From 081d835c040a90f8ee76807354355062ac521dfb Mon Sep 17 00:00:00 2001

From: Eirik Aavitsland <eirik.aavitsland@qt.io>

Date: Tue, 13 Apr 2021 14:23:45 +0200

Subject: [PATCH] Avoid processing-intensive painting of high number of tiny

 dashes

When stroking a dashed path, an unnecessary amount of processing would

be spent if there is a huge number of dashes visible, e.g. because of

scaling. Since the dashes are too small to be indivdually visible

anyway, just replace with a semi-transparent solid line for such

cases.

Pick-to: 6.1 6.0 5.15

Change-Id: I9e9f7861257ad5bce46a0cf113d1a9d7824911e6

Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

(cherry picked from commit f4d791b330d02777fcaf02938732892eb3167e9b)

* asturmlechner 2021-08-21:

Conflict from preceding 94dd2ceb in dev branch:

	src/gui/painting/qpaintengineex.cpp

	Resolved via:

     if (pen.style() > Qt::SolidLine) {

         QRectF cpRect = path.controlPointRect();

         const QTransform &xf = state()->matrix;

-        if (pen.isCosmetic()) {

+        if (qt_pen_is_cosmetic(pen, state()->renderHints)){

             clipRect = d->exDeviceRect;

             cpRect.translate(xf.dx(), xf.dy());

         } else {

FTBFS from preceding 471e4fcb in dev branch changing QVector to QList:

	Resolved via:

         QRectF extentRect = cpRect.adjusted(-pw, -pw, pw, pw) & clipRect;

         qreal extent = qMax(extentRect.width(), extentRect.height());

         qreal patternLength = 0;

-        const QList<qreal> pattern = pen.dashPattern();

+        const QVector<qreal> pattern = pen.dashPattern();

         const int patternSize = qMin(pattern.size(), 32);

         for (int i = 0; i < patternSize; i++)

             patternLength += qMax(pattern.at(i), qreal(0));

---

 src/gui/painting/qpaintengineex.cpp           | 44 +++++++++++++++----

 .../other/lancelot/scripts/tinydashes.qps     | 34 ++++++++++++++

 2 files changed, 69 insertions(+), 9 deletions(-)

 create mode 100644 tests/auto/other/lancelot/scripts/tinydashes.qps

diff --git a/src/gui/painting/qpaintengineex.cpp b/src/gui/painting/qpaintengineex.cpp

index 5d8f89eadd..55fdb0c2a0 100644

--- a/src/gui/painting/qpaintengineex.cpp

+++ b/src/gui/painting/qpaintengineex.cpp

@@ -385,7 +385,7 @@ QPainterState *QPaintEngineEx::createState(QPainterState *orig) const

 Q_GUI_EXPORT extern bool qt_scaleForTransform(const QTransform &transform, qreal *scale); // qtransform.cpp

-void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &pen)

+void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &inPen)

 {

 #ifdef QT_DEBUG_DRAW

     qDebug() << "QPaintEngineEx::stroke()" << pen;

@@ -403,6 +403,38 @@ void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &pen)

         d->stroker.setCubicToHook(qpaintengineex_cubicTo);

     }

+    QRectF clipRect;

+    QPen pen = inPen;

+    if (pen.style() > Qt::SolidLine) {

+        QRectF cpRect = path.controlPointRect();

+        const QTransform &xf = state()->matrix;

+        if (qt_pen_is_cosmetic(pen, state()->renderHints)){

+            clipRect = d->exDeviceRect;

+            cpRect.translate(xf.dx(), xf.dy());

+        } else {

+            clipRect = xf.inverted().mapRect(QRectF(d->exDeviceRect));

+        }

+        // Check to avoid generating unwieldy amount of dashes that will not be visible anyway

+        QRectF extentRect = cpRect & clipRect;

+        qreal extent = qMax(extentRect.width(), extentRect.height());

+        qreal patternLength = 0;

+        const QVector<qreal> pattern = pen.dashPattern();

+        const int patternSize = qMin(pattern.size(), 32);

+        for (int i = 0; i < patternSize; i++)

+            patternLength += qMax(pattern.at(i), qreal(0));

+        if (pen.widthF())

