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Use more numerically robust algorithm to compute QBezier::pointAt().

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QBezier::pointAt() could potentially return values outside the bezier's
bounds, even when the bezier was a straight horizontal line. For
example, with y = 0.5, it would produce y=0.5 or y=0.49999999999999 for
different values of t, which when rounded cause jittering in a QML
PathView.

Task-number: QTBUG-17007
Task-number: QTBUG-18133
Cherry-pick-of: 8b66982ec7b4b5d2071931c288973dce73dc9875
Change-Id: I4ecac7b9085aaaaaaaaaaaaaaaaaaaaaa7d7b0bc
Reviewed-on: http://codereview.qt.nokia.com/2467
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>
This commit is contained in:
Alan Alpert 2011-08-02 11:26:24 +10:00 committed by Qt by Nokia
parent 1eea477323
commit 4334d07f52
2 changed files with 39 additions and 18 deletions
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36
src/gui/painting/qbezier_p.h
View File

@ -162,27 +162,27 @@ inline void QBezier::coefficients(qreal t, qreal &a, qreal &b, qreal &c, qreal &
inline QPointF QBezier::pointAt(qreal t) const
{
#if 1
qreal a, b, c, d;
coefficients(t, a, b, c, d);
return QPointF(a*x1 + b*x2 + c*x3 + d*x4, a*y1 + b*y2 + c*y3 + d*y4);
#else
// numerically more stable:
qreal x, y;
qreal m_t = 1. - t;
qreal a = x1*m_t + x2*t;
qreal b = x2*m_t + x3*t;
qreal c = x3*m_t + x4*t;
a = a*m_t + b*t;
b = b*m_t + c*t;
qreal x = a*m_t + b*t;
qreal a = y1*m_t + y2*t;
qreal b = y2*m_t + y3*t;
qreal c = y3*m_t + y4*t;
a = a*m_t + b*t;
b = b*m_t + c*t;
qreal y = a*m_t + b*t;
{
qreal a = x1*m_t + x2*t;
qreal b = x2*m_t + x3*t;
qreal c = x3*m_t + x4*t;
a = a*m_t + b*t;
b = b*m_t + c*t;
x = a*m_t + b*t;
}
{
qreal a = y1*m_t + y2*t;
qreal b = y2*m_t + y3*t;
qreal c = y3*m_t + y4*t;
a = a*m_t + b*t;
b = b*m_t + c*t;
y = a*m_t + b*t;
}
return QPointF(x, y);
#endif
}
inline QPointF QBezier::normalVector(qreal t) const

21
tests/auto/qpainterpath/tst_qpainterpath.cpp
View File

@ -114,6 +114,8 @@ private slots:
void connectPathMoveTo();
void translate();
void lineWithinBounds();
};
// Testing get/set functions
@ -1306,6 +1308,25 @@ void tst_QPainterPath::translate()
QCOMPARE(complexPath.translated(-offset), untranslatedComplexPath);
}
void tst_QPainterPath::lineWithinBounds()
{
const int iteration_count = 3;
volatile const qreal yVal = 0.5;
QPointF a(0.0, yVal);
QPointF b(1000.0, yVal);
QPointF c(2000.0, yVal);
QPointF d(3000.0, yVal);
QPainterPath path;
path.moveTo(QPointF(0, yVal));
path.cubicTo(QPointF(1000.0, yVal), QPointF(2000.0, yVal), QPointF(3000.0, yVal));
for(int i=0; i<=iteration_count; i++) {
qreal actual = path.pointAtPercent(qreal(i) / iteration_count).y();
QVERIFY(actual == yVal); // don't use QCOMPARE, don't want fuzzy comparison
}
}
QTEST_APPLESS_MAIN(tst_QPainterPath)
#include "tst_qpainterpath.moc"