void RenderMultiColumnFlowThread::computeLineGridPaginationOrigin(LayoutState& layoutState) const
{
if (!progressionIsInline())
return;
// We need to cache a line grid pagination origin so that we understand how to reset the line grid
// at the top of each column.
// Get the current line grid and offset.
const auto lineGrid = layoutState.lineGrid();
if (!lineGrid)
return;
// Get the hypothetical line box used to establish the grid.
auto lineGridBox = lineGrid->lineGridBox();
if (!lineGridBox)
return;
bool isHorizontalWritingMode = lineGrid->isHorizontalWritingMode();
LayoutUnit lineGridBlockOffset = isHorizontalWritingMode ? layoutState.lineGridOffset().height() : layoutState.lineGridOffset().width();
// Now determine our position on the grid. Our baseline needs to be adjusted to the nearest baseline multiple
// as established by the line box.
// FIXME: Need to handle crazy line-box-contain values that cause the root line box to not be considered. I assume
// the grid should honor line-box-contain.
LayoutUnit gridLineHeight = lineGridBox->lineBottomWithLeading() - lineGridBox->lineTopWithLeading();
if (!gridLineHeight)
return;
LayoutUnit firstLineTopWithLeading = lineGridBlockOffset + lineGridBox->lineTopWithLeading();
if (layoutState.isPaginated() && layoutState.pageLogicalHeight()) {
LayoutUnit pageLogicalTop = isHorizontalWritingMode ? layoutState.pageOffset().height() : layoutState.pageOffset().width();
if (pageLogicalTop > firstLineTopWithLeading) {
// Shift to the next highest line grid multiple past the page logical top. Cache the delta
// between this new value and the page logical top as the pagination origin.
LayoutUnit remainder = roundToInt(pageLogicalTop - firstLineTopWithLeading) % roundToInt(gridLineHeight);
LayoutUnit paginationDelta = gridLineHeight - remainder;
if (isHorizontalWritingMode)
layoutState.setLineGridPaginationOrigin(LayoutSize(layoutState.lineGridPaginationOrigin().width(), paginationDelta));
else
layoutState.setLineGridPaginationOrigin(LayoutSize(paginationDelta, layoutState.lineGridPaginationOrigin().height()));
}
}
}
LayoutUnit RootInlineBox::lineSnapAdjustment(LayoutUnit delta) const
{
// If our block doesn't have snapping turned on, do nothing.
// FIXME: Implement bounds snapping.
if (blockFlow().style().lineSnap() == LineSnapNone)
return 0;
// Get the current line grid and offset.
LayoutState* layoutState = blockFlow().view().layoutState();
RenderBlockFlow* lineGrid = layoutState->lineGrid();
LayoutSize lineGridOffset = layoutState->lineGridOffset();
if (!lineGrid || lineGrid->style().writingMode() != blockFlow().style().writingMode())
return 0;
// Get the hypothetical line box used to establish the grid.
RootInlineBox* lineGridBox = lineGrid->lineGridBox();
if (!lineGridBox)
return 0;
LayoutUnit lineGridBlockOffset = lineGrid->isHorizontalWritingMode() ? lineGridOffset.height() : lineGridOffset.width();
LayoutUnit blockOffset = blockFlow().isHorizontalWritingMode() ? layoutState->layoutOffset().height() : layoutState->layoutOffset().width();
// Now determine our position on the grid. Our baseline needs to be adjusted to the nearest baseline multiple
// as established by the line box.
// FIXME: Need to handle crazy line-box-contain values that cause the root line box to not be considered. I assume
// the grid should honor line-box-contain.
LayoutUnit gridLineHeight = lineGridBox->lineBottomWithLeading() - lineGridBox->lineTopWithLeading();
if (!gridLineHeight)
return 0;
LayoutUnit lineGridFontAscent = lineGrid->style().fontMetrics().ascent(baselineType());
LayoutUnit lineGridFontHeight = lineGridBox->logicalHeight();
LayoutUnit firstTextTop = lineGridBlockOffset + lineGridBox->logicalTop();
LayoutUnit firstLineTopWithLeading = lineGridBlockOffset + lineGridBox->lineTopWithLeading();
LayoutUnit firstBaselinePosition = firstTextTop + lineGridFontAscent;
LayoutUnit currentTextTop = blockOffset + logicalTop() + delta;
LayoutUnit currentFontAscent = blockFlow().style().fontMetrics().ascent(baselineType());
LayoutUnit currentBaselinePosition = currentTextTop + currentFontAscent;
LayoutUnit lineGridPaginationOrigin = isHorizontal() ? layoutState->lineGridPaginationOrigin().height() : layoutState->lineGridPaginationOrigin().width();
// If we're paginated, see if we're on a page after the first one. If so, the grid resets on subsequent pages.
// FIXME: If the grid is an ancestor of the pagination establisher, then this is incorrect.
LayoutUnit pageLogicalTop = 0;
if (layoutState->isPaginated() && layoutState->pageLogicalHeight()) {
pageLogicalTop = blockFlow().pageLogicalTopForOffset(lineTopWithLeading() + delta);
if (pageLogicalTop > firstLineTopWithLeading)
firstTextTop = pageLogicalTop + lineGridBox->logicalTop() - lineGrid->borderAndPaddingBefore() + lineGridPaginationOrigin;
}
if (blockFlow().style().lineSnap() == LineSnapContain) {
// Compute the desired offset from the text-top of a grid line.
// Look at our height (logicalHeight()).
// Look at the total available height. It's going to be (textBottom - textTop) + (n-1)*(multiple with leading)
// where n is number of grid lines required to enclose us.
if (logicalHeight() <= lineGridFontHeight)
firstTextTop += (lineGridFontHeight - logicalHeight()) / 2;
else {
LayoutUnit numberOfLinesWithLeading = ceilf(static_cast<float>(logicalHeight() - lineGridFontHeight) / gridLineHeight);
LayoutUnit totalHeight = lineGridFontHeight + numberOfLinesWithLeading * gridLineHeight;
firstTextTop += (totalHeight - logicalHeight()) / 2;
}
firstBaselinePosition = firstTextTop + currentFontAscent;
} else
firstBaselinePosition = firstTextTop + lineGridFontAscent;
// If we're above the first line, just push to the first line.
if (currentBaselinePosition < firstBaselinePosition)
return delta + firstBaselinePosition - currentBaselinePosition;
// Otherwise we're in the middle of the grid somewhere. Just push to the next line.
LayoutUnit baselineOffset = currentBaselinePosition - firstBaselinePosition;
LayoutUnit remainder = roundToInt(baselineOffset) % roundToInt(gridLineHeight);
LayoutUnit result = delta;
if (remainder)
result += gridLineHeight - remainder;
// If we aren't paginated we can return the result.
if (!layoutState->isPaginated() || !layoutState->pageLogicalHeight() || result == delta)
return result;
// We may end up shifted to a new page. We need to do a re-snap when that happens.
LayoutUnit newPageLogicalTop = blockFlow().pageLogicalTopForOffset(lineBottomWithLeading() + result);
if (newPageLogicalTop == pageLogicalTop)
return result;
// Put ourselves at the top of the next page to force a snap onto the new grid established by that page.
return lineSnapAdjustment(newPageLogicalTop - (blockOffset + lineTopWithLeading()));
}
