QMacStyle - take into account that native controls are transparent now

We use NSButton to emulate tabs in QTabWidget. Starting from 10.14
in dark theme those button objects tend to be somewhat transparent,
thus widget's frame is visible through tab buttons. This is true for
native controls also - NSButton, NSSegmentedControl, NSTabView - they
all show the similar behavior. The only difference is NSTabView, which
is the closest control to our QTabWidget - tab buttons are transparent,
but they (AppKit) it would appear just do not draw the frame under
this area. Let's do the same, but using clipping.

Task-number: QTBUG-71741
Change-Id: I9f19014d0db5f36bacf76ee0068fae6eee793c0f
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 29 insertions, 0 deletions

diff --git a/src/plugins/styles/mac/qmacstyle_mac.mm b/src/plugins/styles/mac/qmacstyle_mac.mm
index b84448d5e2..c2b6fbfead 100644
--- a/src/plugins/styles/mac/qmacstyle_mac.mm
+++ b/src/plugins/styles/mac/qmacstyle_mac.mm
@@ -130,6 +130,7 @@
 #include <QtWidgets/qgraphicsview.h>
 #endif
 #include <QtCore/qvariant.h>
+#include <QtCore/qvarlengtharray.h>
 #include <private/qstylehelper_p.h>
 #include <private/qstyleanimation_p.h>
 #include <qpa/qplatformfontdatabase.h>
@@ -314,6 +315,26 @@ static QLinearGradient titlebarGradientInactive()
     return qt_mac_applicationIsInDarkMode() ? darkGradient : lightGradient;
 }
 
+static void clipTabBarFrame(const QStyleOption *option, const QMacStyle *style, CGContextRef ctx)
+{
+    Q_ASSERT(option);
+    Q_ASSERT(style);
+    Q_ASSERT(ctx);
+
+    if (qt_mac_applicationIsInDarkMode()) {
+        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);
+        const QRegion clipPath = QRegion(option->rect) - tabBarRect;
+        QVarLengthArray<CGRect, 3> cgRects;
+        for (const QRect &qtRect : clipPath)
+            cgRects.push_back(qtRect.toCGRect());
+        if (cgRects.size())
+            CGContextClipToRects(ctx, &cgRects[0], size_t(cgRects.size()));
+    }
+}
+
 static const QColor titlebarSeparatorLineActive(111, 111, 111);
 static const QColor titlebarSeparatorLineInactive(131, 131, 131);
 static const QColor darkModeSeparatorLine(88, 88, 88);
@@ -2976,6 +2997,8 @@ void QMacStyle::drawPrimitive(PrimitiveElement pe, const QStyleOption *opt, QPai
         // QDarkNSBox, of type NSBoxCustom. Its appearance is close enough to the real thing so
         // we can use this for now.
         d->drawNSViewInRect(box, opt->rect, p, ^(CGContextRef ctx, const CGRect &rect) {
+            if (QTabWidget *tabWidget = qobject_cast<QTabWidget *>(opt->styleObject))
+                clipTabBarFrame(opt, this, ctx);
             CGContextTranslateCTM(ctx, 0, rect.origin.y + rect.size.height);
             CGContextScaleCTM(ctx, 1, -1);
             if (QOperatingSystemVersion::current() < QOperatingSystemVersion::MacOSMojave
@@ -3699,6 +3722,12 @@ void QMacStyle::drawControl(ControlElement ce, const QStyleOption *opt, QPainter
             // inFrame:withView:], -[drawRect:] or anything in between. Besides,
             // there's no public API do draw the pressed state, AFAICS. We'll use
             // a push NSButton instead and clip the CGContext.
+            // NOTE/TODO: this is not true. On 10.13 NSSegmentedControl works with
+            // some (black?) magic/magic dances, on 10.14 it simply works (was
+            // it fixed in AppKit?). But, indeed, we cannot make a tab 'pressed'
+            // with NSSegmentedControl (only selected), so we stay with buttons
+            // (mixing buttons and NSSegmentedControl for such a simple thing
+            // is too much work).
 
             const auto cs = d->effectiveAquaSizeConstrain(opt, w);
             // Extra hacks to get the proper pressed appreance when not selected or selected and inactive