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QDashStroker: cap the number of repetitions of the pattern

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Since the dashing is computed even outside the clipping and device
area, painting very long dashed lines could consume unexpected amounts
of time and resources. Fix by placing a limit on the dashing, and fall
back to solid line drawing if hit.

Fixes: QTBUG-95594
Pick-to: 6.2 6.1 5.15
Change-Id: Ida05ecd8fe6df402c9e669206fd5cec4a9f5386a
Reviewed-by: Robert Löhning <robert.loehning@qt.io>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
This commit is contained in:
Eirik Aavitsland 2021-08-17 13:50:50 +02:00
parent cf34fca4d0
commit 279a434c1c
4 changed files with 38 additions and 23 deletions
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5
src/gui/painting/qpaintengine_raster.cpp
View File

@ -3265,6 +3265,11 @@ void QRasterPaintEnginePrivate::rasterizeLine_dashed(QLineF line,
qreal length = line.length();
Q_ASSERT(length > 0);
if (length / (patternLength * width) > QDashStroker::repetitionLimit()) {
rasterizer->rasterizeLine(line.p1(), line.p2(), width / length, squareCap);
return;
}
while (length > 0) {
const bool rasterize = *inDash;
qreal dash = (pattern.at(*dashIndex) - *dashOffset) * width;

2
src/gui/painting/qpaintengineex.cpp
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@ -426,7 +426,7 @@ void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &inPen)
patternLength *= pw;
if (qFuzzyIsNull(patternLength)) {
pen.setStyle(Qt::NoPen);
} else if (extent / patternLength > 10000) {
} else if (extent / patternLength > QDashStroker::repetitionLimit()) {
// approximate stream of tiny dashes with semi-transparent solid line
pen.setStyle(Qt::SolidLine);
QColor color(pen.color());

53
src/gui/painting/qstroker.cpp
View File

@ -1179,32 +1179,41 @@ void QDashStroker::processCurrentSubpath()
bool done = pos >= estop;
if (clipping) {
// Check if the entire line can be clipped away.
if (!lineIntersectsRect(prev, e, clip_tl, clip_br)) {
// Cut away full dash sequences.
elen -= qFloor(elen * invSumLength) * sumLength;
// Update dash offset.
while (!done) {
qreal dpos = pos + dashes[idash] - doffset - estart;
// Check if the entire line should be clipped away or simplified
bool clipIt = clipping && !lineIntersectsRect(prev, e, clip_tl, clip_br);
bool skipDashing = elen * invSumLength > repetitionLimit();
if (skipDashing || clipIt) {
// Cut away full dash sequences.
elen -= std::floor(elen * invSumLength) * sumLength;
// Update dash offset.
while (!done) {
qreal dpos = pos + dashes[idash] - doffset - estart;
Q_ASSERT(dpos >= 0);
Q_ASSERT(dpos >= 0);
if (dpos > elen) { // dash extends this line
doffset = dashes[idash] - (dpos - elen); // subtract the part already used
pos = estop; // move pos to next path element
done = true;
} else { // Dash is on this line
pos = dpos + estart;
done = pos >= estop;
if (++idash >= dashCount)
idash = 0;
doffset = 0; // full segment so no offset on next.
}
if (dpos > elen) { // dash extends this line
doffset = dashes[idash] - (dpos - elen); // subtract the part already used
pos = estop; // move pos to next path element
done = true;
} else { // Dash is on this line
pos = dpos + estart;
done = pos >= estop;
if (++idash >= dashCount)
idash = 0;
doffset = 0; // full segment so no offset on next.
}
hasMoveTo = false;
move_to_pos = e;
}
if (clipIt) {
hasMoveTo = false;
} else {
// skip costly dashing, just draw solid line
if (!hasMoveTo) {
emitMoveTo(move_to_pos.x, move_to_pos.y);
hasMoveTo = true;
}
emitLineTo(e.x, e.y);
}
move_to_pos = e;
}
// Dash away...

1
src/gui/painting/qstroker_p.h
View File

@ -268,6 +268,7 @@ public:
QStroker *stroker() const { return m_stroker; }
static QList<qfixed> patternForStyle(Qt::PenStyle style);
static int repetitionLimit() { return 10000; }
void setDashPattern(const QList<qfixed> &dashPattern) { m_dashPattern = dashPattern; }
QList<qfixed> dashPattern() const { return m_dashPattern; }