Polish the Mandelbrot Example

Fix warnings about float constants and comparison.
Use member or constructor initialization.
Introduce some const for clarity.
Use Qt_CONFIG.

Task-number: QTBUG-81254
Change-Id: I71a6ebfba397c0f8e1dd2e61167233c8e5c137af
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

3 files changed, 29 insertions, 33 deletions

diff --git a/examples/corelib/threads/mandelbrot/mandelbrotwidget.cpp b/examples/corelib/threads/mandelbrot/mandelbrotwidget.cpp
index 822791533b..420fd6186a 100644
--- a/examples/corelib/threads/mandelbrot/mandelbrotwidget.cpp
+++ b/examples/corelib/threads/mandelbrot/mandelbrotwidget.cpp
@@ -56,29 +56,28 @@
 #include <math.h>
 
 //! [0]
-const double DefaultCenterX = -0.637011f;
-const double DefaultCenterY = -0.0395159f;
-const double DefaultScale = 0.00403897f;
+const double DefaultCenterX = -0.637011;
+const double DefaultCenterY = -0.0395159;
+const double DefaultScale = 0.00403897;
 
-const double ZoomInFactor = 0.8f;
+const double ZoomInFactor = 0.8;
 const double ZoomOutFactor = 1 / ZoomInFactor;
 const int ScrollStep = 20;
 //! [0]
 
 //! [1]
-MandelbrotWidget::MandelbrotWidget(QWidget *parent)
-    : QWidget(parent)
+MandelbrotWidget::MandelbrotWidget(QWidget *parent) :
+    QWidget(parent),
+    centerX(DefaultCenterX),
+    centerY(DefaultCenterY),
+    pixmapScale(DefaultScale),
+    curScale(DefaultScale)
 {
-    centerX = DefaultCenterX;
-    centerY = DefaultCenterY;
-    pixmapScale = DefaultScale;
-    curScale = DefaultScale;
-
     connect(&thread, &RenderThread::renderedImage,
             this, &MandelbrotWidget::updatePixmap);
 
     setWindowTitle(tr("Mandelbrot"));
-#ifndef QT_NO_CURSOR
+#if QT_CONFIG(cursor)
     setCursor(Qt::CrossCursor);
 #endif
     resize(550, 400);
@@ -102,7 +101,7 @@ void MandelbrotWidget::paintEvent(QPaintEvent * /* event */)
 //! [4]
 
 //! [5]
-    if (curScale == pixmapScale) {
+    if (qFuzzyCompare(curScale, pixmapScale)) {
 //! [5] //! [6]
         painter.drawPixmap(pixmapOffset, pixmap);
 //! [6] //! [7]
@@ -176,8 +175,8 @@ void MandelbrotWidget::keyPressEvent(QKeyEvent *event)
 //! [12]
 void MandelbrotWidget::wheelEvent(QWheelEvent *event)
 {
-    int numDegrees = event->angleDelta().y() / 8;
-    double numSteps = numDegrees / 15.0f;
+    const int numDegrees = event->angleDelta().y() / 8;
+    const double numSteps = numDegrees / double(15);
     zoom(pow(ZoomInFactor, numSteps));
 }
 //! [12]
diff --git a/examples/corelib/threads/mandelbrot/renderthread.cpp b/examples/corelib/threads/mandelbrot/renderthread.cpp
index eee44c7242..22ce81c32d 100644
--- a/examples/corelib/threads/mandelbrot/renderthread.cpp
+++ b/examples/corelib/threads/mandelbrot/renderthread.cpp
@@ -57,9 +57,6 @@
 RenderThread::RenderThread(QObject *parent)
     : QThread(parent)
 {
-    restart = false;
-    abort = false;
-
     for (int i = 0; i < ColormapSize; ++i)
         colormap[i] = rgbFromWaveLength(380.0 + (i * 400.0 / ColormapSize));
 }
@@ -102,10 +99,10 @@ void RenderThread::run()
 {
     forever {
         mutex.lock();
-        QSize resultSize = this->resultSize;
-        double scaleFactor = this->scaleFactor;
-        double centerX = this->centerX;
-        double centerY = this->centerY;
+        const QSize resultSize = this->resultSize;
+        const double scaleFactor = this->scaleFactor;
+        const double centerX = this->centerX;
+        const double centerY = this->centerY;
         mutex.unlock();
 //! [3]
 
@@ -128,20 +125,20 @@ void RenderThread::run()
                 if (abort)
                     return;
 
-                uint *scanLine =
+                auto scanLine =
                         reinterpret_cast<uint *>(image.scanLine(y + halfHeight));
-                double ay = centerY + (y * scaleFactor);
+                const double ay = centerY + (y * scaleFactor);
 
                 for (int x = -halfWidth; x < halfWidth; ++x) {
-                    double ax = centerX + (x * scaleFactor);
+                    const double ax = centerX + (x * scaleFactor);
                     double a1 = ax;
                     double b1 = ay;
                     int numIterations = 0;
 
                     do {
                         ++numIterations;
-                        double a2 = (a1 * a1) - (b1 * b1) + ax;
-                        double b2 = (2 * a1 * b1) + ay;
+                        const double a2 = (a1 * a1) - (b1 * b1) + ax;
+                        const double b2 = (2 * a1 * b1) + ay;
                         if ((a2 * a2) + (b2 * b2) > Limit)
                             break;
 
@@ -187,9 +184,9 @@ void RenderThread::run()
 //! [10]
 uint RenderThread::rgbFromWaveLength(double wave)
 {
-    double r = 0.0;
-    double g = 0.0;
-    double b = 0.0;
+    double r = 0;
+    double g = 0;
+    double b = 0;
 
     if (wave >= 380.0 && wave <= 440.0) {
         r = -1.0 * (wave - 440.0) / (440.0 - 380.0);
diff --git a/examples/corelib/threads/mandelbrot/renderthread.h b/examples/corelib/threads/mandelbrot/renderthread.h
index 4f0394d554..934cc17d74 100644
--- a/examples/corelib/threads/mandelbrot/renderthread.h
+++ b/examples/corelib/threads/mandelbrot/renderthread.h
@@ -78,7 +78,7 @@ protected:
     void run() override;
 
 private:
-    uint rgbFromWaveLength(double wave);
+    static uint rgbFromWaveLength(double wave);
 
     QMutex mutex;
     QWaitCondition condition;
@@ -86,8 +86,8 @@ private:
     double centerY;
     double scaleFactor;
     QSize resultSize;
-    bool restart;
-    bool abort;
+    bool restart = false;
+    bool abort = false;
 
     enum { ColormapSize = 512 };
     uint colormap[ColormapSize];