Windows style: Scale native metrics per monitor

The native sizes returned by the metrics and theme functions refer
to the primary monitor. They need adaption when showing on a secondary
monitor with differing logical DPI.
Introduce a helper function
QWindowsStylePrivate::nativeMetricScaleFactor() to calculate the
total factor.

Task-number: QTBUG-49374
Change-Id: I34c843ff34108424e1ef0aafcf9f563d17ebbc89
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

4 files changed, 67 insertions, 19 deletions

diff --git a/src/widgets/styles/qwindowsstyle.cpp b/src/widgets/styles/qwindowsstyle.cpp
index 536ef2d49a..a0830a1f92 100644
--- a/src/widgets/styles/qwindowsstyle.cpp
+++ b/src/widgets/styles/qwindowsstyle.cpp
@@ -59,8 +59,12 @@
 #include "qlistview.h"
 #include <private/qmath_p.h>
 #include <qmath.h>
+#include <QtGui/qscreen.h>
+#include <QtGui/qwindow.h>
 #include <qpa/qplatformtheme.h>
+#include <qpa/qplatformscreen.h>
 #include <private/qguiapplication_p.h>
+#include <private/qhighdpiscaling_p.h>
 
 #include <private/qstylehelper_p.h>
 #include <private/qstyleanimation_p.h>
@@ -395,6 +399,47 @@ int QWindowsStylePrivate::fixedPixelMetric(QStyle::PixelMetric pm)
     return QWindowsStylePrivate::InvalidMetric;
 }
 
+static QWindow *windowOf(const QWidget *w)
+{
+    QWindow *result = Q_NULLPTR;
+    if (w) {
+        result = w->windowHandle();
+        if (!result) {
+            if (const QWidget *np = w->nativeParentWidget())
+                result = np->windowHandle();
+        }
+    }
+    return result;
+}
+
+static QScreen *screenOf(const QWidget *w)
+{
+    if (const QWindow *window = windowOf(w))
+        return window->screen();
+    return QGuiApplication::primaryScreen();
+}
+
+// Calculate the overall scale factor to obtain Qt Device Independent
+// Pixels from a native Windows size. Divide by devicePixelRatio
+// and account for secondary screens with differing logical DPI.
+qreal QWindowsStylePrivate::nativeMetricScaleFactor(const QWidget *widget)
+{
+    if (!QHighDpiScaling::isActive())
+        return 1;
+    qreal result = qreal(1) / QWindowsStylePrivate::devicePixelRatio(widget);
+    if (QGuiApplicationPrivate::screen_list.size() > 1) {
+        const QScreen *primaryScreen = QGuiApplication::primaryScreen();
+        const QScreen *screen = screenOf(widget);
+        if (screen != primaryScreen) {
+            const qreal primaryLogicalDpi = primaryScreen->handle()->logicalDpi().first;
+            const qreal logicalDpi = screen->handle()->logicalDpi().first;
+            if (!qFuzzyCompare(primaryLogicalDpi, logicalDpi))
+                result *= logicalDpi / primaryLogicalDpi;
+        }
+    }
+    return result;
+}
+
 /*!
   \reimp
 */
@@ -402,7 +447,7 @@ int QWindowsStyle::pixelMetric(PixelMetric pm, const QStyleOption *opt, const QW
 {
     int ret = QWindowsStylePrivate::pixelMetricFromSystemDp(pm, opt, widget);
     if (ret != QWindowsStylePrivate::InvalidMetric)
-        return qRound(qreal(ret) / QWindowsStylePrivate::devicePixelRatio(widget));
+        return qRound(qreal(ret) * QWindowsStylePrivate::nativeMetricScaleFactor(widget));
 
