From 6d361300ba2b72211ab2ad4830448d7fc1b34be9 Mon Sep 17 00:00:00 2001
From: "r.kuznetsov" <r.kuznetsov@corp.mail.ru>
Date: Tue, 1 Sep 2015 10:35:40 +0300
Subject: [PATCH] Tuned kinetic scroll

---
 drape_frontend/kinetic_scroller.cpp | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/drape_frontend/kinetic_scroller.cpp b/drape_frontend/kinetic_scroller.cpp
index ea2eb31394..91d3bb923c 100644
--- a/drape_frontend/kinetic_scroller.cpp
+++ b/drape_frontend/kinetic_scroller.cpp
@@ -5,6 +5,12 @@
 namespace df
 {
 
+double const kKineticDuration = 0.375;
+double const kKineticFeedback = 0.2;
+double const kKineticFadeoff = 5.0;
+double const kKineticThreshold = 10.0;
+double const kKineticInertia = 0.8;
+
 class KineticScrollAnimation : public BaseModelViewAnimation
 {
 public:
@@ -23,7 +29,7 @@ public:
   {
     // current position = target position - amplutide * e ^ (elapsed / duration)
     // we calculate current position not based on start position, but based on target position
-    return m2::AnyRectD(m_targetCenter - m_direction * exp(-GetT()), m_angle, m_localRect);
+    return m2::AnyRectD(m_targetCenter - m_direction * exp(-kKineticFadeoff * GetT()), m_angle, m_localRect);
   }
 
   m2::AnyRectD GetTargetRect() const override
@@ -75,7 +81,7 @@ void KineticScroller::GrabViewRect(ScreenBase const & modelView, double timeStam
   // velocity on pixels
   double v = pxDeltaLength / elapsed;
   // at this point length(m_direction) already in pixel space, and delta normalized
-  m_direction = delta * 0.8 * v + m_direction * 0.2;
+  m_direction = delta * kKineticInertia * v + m_direction * (1.0 - kKineticInertia);
 
   m_lastTimestamp = timeStamp;
   m_lastRect = modelView.GlobalRect();
@@ -89,17 +95,16 @@ void KineticScroller::CancelGrab()
 
 unique_ptr<BaseModelViewAnimation> KineticScroller::CreateKineticAnimation(ScreenBase const & modelView)
 {
-  static double VELOCITY_THRESHOLD = 10.0 * VisualParams::Instance().GetVisualScale();
-  if (m_direction.Length() < VELOCITY_THRESHOLD)
+  static double kVelocityThreshold = kKineticThreshold * VisualParams::Instance().GetVisualScale();
+  if (m_direction.Length() < kVelocityThreshold)
     return unique_ptr<BaseModelViewAnimation>();
 
-  double const KINETIC_DURATION = 0.375;
   // Before we start animation we have to convert length(m_direction) from pixel space to mercator space
   m2::PointD center = m_lastRect.GlobalCenter();
-  double glbLength = 0.5 * (modelView.PtoG(modelView.GtoP(center) + m_direction) - center).Length();
+  double glbLength = kKineticFeedback * (modelView.PtoG(modelView.GtoP(center) + m_direction) - center).Length();
   return unique_ptr<BaseModelViewAnimation>(new KineticScrollAnimation(m_lastRect,
                                                                        m_direction.Normalize() * glbLength,
-                                                                       KINETIC_DURATION));
+                                                                       kKineticDuration));
 }
 
 } // namespace df