WelcomePage: Workaround broken QFrame in HighDPI cases

This change introduces Core::WelcomeFrame which draws proper rectangles.
The need for this workaround is unfortunate, but the very visible
regression with the new welcome mode would be worse.

Task-number: QTBUG-59116
Change-Id: I158b8309cf396a247136d7017406ca1f7bce2407
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/coreplugin/iwelcomepage.cpp

@@ -33,6 +33,7 @@
 #include <QHBoxLayout>
 #include <QLabel>
 #include <QMetaEnum>
+#include <QPainter>
 #include <QPixmap>
 #include <QUrl>
 
@@ -90,6 +91,25 @@ static QPalette buttonPalette(bool isActive, bool isCursorInside, bool forText)
     return pal;
 }
 
+WelcomePageFrame::WelcomePageFrame(QWidget *parent)
+    : QWidget(parent)
+{
+    setContentsMargins(1, 1, 1, 1);
+}
+
+void WelcomePageFrame::paintEvent(QPaintEvent *event)
+{
+    QWidget::paintEvent(event);
+
+    const QRectF adjustedRect(QRectF(rect()).adjusted(0.5, 0.5, -0.5, -0.5));
+    QPen pen(palette().color(QPalette::WindowText));
+    pen.setJoinStyle(Qt::MiterJoin);
+
+    QPainter p(this);
+    p.setPen(pen);
+    p.drawRect(adjustedRect);
+}
+
 class WelcomePageButtonPrivate
 {
 public:
@@ -107,11 +127,9 @@ public:
 };
 
 WelcomePageButton::WelcomePageButton(QWidget *parent)
-    : QFrame(parent), d(new WelcomePageButtonPrivate(this))
+    : WelcomePageFrame(parent), d(new WelcomePageButtonPrivate(this))
 {
     setAutoFillBackground(true);
-    setFrameShape(QFrame::Box);
-    setFrameShadow(QFrame::Plain);
     setPalette(buttonPalette(false, false, false));
 
     QFont f = font();

src/plugins/coreplugin/iwelcomepage.h

@@ -29,7 +29,7 @@
 
 #include "id.h"
 
-#include <QFrame>
+#include <QWidget>
 #include <QObject>
 
 #include <functional>
@@ -61,7 +61,15 @@ public:
 
 class WelcomePageButtonPrivate;
 
-class CORE_EXPORT WelcomePageButton : public QFrame
+class CORE_EXPORT WelcomePageFrame : public QWidget
+{
+public:
+    WelcomePageFrame(QWidget *parent);
+
+    void paintEvent(QPaintEvent *event) override;
+};
+
+class CORE_EXPORT WelcomePageButton : public WelcomePageFrame
 {
 public:
     WelcomePageButton(QWidget *parent);

src/plugins/qtsupport/gettingstartedwelcomepage.cpp

@@ -244,15 +244,12 @@ static QString resourcePath()
     return FileUtils::normalizePathName(ICore::resourcePath());
 }
 
-class SearchBox : public QFrame
+class SearchBox : public WelcomePageFrame
 {
 public:
     SearchBox(QWidget *parent)
-        : QFrame(parent)
+        : WelcomePageFrame(parent)
     {
-        setFrameShape(QFrame::Box);
-        setFrameShadow(QFrame::Plain);
-
         QPalette pal;
         pal.setColor(QPalette::Base, themeColor(Theme::Welcome_BackgroundColor));