Make QPen default to 1-width non-cosmetic.

Use the Qt4CompatiblePainting render hint when painting with QPainter to
treat default constructed QPens as cosmetic still.

The NonCosmeticDefaultPen render hint gets documented as obsolete, since
it was in any case not respected by the raster nor OpenGL paint engine.

Change-Id: I04d910e9700baf7f13a8aac07a3633014bb9283e
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>

14 files changed, 79 insertions, 83 deletions

diff --git a/src/gui/opengl/qopenglpaintengine.cpp b/src/gui/opengl/qopenglpaintengine.cpp
index e0f1fe50a6..8e967207d4 100644
--- a/src/gui/opengl/qopenglpaintengine.cpp
+++ b/src/gui/opengl/qopenglpaintengine.cpp
@@ -1194,7 +1194,7 @@ void QOpenGL2PaintEngineEx::stroke(const QVectorPath &path, const QPen &pen)
         return;
 
     QOpenGL2PaintEngineState *s = state();
-    if (pen.isCosmetic() && !qt_scaleForTransform(s->transform(), 0)) {
+    if (qt_pen_is_cosmetic(pen, state()->renderHints) && !qt_scaleForTransform(s->transform(), 0)) {
         // QTriangulatingStroker class is not meant to support cosmetically sheared strokes.
         QPaintEngineEx::stroke(path, pen);
         return;
@@ -1229,15 +1229,16 @@ void QOpenGL2PaintEngineExPrivate::stroke(const QVectorPath &path, const QPen &p
                                                         : QRectF(0, 0, width, height));
 
     if (penStyle == Qt::SolidLine) {
-        stroker.process(path, pen, clip);
+        stroker.process(path, pen, clip, s->renderHints);
 
     } else { // Some sort of dash
-        dasher.process(path, pen, clip);
+        dasher.process(path, pen, clip, s->renderHints);
 
         QVectorPath dashStroke(dasher.points(),
                                dasher.elementCount(),
-                               dasher.elementTypes());
-        stroker.process(dashStroke, pen, clip);
+                               dasher.elementTypes(),
+                               s->renderHints);
+        stroker.process(dashStroke, pen, clip, s->renderHints);
     }
 
     if (!stroker.vertexCount())
@@ -1261,7 +1262,7 @@ void QOpenGL2PaintEngineExPrivate::stroke(const QVectorPath &path, const QPen &p
                       ? qMax(pen.miterLimit() * width, width)
                       : width;
 
-        if (pen.isCosmetic())
+        if (qt_pen_is_cosmetic(pen, q->state()->renderHints))
             extra = extra * inverseScale;
 
         QRectF bounds = path.controlPointRect().adjusted(-extra, -extra, extra, extra);
diff --git a/src/gui/opengl/qtriangulatingstroker.cpp b/src/gui/opengl/qtriangulatingstroker.cpp
index 0be6e12721..6c8ab7d607 100644
--- a/src/gui/opengl/qtriangulatingstroker.cpp
+++ b/src/gui/opengl/qtriangulatingstroker.cpp
@@ -81,7 +81,7 @@ static inline void skipDuplicatePoints(const qreal **pts, const qreal *endPts)
     }
 }
 
-void QTriangulatingStroker::process(const QVectorPath &path, const QPen &pen, const QRectF &)
+void QTriangulatingStroker::process(const QVectorPath &path, const QPen &pen, const QRectF &, QPainter::RenderHints hints)
 {
     const qreal *pts = path.points();
     const QPainterPath::ElementType *types = path.elements();
@@ -95,7 +95,7 @@ void QTriangulatingStroker::process(const QVectorPath &path, const QPen &pen, co
 
     m_width = realWidth / 2;
 
-    bool cosmetic = pen.isCosmetic();
+    bool cosmetic = qt_pen_is_cosmetic(pen, hints);
     if (cosmetic) {
         m_width = m_width * m_inv_scale;
     }
@@ -519,14 +519,14 @@ QDashedStrokeProcessor::QDashedStrokeProcessor()
     m_dash_stroker.setCubicToHook(qdashprocessor_cubicTo);
 }
 
-void QDashedStrokeProcessor::process(const QVectorPath &path, const QPen &pen, const QRectF &clip)
+void QDashedStrokeProcessor::process(const QVectorPath &path, const QPen &pen, const QRectF &clip, QPainter::RenderHints hints)
 {
 
     const qreal *pts = path.points();
     const QPainterPath::ElementType *types = path.elements();
     int count = path.elementCount();
 
