Widgets/Styles: add helper function to get devicePixelRatio

Retrieving the devicePixelRatio is a common task and therefore small
helper functions were created in various files. Combine them in one
global (private) place and use it everywhere.

Pick-to: 6.8
Change-Id: I334aa1da359496dd2fe08394c1da3c916009d8f0
Reviewed-by: Axel Spoerl <[email protected]>

6 files changed, 73 insertions, 66 deletions

diff --git a/src/widgets/styles/qcommonstyle.cpp b/src/widgets/styles/qcommonstyle.cpp
index b82aa8a334b..ed891b47069 100644
--- a/src/widgets/styles/qcommonstyle.cpp
+++ b/src/widgets/styles/qcommonstyle.cpp
@@ -91,11 +91,6 @@ Q_STATIC_LOGGING_CATEGORY(lcCommonStyle, "qt.widgets.commonstyle");
 
 using namespace Qt::StringLiterals;
 
-static qreal qt_getDevicePixelRatio(const QWidget *widget)
-{
-    return widget ? widget->devicePixelRatio() : qApp->devicePixelRatio();
-}
-
 struct QPainterStateSaver
 {
    QPainterStateSaver(QPainter *p, bool bSaveRestore = true)
@@ -421,7 +416,7 @@ void QCommonStyle::drawPrimitive(PrimitiveElement pe, const QStyleOption *opt, Q
             mode = QIcon::Disabled;
 
         QIcon::State state = opt->state & State_Sunken ? QIcon::On : QIcon::Off;
-        QPixmap pixmap = d->tabBarcloseButtonIcon.pixmap(QSize(size, size), p->device()->devicePixelRatio(), mode, state);
+        QPixmap pixmap = d->tabBarcloseButtonIcon.pixmap(QSize(size, size), QStyleHelper::getDpr(p), mode, state);
         proxy()->drawItemPixmap(p, opt->rect, Qt::AlignCenter, pixmap);
         break;
     }
@@ -513,7 +508,7 @@ void QCommonStyle::drawPrimitive(PrimitiveElement pe, const QStyleOption *opt, Q
         int w = br.width();
         int h = br.height();
         QPainterStateSaver pss(p);
-        const qreal devicePixelRatio = p->device()->devicePixelRatio();
+        const qreal devicePixelRatio = QStyleHelper::getDpr(p);
         if (!qFuzzyCompare(devicePixelRatio, qreal(1))) {
             const qreal inverseScale = qreal(1) / devicePixelRatio;
             p->scale(inverseScale, inverseScale);
@@ -550,7 +545,7 @@ void QCommonStyle::drawPrimitive(PrimitiveElement pe, const QStyleOption *opt, Q
         int w = r.width();
         int h = r.height();
         QPainterStateSaver pss(p);
-        const qreal devicePixelRatio = p->device()->devicePixelRatio();
+        const qreal devicePixelRatio = QStyleHelper::getDpr(p);
         if (!qFuzzyCompare(devicePixelRatio, qreal(1))) {
             const qreal inverseScale = qreal(1) / devicePixelRatio;
             p->scale(inverseScale, inverseScale);
@@ -755,7 +750,7 @@ void QCommonStyle::drawPrimitive(PrimitiveElement pe, const QStyleOption *opt, Q
                 break;
             int size = qMin(r.height(), r.width());
             QPixmap pixmap;
-            const qreal dpr = p->device()->devicePixelRatio();
+            const qreal dpr = QStyleHelper::getDpr(p);
             const QString pixmapName = QStyleHelper::uniqueName("$qt_ia-"_L1
                                                      % QLatin1StringView(metaObject()->className())
                                                      % HexString<uint>(pe),
@@ -1392,7 +1387,7 @@ void QCommonStyle::drawControl(ControlElement element, const QStyleOption *opt,
                 if (button->state & State_On)
                     state = QIcon::On;
 
