[LyX/master] #12434 add event handler for pinch-to-zoom gesture

[Stephan Witt]

commit d4324034300f73f76e5ac34fb1e7653fa6e2ddf5
Author: Stephan Witt <switt at lyx.org>
Date:   Mon Jan 3 07:37:03 2022 +0100

    #12434 add event handler for pinch-to-zoom gesture
---
 src/frontends/qt/GuiView.cpp |   20 ++++++++++++++++++++
 1 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/src/frontends/qt/GuiView.cpp b/src/frontends/qt/GuiView.cpp
index ffcbc3d..791a2c2 100644
--- a/src/frontends/qt/GuiView.cpp
+++ b/src/frontends/qt/GuiView.cpp
@@ -110,6 +110,8 @@
 #include <QTimer>
 #include <QUrl>
 #include <QWindowStateChangeEvent>
+#include <QGestureEvent>
+#include <QPinchGesture>
 
 
 // sync with GuiAlert.cpp
@@ -694,6 +696,9 @@ GuiView::GuiView(int id)
 	connect(statusBar(), SIGNAL(customContextMenuRequested(QPoint)),
 		this, SLOT(showZoomContextMenu()));
 
+	// enable pinch to zoom
+	grabGesture(Qt::PinchGesture);
+
 	int const iconheight = max(int(d.normalIconSize), fm.height());
 	QSize const iconsize(iconheight, iconheight);
 
@@ -1621,6 +1626,21 @@ bool GuiView::event(QEvent * e)
 		return QMainWindow::event(e);
 	}
 
+	case QEvent::Gesture: {
+		QGestureEvent *ge = static_cast<QGestureEvent*>(e);
+		QGesture *gp = ge->gesture(Qt::PinchGesture);
+		if (gp) {
+			QPinchGesture *pinch = static_cast<QPinchGesture *>(gp);
+			QPinchGesture::ChangeFlags changeFlags = pinch->changeFlags();
+			if (changeFlags & QPinchGesture::ScaleFactorChanged) {
+				qreal factor = lyxrc.currentZoom*pinch->scaleFactor();
+				//factor = ceil(factor/20)*20;
+				zoomValueChanged(factor);
+			}
+		}
+		return QMainWindow::event(e);
+	}
+
 	default:
 		return QMainWindow::event(e);
 	}