From b116a92be3af709192fcdce8a787c64f6defeb8d Mon Sep 17 00:00:00 2001
From: Maxime Gimeno <maxime.gimeno@gmail.com>
Date: Fri, 23 Oct 2020 12:21:16 +0200
Subject: [PATCH] Center the camera on the cursor at first tick of optical zoom

---
 GraphicsView/include/CGAL/Qt/qglviewer.h      |  4 ++-
 GraphicsView/include/CGAL/Qt/qglviewer_impl.h | 26 ++++++++++---------
 2 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/GraphicsView/include/CGAL/Qt/qglviewer.h b/GraphicsView/include/CGAL/Qt/qglviewer.h
index 540e15119a1..045ae469063 100644
--- a/GraphicsView/include/CGAL/Qt/qglviewer.h
+++ b/GraphicsView/include/CGAL/Qt/qglviewer.h
@@ -1167,7 +1167,6 @@ protected:
   QMap<WheelBindingPrivate, MouseActionPrivate> wheelBinding_;
   QMap<ClickBindingPrivate, qglviewer::ClickAction> clickBinding_;
   ::Qt::Key currentlyPressedKey_;
-  bool z_is_pressed;
   // S t a t e   F i l e
   QString stateFileName_;
 
@@ -1212,6 +1211,9 @@ protected:
   bool is_sharing;
   bool is_linked;
   QOpenGLContext* shared_context;
+  // Zoom
+  bool _first_tick;
+
 public:
   //! Is used to know if the openGL context is 4.3 or ES 2.0.
   //! @returns `true` if the context is 4.3.
diff --git a/GraphicsView/include/CGAL/Qt/qglviewer_impl.h b/GraphicsView/include/CGAL/Qt/qglviewer_impl.h
index 411f9d18bc2..add5d8df7fd 100644
--- a/GraphicsView/include/CGAL/Qt/qglviewer_impl.h
+++ b/GraphicsView/include/CGAL/Qt/qglviewer_impl.h
@@ -155,6 +155,7 @@ void CGAL::QGLViewer::defaultConstructor() {
   is_sharing = false;
   is_linked = false;
   shared_context = nullptr;
+  _first_tick  = true;
 }
 
 CGAL_INLINE_FUNCTION
@@ -1544,6 +1545,17 @@ void CGAL::QGLViewer::wheelEvent(QWheelEvent *e) {
       MouseActionPrivate map = wheelBinding_[wbp];
       switch (map.handler) {
       case qglviewer::CAMERA:
+        if(currentlyPressedKey_ == ::Qt::Key_Z && _first_tick)
+        {
+          _first_tick = false;
+          makeCurrent();
+          //orient camera to the cursor.
+          bool found = false;
+          qglviewer::Vec point;
+          point = camera()->pointUnderPixel(mapFromGlobal(QCursor::pos()), found);
+          if(found)
+            camera()->lookAt(point);
+        }
         camera()->frame()->startAction(map.action, map.withConstraint);
         camera()->frame()->wheelEvent(e, camera());
         break;
@@ -2263,21 +2275,11 @@ void CGAL::QGLViewer::keyPressEvent(QKeyEvent *e) {
 
   const ::Qt::Key key = ::Qt::Key(e->key());
 
-  const ::Qt::KeyboardModifiers modifiers = e->modifiers();
-
   if(key == ::Qt::Key_Z && ! e->isAutoRepeat())
   {
-    makeCurrent();
-    //orient camera to the cursor.
-    bool found = false;
-    qglviewer::Vec point;
-    point = camera()->pointUnderPixel(mapFromGlobal(QCursor::pos()), found);
-    if(!found)
-      return;
-    camera()->lookAt(point);
-    update();
-    return;
+    _first_tick = true;
   }
+  const ::Qt::KeyboardModifiers modifiers = e->modifiers();
   QMap<qglviewer::KeyboardAction, unsigned int>::ConstIterator it = keyboardBinding_
                                                              .begin(),
                                                     end =