     ret = QWindowsStylePrivate::fixedPixelMetric(pm);
     if (ret != QWindowsStylePrivate::InvalidMetric)
diff --git a/src/widgets/styles/qwindowsstyle_p_p.h b/src/widgets/styles/qwindowsstyle_p_p.h
index 7971b84923..dc5a15db70 100644
--- a/src/widgets/styles/qwindowsstyle_p_p.h
+++ b/src/widgets/styles/qwindowsstyle_p_p.h
@@ -66,6 +66,7 @@ public:
     static int fixedPixelMetric(QStyle::PixelMetric pm);
     static qreal devicePixelRatio(const QWidget *widget = 0)
         { return widget ? widget->devicePixelRatioF() : QWindowsStylePrivate::appDevicePixelRatio(); }
+    static qreal nativeMetricScaleFactor(const QWidget *widget = Q_NULLPTR);
 
     bool hasSeenAlt(const QWidget *widget) const;
     bool altDown() const { return alt_down; }
@@ -98,3 +99,4 @@ QT_END_NAMESPACE
 #endif // QT_NO_STYLE_WINDOWS
 
 #endif //QWINDOWSSTYLE_P_P_H
+;
diff --git a/src/widgets/styles/qwindowsvistastyle.cpp b/src/widgets/styles/qwindowsvistastyle.cpp
index 2ce54fe207..fe9684a25f 100644
--- a/src/widgets/styles/qwindowsvistastyle.cpp
+++ b/src/widgets/styles/qwindowsvistastyle.cpp
@@ -426,7 +426,7 @@ void QWindowsVistaStyle::drawPrimitive(PrimitiveElement element, const QStyleOpt
                 XPThemeData themeSize = theme;
                 themeSize.partId = TVP_HOTGLYPH;
                 themeSize.stateId = GLPS_OPENED;
-                const QSizeF size = themeSize.size() / QWindowsXPStylePrivate::devicePixelRatio(widget);
+                const QSizeF size = themeSize.size() * QWindowsStylePrivate::nativeMetricScaleFactor(widget);
                 decoration_size = qRound(qMax(size.width(), size.height()));
             }
             int mid_h = option->rect.x() + option->rect.width() / 2;
@@ -988,7 +988,7 @@ void QWindowsVistaStyle::drawControl(ControlElement element, const QStyleOption
                 XPThemeData theme(widget, 0, QWindowsXPStylePrivate::ToolBarTheme,
                                   TP_DROPDOWNBUTTON);
                 if (theme.isValid()) {
-                    const QSizeF size = theme.size() / QWindowsXPStylePrivate::devicePixelRatio(widget);
+                    const QSizeF size = theme.size() * QWindowsStylePrivate::nativeMetricScaleFactor(widget);
                     if (!size.isEmpty()) {
                         mbiw = qRound(size.width());
                         mbih = qRound(size.height());
@@ -1184,8 +1184,8 @@ void QWindowsVistaStyle::drawControl(ControlElement element, const QStyleOption
                 XPThemeData themeSize = theme;
                 themeSize.partId = MENU_POPUPCHECK;
                 themeSize.stateId = 0;
-                const QSizeF size = themeSize.size() / QWindowsXPStylePrivate::devicePixelRatio(widget);
-                const QMarginsF margins = themeSize.margins() / QWindowsXPStylePrivate::devicePixelRatio(widget);
+                const QSizeF size = themeSize.size() * QWindowsStylePrivate::nativeMetricScaleFactor(widget);
+                const QMarginsF margins = themeSize.margins() * QWindowsStylePrivate::nativeMetricScaleFactor(widget);
                 checkcol = qMax(menuitem->maxIconWidth, qRound(gutterWidth + size.width() + margins.left() + margins.right()));
             }
             QRect rect = option->rect;
@@ -1210,7 +1210,7 @@ void QWindowsVistaStyle::drawControl(ControlElement element, const QStyleOption
 
