Fixed bug in QPainterPath::intersected().

When we compute the angle delta we can't use qFuzzyCompare as it will
cause slightly negative deltas to be snapped to 0, causing the winged
edge builder to put path edges in the wrong order.

Task-number: QTBUG-3778
Reviewed-by: Trond

2 files changed, 32 insertions, 4 deletions

diff --git a/src/gui/painting/qpathclipper.cpp b/src/gui/painting/qpathclipper.cpp
index 949a820..00e74ba 100644
--- a/src/gui/painting/qpathclipper.cpp
+++ b/src/gui/painting/qpathclipper.cpp
@@ -935,10 +935,9 @@ qreal QWingedEdge::delta(int vertex, int a, int b) const
 
     qreal result = b_angle - a_angle;
 
-    if (qFuzzyIsNull(result) || qFuzzyCompare(result, 128))
-        return 0;
-
-    if (result < 0)
+    if (result >= 128.)
+        return result - 128.;
+    else if (result < 0)
         return result + 128.;
     else
         return result;
diff --git a/tests/auto/qpathclipper/tst_qpathclipper.cpp b/tests/auto/qpathclipper/tst_qpathclipper.cpp
index 38d253a..db5a13e 100644
--- a/tests/auto/qpathclipper/tst_qpathclipper.cpp
+++ b/tests/auto/qpathclipper/tst_qpathclipper.cpp
@@ -95,6 +95,8 @@ private slots:
 
     void task209056();
     void task251909();
+
+    void qtbug3778();
 };
 
 Q_DECLARE_METATYPE(QPainterPath)
@@ -1346,6 +1348,33 @@ void tst_QPathClipper::task251909()
     QVERIFY(result.elementCount() <= 5);
 }
 
+void tst_QPathClipper::qtbug3778()
+{
+    QPainterPath path1;
+    path1.moveTo(200, 3.22409e-5);
+    // e-5 and higher leads to a bug
+    // Using 3.22409e-4 starts to work correctly
+    path1.lineTo(0, 0);
+    path1.lineTo(1.07025e-13, 1450);
+    path1.lineTo(750, 950);
+    path1.lineTo(950, 750);
+    path1.lineTo(200, 3.22409e-13);
+
+    QPainterPath path2;
+    path2.moveTo(0, 0);
+    path2.lineTo(200, 800);
+    path2.lineTo(600, 1500);
+    path2.lineTo(1500, 1400);
+    path2.lineTo(1900, 1200);
+    path2.lineTo(2000, 1000);
+    path2.lineTo(1400, 0);
+    path2.lineTo(0, 0);
+
+    QPainterPath p12 = path1.intersected(path2);
+
+    QVERIFY(p12.contains(QPointF(100, 100)));
+}
+
 QTEST_APPLESS_MAIN(tst_QPathClipper)