QMacStyle: fix tab widget's tab bar

Alas, this thing strikes back: I have to use clip to remove the
part of NSBox coming through the transparent buttons, but this
works (as I've noticed recently) only for 'North' and 'West' tab
positions. For 'South' and 'East' different geomety adjustments
are required.

Change-Id: Id1f77bc1869e82e710132a2f4402cc3c8be3ab01
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 25 insertions, 1 deletions

diff --git a/src/plugins/styles/mac/qmacstyle_mac.mm b/src/plugins/styles/mac/qmacstyle_mac.mm
index 93d2681fd8..5aa7befb84 100644
--- a/src/plugins/styles/mac/qmacstyle_mac.mm
+++ b/src/plugins/styles/mac/qmacstyle_mac.mm
@@ -236,6 +236,18 @@ static QLinearGradient titlebarGradientInactive()
 }
 
 #if QT_CONFIG(tabwidget)
+/*
+    Since macOS 10.14 AppKit is using transparency more extensively, especially for the
+    dark theme. Inactive buttons, for example, are semi-transparent. And we use them to
+    draw tab widget's tab bar. The combination of NSBox (also a part of tab widget)
+    and these transparent buttons gives us an undesired side-effect: an outline of
+    NSBox is visible through transparent buttons. To avoid this, we have this hack below:
+    we clip the area where the line would be visible through the buttons. The area we
+    want to clip away can be described as an intersection of the option's rect and
+    the tab widget's tab bar rect. But some adjustments are required, since those rects
+    are anyway adjusted during the rendering and they are not exactly what you'll see on
+    the screen. Thus this switch-statement inside.
+*/
 static void clipTabBarFrame(const QStyleOption *option, const QMacStyle *style, CGContextRef ctx)
 {
     Q_ASSERT(option);
@@ -246,7 +258,19 @@ static void clipTabBarFrame(const QStyleOption *option, const QMacStyle *style,
         QTabWidget *tabWidget = qobject_cast<QTabWidget *>(option->styleObject);
         Q_ASSERT(tabWidget);
 
-        const QRect tabBarRect = style->subElementRect(QStyle::SE_TabWidgetTabBar, option, tabWidget).adjusted(2, 2, -3, -2);
+        QRect tabBarRect = style->subElementRect(QStyle::SE_TabWidgetTabBar, option, tabWidget).adjusted(2, 0, -3, 0);
+        switch (tabWidget->tabPosition()) {
+        case QTabWidget::South:
+            tabBarRect.setY(tabBarRect.y() + tabBarRect.height() / 2);
+            break;
+        case QTabWidget::North:
+        case QTabWidget::West:
+            tabBarRect = tabBarRect.adjusted(0, 2, 0, -2);
+            break;
+        case QTabWidget::East:
+            tabBarRect = tabBarRect.adjusted(tabBarRect.width() / 2, 2, tabBarRect.width() / 2, -2);
+        }
+
         const QRegion clipPath = QRegion(option->rect) - tabBarRect;
         QVarLengthArray<CGRect, 3> cgRects;
         for (const QRect &qtRect : clipPath)