-    bool cosmetic = pen.isCosmetic();
+    bool cosmetic = qt_pen_is_cosmetic(pen, hints);
 
     m_points.reset();
     m_types.reset();
diff --git a/src/gui/opengl/qtriangulatingstroker_p.h b/src/gui/opengl/qtriangulatingstroker_p.h
index 295ddbab5a..ba21c0820f 100644
--- a/src/gui/opengl/qtriangulatingstroker_p.h
+++ b/src/gui/opengl/qtriangulatingstroker_p.h
@@ -55,7 +55,7 @@ class Q_GUI_EXPORT QTriangulatingStroker
 {
 public:
     QTriangulatingStroker() : m_vertices(0) {}
-    void process(const QVectorPath &path, const QPen &pen, const QRectF &clip);
+    void process(const QVectorPath &path, const QPen &pen, const QRectF &clip, QPainter::RenderHints hints);
 
     inline int vertexCount() const { return m_vertices.size(); }
     inline const float *vertices() const { return m_vertices.data(); }
@@ -97,7 +97,7 @@ class Q_GUI_EXPORT QDashedStrokeProcessor
 public:
     QDashedStrokeProcessor();
 
-    void process(const QVectorPath &path, const QPen &pen, const QRectF &clip);
+    void process(const QVectorPath &path, const QPen &pen, const QRectF &clip, QPainter::RenderHints hints);
 
     inline void addElement(QPainterPath::ElementType type, qreal x, qreal y) {
         m_points.add(x);
diff --git a/src/gui/painting/qcosmeticstroker.cpp b/src/gui/painting/qcosmeticstroker.cpp
index 2eab7b25c5..7fcab1f087 100644
--- a/src/gui/painting/qcosmeticstroker.cpp
+++ b/src/gui/painting/qcosmeticstroker.cpp
@@ -275,7 +275,7 @@ void QCosmeticStroker::setup()
     qreal width = state->lastPen.widthF();
     if (width == 0)
         opacity = 256;
-    else if (state->lastPen.isCosmetic())
+    else if (qt_pen_is_cosmetic(state->lastPen, state->renderHints))
         opacity = (int) 256*width;
     else
         opacity = (int) 256*width*state->txscale;
diff --git a/src/gui/painting/qpaintbuffer.cpp b/src/gui/painting/qpaintbuffer.cpp
index 1e5a00e835..d7b16114b8 100644
--- a/src/gui/painting/qpaintbuffer.cpp
+++ b/src/gui/painting/qpaintbuffer.cpp
@@ -680,7 +680,7 @@ void QPaintBufferEngine::penChanged()
         } else {
             qreal penWidth = (pen.widthF() == 0) ? 1 : pen.widthF();
             QPointF transformedWidth(penWidth, penWidth);
-            if (!pen.isCosmetic())
+            if (!qt_pen_is_cosmetic(pen, state()->renderHints))
                 transformedWidth = painter()->transform().map(transformedWidth);
             buffer->penWidthAdjustment = transformedWidth.x() / 2.0;
         }
diff --git a/src/gui/painting/qpaintengine.cpp b/src/gui/painting/qpaintengine.cpp
index 09b1f0a8e4..339421f5e2 100644
--- a/src/gui/painting/qpaintengine.cpp
+++ b/src/gui/painting/qpaintengine.cpp
@@ -445,7 +445,7 @@ void QPaintEngine::drawPoints(const QPointF *points, int pointCount)
     p->save();
 
     QTransform transform;
-    if (p->pen().isCosmetic()) {
+    if (qt_pen_is_cosmetic(p->pen(), p->renderHints())) {
         transform = p->transform();
         p->setTransform(QTransform());
     }
diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index e0eab8dc73..1a63ced897 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -771,7 +771,7 @@ void QRasterPaintEngine::updatePen(const QPen &pen)
     } else if (pen_style != Qt::NoPen) {
         if (!d->dashStroker)
             d->dashStroker.reset(new QDashStroker(&d->basicStroker));
-        if (pen.isCosmetic()) {
+        if (qt_pen_is_cosmetic(pen, s->renderHints)) {
             d->dashStroker->setClipRect(d->deviceRect);
         } else {
             // ### I've seen this inverted devrect multiple places now...
@@ -786,10 +786,11 @@ void QRasterPaintEngine::updatePen(const QPen &pen)
     }
 
