Painting: Fix capping of polylines having endpoint == startpoint

A polyline should not be closed like a polygon, even if the start and
end points are identical. But when the primitive was broken down to a
vector path, the stroker no longer had available the information that
it should be open, and so would join the start and end points.

Fixes: QTBUG-65393
Change-Id: I0a566f91cf1a2843fda662b393dbae78c3c38f06
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

4 files changed, 15 insertions, 4 deletions

diff --git a/src/gui/painting/qpaintengineex.cpp b/src/gui/painting/qpaintengineex.cpp
index 9f07af92e4..81ce5c60c5 100644
--- a/src/gui/painting/qpaintengineex.cpp
+++ b/src/gui/painting/qpaintengineex.cpp
@@ -439,6 +439,9 @@ void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &pen)
         }
     }
 
+    if (d->activeStroker == &d->stroker)
+        d->stroker.setForceOpen(path.hasExplicitOpen());
+
     const QPainterPath::ElementType *types = path.elements();
     const qreal *points = path.points();
     int pointCount = path.elementCount();
diff --git a/src/gui/painting/qstroker.cpp b/src/gui/painting/qstroker.cpp
index 4776545be6..0a3d802b21 100644
--- a/src/gui/painting/qstroker.cpp
+++ b/src/gui/painting/qstroker.cpp
@@ -369,7 +369,8 @@ void QStrokerOps::strokeEllipse(const QRectF &rect, void *data, const QTransform
 QStroker::QStroker()
     : m_capStyle(SquareJoin), m_joinStyle(FlatJoin),
       m_back1X(0), m_back1Y(0),
-      m_back2X(0), m_back2Y(0)
+      m_back2X(0), m_back2Y(0),
+      m_forceOpen(false)
 {
     m_strokeWidth = qt_real_to_fixed(1);
     m_miterLimit = qt_real_to_fixed(2);
@@ -748,7 +749,7 @@ template <class Iterator> bool qt_stroke_side(Iterator *it,
         }
     }
 
-    if (start == prev) {
+    if (start == prev && !stroker->forceOpen()) {
         // closed subpath, join first and last point
 #ifdef QPP_STROKE_DEBUG
         qDebug("\n ---> (side) closed subpath");
diff --git a/src/gui/painting/qstroker_p.h b/src/gui/painting/qstroker_p.h
index 1a7c184e1a..722a0904f3 100644
--- a/src/gui/painting/qstroker_p.h
+++ b/src/gui/painting/qstroker_p.h
@@ -222,6 +222,9 @@ public:
     void setMiterLimit(qfixed length) { m_miterLimit = length; }
     qfixed miterLimit() const { return m_miterLimit; }
 
+    void setForceOpen(bool state) { m_forceOpen = state; }
+    bool forceOpen() { return m_forceOpen; }
+
     void joinPoints(qfixed x, qfixed y, const QLineF &nextLine, LineJoinMode join);
     inline void emitMoveTo(qfixed x, qfixed y);
     inline void emitLineTo(qfixed x, qfixed y);
@@ -247,6 +250,8 @@ protected:
 
     qfixed m_back2X;
     qfixed m_back2Y;
+
+    bool m_forceOpen;
 };
 
 class Q_GUI_EXPORT QDashStroker : public QStrokerOps
diff --git a/src/gui/painting/qvectorpath_p.h b/src/gui/painting/qvectorpath_p.h
index d1b08ed423..8580598784 100644
--- a/src/gui/painting/qvectorpath_p.h
+++ b/src/gui/painting/qvectorpath_p.h
@@ -99,7 +99,8 @@ public:
         // Shape rendering specifiers...
         OddEvenFill             = 0x1000,
         WindingFill             = 0x2000,
-        ImplicitClose           = 0x4000
+        ImplicitClose           = 0x4000,
+        ExplicitOpen            = 0x8000
     };
 
     // ### Falcon: introduca a struct XY for points so lars is not so confused...
@@ -124,6 +125,7 @@ public:
 
     inline bool isCacheable() const { return m_hints & ShouldUseCacheHint; }
     inline bool hasImplicitClose() const { return m_hints & ImplicitClose; }
+    inline bool hasExplicitOpen() const { return m_hints & ExplicitOpen; }
     inline bool hasWindingFill() const { return m_hints & WindingFill; }
 
     inline void makeCacheable() const { m_hints |= ShouldUseCacheHint; m_cache = 0; }
@@ -142,7 +144,7 @@ public:
         case QPaintEngine::ConvexMode: return ConvexPolygonHint | ImplicitClose;
         case QPaintEngine::OddEvenMode: return PolygonHint | OddEvenFill | ImplicitClose;
         case QPaintEngine::WindingMode: return PolygonHint | WindingFill | ImplicitClose;
-        case QPaintEngine::PolylineMode: return PolygonHint;
+        case QPaintEngine::PolylineMode: return PolygonHint | ExplicitOpen;
         default: return 0;
         }
     }