-                QPixmap pixmap = button->icon.pixmap(button->iconSize, p->device()->devicePixelRatio(), mode, state);
+                QPixmap pixmap = button->icon.pixmap(button->iconSize, QStyleHelper::getDpr(p), mode, state);
                 int pixmapWidth = pixmap.width() / pixmap.devicePixelRatio();
                 int pixmapHeight = pixmap.height() / pixmap.devicePixelRatio();
                 int labelWidth = pixmapWidth;
@@ -1466,7 +1461,7 @@ void QCommonStyle::drawControl(ControlElement element, const QStyleOption *opt,
             QPixmap pix;
             QRect textRect = btn->rect;
             if (!btn->icon.isNull()) {
-                pix = btn->icon.pixmap(btn->iconSize, p->device()->devicePixelRatio(), btn->state & State_Enabled ? QIcon::Normal : QIcon::Disabled);
+                pix = btn->icon.pixmap(btn->iconSize, QStyleHelper::getDpr(p), btn->state & State_Enabled ? QIcon::Normal : QIcon::Disabled);
                 proxy()->drawItemPixmap(p, btn->rect, alignment, pix);
                 if (btn->direction == Qt::RightToLeft)
                     textRect.setRight(textRect.right() - btn->iconSize.width() - 4);
@@ -1508,7 +1503,7 @@ void QCommonStyle::drawControl(ControlElement element, const QStyleOption *opt,
             if (!proxy()->styleHint(SH_UnderlineShortcut, mbi, widget))
                 alignment |= Qt::TextHideMnemonic;
             int iconExtent = proxy()->pixelMetric(PM_SmallIconSize, opt, widget);
-            QPixmap pix = mbi->icon.pixmap(QSize(iconExtent, iconExtent), p->device()->devicePixelRatio(), (mbi->state & State_Enabled) ? QIcon::Normal : QIcon::Disabled);
+            QPixmap pix = mbi->icon.pixmap(QSize(iconExtent, iconExtent), QStyleHelper::getDpr(p), (mbi->state & State_Enabled) ? QIcon::Normal : QIcon::Disabled);
             if (!pix.isNull())
                 proxy()->drawItemPixmap(p,mbi->rect, alignment, pix);
             else
@@ -1665,7 +1660,7 @@ void QCommonStyle::drawControl(ControlElement element, const QStyleOption *opt,
             if (!header->icon.isNull()) {
                 int iconExtent = proxy()->pixelMetric(PM_SmallIconSize, opt, widget);
                 QPixmap pixmap
-                    = header->icon.pixmap(QSize(iconExtent, iconExtent), p->device()->devicePixelRatio(), (header->state & State_Enabled) ? QIcon::Normal : QIcon::Disabled);
+                    = header->icon.pixmap(QSize(iconExtent, iconExtent), QStyleHelper::getDpr(p), (header->state & State_Enabled) ? QIcon::Normal : QIcon::Disabled);
                 int pixw = pixmap.width() / pixmap.devicePixelRatio();
 
                 QRect aligned = alignedRect(header->direction, QFlag(header->iconAlignment), pixmap.size() / pixmap.devicePixelRatio(), rect);
@@ -1736,7 +1731,7 @@ void QCommonStyle::drawControl(ControlElement element, const QStyleOption *opt,
                         mode = QIcon::Active;
                     else
                         mode = QIcon::Normal;
-                    pm = toolbutton->icon.pixmap(toolbutton->rect.size().boundedTo(toolbutton->iconSize), p->device()->devicePixelRatio(),
+                    pm = toolbutton->icon.pixmap(toolbutton->rect.size().boundedTo(toolbutton->iconSize), QStyleHelper::getDpr(p),
                                                  mode, state);
                     pmSize = pm.size() / pm.devicePixelRatio();
                 }
@@ -1954,7 +1949,7 @@ void QCommonStyle::drawControl(ControlElement element, const QStyleOption *opt,
             bool enabled = tb->state & State_Enabled;
             bool selected = tb->state & State_Selected;
             int iconExtent = proxy()->pixelMetric(QStyle::PM_SmallIconSize, tb, widget);
-            QPixmap pm = tb->icon.pixmap(QSize(iconExtent, iconExtent), p->device()->devicePixelRatio(),
+            QPixmap pm = tb->icon.pixmap(QSize(iconExtent, iconExtent), QStyleHelper::getDpr(p),
                                          enabled ? QIcon::Normal : QIcon::Disabled);
 
             QRect cr = subElementRect(QStyle::SE_ToolBoxTabContents, tb, widget);
@@ -2031,7 +2026,7 @@ void QCommonStyle::drawControl(ControlElement element, const QStyleOption *opt,
                 tr = proxy()->subElementRect(SE_TabBarTabText, opt, widget);
 
