Brush up the mandelbrot example

The example refines the image by running a number of passes
with increasing number of iterations, which is not really
visible to the user. Set an informational text string on
the generated image which provides this information
along with the elapsed time.
The idea is to do the same to the corresponding
Qt for Python example to have some sort of speed comparison
for number crunching.

Add a command line option for the number of passes.

Make the window a bit larger to accommodate the
information.

Change-Id: I2afc1009ab53b580123d82a6aa645d9ffaa63ea2
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

examples/corelib/threads/mandelbrot/main.cpp

@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2021 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
@@ -52,11 +52,43 @@
 
 #include <QApplication>
 
+#include <QScreen>
+
+#include <QCommandLineParser>
+#include <QCommandLineOption>
+#include <QDebug>
+#include <QRect>
+
 //! [0]
 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);
+
+    QCommandLineParser parser;
+    parser.setApplicationDescription("Qt Mandelbrot Example");
+    parser.addHelpOption();
+    parser.addVersionOption();
+    QCommandLineOption passesOption("passes", "Number of passes (1-8)", "passes");
+    parser.addOption(passesOption);
+    parser.process(app);
+
+    if (parser.isSet(passesOption)) {
+        const auto passesStr = parser.value(passesOption);
+        bool ok;
+        const int passes = passesStr.toInt(&ok);
+        if (!ok || passes < 1 || passes > 8) {
+            qWarning() << "Invalid value:" << passesStr;
+            return -1;
+        }
+        RenderThread::setNumPasses(passes);
+    }
+
     MandelbrotWidget widget;
+    const auto geometry = widget.screen()->availableGeometry();
+    widget.resize((2 * geometry.size()) / 3);
+    const auto pos = (geometry.size() - widget.size()) / 2;
+    widget.move(geometry.topLeft() + QPoint(pos.width(), pos.height()));
+
     widget.show();
     return app.exec();
 }

examples/corelib/threads/mandelbrot/mandelbrotwidget.cpp

@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2021 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
@@ -73,6 +73,8 @@ MandelbrotWidget::MandelbrotWidget(QWidget *parent) :
     pixmapScale(DefaultScale),
     curScale(DefaultScale)
 {
+    help = tr("Use mouse wheel or the '+' and '-' keys to zoom. "
+              "Press and hold left mouse button to scroll.");
     connect(&thread, &RenderThread::renderedImage,
             this, &MandelbrotWidget::updatePixmap);
 
@@ -80,8 +82,6 @@ MandelbrotWidget::MandelbrotWidget(QWidget *parent) :
 #if QT_CONFIG(cursor)
     setCursor(Qt::CrossCursor);
 #endif
-    resize(550, 400);
-
 }
 //! [1]
 
@@ -127,8 +127,9 @@ void MandelbrotWidget::paintEvent(QPaintEvent * /* event */)
     }
 //! [8] //! [9]
 
-    QString text = tr("Use mouse wheel or the '+' and '-' keys to zoom. "
-                      "Press and hold left mouse button to scroll.");
+    QString text = help;
+    if (!info.isEmpty())
+        text += ' ' + info;
     QFontMetrics metrics = painter.fontMetrics();
     int textWidth = metrics.horizontalAdvance(text);
 
@@ -169,6 +170,9 @@ void MandelbrotWidget::keyPressEvent(QKeyEvent *event)
     case Qt::Key_Up:
         scroll(0, +ScrollStep);
         break;
+    case Qt::Key_Q:
+        close();
+        break;
     default:
         QWidget::keyPressEvent(event);
     }
@@ -226,6 +230,8 @@ void MandelbrotWidget::updatePixmap(const QImage &image, double scaleFactor)
     if (!lastDragPos.isNull())
         return;
 
+    info = image.text(RenderThread::infoKey());
+
     pixmap = QPixmap::fromImage(image);
     pixmapOffset = QPoint();
     lastDragPos = QPoint();

examples/corelib/threads/mandelbrot/mandelbrotwidget.h

@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2021 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
@@ -86,6 +86,8 @@ private:
     QPixmap pixmap;
     QPoint pixmapOffset;
     QPoint lastDragPos;
+    QString help;
+    QString info;
     double centerX;
     double centerY;
     double pixmapScale;

examples/corelib/threads/mandelbrot/renderthread.cpp

@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2021 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
@@ -51,8 +51,14 @@
 #include "renderthread.h"
 
 #include <QImage>
+
+#include <QElapsedTimer>
+#include <QTextStream>
+
 #include <cmath>
 
+int RenderThread::numPasses = 8;
+
 //! [0]
 RenderThread::RenderThread(QObject *parent)
     : QThread(parent)
@@ -98,6 +104,7 @@ void RenderThread::render(double centerX, double centerY, double scaleFactor,
 //! [3]
 void RenderThread::run()
 {
+    QElapsedTimer timer;
     forever {
         mutex.lock();
         const double devicePixelRatio = this->devicePixelRatio;
@@ -116,13 +123,14 @@ void RenderThread::run()
         QImage image(resultSize, QImage::Format_RGB32);
         image.setDevicePixelRatio(devicePixelRatio);
 
-        const int NumPasses = 8;
         int pass = 0;
-        while (pass < NumPasses) {
+        while (pass < numPasses) {
             const int MaxIterations = (1 << (2 * pass + 6)) + 32;
             const int Limit = 4;
             bool allBlack = true;
 
+            timer.restart();
+
             for (int y = -halfHeight; y < halfHeight; ++y) {
                 if (restart)
                     break;
@@ -165,8 +173,20 @@ void RenderThread::run()
             if (allBlack && pass == 0) {
                 pass = 4;
             } else {
-                if (!restart)
+                if (!restart) {
+                    QString message;
+                    QTextStream str(&message);
+                    str << " Pass " << (pass + 1) << '/' << numPasses
+                        << ", max iterations: " << MaxIterations << ", time: ";
+                    const auto elapsed = timer.elapsed();
+                    if (elapsed > 2000)
+                        str << (elapsed / 1000) << 's';
+                    else
+                        str << elapsed << "ms";
+                    image.setText(infoKey(), message);
+
                     emit renderedImage(image, requestedScaleFactor);
+                }
 //! [5] //! [6]
                 ++pass;
             }

examples/corelib/threads/mandelbrot/renderthread.h

@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2021 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
@@ -72,6 +72,10 @@ public:
     void render(double centerX, double centerY, double scaleFactor, QSize resultSize,
                 double devicePixelRatio);
 
+    static void setNumPasses(int n) { numPasses = n; }
+
+    static QString infoKey() { return QStringLiteral("info"); }
+
 signals:
     void renderedImage(const QImage &image, double scaleFactor);
 
@@ -88,6 +92,7 @@ private:
     double scaleFactor;
     double devicePixelRatio;
     QSize resultSize;
+    static int numPasses;
     bool restart = false;
     bool abort = false;