             if (menuitem->menuItemType == QStyleOptionMenuItem::Separator) {
                 int yoff = y-2 + h / 2;
-                const int separatorSize = 6 / QWindowsXPStylePrivate::devicePixelRatio(widget);
+                const int separatorSize = qRound(qreal(6) * QWindowsStylePrivate::nativeMetricScaleFactor(widget));
                 QPoint p1 = QPoint(x + checkcol, yoff);
                 QPoint p2 = QPoint(x + w + separatorSize, yoff);
                 stateId = MBI_HOT;
@@ -1243,8 +1243,8 @@ void QWindowsVistaStyle::drawControl(ControlElement element, const QStyleOption
                 XPThemeData themeSize = theme;
                 themeSize.partId = MENU_POPUPCHECK;
                 themeSize.stateId = 0;
-                const QSizeF size = themeSize.size() / QWindowsXPStylePrivate::devicePixelRatio(widget);
-                const QMarginsF margins = themeSize.margins() / QWindowsXPStylePrivate::devicePixelRatio(widget);
+                const QSizeF size = themeSize.size() * QWindowsStylePrivate::nativeMetricScaleFactor(widget);
+                const QMarginsF margins = themeSize.margins() * QWindowsStylePrivate::nativeMetricScaleFactor(widget);
                 QRect checkRect(0, 0, qRound(size.width() + margins.left() + margins.right()),
                                 qRound(size.height() + margins.bottom() + margins.top()));
                 checkRect.moveCenter(vCheckRect.center());
@@ -1856,8 +1856,8 @@ QSize QWindowsVistaStyle::sizeFromContents(ContentsType type, const QStyleOption
             XPThemeData themeSize = theme;
             themeSize.partId = MENU_POPUPCHECK;
             themeSize.stateId = 0;
-            const QSizeF size = themeSize.size() / QWindowsXPStylePrivate::devicePixelRatio(widget);
-            const QMarginsF margins = themeSize.margins() / QWindowsXPStylePrivate::devicePixelRatio(widget);
+            const QSizeF size = themeSize.size() * QWindowsStylePrivate::nativeMetricScaleFactor(widget);
+            const QMarginsF margins = themeSize.margins() * QWindowsStylePrivate::nativeMetricScaleFactor(widget);
             minimumHeight = qMax(qRound(size.height() + margins.bottom() + margins.top()), sz.height());
             sz.rwidth() += qRound(size.width() + margins.left() + margins.right());
         }
@@ -1967,7 +1967,7 @@ QRect QWindowsVistaStyle::subElementRect(SubElement element, const QStyleOption
             int arrowWidth = 13;
             int arrowHeight = 5;
             if (theme.isValid()) {
-                const QSizeF size = theme.size() / QWindowsXPStylePrivate::devicePixelRatio(widget);
+                const QSizeF size = theme.size() * QWindowsStylePrivate::nativeMetricScaleFactor(widget);
                 if (!size.isEmpty()) {
                     arrowWidth = qRound(size.width());
                     arrowHeight = qRound(size.height());
@@ -2450,7 +2450,7 @@ QIcon QWindowsVistaStyle::standardIcon(StandardPixmap standardIcon,
                               QWindowsXPStylePrivate::ButtonTheme,
                               BP_COMMANDLINKGLYPH, CMDLGS_NORMAL);
             if (theme.isValid()) {
-                const QSize size = (theme.size() / QWindowsXPStylePrivate::devicePixelRatio(widget)).toSize();
+                const QSize size = (theme.size() * QWindowsStylePrivate::nativeMetricScaleFactor(widget)).toSize();
                 QIcon linkGlyph;
                 QPixmap pm(size);
                 pm.fill(Qt::transparent);
diff --git a/src/widgets/styles/qwindowsxpstyle.cpp b/src/widgets/styles/qwindowsxpstyle.cpp
index a850787af0..f2ee8e0b47 100644
--- a/src/widgets/styles/qwindowsxpstyle.cpp
+++ b/src/widgets/styles/qwindowsxpstyle.cpp
@@ -481,7 +481,7 @@ const QPixmap *QWindowsXPStylePrivate::tabBody(QWidget *widget)
 {
     if (!tabbody) {
         XPThemeData theme(0, 0, QWindowsXPStylePrivate::TabTheme, TABP_BODY);
-        const QSize size = (theme.size() / QWindowsXPStylePrivate::devicePixelRatio(widget)).toSize();
+        const QSize size = (theme.size() * QWindowsStylePrivate::nativeMetricScaleFactor(widget)).toSize();
 
