QDockWidgetTitleButton: Limit icon size to dpiScaled(10) on Windows

Adding larger pixmaps to the icon caused the icon to grow.

Task-number: QTBUG-38776
Change-Id: I29148d70afa55e287f2ad254e449a98c4aa631fb
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@qt.io>

1 files changed, 47 insertions, 5 deletions

diff --git a/src/widgets/widgets/qdockwidget.cpp b/src/widgets/widgets/qdockwidget.cpp
index 26060052d3..ac76217ece 100644
--- a/src/widgets/widgets/qdockwidget.cpp
+++ b/src/widgets/widgets/qdockwidget.cpp
@@ -53,6 +53,7 @@
 #include <qdebug.h>
 
 #include <private/qwidgetresizehandler_p.h>
+#include <private/qstylesheetstyle_p.h>
 
 #include "qdockwidget_p.h"
 #include "qmainwindowlayout_p.h"
@@ -127,8 +128,15 @@ public:
     void enterEvent(QEvent *event) override;
     void leaveEvent(QEvent *event) override;
     void paintEvent(QPaintEvent *event) override;
-};
 
+protected:
+    bool event(QEvent *event) override;
+
+private:
+    QSize dockButtonIconSize() const;
+
+    mutable int m_iconSize = -1;
+};
 
 QDockWidgetTitleButton::QDockWidgetTitleButton(QDockWidget *dockWidget)
     : QAbstractButton(dockWidget)
@@ -136,14 +144,49 @@ QDockWidgetTitleButton::QDockWidgetTitleButton(QDockWidget *dockWidget)
     setFocusPolicy(Qt::NoFocus);
 }
 
+bool QDockWidgetTitleButton::event(QEvent *event)
+{
+    switch (event->type()) {
+    case QEvent::StyleChange:
+    case QEvent::ScreenChangeInternal:
+        m_iconSize = -1;
+        break;
+    default:
+        break;
+    }
+    return QAbstractButton::event(event);
+}
+
+static inline bool isWindowsStyle(const QStyle *style)
+{
+    // Note: QStyleSheetStyle inherits QWindowsStyle
+    const QStyle *effectiveStyle = style->inherits("QStyleSheetStyle")
+        ? static_cast<const QStyleSheetStyle *>(style)->baseStyle()
+        : style;
+    return effectiveStyle->inherits("QWindowsStyle");
+}
+
+QSize QDockWidgetTitleButton::dockButtonIconSize() const
+{
+    if (m_iconSize < 0) {
+        m_iconSize = style()->pixelMetric(QStyle::PM_SmallIconSize, nullptr, this);
+        // Dock Widget title buttons on Windows where historically limited to size 10
+        // (from small icon size 16) since only a 10x10 XPM was provided.
+        // Adding larger pixmaps to the icons thus caused the icons to grow; limit
+        // this to qpiScaled(10) here.
+        if (isWindowsStyle(style()))
+            m_iconSize = qMin((10 * logicalDpiX()) / 96, m_iconSize);
+    }
+    return QSize(m_iconSize, m_iconSize);
+}
+
 QSize QDockWidgetTitleButton::sizeHint() const
 {
     ensurePolished();
 
     int size = 2*style()->pixelMetric(QStyle::PM_DockWidgetTitleBarButtonMargin, 0, this);
     if (!icon().isNull()) {
-        int iconSize = style()->pixelMetric(QStyle::PM_SmallIconSize, 0, this);
-        QSize sz = icon().actualSize(QSize(iconSize, iconSize));
+        const QSize sz = icon().actualSize(dockButtonIconSize());
         size += qMax(sz.width(), sz.height());
     }
 
@@ -186,8 +229,7 @@ void QDockWidgetTitleButton::paintEvent(QPaintEvent *)
     opt.activeSubControls = 0;
     opt.features = QStyleOptionToolButton::None;
     opt.arrowType = Qt::NoArrow;
-    int size = style()->pixelMetric(QStyle::PM_SmallIconSize, 0, this);
-    opt.iconSize = QSize(size, size);
+    opt.iconSize = dockButtonIconSize();
     style()->drawComplexControl(QStyle::CC_ToolButton, &opt, &p, this);
 }