     ensureRasterState(); // needed because of tx_noshear...
+    bool cosmetic = qt_pen_is_cosmetic(pen, s->renderHints);
     s->flags.fast_pen = pen_style > Qt::NoPen
             && s->penData.blend
-            && ((pen.isCosmetic() && penWidth <= 1)
-                || (!pen.isCosmetic() && s->flags.tx_noshear && penWidth * s->txscale <= 1));
+            && ((cosmetic && penWidth <= 1)
+                || (!cosmetic && s->flags.tx_noshear && penWidth * s->txscale <= 1));
 
     s->flags.non_complex_pen = qpen_capStyle(s->lastPen) <= Qt::SquareCap && s->flags.tx_noshear;
 
@@ -1610,7 +1611,7 @@ void QRasterPaintEngine::stroke(const QVectorPath &path, const QPen &pen)
         stroker.setLegacyRoundingEnabled(s->flags.legacy_rounding);
         stroker.drawPath(path);
     } else if (s->flags.non_complex_pen && path.shape() == QVectorPath::LinesHint) {
-        qreal width = s->lastPen.isCosmetic()
+        qreal width = qt_pen_is_cosmetic(s->lastPen, s->renderHints)
                       ? (qpen_widthf(s->lastPen) == 0 ? 1 : qpen_widthf(s->lastPen))
                       : qpen_widthf(s->lastPen) * s->txscale;
         int dashIndex = 0;
diff --git a/src/gui/painting/qpaintengineex.cpp b/src/gui/painting/qpaintengineex.cpp
index dd93a58635..113cbd8a8e 100644
--- a/src/gui/painting/qpaintengineex.cpp
+++ b/src/gui/painting/qpaintengineex.cpp
@@ -435,7 +435,7 @@ void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &pen)
     }
 
     if (pen.style() > Qt::SolidLine) {
-        if (pen.isCosmetic()) {
+        if (qt_pen_is_cosmetic(pen, state()->renderHints)){
             d->activeStroker->setClipRect(d->exDeviceRect);
         } else {
             QRectF clipRect = state()->matrix.inverted().mapRect(QRectF(d->exDeviceRect));
@@ -462,7 +462,7 @@ void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &pen)
         flags |= QVectorPath::CurvedShapeMask;
 
     // ### Perspective Xforms are currently not supported...
-    if (!pen.isCosmetic()) {
+    if (!qt_pen_is_cosmetic(pen, state()->renderHints)) {
         // We include cosmetic pens in this case to avoid having to
         // change the current transform. Normal transformed,
         // non-cosmetic pens will be transformed as part of fill
diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index 69267b259b..090faf15aa 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -897,26 +897,8 @@ void QPainterPrivate::updateState(QPainterState *newState)
 
     if (!newState) {
         engine->state = newState;
-
     } else if (newState->state() || engine->state!=newState) {
-        bool setNonCosmeticPen = (newState->renderHints & QPainter::NonCosmeticDefaultPen)
-                                 && newState->pen.widthF() == 0;
-        if (setNonCosmeticPen) {
-            // Override the default pen's cosmetic state if the
-            // NonCosmeticDefaultPen render hint is used.
-            QPen oldPen = newState->pen;
-            newState->pen.setWidth(1);
-            newState->pen.setCosmetic(false);
-            newState->dirtyFlags |= QPaintEngine::DirtyPen;
-
-            updateStateImpl(newState);
-
-            // Restore the state pen back to its default to preserve visible
-            // state.
-            newState->pen = oldPen;
-        } else {
-            updateStateImpl(newState);
-        }
+        updateStateImpl(newState);
     }
 }
 
@@ -1417,14 +1399,13 @@ void QPainterPrivate::updateState(QPainterState *newState)
     indicating that the engine should use fragment programs and offscreen
     rendering for antialiasing.
 
-    \value NonCosmeticDefaultPen The engine should interpret pens with a width
-    of 0 (which otherwise enables QPen::isCosmetic()) as being a non-cosmetic
-    pen with a width of 1.
+    \value NonCosmeticDefaultPen This value is obsolete, the default for QPen
+    is now non-cosmetic.
 
     \value Qt4CompatiblePainting Compatibility hint telling the engine to use the
     same X11 based fill rules as in Qt 4, where aliased rendering is offset
-    by slightly less than half a pixel. Potentially useful when porting a
-    Qt 4 application to Qt 5.
+    by slightly less than half a pixel. Also will treat default constructed pens
+    as cosmetic. Potentially useful when porting a Qt 4 application to Qt 5.
 