             if (!tab->icon.isNull()) {
-                QPixmap tabIcon = tab->icon.pixmap(tab->iconSize, p->device()->devicePixelRatio(),
+                QPixmap tabIcon = tab->icon.pixmap(tab->iconSize, QStyleHelper::getDpr(p),
                                                    (tab->state & State_Enabled) ? QIcon::Normal
                                                                                 : QIcon::Disabled,
                                                    (tab->state & State_Selected) ? QIcon::On
@@ -2232,7 +2227,7 @@ void QCommonStyle::drawControl(ControlElement element, const QStyleOption *opt,
             if (!cb->currentIcon.isNull()) {
                 QIcon::Mode mode = cb->state & State_Enabled ? QIcon::Normal
                                                              : QIcon::Disabled;
-                QPixmap pixmap = cb->currentIcon.pixmap(cb->iconSize, p->device()->devicePixelRatio(), mode);
+                QPixmap pixmap = cb->currentIcon.pixmap(cb->iconSize, QStyleHelper::getDpr(p), mode);
                 QRect iconRect(editRect);
                 iconRect.setWidth(cb->iconSize.width() + 4);
                 iconRect = alignedRect(cb->direction,
@@ -2539,7 +2534,7 @@ QRect QCommonStyle::subElementRect(SubElement sr, const QStyleOption *opt,
             if (!btn->icon.isNull()) {
                 iconRect = itemPixmapRect(cr, Qt::AlignAbsolute | Qt::AlignLeft | Qt::AlignVCenter
                                         | Qt::TextShowMnemonic,
-                                   btn->icon.pixmap(btn->iconSize, qt_getDevicePixelRatio(widget), QIcon::Normal));
+                                   btn->icon.pixmap(btn->iconSize, QStyleHelper::getDpr(widget), QIcon::Normal));
                 if (!textRect.isEmpty())
                     textRect.translate(iconRect.right() + 4, 0);
             }
@@ -2587,7 +2582,7 @@ QRect QCommonStyle::subElementRect(SubElement sr, const QStyleOption *opt,
             }
             if (!btn->icon.isNull()) {
                 iconRect = itemPixmapRect(cr, Qt::AlignAbsolute | Qt::AlignLeft | Qt::AlignVCenter | Qt::TextShowMnemonic,
-                                   btn->icon.pixmap(btn->iconSize, qt_getDevicePixelRatio(widget), QIcon::Normal));
+                                   btn->icon.pixmap(btn->iconSize, QStyleHelper::getDpr(widget), QIcon::Normal));
                 if (!textRect.isEmpty())
                     textRect.translate(iconRect.right() + 4, 0);
             }
@@ -3579,9 +3574,9 @@ void QCommonStyle::drawComplexControl(ComplexControl cc, const QStyleOptionCompl
                     || qobject_cast<const QDockWidget *>(widget)
 #endif
                     )
-                    pm = proxy()->standardIcon(SP_DockWidgetCloseButton, &tool, widget).pixmap(QSize(10, 10), p->device()->devicePixelRatio());
+                    pm = proxy()->standardIcon(SP_DockWidgetCloseButton, &tool, widget).pixmap(QSize(10, 10), QStyleHelper::getDpr(p));
                 else
-                    pm = proxy()->standardIcon(SP_TitleBarCloseButton, &tool, widget).pixmap(QSize(10, 10), p->device()->devicePixelRatio());
+                    pm = proxy()->standardIcon(SP_TitleBarCloseButton, &tool, widget).pixmap(QSize(10, 10), QStyleHelper::getDpr(p));
                 tool.rect = ir;
                 tool.state = down ? State_Sunken : State_Raised;
                 proxy()->drawPrimitive(PE_PanelButtonTool, &tool, p, widget);
@@ -3599,7 +3594,7 @@ void QCommonStyle::drawComplexControl(ComplexControl cc, const QStyleOptionCompl
                 ir = proxy()->subControlRect(CC_TitleBar, tb, SC_TitleBarMaxButton, widget);
 
                 down = tb->activeSubControls & SC_TitleBarMaxButton && (opt->state & State_Sunken);
-                pm = proxy()->standardIcon(SP_TitleBarMaxButton, &tool, widget).pixmap(QSize(10, 10), p->device()->devicePixelRatio());
+                pm = proxy()->standardIcon(SP_TitleBarMaxButton, &tool, widget).pixmap(QSize(10, 10), QStyleHelper::getDpr(p));
                 tool.rect = ir;
                 tool.state = down ? State_Sunken : State_Raised;
                 proxy()->drawPrimitive(PE_PanelButtonTool, &tool, p, widget);
@@ -3616,7 +3611,7 @@ void QCommonStyle::drawComplexControl(ComplexControl cc, const QStyleOptionCompl
                     && !(tb->titleBarState & Qt::WindowMinimized)) {
                 ir = proxy()->subControlRect(CC_TitleBar, tb, SC_TitleBarMinButton, widget);
                 down = tb->activeSubControls & SC_TitleBarMinButton && (opt->state & State_Sunken);
-                pm = proxy()->standardIcon(SP_TitleBarMinButton, &tool, widget).pixmap(QSize(10, 10), p->device()->devicePixelRatio());
+                pm = proxy()->standardIcon(SP_TitleBarMinButton, &tool, widget).pixmap(QSize(10, 10), QStyleHelper::getDpr(p));
                 tool.rect = ir;
                 tool.state = down ? State_Sunken : State_Raised;
                 proxy()->drawPrimitive(PE_PanelButtonTool, &tool, p, widget);
@@ -3637,7 +3632,7 @@ void QCommonStyle::drawComplexControl(ComplexControl cc, const QStyleOptionCompl
             if (drawNormalButton) {
                 ir = proxy()->subControlRect(CC_TitleBar, tb, SC_TitleBarNormalButton, widget);
                 down = tb->activeSubControls & SC_TitleBarNormalButton && (opt->state & State_Sunken);
-                pm = proxy()->standardIcon(SP_TitleBarNormalButton, &tool, widget).pixmap(QSize(10, 10), p->device()->devicePixelRatio());
+                pm = proxy()->standardIcon(SP_TitleBarNormalButton, &tool, widget).pixmap(QSize(10, 10), QStyleHelper::getDpr(p));
                 tool.rect = ir;
                 tool.state = down ? State_Sunken : State_Raised;
                 proxy()->drawPrimitive(PE_PanelButtonTool, &tool, p, widget);
@@ -3654,7 +3649,7 @@ void QCommonStyle::drawComplexControl(ComplexControl cc, const QStyleOptionCompl
                     && !(tb->titleBarState & Qt::WindowMinimized)) {
                 ir = proxy()->subControlRect(CC_TitleBar, tb, SC_TitleBarShadeButton, widget);
                 down = (tb->activeSubControls & SC_TitleBarShadeButton && (opt->state & State_Sunken));
-                pm = proxy()->standardIcon(SP_TitleBarShadeButton, &tool, widget).pixmap(QSize(10, 10), p->device()->devicePixelRatio());
+                pm = proxy()->standardIcon(SP_TitleBarShadeButton, &tool, widget).pixmap(QSize(10, 10), QStyleHelper::getDpr(p));
                 tool.rect = ir;
                 tool.state = down ? State_Sunken : State_Raised;
                 proxy()->drawPrimitive(PE_PanelButtonTool, &tool, p, widget);
@@ -3671,7 +3666,7 @@ void QCommonStyle::drawComplexControl(ComplexControl cc, const QStyleOptionCompl
                 ir = proxy()->subControlRect(CC_TitleBar, tb, SC_TitleBarUnshadeButton, widget);
 
