Refactor QHighDpiScaling internals and usage

Overall goal is to simplify, separate concerns, and
improve cross-platform-ness and testability.

QT_SCALE_FACTOR is now a pure cross-platform global
scale factor setter has no "auto". "auto" requires
input from the platform plugin via QPlatformScreen::
pixelDensity() and gets a separate environment variable:
QT_AUTO_SCREEN_SCALE_FACTOR

The effective scale factor (aka devicePixelRatio) is now
computed as the product of the global, screen, and
window scale factors. This matches how devicePixelRatio
is computed in general (the window system devicePixelRatio
is also a factor), and makes QT_SCALE_FACTOR
work consistently regardless if there is a window
scale factor set or not. This also means we can remove
the if/else casing from the nativePixels conversion
functions.

Add QHighDpiScaling initializer which reads the environment
variables and sets the "active" variables. Call it
during QGuiApplication construction, before the platform
plugin is created

Add per-screen scale factor setting capability to
the manual test. This makes it possible to test
this logic on all platforms. The command line argument
is --screen-scale-factor.

Change-Id: I054337cbae37a01cdd731d26d9cb628fcecdb652
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@theqtcompany.com>

1 files changed, 63 insertions, 64 deletions

diff --git a/tests/manual/highdpi/main.cpp b/tests/manual/highdpi/main.cpp
index b6305ba1d4..fb5ff33232 100644
--- a/tests/manual/highdpi/main.cpp
+++ b/tests/manual/highdpi/main.cpp
@@ -56,69 +56,64 @@
 #include <QDebug>
 #include <private/qhighdpiscaling_p.h>
 
-class ScaleFactorSetter : public QWidget
+class ScreenScaleFactorSetter : public QWidget
 {
 Q_OBJECT
 public:
-    ScaleFactorSetter();
-    QLabel *label;
-    QSlider *slider;
-    QLabel *scaleFactorLabel;
-    QHBoxLayout *layout;
-private Q_SLOTS:
-    void scaleFactorChanged(int scaleFactor);
+    ScreenScaleFactorSetter();
 };
 
-// Shows a slider which sets the scale factor for all windows.
-ScaleFactorSetter::ScaleFactorSetter()
+ScreenScaleFactorSetter::ScreenScaleFactorSetter()
 {
-    label = new QLabel("Scale Factor");
-    slider = new QSlider();
-    slider->setOrientation(Qt::Horizontal);
-    slider->setMinimum(1);
-    slider->setMaximum(40);
-    slider->setValue(10);
-    slider->setTracking(true);
-    slider->setTickInterval(5);
-    slider->setTickPosition(QSlider::TicksBelow);
-    scaleFactorLabel = new QLabel("1.0");
-
-    layout = new QHBoxLayout();
-    layout->addWidget(label);
-    layout->addWidget(slider);
-    layout->addWidget(scaleFactorLabel);
-    setLayout(layout);
+    setWindowTitle("screen scale factors");
+    setObjectName("controller"); // make WindowScaleFactorSetter skip this window
 
-    connect(slider, SIGNAL(valueChanged(int)), this, SLOT(scaleFactorChanged(int)));
-}
+    QVBoxLayout *layout = new QVBoxLayout;
+    setLayout(layout);
 
