Make splashscreen work on hi-DPI displays

There seem to be multiple ways of doing "hi-dpi" in Qt, one is what MacOS
introduced with retina which the splashscreen already supported.

This adds support for the much higher than 96DPI screens that would
scale the fonts, but not the pixmaps.

Author: zander

src/qt/splashscreen.cpp

@@ -26,18 +26,12 @@ SplashScreen::SplashScreen(Qt::WindowFlags f, const NetworkStyle *networkStyle)
     QWidget(0, f), curAlignment(0)
 {
     // set reference point, paddings
-    int paddingRight            = 50;
-    int paddingTop              = 50;
-    int titleVersionVSpace      = 17;
+    int paddingRight = 50;
+    int paddingTop = 50;
+    int titleVersionVSpace = 17;
     int titleCopyrightVSpaceCore = 40;
     int titleCopyrightVSpaceClassic = 54;
 
-    float fontFactor            = 1.0;
-    float devicePixelRatio      = 1.0;
-#if QT_VERSION > 0x050100
-    devicePixelRatio = ((QGuiApplication*)QCoreApplication::instance())->devicePixelRatio();
-#endif
-
     // define text to place
     QString titleText       = tr("Bitcoin Classic");
     QString versionText     = QString("Version %1").arg(QString::fromStdString(FormatFullVersion()));
@@ -48,16 +42,30 @@ SplashScreen::SplashScreen(Qt::WindowFlags f, const NetworkStyle *networkStyle)
     QString font            = QApplication::font().toString();
 
     // create a bitmap according to device pixelratio
-    QSize splashSize(480*devicePixelRatio,320*devicePixelRatio);
+    float devicePixelRatio;
+    bool useMorePixels = false;
+#if QT_VERSION > 0x050100
+    devicePixelRatio = qobject_cast<QGuiApplication*>(QCoreApplication::instance())->devicePixelRatio();
+    if (qFuzzyCompare(devicePixelRatio, (float) 1)) {
+        useMorePixels = true;
+        devicePixelRatio = logicalDpiX() / (float) 96;
+    }
+#else
+    devicePixelRatio = 1.0;
+#endif
+
+    QSize splashSize(480 * devicePixelRatio, 320 * devicePixelRatio);
     pixmap = QPixmap(splashSize);
 
 #if QT_VERSION > 0x050100
-    // change to HiDPI if it makes sense
-    pixmap.setDevicePixelRatio(devicePixelRatio);
+    if (!useMorePixels) // change to HiDPI if it makes sense
+        pixmap.setDevicePixelRatio(devicePixelRatio);
 #endif
 
     QPainter pixPaint(&pixmap);
     pixPaint.setPen(QColor(100,100,100));
+    if (useMorePixels) // change to HiDPI if it makes sense
+        pixPaint.scale(devicePixelRatio, devicePixelRatio);
 
     // draw a slightly radial gradient
     QRadialGradient gradient(QPoint(0,0), splashSize.width()/devicePixelRatio);
@@ -74,18 +82,20 @@ SplashScreen::SplashScreen(Qt::WindowFlags f, const NetworkStyle *networkStyle)
 
     pixPaint.drawPixmap(rectIcon, icon);
 
-    // check font size and drawing with
-    pixPaint.setFont(QFont(font, 33*fontFactor));
-    QFontMetrics fm = pixPaint.fontMetrics();
+    // check font size and drawing width
+    float fontFactor = 1.0;
+    if (useMorePixels) // fonts are set in Point, but we used painter::scale(), so we have to counter that.
+        fontFactor /= devicePixelRatio;
+    pixPaint.setFont(QFont(font, 33 * fontFactor));
+    QFontMetrics fm(pixPaint.fontMetrics());
     int titleTextWidth  = fm.width(titleText);
-    if(titleTextWidth > 160) {
-        // strange font rendering, Arial probably not found
-        fontFactor = 0.75;
+    if (titleTextWidth > 160) { // strange font rendering, Arial probably not found
+        fontFactor *= 0.75;
+        pixPaint.setFont(QFont(font, 33 * fontFactor));
+        fm = pixPaint.fontMetrics();
+        titleTextWidth  = fm.width(titleText);
     }
 
-    pixPaint.setFont(QFont(font, 33*fontFactor));
-    fm = pixPaint.fontMetrics();
-    titleTextWidth  = fm.width(titleText);
     pixPaint.drawText(pixmap.width()/devicePixelRatio-titleTextWidth-paddingRight,paddingTop,titleText);
 
     pixPaint.setFont(QFont(font, 15*fontFactor));
@@ -118,6 +128,9 @@ SplashScreen::SplashScreen(Qt::WindowFlags f, const NetworkStyle *networkStyle)
     // Set window title
     setWindowTitle(titleText + " " + titleAddText);
 
+    if (useMorePixels) // if scaling uses more pixels, actually allow the windows to have larger pixelsize
+        devicePixelRatio = 1;
+
     // Resize window and move to center of desktop, disallow resizing
     QRect r(QPoint(), QSize(pixmap.size().width()/devicePixelRatio,pixmap.size().height()/devicePixelRatio));
     resize(r.size());