                 down = tb->activeSubControls & SC_TitleBarUnshadeButton  && (opt->state & State_Sunken);
-                pm = proxy()->standardIcon(SP_TitleBarUnshadeButton, &tool, widget).pixmap(QSize(10, 10), p->device()->devicePixelRatio());
+                pm = proxy()->standardIcon(SP_TitleBarUnshadeButton, &tool, widget).pixmap(QSize(10, 10), QStyleHelper::getDpr(p));
                 tool.rect = ir;
                 tool.state = down ? State_Sunken : State_Raised;
                 proxy()->drawPrimitive(PE_PanelButtonTool, &tool, p, widget);
@@ -3686,7 +3681,7 @@ void QCommonStyle::drawComplexControl(ComplexControl cc, const QStyleOptionCompl
                 ir = proxy()->subControlRect(CC_TitleBar, tb, SC_TitleBarContextHelpButton, widget);
 
                 down = tb->activeSubControls & SC_TitleBarContextHelpButton  && (opt->state & State_Sunken);
-                pm = proxy()->standardIcon(SP_TitleBarContextHelpButton, &tool, widget).pixmap(QSize(10, 10), p->device()->devicePixelRatio());
+                pm = proxy()->standardIcon(SP_TitleBarContextHelpButton, &tool, widget).pixmap(QSize(10, 10), QStyleHelper::getDpr(p));
                 tool.rect = ir;
                 tool.state = down ? State_Sunken : State_Raised;
                 proxy()->drawPrimitive(PE_PanelButtonTool, &tool, p, widget);
@@ -3702,7 +3697,7 @@ void QCommonStyle::drawComplexControl(ComplexControl cc, const QStyleOptionCompl
                     tb->icon.paint(p, ir);
                 } else {
                     int iconSize = proxy()->pixelMetric(PM_SmallIconSize, tb, widget);
-                    pm = proxy()->standardIcon(SP_TitleBarMenuButton, &tool, widget).pixmap(QSize(iconSize, iconSize), p->device()->devicePixelRatio());
+                    pm = proxy()->standardIcon(SP_TitleBarMenuButton, &tool, widget).pixmap(QSize(iconSize, iconSize), QStyleHelper::getDpr(p));
                     tool.rect = ir;
                     QPainterStateSaver pss(p);
                     proxy()->drawItemPixmap(p, ir, Qt::AlignCenter, pm);
@@ -3887,7 +3882,7 @@ void QCommonStyle::drawComplexControl(ComplexControl cc, const QStyleOptionCompl
                 }
                 btnOpt.rect = proxy()->subControlRect(CC_MdiControls, opt, SC_MdiCloseButton, widget);
                 proxy()->drawPrimitive(PE_PanelButtonCommand, &btnOpt, p, widget);
-                QPixmap pm = proxy()->standardIcon(SP_TitleBarCloseButton).pixmap(buttonIconSize, p->device()->devicePixelRatio());
+                QPixmap pm = proxy()->standardIcon(SP_TitleBarCloseButton).pixmap(buttonIconSize, QStyleHelper::getDpr(p));
                 proxy()->drawItemPixmap(p, btnOpt.rect.translated(bsx, bsy), Qt::AlignCenter, pm);
             }
             if (opt->subControls & QStyle::SC_MdiNormalButton) {
@@ -3904,7 +3899,7 @@ void QCommonStyle::drawComplexControl(ComplexControl cc, const QStyleOptionCompl
                 }
                 btnOpt.rect = proxy()->subControlRect(CC_MdiControls, opt, SC_MdiNormalButton, widget);
                 proxy()->drawPrimitive(PE_PanelButtonCommand, &btnOpt, p, widget);
-                QPixmap pm = proxy()->standardIcon(SP_TitleBarNormalButton).pixmap(buttonIconSize, p->device()->devicePixelRatio());
+                QPixmap pm = proxy()->standardIcon(SP_TitleBarNormalButton).pixmap(buttonIconSize, QStyleHelper::getDpr(p));
                 proxy()->drawItemPixmap(p, btnOpt.rect.translated(bsx, bsy), Qt::AlignCenter, pm);
             }
             if (opt->subControls & QStyle::SC_MdiMinButton) {
@@ -3921,7 +3916,7 @@ void QCommonStyle::drawComplexControl(ComplexControl cc, const QStyleOptionCompl
                 }
                 btnOpt.rect = proxy()->subControlRect(CC_MdiControls, opt, SC_MdiMinButton, widget);
                 proxy()->drawPrimitive(PE_PanelButtonCommand, &btnOpt, p, widget);
-                QPixmap pm = proxy()->standardIcon(SP_TitleBarMinButton).pixmap(buttonIconSize, p->device()->devicePixelRatio());
+                QPixmap pm = proxy()->standardIcon(SP_TitleBarMinButton).pixmap(buttonIconSize, QStyleHelper::getDpr(p));
                 proxy()->drawItemPixmap(p, btnOpt.rect.translated(bsx, bsy), Qt::AlignCenter, pm);
             }
         }
@@ -5529,19 +5524,19 @@ QPixmap QCommonStyle::standardPixmap(StandardPixmap sp, const QStyleOption *opti
 