+            patternLength *= pen.widthF();

+        if (qFuzzyIsNull(patternLength)) {

+            pen.setStyle(Qt::NoPen);

+        } else if (extent / patternLength > 10000) {

+            // approximate stream of tiny dashes with semi-transparent solid line

+            pen.setStyle(Qt::SolidLine);

+            QColor color(pen.color());

+            color.setAlpha(color.alpha() / 2);

+            pen.setColor(color);

+        }

+    }

+

     if (!qpen_fast_equals(pen, d->strokerPen)) {

         d->strokerPen = pen;

         d->stroker.setJoinStyle(pen.joinStyle());

@@ -430,14 +462,8 @@ void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &pen)

         return;

     }

-    if (pen.style() > Qt::SolidLine) {

-        if (qt_pen_is_cosmetic(pen, state()->renderHints)){

-            d->activeStroker->setClipRect(d->exDeviceRect);

-        } else {

-            QRectF clipRect = state()->matrix.inverted().mapRect(QRectF(d->exDeviceRect));

-            d->activeStroker->setClipRect(clipRect);

-        }

-    }

+    if (!clipRect.isNull())

+        d->activeStroker->setClipRect(clipRect);

     if (d->activeStroker == &d->stroker)

         d->stroker.setForceOpen(path.hasExplicitOpen());

diff --git a/tests/auto/other/lancelot/scripts/tinydashes.qps b/tests/auto/other/lancelot/scripts/tinydashes.qps

new file mode 100644

index 0000000000..d41ced7f5f

--- /dev/null

+++ b/tests/auto/other/lancelot/scripts/tinydashes.qps

@@ -0,0 +1,34 @@

+# Version: 1

+# CheckVsReference: 5%

+

+path_addEllipse mypath 20.0 20.0 200.0 200.0

+

+save

+setPen blue 20 SolidLine FlatCap

+pen_setCosmetic true

+pen_setDashPattern [ 0.0004 0.0004 ]

+setBrush yellow

+

+drawPath mypath

+translate 300 0

+setRenderHint Antialiasing true

+drawPath mypath

+restore

+

+path_addEllipse bigpath 200000.0 200000.0 2000000.0 2000000.0

+

+setPen blue 20 DotLine FlatCap

+setBrush yellow

+

+save

+translate 0 300

+scale 0.0001 0.00011

+drawPath bigpath

+restore

+

+save

+translate 300 300

+setRenderHint Antialiasing true

+scale 0.0001 0.00011

+drawPath bigpath

+restore

--

GitLab

From 6b400e3147dcfd8cc3a393ace1bd118c93762e0c Mon Sep 17 00:00:00 2001

From: Eirik Aavitsland <eirik.aavitsland@qt.io>

Date: Fri, 23 Jul 2021 15:53:56 +0200

Subject: [PATCH] Improve fix for avoiding huge number of tiny dashes

MIME-Version: 1.0

Content-Type: text/plain; charset=UTF-8

Content-Transfer-Encoding: 8bit

Some pathological cases were not caught by the previous fix.

Fixes: QTBUG-95239

Pick-to: 6.2 6.1 5.15

Change-Id: I0337ee3923ff93ccb36c4d7b810a9c0667354cc5

Reviewed-by: Robert Löhning <robert.loehning@qt.io>

---

 src/gui/painting/qpaintengineex.cpp | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/gui/painting/qpaintengineex.cpp b/src/gui/painting/qpaintengineex.cpp

index 2997d533107..22e9a621c3c 100644

--- a/src/gui/painting/qpaintengineex.cpp

+++ b/src/gui/painting/qpaintengineex.cpp

@@ -426,7 +426,7 @@ void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &inPen)

             patternLength *= pen.widthF();

         if (qFuzzyIsNull(patternLength)) {

             pen.setStyle(Qt::NoPen);

-        } else if (extent / patternLength > 10000) {

+        } else if (qFuzzyIsNull(extent) || extent / patternLength > 10000) {

             // approximate stream of tiny dashes with semi-transparent solid line

             pen.setStyle(Qt::SolidLine);

             QColor color(pen.color());

From 427df34efdcb56582a9ae9f7d2d1f39eeff70328 Mon Sep 17 00:00:00 2001

From: Eirik Aavitsland <eirik.aavitsland@qt.io>

Date: Fri, 30 Jul 2021 13:03:49 +0200

Subject: [PATCH] Refix for avoiding huge number of tiny dashes

Previous fix hit too widely so some valid horizontal and vertical

lines were affected; the root problem being that such lines have an

empty control point rect (width or height is 0). Fix by caculating in

the pen width.

