[Blueprint] Add force focus when mouse enters render window

Changelog.md

@@ -5,6 +5,9 @@
 1. Add ability to save worlds to SDFormat
     * [BitBucket pull request 545](https://osrf-migration.github.io/ignition-gh-pages/#!/ignitionrobotics/ign-gazebo/pull-requests/545)
 
+1. Add window focus upon mouse entering the render window
+    * [Github pull request 95](https://github.com/ignitionrobotics/ign-gazebo/pull/95)
+
 ### Ignition Gazebo 2.16.0 (2020-03-24)
 
 1. Add support for computing model bounding box in physics system

src/gui/plugins/scene3d/GzScene3D.qml

@@ -37,6 +37,9 @@ Rectangle {
     anchors.fill: parent
     hoverEnabled: true
     acceptedButtons: Qt.NoButton
+    onEntered: {
+      GzScene3D.OnFocusWindow()
+    }
   }
 
   RenderWindow {

src/gui/plugins/scene3d/Scene3D.cc

@@ -2047,6 +2047,13 @@ void Scene3D::OnDropped(const QString &_drop, int _mouseX, int _mouseY)
       req, cb);
 }
 
+/////////////////////////////////////////////////
+void Scene3D::OnFocusWindow()
+{
+  auto renderWindow = this->PluginItem()->findChild<RenderWindowItem *>();
+  renderWindow->forceActiveFocus();
+}
+
 /////////////////////////////////////////////////
 void RenderWindowItem::SetXYZSnap(const math::Vector3d &_xyz)
 {

src/gui/plugins/scene3d/Scene3D.hh

@@ -96,6 +96,10 @@ inline namespace IGNITION_GAZEBO_VERSION_NAMESPACE {
     public slots: void OnDropped(const QString &_drop,
         int _mouseX, int _mouseY);
 
+    /// \brief Callback when the mouse enters the render window to
+    /// focus the window for mouse/key events
+    public slots: void OnFocusWindow();
+
     // Documentation inherited
     protected: bool eventFilter(QObject *_obj, QEvent *_event) override;