     icon = d->iconFromWindowsTheme(sp, option, widget);
     if (!icon.isNull())
-        return icon.pixmap(QSize(16, 16), qt_getDevicePixelRatio(widget));
+        return icon.pixmap(QSize(16, 16), QStyleHelper::getDpr(widget));
 
     icon = d->iconFromApplicationTheme(sp, option, widget);
     if (!icon.isNull())
-        return icon.pixmap(QSize(16, 16), qt_getDevicePixelRatio(widget));
+        return icon.pixmap(QSize(16, 16), QStyleHelper::getDpr(widget));
 
     icon = d->iconFromMacTheme(sp, option, widget);
     if (!icon.isNull())
-        return icon.pixmap(QSize(16, 16), qt_getDevicePixelRatio(widget));
+        return icon.pixmap(QSize(16, 16), QStyleHelper::getDpr(widget));
 
     icon = d->iconFromResourceTheme(sp, option, widget);
     if (!icon.isNull())
-        return icon.pixmap(QSize(16, 16), qt_getDevicePixelRatio(widget));
+        return icon.pixmap(QSize(16, 16), QStyleHelper::getDpr(widget));
 
 #ifndef QT_NO_IMAGEFORMAT_XPM
     switch (sp) {
@@ -5616,7 +5611,7 @@ QIcon QCommonStylePrivate::iconFromWindowsTheme(QCommonStyle::StandardPixmap sta
     case QStyle::SP_MessageBoxQuestion:
         if (const QPlatformTheme *theme = QGuiApplicationPrivate::platformTheme()) {
             QPlatformTheme::StandardPixmap sp = static_cast<QPlatformTheme::StandardPixmap>(standardIcon);
-            const auto dpr = qt_getDevicePixelRatio(widget);
+            const auto dpr = QStyleHelper::getDpr(widget);
             const QList<QSize> sizes = theme->themeHint(QPlatformTheme::IconPixmapSizes).value<QList<QSize>>();
             for (const QSize &size : sizes) {
                 QPixmap pixmap = theme->standardPixmap(sp, size * dpr);
@@ -5631,7 +5626,7 @@ QIcon QCommonStylePrivate::iconFromWindowsTheme(QCommonStyle::StandardPixmap sta
             QPlatformTheme::StandardPixmap spOff = static_cast<QPlatformTheme::StandardPixmap>(standardIcon);
             QPlatformTheme::StandardPixmap spOn = standardIcon == QStyle::SP_DirIcon ? QPlatformTheme::DirOpenIcon
                                                                                      : QPlatformTheme::DirLinkOpenIcon;
-            const auto dpr = qt_getDevicePixelRatio(widget);
+            const auto dpr = QStyleHelper::getDpr(widget);
             const QList<QSize> sizes = theme->themeHint(QPlatformTheme::IconPixmapSizes).value<QList<QSize>>();
             for (const QSize &size : sizes) {
                 const QSizeF pixSize = size * dpr;
@@ -5763,7 +5758,7 @@ QIcon QCommonStylePrivate::iconFromApplicationTheme(QCommonStyle::StandardPixmap
                 const QIcon baseIcon = iconFromApplicationTheme(si, option, widget);
                 if (!linkIcon.isNull() || !baseIcon.isNull()) {
                     const auto sizes = baseIcon.availableSizes(QIcon::Normal, QIcon::Off);
-                    const auto dpr = qt_getDevicePixelRatio(widget);
+                    const auto dpr = QStyleHelper::getDpr(widget);
                     for (const auto size : sizes) {
                         QPixmap basePixmap = baseIcon.pixmap(size, dpr);
                         QPixmap linkPixmap = linkIcon.pixmap(size / 2, dpr);
diff --git a/src/widgets/styles/qdrawutil.cpp b/src/widgets/styles/qdrawutil.cpp
index 5bdbdb11395..14fb3a41678 100644
--- a/src/widgets/styles/qdrawutil.cpp
+++ b/src/widgets/styles/qdrawutil.cpp
@@ -6,6 +6,7 @@
 #include "qpixmapcache.h"
 #include "qpainter.h"
 #include "qpalette.h"
+#include "qstylehelper_p.h"
 #include <private/qpaintengineex_p.h>
 #include <qvarlengtharray.h>
 #include <qmath.h>
@@ -92,7 +93,7 @@ void qDrawShadeLine(QPainter *p, int x1, int y1, int x2, int y2,
         return;
     }
     PainterStateGuard painterGuard(p);
-    const qreal devicePixelRatio = p->device()->devicePixelRatio();
+    const qreal devicePixelRatio = QStyleHelper::getDpr(p);
     if (!qFuzzyCompare(devicePixelRatio, qreal(1))) {
         painterGuard.save();
         const qreal inverseScale = qreal(1) / devicePixelRatio;
@@ -223,7 +224,7 @@ void qDrawShadeRect(QPainter *p, int x, int y, int w, int h,
     }
 