Pick-to: 6.2 6.1 5.15

Change-Id: I7a436e873f6d485028f6759d0e2c6456f07eebdc

Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

(cherry picked from commit 84aba80944a2e1c3058d7a1372e0e66676411884)

---

 src/gui/painting/qpaintengineex.cpp           |  8 ++---

 .../gui/painting/qpainter/tst_qpainter.cpp    | 31 +++++++++++++++++++

 2 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/src/gui/painting/qpaintengineex.cpp b/src/gui/painting/qpaintengineex.cpp

index 19e4b23423..9fe510827a 100644

--- a/src/gui/painting/qpaintengineex.cpp

+++ b/src/gui/painting/qpaintengineex.cpp

@@ -415,18 +415,18 @@ void QPaintEngineEx::stroke(const QVectorPath &path, const QPen &inPen)

             clipRect = xf.inverted().mapRect(QRectF(d->exDeviceRect));

         }

         // Check to avoid generating unwieldy amount of dashes that will not be visible anyway

-        QRectF extentRect = cpRect & clipRect;

+        qreal pw = pen.widthF() ? pen.widthF() : 1;

+        QRectF extentRect = cpRect.adjusted(-pw, -pw, pw, pw) & clipRect;

         qreal extent = qMax(extentRect.width(), extentRect.height());

         qreal patternLength = 0;

         const QVector<qreal> pattern = pen.dashPattern();

         const int patternSize = qMin(pattern.size(), 32);

         for (int i = 0; i < patternSize; i++)

             patternLength += qMax(pattern.at(i), qreal(0));

-        if (pen.widthF())

-            patternLength *= pen.widthF();

+        patternLength *= pw;

         if (qFuzzyIsNull(patternLength)) {

             pen.setStyle(Qt::NoPen);

-        } else if (qFuzzyIsNull(extent) || extent / patternLength > 10000) {

+        } else if (extent / patternLength > 10000) {

             // approximate stream of tiny dashes with semi-transparent solid line

             pen.setStyle(Qt::SolidLine);

             QColor color(pen.color());

diff --git a/tests/auto/gui/painting/qpainter/tst_qpainter.cpp b/tests/auto/gui/painting/qpainter/tst_qpainter.cpp

index 42e98ce363..d7c3f95f1d 100644

--- a/tests/auto/gui/painting/qpainter/tst_qpainter.cpp

+++ b/tests/auto/gui/painting/qpainter/tst_qpainter.cpp

@@ -308,6 +308,7 @@ private slots:

     void fillPolygon();

     void drawImageAtPointF();

+    void scaledDashes();

 private:

     void fillData();

@@ -5468,6 +5469,36 @@ void tst_QPainter::drawImageAtPointF()

     paint.end();

 }

+void tst_QPainter::scaledDashes()

+{

+    // Test that we do not hit the limit-huge-number-of-dashes path

+    QRgb fore = qRgb(0, 0, 0xff);

+    QRgb back = qRgb(0xff, 0xff, 0);

+    QImage image(5, 32, QImage::Format_RGB32);

+    image.fill(back);

+    QPainter p(&image);

+    QPen pen(QColor(fore), 3, Qt::DotLine);

+    p.setPen(pen);

+    p.scale(1, 2);

+    p.drawLine(2, 0, 2, 16);

+    p.end();

+

+    bool foreFound = false;

+    bool backFound = false;

+    int i = 0;

+    while (i < 32 && (!foreFound || !backFound)) {

+        QRgb pix = image.pixel(3, i);

+        if (pix == fore)

+            foreFound = true;

+        else if (pix == back)

+            backFound = true;

+        i++;

+    }

+

+    QVERIFY(foreFound);

+    QVERIFY(backFound);

+}

+

 QTEST_MAIN(tst_QPainter)

 #include "tst_qpainter.moc"

--

GitLab