     \sa renderHints(), setRenderHint(), {QPainter#Rendering
     Quality}{Rendering Quality}, {Concentric Circles Example}
@@ -3849,13 +3830,10 @@ void QPainter::setPen(const QColor &color)
         return;
     }
 
-    if (d->state->pen.style() == Qt::SolidLine
-        && d->state->pen.widthF() == 0
-        && d->state->pen.isSolid()
-        && d->state->pen.color() == color)
-        return;
+    QPen pen(color.isValid() ? color : QColor(Qt::black));
 
-    QPen pen(color.isValid() ? color : QColor(Qt::black), 0, Qt::SolidLine);
+    if (d->state->pen == pen)
+        return;
 
     d->state->pen = pen;
     if (d->extended)
@@ -3904,7 +3882,7 @@ void QPainter::setPen(const QPen &pen)
 /*!
     \overload
 
-    Sets the painter's pen to have the given \a style, width 0 and
+    Sets the painter's pen to have the given \a style, width 1 and
     black color.
 */
 
@@ -3916,15 +3894,12 @@ void QPainter::setPen(Qt::PenStyle style)
         return;
     }
 
-    if (d->state->pen.style() == style
-        && (style == Qt::NoPen || (d->state->pen.widthF() == 0
-                                   && d->state->pen.isSolid()
-                                   && d->state->pen.color() == QColor(Qt::black))))
+    QPen pen = QPen(style);
+
+    if (d->state->pen == pen)
         return;
 
-    // QPen(Qt::NoPen) is to avoid creating QPenData, including its brush (from the color)
-    // Note that this works well as long as QPen(Qt::NoPen) returns a black, zero-width pen
-    d->state->pen = (style == Qt::NoPen) ? QPen(Qt::NoPen) : QPen(Qt::black, 0, style);
+    d->state->pen = pen;
 
     if (d->extended)
         d->extended->penChanged();
diff --git a/src/gui/painting/qpainter_p.h b/src/gui/painting/qpainter_p.h
index 6ad1cb07cc..0e46cee4b5 100644
--- a/src/gui/painting/qpainter_p.h
+++ b/src/gui/painting/qpainter_p.h
@@ -241,10 +241,6 @@ public:
     void updateMatrix();
     void updateInvMatrix();
 
-    int rectSubtraction() const {
-        return state->pen.style() != Qt::NoPen && state->pen.width() == 0 ? 1 : 0;
-    }
-
     void checkEmulation();
 
     static QPainterPrivate *get(QPainter *painter)
@@ -269,6 +265,11 @@ Q_GUI_EXPORT void qt_draw_helper(QPainterPrivate *p, const QPainterPath &path, Q
 
 QString qt_generate_brush_key(const QBrush &brush);
 
+inline bool qt_pen_is_cosmetic(const QPen &pen, QPainter::RenderHints hints)
+{
+    return pen.isCosmetic() || (const_cast<QPen &>(pen).data_ptr()->defaultWidth && (hints & QPainter::Qt4CompatiblePainting));
+}
+
 QT_END_NAMESPACE
 
 #endif // QPAINTER_P_H
diff --git a/src/gui/painting/qpdf.cpp b/src/gui/painting/qpdf.cpp
index d2aa938aed..1d07d44dd8 100644
--- a/src/gui/painting/qpdf.cpp
+++ b/src/gui/painting/qpdf.cpp
@@ -44,6 +44,7 @@
 #include <qfile.h>
 #include <qtemporaryfile.h>
 #include <private/qmath_p.h>
+#include <private/qpainter_p.h>
 #include <qnumeric.h>
 #include "private/qfont_p.h"
 #include <qimagewriter.h>
@@ -784,7 +785,7 @@ QPdf::Stroker::Stroker()
     basicStroker.setStrokeWidth(.1);
 }
 
-void QPdf::Stroker::setPen(const QPen &pen)
+void QPdf::Stroker::setPen(const QPen &pen, QPainter::RenderHints hints)
 {
     if (pen.style() == Qt::NoPen) {
         stroker = 0;
@@ -792,7 +793,7 @@ void QPdf::Stroker::setPen(const QPen &pen)
     }
     qreal w = pen.widthF();
     bool zeroWidth = w < 0.0001;
-    cosmeticPen = pen.isCosmetic();
+    cosmeticPen = qt_pen_is_cosmetic(pen, hints);
     if (zeroWidth)
         w = .1;
 