     PainterStateGuard painterGuard(p);
-    const qreal devicePixelRatio = p->device()->devicePixelRatio();
+    const qreal devicePixelRatio = QStyleHelper::getDpr(p);
     if (!qFuzzyCompare(devicePixelRatio, qreal(1))) {
         painterGuard.save();
         const qreal inverseScale = qreal(1) / devicePixelRatio;
@@ -337,7 +338,7 @@ void qDrawShadePanel(QPainter *p, int x, int y, int w, int h,
     }
 
     PainterStateGuard painterGuard(p);
-    const qreal devicePixelRatio = p->device()->devicePixelRatio();
+    const qreal devicePixelRatio = QStyleHelper::getDpr(p);
     bool isTranslated = false;
     if (!qFuzzyCompare(devicePixelRatio, qreal(1))) {
         painterGuard.save();
@@ -433,7 +434,7 @@ static void qDrawWinShades(QPainter *p,
         return;
 
     PainterStateGuard painterGuard(p);
-    const qreal devicePixelRatio = p->device()->devicePixelRatio();
+    const qreal devicePixelRatio = QStyleHelper::getDpr(p);
     bool isTranslated = false;
     if (!qFuzzyCompare(devicePixelRatio, qreal(1))) {
         painterGuard.save();
@@ -581,7 +582,7 @@ void qDrawPlainRect(QPainter *p, int x, int y, int w, int h, const QColor &c,
     }
 
     PainterStateGuard painterGuard(p);
-    const qreal devicePixelRatio = p->device()->devicePixelRatio();
+    const qreal devicePixelRatio = QStyleHelper::getDpr(p);
     if (!qFuzzyCompare(devicePixelRatio, qreal(1))) {
         painterGuard.save();
         const qreal inverseScale = qreal(1) / devicePixelRatio;
@@ -648,7 +649,7 @@ void qDrawPlainRoundedRect(QPainter *p, int x, int y, int w, int h,
     }
 
     PainterStateGuard painterGuard(p);
-    const qreal devicePixelRatio = p->device()->devicePixelRatio();
+    const qreal devicePixelRatio = QStyleHelper::getDpr(p);
     if (!qFuzzyCompare(devicePixelRatio, qreal(1))) {
         painterGuard.save();
         const qreal inverseScale = qreal(1) / devicePixelRatio;
diff --git a/src/widgets/styles/qfusionstyle.cpp b/src/widgets/styles/qfusionstyle.cpp
index b8795379bdb..ca281ece401 100644
--- a/src/widgets/styles/qfusionstyle.cpp
+++ b/src/widgets/styles/qfusionstyle.cpp
@@ -145,7 +145,7 @@ static void qt_fusion_draw_arrow(Qt::ArrowType type, QPainter *painter, const QS
         return;
 
     const qreal dpi = QStyleHelper::dpi(option);
-    const qreal dpr = painter->device()->devicePixelRatio();
+    const qreal dpr = QStyleHelper::getDpr(painter);
     const int arrowWidth = int(QStyleHelper::dpiScaled(14, dpi));
     const int arrowHeight = int(QStyleHelper::dpiScaled(8, dpi));
 
@@ -890,7 +890,7 @@ void QFusionStyle::drawControl(ControlElement element, const QStyleOption *optio
             if (!cb->currentIcon.isNull()) {
                 QIcon::Mode mode = cb->state & State_Enabled ? QIcon::Normal
                                                              : QIcon::Disabled;
-                QPixmap pixmap = cb->currentIcon.pixmap(cb->iconSize, painter->device()->devicePixelRatio(), mode);
+                QPixmap pixmap = cb->currentIcon.pixmap(cb->iconSize, QStyleHelper::getDpr(painter), mode);
                 QRect iconRect(editRect);
                 iconRect.setWidth(cb->iconSize.width() + 4);
                 iconRect = alignedRect(cb->direction,
@@ -1138,7 +1138,7 @@ void QFusionStyle::drawControl(ControlElement element, const QStyleOption *optio
         if (const QStyleOptionHeader *header = qstyleoption_cast<const QStyleOptionHeader *>(option)) {
             const QStyleOptionHeaderV2 *headerV2 = qstyleoption_cast<const QStyleOptionHeaderV2 *>(option);
             const bool isSectionDragTarget = headerV2 ? headerV2->isSectionDragTarget : false;
-            const qreal dpr = painter->device()->devicePixelRatio();
+            const qreal dpr = QStyleHelper::getDpr(painter);
             const QString pixmapName = QStyleHelper::uniqueName("headersection-"_L1
                                                                     % HexString(header->position)
                                                                     % HexString(header->orientation)
@@ -1528,9 +1528,9 @@ void QFusionStyle::drawControl(ControlElement element, const QStyleOption *optio
                     iconSize = combo->iconSize();
 #endif
                 if (checked)
-                    pixmap = menuItem->icon.pixmap(iconSize, painter->device()->devicePixelRatio(), mode, QIcon::On);
+                    pixmap = menuItem->icon.pixmap(iconSize, QStyleHelper::getDpr(painter), mode, QIcon::On);
                 else
-                    pixmap = menuItem->icon.pixmap(iconSize, painter->device()->devicePixelRatio(), mode);
+                    pixmap = menuItem->icon.pixmap(iconSize, QStyleHelper::getDpr(painter), mode);
 
