From c949c0c407bbd1742a03b7189ee42c59f03dcbae Mon Sep 17 00:00:00 2001
From: Daria Volvenkova <d.volvenkova@corp.mail.ru>
Date: Mon, 6 Jun 2016 11:54:32 +0300
Subject: [PATCH] Set perspective angle automatically when the scale is
 changing.

---
 drape_frontend/navigator.cpp         |  7 +++++++
 drape_frontend/navigator.hpp         |  1 +
 drape_frontend/user_event_stream.cpp |  3 +++
 geometry/screenbase.cpp              | 25 +++++++++++++++++++++++++
 geometry/screenbase.hpp              |  3 +++
 5 files changed, 39 insertions(+)

diff --git a/drape_frontend/navigator.cpp b/drape_frontend/navigator.cpp
index f695b9917e..b68c595e37 100644
--- a/drape_frontend/navigator.cpp
+++ b/drape_frontend/navigator.cpp
@@ -307,6 +307,13 @@ void Navigator::Disable3dMode()
     m_Screen.ResetPerspective();
 }
 
+bool Navigator::UpdatePerspective()
+{
+  bool const isPerspective = m_Screen.isPerspective();
+  m_Screen.UpdatePerspectiveParameters();
+  return isPerspective != m_Screen.isPerspective();
+}
+
 m2::AnyRectD ToRotated(Navigator const & navigator, m2::RectD const & rect)
 {
   double const dx = rect.SizeX();
diff --git a/drape_frontend/navigator.hpp b/drape_frontend/navigator.hpp
index ba6773e442..6e05419e81 100644
--- a/drape_frontend/navigator.hpp
+++ b/drape_frontend/navigator.hpp
@@ -46,6 +46,7 @@ public:
   void Enable3dMode(double currentRotationAngle, double maxRotationAngle, double angleFOV);
   void SetRotationIn3dMode(double rotationAngle);
   void Disable3dMode();
+  bool UpdatePerspective();
 
 private:
   // Internal screen corresponding to the state when navigation began with StartDrag or StartScale.
diff --git a/drape_frontend/user_event_stream.cpp b/drape_frontend/user_event_stream.cpp
index 622c4b6a10..4fe138b586 100644
--- a/drape_frontend/user_event_stream.cpp
+++ b/drape_frontend/user_event_stream.cpp
@@ -267,6 +267,9 @@ ScreenBase const & UserEventStream::ProcessEvents(bool & modelViewChanged, bool
       DetectLongTap(m_touches[0]);
   }
 
+  if (m_modelViewChanged)
+    m_viewportChanged |= m_navigator.UpdatePerspective();
+
   modelViewChanged = m_modelViewChanged;
   viewportChanged = m_viewportChanged;
   m_modelViewChanged = false;
diff --git a/geometry/screenbase.cpp b/geometry/screenbase.cpp
index b46a6da78c..fd5ce38f9b 100644
--- a/geometry/screenbase.cpp
+++ b/geometry/screenbase.cpp
@@ -75,6 +75,31 @@ void ScreenBase::UpdateDependentParameters()
   m_ClipRect = m_GlobalRect.GetGlobalRect();
 }
 
+double ScreenBase::CalculatePerspectiveAngle(double scale)
+{
+  double const kStartPerspectiveScale = 0.13e-4;
+  double const kMaxScale = 0.13e-5;
+  double const kMaxPerspectiveAngle = math::pi4;
+
+  if (scale > kStartPerspectiveScale)
+    return 0.0;
+  return kMaxPerspectiveAngle * (kStartPerspectiveScale - scale) / (kStartPerspectiveScale - kMaxScale);
+}
+
+void ScreenBase::UpdatePerspectiveParameters()
+{
+  double const angle = CalculatePerspectiveAngle(m_Scale);
+  if (angle > 0.0)
+  {
+    if (m_isPerspective)
+      SetRotationAngle(angle);
+    else
+      ApplyPerspective(angle, math::pi4, math::pi / 3);
+  }
+  else if (m_isPerspective)
+    ResetPerspective();
+}
+
 void ScreenBase::SetFromRects(m2::AnyRectD const & glbRect, m2::RectD const & pxRect)
 {
   double hScale = glbRect.GetLocalRect().SizeX() / pxRect.SizeX();
diff --git a/geometry/screenbase.hpp b/geometry/screenbase.hpp
index 93959d9998..ef5125d9e4 100644
--- a/geometry/screenbase.hpp
+++ b/geometry/screenbase.hpp
@@ -126,6 +126,7 @@ public:
   m2::AnyRectD const & GlobalRect() const { return m_GlobalRect; }
   m2::RectD const & ClipRect() const { return m_ClipRect; }
 
+  void UpdatePerspectiveParameters();
   void ApplyPerspective(double currentRotationAngle, double maxRotationAngle, double angleFOV);
   void ResetPerspective();
 
@@ -156,6 +157,8 @@ public:
                                      m2::PointD const & newPt1, m2::PointD const & newPt2,
                                      bool allowRotate);
 
+  static double CalculatePerspectiveAngle(double scale);
+
   /// Setting GtoP matrix extracts the Angle and m_Org parameters, leaving PixelRect intact
   void SetGtoPMatrix(MatrixT const & m);