         tabbody = new QPixmap(size.width(), QApplication::desktop()->screenGeometry().height());
         QPainter painter(tabbody);
@@ -3449,7 +3449,7 @@ int QWindowsXPStyle::pixelMetric(PixelMetric pm, const QStyleOption *option, con
 
     int res = QWindowsXPStylePrivate::pixelMetricFromSystemDp(pm, option, widget);
     if (res != QWindowsStylePrivate::InvalidMetric)
-        return qRound(qreal(res) / QWindowsStylePrivate::devicePixelRatio(widget));
+        return qRound(qreal(res) * QWindowsStylePrivate::nativeMetricScaleFactor(widget));
 
     res = 0;
     switch (pm) {
@@ -3595,9 +3595,10 @@ QRect QWindowsXPStyle::subControlRect(ComplexControl cc, const QStyleOptionCompl
             const int height = tb->rect.height();
             const int width = tb->rect.width();
             const int buttonMargin = int(QStyleHelper::dpiScaled(4));
-            int buttonHeight = qRound(qreal(GetSystemMetrics(SM_CYSIZE)) / QWindowsStylePrivate::devicePixelRatio(widget))
+            const qreal factor = QWindowsStylePrivate::nativeMetricScaleFactor(widget);
+            int buttonHeight = qRound(qreal(GetSystemMetrics(SM_CYSIZE)) * factor)
                 - buttonMargin;
-            int buttonWidth = qRound(qreal(GetSystemMetrics(SM_CXSIZE)) / QWindowsStylePrivate::devicePixelRatio(widget))
+            int buttonWidth = qRound(qreal(GetSystemMetrics(SM_CXSIZE)) * factor)
                 - buttonMargin;
             const int delta = buttonWidth + 2;
             int controlTop = option->rect.bottom() - buttonHeight - 2;
@@ -3967,7 +3968,7 @@ QPixmap QWindowsXPStyle::standardPixmap(StandardPixmap standardPixmap, const QSt
             if (widget && widget->isWindow()) {
                 XPThemeData theme(widget, 0, QWindowsXPStylePrivate::WindowTheme, WP_SMALLCLOSEBUTTON, CBS_NORMAL);
                 if (theme.isValid()) {
-                    const QSize size = (theme.size() / QWindowsXPStylePrivate::devicePixelRatio(widget)).toSize();
+                    const QSize size = (theme.size() * QWindowsStylePrivate::nativeMetricScaleFactor(widget)).toSize();
                     return QIcon(QWindowsStyle::standardPixmap(standardPixmap, option, widget)).pixmap(size);
                 }
             }
@@ -4001,7 +4002,7 @@ QIcon QWindowsXPStyle::standardIcon(StandardPixmap standardIcon,
                 XPThemeData theme(0, 0, QWindowsXPStylePrivate::WindowTheme,
                                   WP_MAXBUTTON, MAXBS_NORMAL);
                 if (theme.isValid()) {
-                    const QSize size = (themeSize.size() / QWindowsXPStylePrivate::devicePixelRatio(widget)).toSize();
+                    const QSize size = (themeSize.size() * QWindowsStylePrivate::nativeMetricScaleFactor(widget)).toSize();
                     QPixmap pm(size);
                     pm.fill(Qt::transparent);
                     QPainter p(&pm);
@@ -4035,7 +4036,7 @@ QIcon QWindowsXPStyle::standardIcon(StandardPixmap standardIcon,
                 XPThemeData theme(0, 0, QWindowsXPStylePrivate::WindowTheme,
                                   WP_SMALLCLOSEBUTTON, CBS_NORMAL);
                 if (theme.isValid()) {
-                    const QSize size = (theme.size() / QWindowsXPStylePrivate::devicePixelRatio(widget)).toSize();
+                    const QSize size = (theme.size() * QWindowsStylePrivate::nativeMetricScaleFactor(widget)).toSize();
                     QPixmap pm(size);
                     pm.fill(Qt::transparent);
                     QPainter p(&pm);