                 QRect pmr(QPoint(0, 0), pixmap.deviceIndependentSize().toSize());
                 pmr.moveCenter(vCheckRect.center());
@@ -1881,7 +1881,7 @@ void QFusionStyle::drawComplexControl(ComplexControl control, const QStyleOption
 #if QT_CONFIG(spinbox)
     case CC_SpinBox:
         if (const QStyleOptionSpinBox *spinBox = qstyleoption_cast<const QStyleOptionSpinBox *>(option)) {
-            const qreal dpr = painter->device()->devicePixelRatio();
+            const qreal dpr = QStyleHelper::getDpr(painter);
             QPixmap cache;
             QString pixmapName = QStyleHelper::uniqueName("spinbox"_L1, spinBox, spinBox->rect.size(), dpr);
             if (!QPixmapCache::find(pixmapName, &cache)) {
@@ -2578,7 +2578,7 @@ void QFusionStyle::drawComplexControl(ComplexControl control, const QStyleOption
             bool hasFocus = option->state & State_HasFocus && option->state & State_KeyboardFocusChange;
             bool sunken = comboBox->state & State_On; // play dead, if combobox has no items
             bool isEnabled = (comboBox->state & State_Enabled);
-            const qreal dpr = painter->device()->devicePixelRatio();
+            const qreal dpr = QStyleHelper::getDpr(painter);
             QPixmap cache;
             const QString pixmapName = QStyleHelper::uniqueName("combobox"_L1
                                                                     % QLatin1StringView(sunken ? "-sunken" : "")
@@ -2675,7 +2675,7 @@ void QFusionStyle::drawComplexControl(ComplexControl control, const QStyleOption
 #if QT_CONFIG(slider)
     case CC_Slider:
         if (const QStyleOptionSlider *slider = qstyleoption_cast<const QStyleOptionSlider *>(option)) {
-            const qreal dpr = painter->device()->devicePixelRatio();
+            const qreal dpr = QStyleHelper::getDpr(painter);
             QRect groove = proxy()->subControlRect(CC_Slider, option, SC_SliderGroove, widget);
             QRect handle = proxy()->subControlRect(CC_Slider, option, SC_SliderHandle, widget);
 
@@ -3714,13 +3714,9 @@ QIcon QFusionStyle::standardIcon(StandardPixmap standardIcon, const QStyleOption
 QPixmap QFusionStyle::standardPixmap(StandardPixmap standardPixmap, const QStyleOption *opt,
                                      const QWidget *widget) const
 {
-    auto getDevicePixelRatio = [](const QWidget *widget)
-    {
-        return widget ? widget->devicePixelRatio() : qApp->devicePixelRatio();
-    };
     const auto icon = iconFromTheme(standardPixmap);
     if (!icon.availableSizes().isEmpty())
-        return icon.pixmap(QSize(16, 16), getDevicePixelRatio(widget));
+        return icon.pixmap(QSize(16, 16), QStyleHelper::getDpr(widget));
     return QCommonStyle::standardPixmap(standardPixmap, opt, widget);
 }
 
diff --git a/src/widgets/styles/qstyle_p.h b/src/widgets/styles/qstyle_p.h
index 59e87810c54..d04dd491520 100644
--- a/src/widgets/styles/qstyle_p.h
+++ b/src/widgets/styles/qstyle_p.h
@@ -47,7 +47,7 @@ inline QPixmap styleCachePixmap(const QSize &size, qreal pixelRatio)
     QRect rect = option->rect; \
     QPixmap internalPixmapCache; \
     QPainter *p = painter; \
-    const auto dpr = p->device()->devicePixelRatio(); \
+    const auto dpr = QStyleHelper::getDpr(p); \
     const QString unique = QStyleHelper::uniqueName((a), option, option->rect.size(), dpr); \
     int txType = painter->deviceTransform().type() | painter->worldTransform().type(); \
     const bool doPixmapCache = (!option->rect.isEmpty()) \
diff --git a/src/widgets/styles/qstylehelper_p.h b/src/widgets/styles/qstylehelper_p.h
index 98470ad1ced..60673163bca 100644
--- a/src/widgets/styles/qstylehelper_p.h
+++ b/src/widgets/styles/qstylehelper_p.h
@@ -8,6 +8,8 @@
 #include <QtGui/qpolygon.h>
 #include <QtCore/qstringbuilder.h>
 #include <QtGui/qaccessible.h>
+#include <QtGui/qpainter.h>
+#include <QtWidgets/qwidget.h>
 
