From 3ec969a001f1c840e3a3d199b8224865ff4990ff Mon Sep 17 00:00:00 2001
From: Ryan Govostes <rgovostes+git@gmail.com>
Date: Wed, 20 Mar 2019 00:19:45 -0400
Subject: [PATCH 3/3] Partial progress towards using the Qt gesture recognition
 API

---
 pv/views/trace/viewport.cpp | 71 ++++++++++++++++++-------------------
 pv/views/trace/viewport.hpp | 16 +++++----
 2 files changed, 44 insertions(+), 43 deletions(-)

diff --git a/pv/views/trace/viewport.cpp b/pv/views/trace/viewport.cpp
index 44c912a..d1522e0 100644
--- a/pv/views/trace/viewport.cpp
+++ b/pv/views/trace/viewport.cpp
@@ -49,11 +49,14 @@ namespace views {
 namespace trace {
 
 Viewport::Viewport(View &parent) :
-	ViewWidget(parent),
-	pinch_zoom_active_(false)
+	ViewWidget(parent)
 {
 	setAutoFillBackground(true);
 	setBackgroundRole(QPalette::Base);
+
+	// Register for gestures
+	grabGesture(Qt::PanGesture);
+	grabGesture(Qt::PinchGesture);
 }
 
 shared_ptr<ViewItem> Viewport::get_mouse_over_item(const QPoint &pt)
@@ -108,49 +111,43 @@ vector< shared_ptr<ViewItem> > Viewport::items()
 	return items;
 }
 
-bool Viewport::touch_event(QTouchEvent *event)
+bool Viewport::event(QEvent *event)
 {
-	QList<QTouchEvent::TouchPoint> touchPoints = event->touchPoints();
-
-	if (touchPoints.count() != 2) {
-		pinch_zoom_active_ = false;
-		return false;
-	}
+	if (event->type() == QEvent::Gesture)
+		return gestureEvent(static_cast<QGestureEvent*>(event));
+	return ViewWidget::event(event);
+}
 
-	const QTouchEvent::TouchPoint &touchPoint0 = touchPoints.first();
-	const QTouchEvent::TouchPoint &touchPoint1 = touchPoints.last();
+bool Viewport::gestureEvent(QGestureEvent *event)
+{
+	assert(event);
 
-	if (!pinch_zoom_active_ ||
-	    (event->touchPointStates() & Qt::TouchPointPressed)) {
-		pinch_offset0_ = (view_.offset() + view_.scale() * touchPoint0.pos().x()).convert_to<double>();
-		pinch_offset1_ = (view_.offset() + view_.scale() * touchPoint1.pos().x()).convert_to<double>();
-		pinch_zoom_active_ = true;
-	}
+	// Handle pinch-to-zoom gestures
+	if (auto pinch = static_cast<QPinchGesture *>(event->gesture(Qt::PinchGesture))) {
+		if (pinch->state() == Qt::GestureStarted) {
+			gesture_start_scale_ = view_.scale();
+			gesture_start_offset_ = view_.offset();
+		}
 
-	double w = touchPoint1.pos().x() - touchPoint0.pos().x();
-	if (abs(w) >= 1.0) {
-		const double scale =
-			fabs((pinch_offset1_ - pinch_offset0_) / w);
-		double offset = pinch_offset0_ - touchPoint0.pos().x() * scale;
-		if (scale > 0)
-			view_.set_scale_offset(scale, offset);
+		// FIXME: Make pinch-to-zoom more intuitive
+		auto flags = QPinchGesture::ScaleFactorChanged | QPinchGesture::CenterPointChanged;
+		if (pinch->changeFlags() & flags) {
+			double scale = gesture_start_scale_ * pinch->totalScaleFactor();
+			double xdelta = pinch->centerPoint().x() - pinch->startCenterPoint().x();
+			pv::util::Timestamp offset = gesture_start_offset_ + xdelta * scale;
+			if (scale > 0.0) {
+				view_.set_scale_offset(scale, offset);
+			}
+		}
+		return true;
 	}
 
-	if (event->touchPointStates() & Qt::TouchPointReleased) {
-		pinch_zoom_active_ = false;
-
-		if (touchPoint0.state() & Qt::TouchPointReleased) {
-			// Primary touch released
-			drag_release();
-		} else {
-			// Update the mouse down fields so that continued
-			// dragging with the primary touch will work correctly
-			mouse_down_point_ = touchPoint0.pos().toPoint();
-			drag();
-		}
+	if (auto pan = static_cast<QPanGesture *>(event->gesture(Qt::PanGesture))) {
+		// TODO: Implement
+		return true;
 	}
 
-	return true;
+	return false;
 }
 
 void Viewport::paintEvent(QPaintEvent*)
diff --git a/pv/views/trace/viewport.hpp b/pv/views/trace/viewport.hpp
index 1b77a0d..d633798 100644
--- a/pv/views/trace/viewport.hpp
+++ b/pv/views/trace/viewport.hpp
@@ -22,9 +22,9 @@
 
 #include <boost/optional.hpp>
 
+#include <QGestureEvent>
 #include <QPoint>
 #include <QTimer>
-#include <QTouchEvent>
 
 #include "pv/util.hpp"
 #include "viewwidget.hpp"
@@ -87,10 +87,15 @@ private:
 	vector< shared_ptr<ViewItem> > items();
 
 	/**
-	 * Handles touch begin update and end events.
+	 * Main event handler; dispatches gesture events to gestureEvent().
+	 */
+	bool event(QEvent *event);
+
+	/**
+	 * Handles gesture-related events.
 	 * @param e the event that triggered this handler.
 	 */
-	bool touch_event(QTouchEvent *event);
+	bool gestureEvent(QGestureEvent *event);
 
 private:
 	void paintEvent(QPaintEvent *event);
@@ -102,9 +107,8 @@ private:
 	boost::optional<pv::util::Timestamp> drag_offset_;
 	int drag_v_offset_;
 
-	double pinch_offset0_;
-	double pinch_offset1_;
-	bool pinch_zoom_active_;
+	double gesture_start_scale_;
+	pv::util::Timestamp gesture_start_offset_;
 };
 
 } // namespace trace
-- 
2.20.1