-void ScaleFactorSetter::scaleFactorChanged(int scaleFactor)
-{
-    // slider value is scale factor times ten;
-    qreal scalefactorF = qreal(scaleFactor) / 10.0;
-
-    // update label, add ".0" if needed.
-    QString number = QString::number(scalefactorF);
-    if (!number.contains("."))
-        number.append(".0");
-    scaleFactorLabel->setText(number);
-
-    // set scale factor on all top-level windows
-    QWindowList windows = QGuiApplication::topLevelWindows();
-    foreach (QWindow *window, windows) {
-
-        // skip this controller window
-        if (window == this->windowHandle())
-            continue;
-
-        qDebug() << "set scale factor on" << window;
-        qreal oldFactor = QHighDpiScaling::factor(window);
-        QHighDpiScaling::setWindowFactor(window, scalefactorF);
-        qreal newFactor = QHighDpiScaling::factor(window);
-        qDebug() << "factor was / is" << oldFactor << newFactor;
-
-        // resize window to keep showing the same amount of content.
-        window->resize(window->size() / oldFactor * newFactor);
+    // set up one scale control line per screen
+    QList<QScreen *> screens = QGuiApplication::screens();
+    foreach (QScreen *screen, screens) {
+        // create scale control line
+        QHBoxLayout *row = new QHBoxLayout;
+        QSize screenSize = screen->geometry().size();
+        QString screenId = screen->name() + " " + QString::number(screenSize.width())
+                                          + " " + QString::number(screenSize.height());
+        QLabel *label = new QLabel(screenId);
+        QSlider *slider = new QSlider();
+        slider->setOrientation(Qt::Horizontal);
+        slider->setMinimum(1);
+        slider->setMaximum(40);
+        slider->setValue(10);
+        slider->setTracking(true);
+        slider->setTickInterval(5);
+        slider->setTickPosition(QSlider::TicksBelow);
+        QLabel *scaleFactorLabel = new QLabel("1.0");
+
+        // set up layouts
+        row->addWidget(label);
+        row->addWidget(slider);
+        row->addWidget(scaleFactorLabel);
+        layout->addLayout(row);
+
+        // handle slider value change
+        connect(slider, &QSlider::valueChanged, [scaleFactorLabel, screen](int scaleFactor){
+            // slider value is scale factor times ten;
+            qreal scalefactorF = qreal(scaleFactor) / 10.0;
+
+            // update label, add ".0" if needed.
+            QString number = QString::number(scalefactorF);
+            if (!number.contains("."))
+                number.append(".0");
+            scaleFactorLabel->setText(number);
+
+            // set scale factor for screen
+            qreal oldFactor = QHighDpiScaling::factor(screen);
+            QHighDpiScaling::setScreenFactor(screen, scalefactorF);
+            qreal newFactor = QHighDpiScaling::factor(screen);
+
+            qDebug() << "factor was / is" << oldFactor << newFactor;
+        });
     }
 }
 
@@ -272,7 +267,7 @@ public:
         int dy = 50;
         int maxX = 500;
 
-        for (int iconIndex = QStyle::SP_TitleBarMenuButton; iconIndex < QStyle::SP_MediaVolumeMuted; ++iconIndex) {
+        for (uint iconIndex = QStyle::SP_TitleBarMenuButton; iconIndex < QStyle::SP_MediaVolumeMuted; ++iconIndex) {
             QIcon icon = qApp->style()->standardIcon(QStyle::StandardPixmap(iconIndex));
             QPainter p(this);
             p.drawPixmap(x, y, icon.pixmap(dx - 5, dy - 5));
@@ -607,11 +602,15 @@ int main(int argc, char **argv)
     QCoreApplication::setApplicationVersion(QT_VERSION_STR);
 
     QCommandLineParser parser;
-    parser.setApplicationDescription("High DPI tester");
+    parser.setApplicationDescription("High DPI tester. Pass one or more of the options to\n"
+                                     "test various high-dpi aspects. \n"
+                                     "--sceen-scale-factor is a special option and opens a configuration"
+                                     " window for setting window and screen scale factors.");
     parser.addHelpOption();
     parser.addVersionOption();
-    QCommandLineOption scaleFactorOption("window-scale-factor", "Show Scale Factor Slider");
-    parser.addOption(scaleFactorOption);
+    QCommandLineOption screenScaleFactorOption("screen-scale-factor", "Show screen scale factor setter.");
+    parser.addOption(screenScaleFactorOption);
+
     QCommandLineOption pixmapPainterOption("pixmap", "Test pixmap painter");
     parser.addOption(pixmapPainterOption);
     QCommandLineOption labelOption("label", "Test Labels");
@@ -633,13 +632,13 @@ int main(int argc, char **argv)
     QCommandLineOption linePainterOption("linepainter", "Test line painting");
     parser.addOption(linePainterOption);
 
-
     parser.process(app);
 
-    QScopedPointer<ScaleFactorSetter> scaleFactorSetter;
-    if (parser.isSet(scaleFactorOption)) {
-        scaleFactorSetter.reset(new ScaleFactorSetter);
-        scaleFactorSetter->show();
+    // special screen scale factor controller
+    QScopedPointer<ScreenScaleFactorSetter> screeScaleFactorSetter;
+    if (parser.isSet(screenScaleFactorOption)) {
+        screeScaleFactorSetter.reset(new ScreenScaleFactorSetter);
+        screeScaleFactorSetter->show();
     }
 
     QScopedPointer<PixmapPainter> pixmapPainter;