/// <summary>
/// Shorten the current line. Currently this is only called when the last thing on the line
/// is a string box. If possible, replace its segment with a shorter one. If this is not possible,
/// and it is not the first thing on the line, remove it altogether. If it IS the first thing on
/// the line, do nothing. We'll live with the bad break, because there is nothing better we know
/// how to do.
/// Returns true if successful, which means FinalizeLine should be called again. False if
/// unsuccessful, to prevent infinite loop.
/// </summary>
private bool Backtrack()
{
var lastBox = m_lines.Last().LastBox as StringBox;
while (lastBox != null)
{
// We want to call FindLineBreak again with the same arguments we used to create the segment
// of lastBox, except that ichLimBacktrack should prevent including the last character.
// (We expect that is is NOT a white-space-only segment, since we were not able to break after it.)
int ichMin = lastBox.IchMin;
int ichLim = ichMin + lastBox.Segment.get_Lim(ichMin);
//int dxWidthLast = lastBox.Segment.get_Width(ichMin, m_layoutInfo.VwGraphics);
int ichLimBacktrack = ichLim - 1;
// skip back one if we're splitting a surrogate.
if (ichLimBacktrack > 0)
{
string charsAtLim = Fetch(ichLimBacktrack - 1, ichLimBacktrack + 1);
if (Surrogates.IsTrailSurrogate(charsAtLim[1]) && Surrogates.IsLeadSurrogate(charsAtLim[0]))
{
ichLimBacktrack--;
}
}
int runIndex = m_renderRunIndex; // what would have beem m_renderRunIndex when making lastBox's segment.
while (runIndex > 0 && ichMin < m_renderRuns[runIndex].RenderStart)
{
runIndex--;
}
var renderer = m_layoutInfo.GetRenderer(m_renderRuns[runIndex].Ws);
int ichRunLim = GetLimitOfRunWithSameRenderer(renderer, runIndex);
ILgSegment seg;
int dichLim, dxWidth;
LgEndSegmentType est;
bool mustGetSomeSeg = m_currentLine.FirstBox == lastBox;
var twsh = LgTrailingWsHandling.ktwshAll;
bool runRtl = m_layoutInfo.RendererFactory.RightToLeft(m_renderRuns[runIndex].Ws);
bool paraRtl = m_para.Style.RightToLeft;
if (runRtl != paraRtl)
{
twsh = LgTrailingWsHandling.ktwshNoWs;
}
var spaceLeftOnCurrentLine = m_spaceLeftOnCurrentLine + lastBox.Width;
renderer.FindBreakPoint(m_layoutInfo.VwGraphics, m_para.Source, null, ichMin,
ichRunLim, ichLimBacktrack, false, mustGetSomeSeg, spaceLeftOnCurrentLine,
LgLineBreak.klbWordBreak,
mustGetSomeSeg ? LgLineBreak.klbClipBreak : LgLineBreak.klbWordBreak, twsh,
false, out seg, out dichLim, out dxWidth, out est, null);
if (seg == null)
{
// can't make any shorter segment here.
// Can we backtrack further by getting rid of this box altogether?
Box boxBefore = m_lines.Last().BoxBefore(lastBox);
if (boxBefore is StringBox)
{
lastBox = (StringBox)boxBefore;
continue;
}
// Currently backtracking should not need to remove a non-string box, because we always allow
// breaking after them. So if boxBefore is not a string box, we can break after it.
m_currentLine.RemoveFrom(lastBox);
m_ichRendered = ichMin;
m_spaceLeftOnCurrentLine = spaceLeftOnCurrentLine;
m_renderRunIndex = AdvanceRenderRunIndexToIch(m_ichRendered, m_renderRunIndex);
return(true);
}
m_currentLine.RemoveFrom(lastBox);
AddBoxToLine(seg, ichMin, dichLim, est, spaceLeftOnCurrentLine);
ILgSegment whiteSpaceSeg;
if (twsh == LgTrailingWsHandling.ktwshNoWs)
{
// Add a white space segment if possible.
renderer.FindBreakPoint(m_layoutInfo.VwGraphics, m_para.Source, null, m_ichRendered,
ichRunLim, ichRunLim, false, true, m_spaceLeftOnCurrentLine, LgLineBreak.klbWordBreak,
LgLineBreak.klbWordBreak, LgTrailingWsHandling.ktwshOnlyWs,
false, out whiteSpaceSeg, out dichLim, out dxWidth, out est, null);
if (seg != null)
{
AddBoxToLine(whiteSpaceSeg, m_ichRendered, dichLim, est, m_spaceLeftOnCurrentLine);
}
}
m_renderRunIndex = AdvanceRenderRunIndexToIch(m_ichRendered, m_renderRunIndex);
return(true);
}
return(false); // no better break available, use the line as it is.
}