@@ -1198,12 +1199,14 @@ void QPdfEngine::updateState(const QPaintEngineState &state)
     if (flags & DirtyPen) {
         d->pen = state.pen();
         d->hasPen = d->pen.style() != Qt::NoPen;
-        d->stroker.setPen(d->pen);
+        d->stroker.setPen(d->pen, state.renderHints());
         QBrush penBrush = d->pen.brush();
         bool oldSimple = d->simplePen;
         d->simplePen = (d->hasPen && (penBrush.style() == Qt::SolidPattern) && penBrush.isOpaque());
         if (oldSimple != d->simplePen)
             flags |= DirtyTransform;
+    } else if (flags & DirtyHints) {
+        d->stroker.setPen(d->pen, state.renderHints());
     }
     if (flags & DirtyBrush) {
         d->brush = state.brush();
diff --git a/src/gui/painting/qpdf_p.h b/src/gui/painting/qpdf_p.h
index ba86803288..735c5d13e0 100644
--- a/src/gui/painting/qpdf_p.h
+++ b/src/gui/painting/qpdf_p.h
@@ -124,7 +124,7 @@ namespace QPdf {
 
     struct Stroker {
         Stroker();
-        void setPen(const QPen &pen);
+        void setPen(const QPen &pen, QPainter::RenderHints hints);
         void strokePath(const QPainterPath &path);
         ByteStream *stream;
         bool first;
diff --git a/src/gui/painting/qpen.cpp b/src/gui/painting/qpen.cpp
index d86a5f0392..6b71c3818f 100644
--- a/src/gui/painting/qpen.cpp
+++ b/src/gui/painting/qpen.cpp
@@ -86,7 +86,7 @@ typedef QPenPrivate QPenData;
 
     \snippet code/src_gui_painting_qpen.cpp 1
 
-    The default pen is a solid black brush with 0 width, square
+    The default pen is a solid black brush with 1 width, square
     cap style (Qt::SquareCap), and  bevel join style (Qt::BevelJoin).
 
     In addition QPen provides the color() and setColor()
@@ -230,9 +230,9 @@ typedef QPenPrivate QPenData;
   \internal
 */
 inline QPenPrivate::QPenPrivate(const QBrush &_brush, qreal _width, Qt::PenStyle penStyle,
-                                Qt::PenCapStyle _capStyle, Qt::PenJoinStyle _joinStyle)
+                                Qt::PenCapStyle _capStyle, Qt::PenJoinStyle _joinStyle, bool _defaultWidth)
     : ref(1), dashOffset(0), miterLimit(2),
-      cosmetic(false)
+      cosmetic(false), defaultWidth(_defaultWidth)
 {
     width = _width;
     brush = _brush;
@@ -261,12 +261,12 @@ public:
 };
 
 Q_GLOBAL_STATIC_WITH_ARGS(QPenDataHolder, defaultPenInstance,
-                          (Qt::black, 0, Qt::SolidLine, qpen_default_cap, qpen_default_join))
+                          (Qt::black, 1, Qt::SolidLine, qpen_default_cap, qpen_default_join))
 Q_GLOBAL_STATIC_WITH_ARGS(QPenDataHolder, nullPenInstance,
-                          (Qt::black, 0, Qt::NoPen, qpen_default_cap, qpen_default_join))
+                          (Qt::black, 1, Qt::NoPen, qpen_default_cap, qpen_default_join))
 
 /*!
-    Constructs a default black solid line pen with 0 width.
+    Constructs a default black solid line pen with 1 width.
 */
 
 QPen::QPen()
@@ -276,7 +276,7 @@ QPen::QPen()
 }
 
 /*!
-    Constructs a black pen with 0 width and the given \a style.
+    Constructs a black pen with 1 width and the given \a style.
 
     \sa setStyle()
 */
@@ -287,20 +287,20 @@ QPen::QPen(Qt::PenStyle style)
         d = nullPenInstance()->pen;
         d->ref.ref();
     } else {
-        d = new QPenData(Qt::black, 0, style, qpen_default_cap, qpen_default_join);
+        d = new QPenData(Qt::black, 1, style, qpen_default_cap, qpen_default_join);
     }
 }
 
 
 /*!
-    Constructs a solid line pen with 0 width and the given \a color.
+    Constructs a solid line pen with 1 width and the given \a color.
 