 #ifndef QSTYLEHELPER_P_H
 #define QSTYLEHELPER_P_H
@@ -29,12 +31,10 @@ QT_BEGIN_NAMESPACE
 
 class QColor;
 class QObject;
-class QPainter;
 class QPalette;
 class QPixmap;
 class QStyleOptionSlider;
 class QStyleOption;
-class QWidget;
 class QWindow;
 
 namespace QStyleHelper
@@ -65,6 +65,21 @@ namespace QStyleHelper
     enum WidgetSizePolicy { SizeLarge = 0, SizeSmall = 1, SizeMini = 2, SizeDefault = -1 };
 
     Q_WIDGETS_EXPORT WidgetSizePolicy widgetSizePolicy(const QWidget *w, const QStyleOption *opt = nullptr);
+
+    // returns the device pixel ratio of the widget or the global one
+    // if widget is a nullptr
+    static inline qreal getDpr(const QWidget *widget)
+    {
+        return widget ? widget->devicePixelRatio()
+                      : qApp->devicePixelRatio();
+    }
+
+    // returns the device pixel ratio of the painters underlying paint device
+    static inline qreal getDpr(const QPainter *painter)
+    {
+        Q_ASSERT(painter && painter->device());
+        return painter->device()->devicePixelRatio();
+    }
 }
 
 
diff --git a/src/widgets/styles/qstylesheetstyle.cpp b/src/widgets/styles/qstylesheetstyle.cpp
index 004326e0a44..17420215e39 100644
--- a/src/widgets/styles/qstylesheetstyle.cpp
+++ b/src/widgets/styles/qstylesheetstyle.cpp
@@ -82,6 +82,7 @@
 #include <QLabel>
 #endif
 #include "qdrawutil.h"
+#include "qstylehelper_p.h"
 
 #include <limits.h>
 #if QT_CONFIG(toolbar)
@@ -3539,7 +3540,7 @@ void QStyleSheetStyle::drawComplexControl(ComplexControl cc, const QStyleOptionC
                 break;
             subRule.drawRule(p, opt->rect);
             QHash<QStyle::SubControl, QRect> layout = titleBarLayout(w, tb);
-            const auto paintDeviceDpr = p->device()->devicePixelRatio();
+            const auto paintDeviceDpr = QStyleHelper::getDpr(p);
 
             QRect ir;
             ir = layout[SC_TitleBarLabel];
@@ -3620,7 +3621,7 @@ void QStyleSheetStyle::renderMenuItemIcon(const QStyleOptionMenuItem *mi, QPaint
     const bool checked = mi->checkType != QStyleOptionMenuItem::NotCheckable && mi->checked;
     const auto iconSize = pixelMetric(PM_SmallIconSize, mi, w);
     const QSize sz(iconSize, iconSize);
-    const QPixmap pixmap(mi->icon.pixmap(sz, p->device()->devicePixelRatio(), mode,
+    const QPixmap pixmap(mi->icon.pixmap(sz, QStyleHelper::getDpr(p), mode,
                         checked ? QIcon::On : QIcon::Off));
     const int pixw = pixmap.width() / pixmap.devicePixelRatio();
     const int pixh = pixmap.height() / pixmap.devicePixelRatio();
@@ -3755,7 +3756,7 @@ void QStyleSheetStyle::drawControl(ControlElement ce, const QStyleOption *opt, Q
                     if (button->state & State_On)
                         state = QIcon::On;
 
-                    const auto paintDeviceDpr = p->device()->devicePixelRatio();
+                    const auto paintDeviceDpr = QStyleHelper::getDpr(p);
                     QPixmap pixmap = icon.pixmap(button->iconSize, paintDeviceDpr, mode, state);
                     int pixmapWidth = pixmap.width() / pixmap.devicePixelRatio();
                     int pixmapHeight = pixmap.height() / pixmap.devicePixelRatio();
@@ -4058,7 +4059,7 @@ void QStyleSheetStyle::drawControl(ControlElement ce, const QStyleOption *opt, Q
                 if (spacing == -1)
                     spacing = 6;
                 QIcon::Mode mode = cb->state & State_Enabled ? QIcon::Normal : QIcon::Disabled;
-                const auto paintDeviceDpr = p->device()->devicePixelRatio();
+                const auto paintDeviceDpr = QStyleHelper::getDpr(p);
                 QPixmap pixmap = cb->currentIcon.pixmap(cb->iconSize, paintDeviceDpr, mode);
                 QRect iconRect(editRect);
                 iconRect.setWidth(cb->iconSize.width());
@@ -5648,8 +5649,7 @@ QPixmap QStyleSheetStyle::standardPixmap(StandardPixmap standardPixmap, const QS
         QRenderRule rule = renderRule(w, opt);
         if (rule.hasStyleHint(s)) {
             QIcon icon = qvariant_cast<QIcon>(rule.styleHint(s));
-            const auto dpr = w ? w->devicePixelRatio() : qApp->devicePixelRatio();
-            return icon.pixmap(QSize(16, 16), dpr);
+            return icon.pixmap(QSize(16, 16), QStyleHelper::getDpr(w));
         }
     }
     return baseStyle()->standardPixmap(standardPixmap, opt, w);