[components-webview] Create screen resolution to layout.css.devPixels…

…PerPx mapping. JB#62599

This is rather simple way to map these. At the same, there ain't
that many screen resolution that we'd like to map. Thus, this
approach is reasoble for our needs.

For testing this, if you have ran browser at least once, you need to
remove __PREFS_WRITTEN__ flag file from your device.

> rm $HOME/.local/share/org.sailfishos/browser/__PREFS_WRITTEN__

GitHub issue:
sailfishos/sailfish-browser#1085

lib/webenginesettings.cpp

@@ -17,6 +17,7 @@
 
 #include <QtCore/QFile>
 #include <QtCore/QLocale>
+#include <QtCore/QMap>
 #include <QtCore/QSettings>
 #include <QtCore/QSize>
 #include <QtCore/QStandardPaths>
@@ -42,6 +43,11 @@ Q_GLOBAL_STATIC(SailfishOS::WebEngineSettingsPrivate, webEngineSettingsPrivateIn
     Singleton class which provides access to the global Web engine settings.
 */
 
+// Let's gather here resolution to layout.css.devPixelsPerPx mappings.
+static QMap<QString, qreal> fixedDevPxMap {
+    { QStringLiteral("1080x2520"), 2.608695652173913 }
+};
+
 static bool testScreenDimensions(qreal pixelRatio)
 {
     QScreen *screen = QGuiApplication::primaryScreen();
@@ -50,6 +56,13 @@ static bool testScreenDimensions(qreal pixelRatio)
     return fmod(w, 1.0) == 0 && fmod(h, 1.0) == 0;
 }
 
+static qreal mappedPixelRatio(const QSize &screenResolution)
+{
+    return fixedDevPxMap.value(QStringLiteral("%1x%2")
+                               .arg(screenResolution.width())
+                               .arg(screenResolution.height()), -1.0);
+}
+
 static quint64 getTotalMemory() {
     struct sysinfo info;
     sysinfo(&info);
@@ -191,20 +204,27 @@ void SailfishOS::WebEngineSettings::initialize()
     qreal touchStartTolerance = dragThreshold / QGuiApplication::primaryScreen()->physicalDotsPerInch();
     engineSettings->setPreference(QString("apz.touch_start_tolerance"), QString("%1f").arg(touchStartTolerance));
 
-    qreal pixelRatio = SAILFISH_WEBENGINE_DEFAULT_PIXEL_RATIO * silicaTheme->pixelRatio();
-    // Round to nearest even rounding factor
-    pixelRatio = qRound(pixelRatio / 0.5) * 0.5;
+    QSize screenResolution = QGuiApplication::primaryScreen()->size();
+    int screenWidth = screenResolution.width();
+
+    qreal pixelRatio = mappedPixelRatio(screenResolution);
+
+    // Try to calculate pixelRatio only if not mapped.
+    if (pixelRatio == -1.0) {
+        pixelRatio = SAILFISH_WEBENGINE_DEFAULT_PIXEL_RATIO * silicaTheme->pixelRatio();
+        // Round to nearest even rounding factor
+        pixelRatio = qRound(pixelRatio / 0.5) * 0.5;
 
-    int screenWidth = QGuiApplication::primaryScreen()->size().width();
 
-    // Do not floor the pixel ratio if the pixel ratio less than 2.0 (1.5 is minimum).
-    if (pixelRatio >= 2.0 && !testScreenDimensions(pixelRatio)) {
-        qreal tempPixelRatio = qFloor(pixelRatio);
-        if (testScreenDimensions(tempPixelRatio)) {
-            pixelRatio = tempPixelRatio;
+        // Do not floor the pixel ratio if the pixel ratio less than 2.0 (1.5 is minimum).
+        if (pixelRatio >= 2.0 && !testScreenDimensions(pixelRatio)) {
+            qreal tempPixelRatio = qFloor(pixelRatio);
+            if (testScreenDimensions(tempPixelRatio)) {
+                pixelRatio = tempPixelRatio;
+            }
+        } else if (screenWidth >= 1080) {
+            pixelRatio = qRound(pixelRatio);
         }
-    } else if (screenWidth >= 1080) {
-        pixelRatio = qRound(pixelRatio);
     }
 
     engineSettings->setPixelRatio(pixelRatio);