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authorAlan Alpert <alan.alpert@nokia.com>2011-08-02 11:26:24 +1000
committerQt by Nokia <qt-info@nokia.com>2011-08-05 10:55:30 +0200
commit4334d07f52dfc1d7fce6ebbad6e9f377ef33dedb (patch)
treeca1e4d1db6318675e3851bdb130b1cd08940cb95
parent1eea4773236a246cf6185f69374c27852905ff5e (diff)
Use more numerically robust algorithm to compute QBezier::pointAt().
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>
-rw-r--r--src/gui/painting/qbezier_p.h36
-rw-r--r--tests/auto/qpainterpath/tst_qpainterpath.cpp21
2 files changed, 39 insertions, 18 deletions
diff --git a/src/gui/painting/qbezier_p.h b/src/gui/painting/qbezier_p.h
index 399dd89140..f1f7eb155a 100644
--- a/src/gui/painting/qbezier_p.h
+++ b/src/gui/painting/qbezier_p.h
@@ -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
diff --git a/tests/auto/qpainterpath/tst_qpainterpath.cpp b/tests/auto/qpainterpath/tst_qpainterpath.cpp
index 3941a11460..33315adc06 100644
--- a/tests/auto/qpainterpath/tst_qpainterpath.cpp
+++ b/tests/auto/qpainterpath/tst_qpainterpath.cpp
@@ -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"