     \sa setBrush(), setColor()
 */
 
 QPen::QPen(const QColor &color)
 {
-    d = new QPenData(color, 0, Qt::SolidLine, qpen_default_cap, qpen_default_join);
+    d = new QPenData(color, 1, Qt::SolidLine, qpen_default_cap, qpen_default_join);
 }
 
 
@@ -315,7 +315,7 @@ QPen::QPen(const QColor &color)
 
 QPen::QPen(const QBrush &brush, qreal width, Qt::PenStyle s, Qt::PenCapStyle c, Qt::PenJoinStyle j)
 {
-    d = new QPenData(brush, width, s, c, j);
+    d = new QPenData(brush, width, s, c, j, false);
 }
 
 /*!
@@ -655,12 +655,15 @@ void QPen::setWidth(int width)
 
 void QPen::setWidthF(qreal width)
 {
-    if (width < 0.f)
+    if (width < 0.f) {
         qWarning("QPen::setWidthF: Setting a pen width with a negative value is not defined");
+        return;
+    }
     if (qAbs(d->width - width) < 0.00000001f)
         return;
     detach();
     d->width = width;
+    d->defaultWidth = false;
 }
 
 
@@ -785,8 +788,7 @@ bool QPen::isSolid() const
     used with. Drawing a shape with a cosmetic pen ensures that its
     outline will have the same thickness at different scale factors.
 
-    A zero width pen is cosmetic by default; pens with a non-zero width
-    are non-cosmetic.
+    A zero width pen is cosmetic by default.
 
     \sa setCosmetic(), widthF()
 */
@@ -848,7 +850,8 @@ bool QPen::operator==(const QPen &p) const
                 || (qFuzzyCompare(pdd->dashOffset, dd->dashOffset) &&
                     pdd->dashPattern == dd->dashPattern))
             && p.d->brush == d->brush
-            && pdd->cosmetic == dd->cosmetic);
+            && pdd->cosmetic == dd->cosmetic
+            && pdd->defaultWidth == dd->defaultWidth);
 }
 
 
@@ -910,6 +913,8 @@ QDataStream &operator<<(QDataStream &s, const QPen &p)
         }
         if (s.version() >= 9)
             s << double(p.dashOffset());
+        if (s.version() >= QDataStream::Qt_5_0)
+            s << bool(dd->defaultWidth);
     }
     return s;
 }
@@ -935,6 +940,7 @@ QDataStream &operator>>(QDataStream &s, QPen &p)
     QVector<qreal> dashPattern;
     double dashOffset = 0;
     bool cosmetic = false;
+    bool defaultWidth = false;
     if (s.version() < QDataStream::Qt_4_3) {
         quint8 style8;
         s >> style8;
@@ -967,6 +973,13 @@ QDataStream &operator>>(QDataStream &s, QPen &p)
             s >> dashOffset;
     }
 
+    if (s.version() >= QDataStream::Qt_5_0) {
+        s >> defaultWidth;
+    } else {
+        // best we can do for legacy pens
+        defaultWidth = qFuzzyIsNull(width);
+    }
+
     p.detach();
     QPenData *dd = static_cast<QPenData *>(p.d);
     dd->width = width;
@@ -978,6 +991,7 @@ QDataStream &operator>>(QDataStream &s, QPen &p)
     dd->miterLimit = miterLimit;
     dd->dashOffset = dashOffset;
     dd->cosmetic = cosmetic;
+    dd->defaultWidth = defaultWidth;
 
     return s;
 }
diff --git a/src/gui/painting/qpen_p.h b/src/gui/painting/qpen_p.h
index 93f2532e63..4b2fcaa71d 100644
--- a/src/gui/painting/qpen_p.h
+++ b/src/gui/painting/qpen_p.h
@@ -60,7 +60,7 @@ QT_BEGIN_NAMESPACE
 class QPenPrivate {
 public:
     QPenPrivate(const QBrush &brush, qreal width, Qt::PenStyle, Qt::PenCapStyle,
-                Qt::PenJoinStyle _joinStyle);
+                Qt::PenJoinStyle _joinStyle, bool defaultWidth = true);
     QAtomicInt ref;
     qreal width;
     QBrush brush;
@@ -71,6 +71,7 @@ public:
     qreal dashOffset;
     qreal miterLimit;
     uint cosmetic : 1;
+    uint defaultWidth : 1; // default-constructed width? used for cosmetic pen compatibility
 };
 
 QT_END_NAMESPACE