[LyX/master] Fix dark/light mode setting and run-time switch with Qt 6.8

[Juergen Spitzmueller]

commit 4560cfd0126e11919a20a671944cad97363d8ba9
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Mon Oct 21 12:34:57 2024 +0200

    Fix dark/light mode setting and run-time switch with Qt 6.8
    
    The old method doesn't work any longer. This one is also announced to
    work cross OSes -- verification on Mac and Win is needed!
---
 src/frontends/qt/ColorCache.cpp     |  7 +++----
 src/frontends/qt/GuiApplication.cpp |  7 ++-----
 src/frontends/qt/GuiView.cpp        | 18 +++++++++++++++---
 3 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/src/frontends/qt/ColorCache.cpp b/src/frontends/qt/ColorCache.cpp
index 2566b75025..de8ff77a56 100644
--- a/src/frontends/qt/ColorCache.cpp
+++ b/src/frontends/qt/ColorCache.cpp
@@ -124,10 +124,9 @@ bool ColorCache::isSystem(ColorCode const color) const
 
 bool ColorCache::isDarkMode() const
 {
-	QPalette palette = QPalette();
-	QColor text_color = palette.color(QPalette::Active, QPalette::WindowText);
-	QColor bg_color = palette.color(QPalette::Active, QPalette::Window);
-	
+	QColor text_color = pal_.color(QPalette::Active, QPalette::WindowText);
+	QColor bg_color = pal_.color(QPalette::Active, QPalette::Window);
+
 	return (text_color.black() < bg_color.black());
 }
 
diff --git a/src/frontends/qt/GuiApplication.cpp b/src/frontends/qt/GuiApplication.cpp
index 082ca57444..5685b1a0ef 100644
--- a/src/frontends/qt/GuiApplication.cpp
+++ b/src/frontends/qt/GuiApplication.cpp
@@ -639,17 +639,14 @@ IconInfo iconInfo(FuncRequest const & f, bool unknown, bool rtl)
 
 QPixmap prepareForDarkMode(QPixmap pixmap)
 {
-	QPalette palette = QPalette();
-	QColor text_color = palette.color(QPalette::Active, QPalette::WindowText);
-	QColor bg_color = palette.color(QPalette::Active, QPalette::Window);
-
 	// guess whether we are in dark mode
-	if (text_color.black() > bg_color.black())
+	if (!theGuiApp()->isInDarkMode())
 		// not in dark mode, do nothing
 		return pixmap;
 
 	// create a layer with black text turned to QPalette::WindowText
 	QPixmap black_overlay(pixmap.size());
+	QColor text_color = theGuiApp()->style()->standardPalette().color(QPalette::Active, QPalette::WindowText);
 	black_overlay.fill(text_color);
 	black_overlay.setMask(pixmap.createMaskFromColor(Qt::black, Qt::MaskOutColor));
 
diff --git a/src/frontends/qt/GuiView.cpp b/src/frontends/qt/GuiView.cpp
index ae2a604b22..99278bcbd4 100644
--- a/src/frontends/qt/GuiView.cpp
+++ b/src/frontends/qt/GuiView.cpp
@@ -659,7 +659,6 @@ GuiView::GuiView(int id)
 
 	stat_counts_ = new GuiClickableLabel(statusBar());
 	stat_counts_->setAlignment(Qt::AlignCenter);
-	stat_counts_->setStyleSheet("padding-left: 5px; padding-right: 5px;");
 	stat_counts_->hide();
 	statusBar()->addPermanentWidget(stat_counts_);
 
@@ -1509,7 +1508,9 @@ void GuiView::showStats()
 		else
 			stats << toqstr(bformat(_("%1$d Characters (no Blanks)"), chars));
 	}
-	stat_counts_->setText(stats.join(qt_(", [[stats separator]]")));
+	// we need to add space before and after manually, using stylesheet
+	// would break with dark mode on Qt >= 6.8.
+	stat_counts_->setText(" " + stats.join(qt_(", [[stats separator]]")) + " ");
 	stat_counts_->show();
 
 	d.time_to_update = d.default_stats_rate;
@@ -1793,7 +1794,17 @@ bool GuiView::event(QEvent * e)
 		return QMainWindow::event(e);
 	}
 
-	// dark/light mode runtime switch support, OS-dependent.
+	// dark/light mode runtime switch support
+#if QT_VERSION >= QT_VERSION_CHECK(6, 8, 0)
+	case QEvent::ThemeChange: {
+		guiApp->setPalette(guiApp->style()->standardPalette());
+		// We need to update metrics here to avoid a crash (#12786)
+		theBufferList().changed(true);
+		refillToolbars();
+		return QMainWindow::event(e);
+	}
+#else
+	// Pre 6.8: OS-dependent
 	// 1. Mac OS X
 	// Limit to Q_OS_MAC as this unnecessarily would also
 	// trigger on Linux with grave performance issues
@@ -1811,6 +1822,7 @@ bool GuiView::event(QEvent * e)
 		theBufferList().changed(true);
 		return QMainWindow::event(e);
 	}
+#endif
 
 	default:
 		return QMainWindow::event(e);