue->calculateComputedLinePosition();

    // 4. Vertical Growing Left: Add one to line position then negate it.
    if (m_cue->getWritingDirection() == VTTCue::VerticalGrowingLeft)
        linePosition = -(linePosition + 1);

    // 5. Let position be the result of multiplying step and line position.
    position = step * linePosition;

    // 6. Vertical Growing Left: Decrease position by the width of the
    // bounding box of the boxes in boxes, then increase position by step.
    if (m_cue->getWritingDirection() == VTTCue::VerticalGrowingLeft) {
        position -= width();
        position += step;
    }

    // 7. If line position is less than zero...
    if (linePosition < 0) {
        // Horizontal / Vertical: ... then increase position by the
        // height / width of the video's rendering area ...
        position += m_cue->getWritingDirection() == VTTCue::Horizontal ? parentBlock->height() : parentBlock->width();

        // ... and negate step.
        step = -step;
    }

    return true;
}

void RenderVTTCue::placeBoxInDefaultPosition(LayoutUnit position, bool& switched)
{
    // 8. Move all boxes in boxes ...
    if (m_cue->getWritingDirection() == VTTCue::Horizontal) {
        // Horizontal: ... down by the distance given by position
        setY(y() + position);
    } else {
        // Vertical: ... right by the distance given by position
        setX(x() + position);
    }

    // 9. Default: Remember the position of all the boxes in boxes as their
    // default position.
    // FIXME: Why the direct conversion between float and LayoutUnit? crbug.com/350474
    m_fallbackPosition = FloatPoint(location());

    // 10. Let switched be false.
    switched = false;
}

bool RenderVTTCue::isOutside() const
{
    return !containingBlock()->absoluteBoundingBoxRect().contains(absoluteContentBox());
}

bool RenderVTTCue::isOverlapping() const
{
    for (RenderObject* box = previousSibling(); box; box = box->previousSibling()) {
        IntRect boxRect = box->absoluteBoundingBoxRect();

        if (absoluteBoundingBoxRect().intersects(boxRect))
            return true;
    }

    return false;
}

bool RenderVTTCue::shouldSwitchDirection(InlineFlowBox* firstLineBox, LayoutUnit step) const
{
    LayoutUnit top = y();
    LayoutUnit left = x();
    LayoutUnit bottom = top + firstLineBox->height();
    LayoutUnit right = left + firstLineBox->width();

    // 12. Horizontal: If step is negative and the top of the first line
    // box in boxes is now above the top of the video's rendering area,
    // or if step is positive and the bottom of the first line box in
    // boxes is now below the bottom of the video's rendering area, jump
    // to the step labeled switch direction.
    LayoutUnit parentHeight = containingBlock()->height();
    if (m_cue->getWritingDirection() == VTTCue::Horizontal && ((step < 0 && top < 0) || (step > 0 && bottom > parentHeight)))
        return true;

    // 12. Vertical: If step is negative and the left edge of the first line
    // box in boxes is now to the left of the left edge of the video's
    // rendering area, or if step is positive and the right edge of the
    // first line box in boxes is now to the right of the right edge of
    // the video's rendering area, jump to the step labeled switch direction.
    LayoutUnit parentWidth = containingBlock()->width();
    if (m_cue->getWritingDirection() != VTTCue::Horizontal && ((step < 0 && left < 0) || (step > 0 && right > parentWidth)))
        return true;

    return false;
}

void RenderVTTCue::moveBoxesByStep(LayoutUnit step)
{
    // 13. Horizontal: Move all the boxes in boxes down by the distance
    // given by step. (If step is negative, then this will actually
    // result in an upwards movement of the boxes in absolute terms.)
    if (m_cue->getWritingDirection() == VTTCue::Horizontal)
        setY(y() + step);

    // 13. Vertical: Move all the boxes in boxes right by the distance
    // given by step. (If step is negative, then this will actually
    // result in a leftwards movement of the boxes in absolute terms.)
    else
        setX(x() + step);
}

bool RenderVTTCue::switchDirection(bool& switched, LayoutUnit& step)
{
    // 15. Switch direction: Move all the boxes in boxes back to their
    // default position as determined in the step above labeled default.
    setX(m_fallbackPosition.x());
    setY(m_fallbackPosition.y());

    // 16. If switched is true, jump to the step labeled done
    // positioning below.
    if (switched)
        return false;

    // 17. Negate step.
    step = -step;

    // 18. Set switched to true.
    switched = true;
    return true;
}

void RenderVTTCue::repositionCueSnapToLinesSet()
{
    InlineFlowBox* firstLineBox;
    LayoutUnit step;
    LayoutUnit position;

    if (!findFirstLineBox(firstLineBox))
        return;

    if (!initializeLayoutParameters(firstLineBox, step, position))
        return;

    bool switched;
    placeBoxInDefaultPosition(position, switched);

    // 11. Step loop: If none of the boxes in boxes would overlap any of the boxes
    // in output and all the boxes in output are within the video's rendering area
    // then jump to the step labeled done positioning.
    while (isOutside() || isOverlapping()) {
        if (!shouldSwitchDirection(firstLineBox, step)) {
            // 13. Move all the boxes in boxes ...
            // 14. Jump back to the step labeled step loop.
            moveBoxesByStep(step);
        } else if (!switchDirection(switched, step)) {
            break;
        }

        // 19. Jump back to the step labeled step loop.
    }

    // Acommodate extra top and bottom padding, border or margin.
    // Note: this is supported only for internal UA styling, not through the cue selector.
    if (hasInlineDirectionBordersPaddingOrMargin()) {
        IntRect containerRect = containingBlock()->absoluteBoundingBoxRect();
        IntRect cueRect = absoluteBoundingBoxRect();

        int topOverflow = cueRect.y() - containerRect.y();
        int bottomOverflow = containerRect.y() + containerRect.height() - cueRect.y() - cueRect.height();

        int adjustment = 0;
        if (topOverflow < 0)
            adjustment = -topOverflow;
        else if (bottomOverflow < 0)
            adjustment = bottomOverflow;

        if (adjustment)
            setY(y() + adjustment);
    }
}

void RenderVTTCue::repositionCueSnapToLinesNotSet()
{
    // FIXME: Implement overlapping detection when snap-to-lines is not set. http://wkb.ug/84296
}

} // namespace WebCore