QPdf: Force miter limit into valid range

Miter limits below 1.0 are not valid in PDF and trigger an error in the
Reader. This change enforces a minimum miter limit of 1.0, and it adds
a manual test for producing a PDF file demonstrating this issue.

Task-number: QTBUG-52641
Change-Id: I1c78b1c4a44579e95e1cddfb459926d304e60165
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

src/gui/painting/qpdf.cpp

@@ -1196,7 +1196,7 @@ void QPdfEngine::setPen()
     switch(d->pen.joinStyle()) {
     case Qt::MiterJoin:
     case Qt::SvgMiterJoin:
-        *d->currentPage << d->pen.miterLimit() << "M ";
+        *d->currentPage << qMax(qreal(1.0), d->pen.miterLimit()) << "M ";
         pdfJoinStyle = 0;
         break;
     case Qt::BevelJoin:

tests/manual/manual.pro

@@ -31,6 +31,7 @@ qsysinfo \
 qtabletevent \
 qtexteditlist \
 qtbug-8933 \
+qtbug-52641 \
 qtouchevent \
 touch \
 qwidget_zorder \

tests/manual/qtbug-52641/main.cpp

+/****************************************************************************
+**
+** Copyright (C) 2016 Kai Pastor
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QApplication>
+#include <QFileDialog>
+#include <QPainter>
+#include <QPdfWriter>
+
+int main(int argc, char *argv[])
+{
+    QApplication a(argc, argv);
+
+    QString filepath = QFileDialog::getSaveFileName(nullptr, "Save File", "",
+                                                    "PDF files (*.pdf)");
+    if (filepath.isEmpty())
+        return 1;
+    QPdfWriter writer(filepath);
+    writer.setPageSize(QPageSize(QPageSize::A4));
+    writer.setResolution(300);
+
+    QPainterPath path;
+    path.moveTo(0,0);
+    path.lineTo(1000,0);
+    path.lineTo(1000,1000);
+    path.lineTo(0,800);
+    path.lineTo(500,100);
+    path.lineTo(800,900);
+    path.lineTo(300,600);
+
+    QPen pen;
+    pen.setWidth(30);
+    pen.setJoinStyle(Qt::MiterJoin);
+
+    // The black path on the first page must always be visible in the PDF viewer.
+    QPainter p(&writer);
+    pen.setMiterLimit(6.0);
+    p.setPen(pen);
+    p.drawPath(path);
+
+    // If a miter limit below 1.0 is written to the PDF,
+    // broken PDF viewers may not show the red path on the second page.
+    writer.newPage();
+    pen.setMiterLimit(0.6);
+    pen.setColor(Qt::red);
+    p.setPen(pen);
+    p.drawPath(path);
+
+    p.end();
+    return 0;
+}

tests/manual/qtbug-52641/qtbug-52641.pro

+TARGET   = qtbug-52641
+TEMPLATE = app
+QT       = core gui widgets
+SOURCES  = main.cpp
+