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Improve readability of QTextLine's handling of (negative) right bearing

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- Helper functions in LineBreakHelper have been renamed from
    adjustFoo to calculateFoo, to signal that they do work, and
    are not adjusting something relative to something else.

  - The use of QFixed(1) and >= 0 has been replaced with an explicit
    constant for the case of the bearing not being calculated yet.

  - A helper function negativeRightBearing() has been added that
    returns the absolute value of any negative right bearing, making
    the width computations simpler.

  - Comments have been added and rewritten to make the logic clearer.

Change-Id: I1d3a0214cfa8b4fed4551f3444b43a37d55bd69b
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@theqtcompany.com>
This commit is contained in:
Tor Arne Vestbø 2015-08-07 15:37:07 +02:00
parent d7b847112a
commit e92c2e119b
1 changed files with 55 additions and 26 deletions
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79
src/gui/text/qtextlayout.cpp
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@ -1605,8 +1605,8 @@ namespace {
bool checkFullOtherwiseExtend(QScriptLine &line);
QFixed calculateNewWidth(const QScriptLine &line) const {
return line.textWidth + tmpData.textWidth + spaceData.textWidth + softHyphenWidth
- qMin(rightBearing, QFixed());
return line.textWidth + tmpData.textWidth + spaceData.textWidth
+ softHyphenWidth + negativeRightBearing();
}
inline glyph_t currentGlyph() const
@ -1626,33 +1626,51 @@ namespace {
}
}
inline void adjustRightBearing(glyph_t glyph)
inline void calculateRightBearing(glyph_t glyph)
{
qreal rb;
fontEngine->getGlyphBearings(glyph, 0, &rb);
rightBearing = qMin(QFixed(), QFixed::fromReal(rb));
// We only care about negative right bearings, so we limit the range
// of the bearing here so that we can assume it's negative in the rest
// of the code, as well ase use QFixed(1) as a sentinel to represent
// the state where we have yet to compute the right bearing.
rightBearing = qMin(QFixed::fromReal(rb), QFixed(0));
}
inline void adjustRightBearing()
inline void calculateRightBearing()
{
if (currentPosition <= 0)
return;
adjustRightBearing(currentGlyph());
calculateRightBearing(currentGlyph());
}
inline void adjustPreviousRightBearing()
inline void calculateRightBearingForPreviousGlyph()
{
if (previousGlyph > 0)
adjustRightBearing(previousGlyph);
calculateRightBearing(previousGlyph);
}
static const QFixed RightBearingNotCalculated;
inline void resetRightBearing()
{
rightBearing = QFixed(1); // Any positive number is defined as invalid since only
// negative right bearings are interesting to us.
rightBearing = RightBearingNotCalculated;
}
// We express the negative right bearing as an absolute number
// so that it can be applied to the width using addition.
inline QFixed negativeRightBearing() const
{
if (rightBearing == RightBearingNotCalculated)
return QFixed(0);
return qAbs(rightBearing);
}
};
const QFixed LineBreakHelper::RightBearingNotCalculated = QFixed(1);
inline bool LineBreakHelper::checkFullOtherwiseExtend(QScriptLine &line)
{
LB_DEBUG("possible break width %f, spacew=%f", tmpData.textWidth.toReal(), spaceData.textWidth.toReal());
@ -1805,7 +1823,7 @@ void QTextLine::layout_helper(int maxGlyphs)
current, lbh.logClusters, lbh.glyphs);
} else {
lbh.tmpData.length++;
lbh.adjustPreviousRightBearing();
lbh.calculateRightBearingForPreviousGlyph();
}
line += lbh.tmpData;
goto found;
@ -1887,22 +1905,29 @@ void QTextLine::layout_helper(int maxGlyphs)
lbh.tmpData.textWidth += lbh.glyphs.advances[lbh.logClusters[lbh.currentPosition - 1]];
}
// The actual width of the text needs to take the right bearing into account. The
// right bearing is left-ward, which means that if the rightmost pixel is to the right
// of the advance of the glyph, the bearing will be negative. We flip the sign
// for the code to be more readable. Logic borrowed from qfontmetrics.cpp.
if (sb_or_ws|breakany) {
// To compute the final width of the text we need to take negative right bearing
// into account (negative right bearing means the glyph has pixel data past the
// advance length). Note that the negative right bearing is an absolute number,
// so that we can apply it to the width using straight forward addition.
// Store previous right bearing (for the already accepted glyph) in case we
// end up breaking due to the current glyph being too wide.
QFixed previousRightBearing = lbh.rightBearing;
// We ignore the right bearing if the minimum negative bearing is too little to
// expand the text beyond the edge.
if (sb_or_ws|breakany) {
QFixed rightBearing = lbh.rightBearing; // store previous right bearing
if (lbh.calculateNewWidth(line) - lbh.minimumRightBearing > line.width)
lbh.adjustRightBearing();
lbh.calculateRightBearing();
if (lbh.checkFullOtherwiseExtend(line)) {
// we are too wide, fix right bearing
if (rightBearing <= 0)
lbh.rightBearing = rightBearing; // take from cache
// We are too wide to accept the next glyph with its bearing, so we restore the
// right bearing to that of the previous glyph (the one that was already accepted),
// so that the bearing can be be applied to the final width of the text below.
if (previousRightBearing != LineBreakHelper::RightBearingNotCalculated)
lbh.rightBearing = previousRightBearing;
else
lbh.adjustPreviousRightBearing();
lbh.calculateRightBearingForPreviousGlyph();
if (!breakany) {
line.textWidth += lbh.softHyphenWidth;
@ -1919,10 +1944,14 @@ void QTextLine::layout_helper(int maxGlyphs)
LB_DEBUG("reached end of line");
lbh.checkFullOtherwiseExtend(line);
found:
if (lbh.rightBearing > 0 && !lbh.whiteSpaceOrObject) // If right bearing has not yet been adjusted
lbh.adjustRightBearing();
line.textAdvance = line.textWidth;
line.textWidth -= qMin(QFixed(), lbh.rightBearing);
// If right bearing has not been calculated yet, do that now
if (lbh.rightBearing == LineBreakHelper::RightBearingNotCalculated && !lbh.whiteSpaceOrObject)
lbh.calculateRightBearing();
// Then apply any negative right bearing
line.textWidth += lbh.negativeRightBearing();
if (line.length == 0) {
LB_DEBUG("no break available in line, adding temp: length %d, width %f, space: length %d, width %f",