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
Reviewed-by: Kim

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/auto/qpainterpath/tst_qpainterpath.cpp b/tests/auto/qpainterpath/tst_qpainterpath.cpp
index 3941a11..33315ad 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"