First Implementation of Snapped Points

ui/events/gestures/fling_curve.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/events/gestures/fling_curve.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/logging.h"
@@ skipping 12 matching lines @@
 inline double GetVelocityAtTime(double t) {
   return -kDefaultAlpha * kDefaultGamma * exp(-kDefaultGamma * t) -
          kDefaultBeta;
 }
 
 inline double GetTimeAtVelocity(double v) {
   return -log((v + kDefaultBeta) / (-kDefaultAlpha * kDefaultGamma)) /
          kDefaultGamma;
 }
 
+inline double GetTimeAtPosition(double p) {
+  // TODO(sunyunjia): Set a range for the time for faster interpolation.
+  double tl = 0;
+  double tr = GetTimeAtVelocity(0);
+  p = GetPositionAtTime(tr) - p;
+  double tm = (tl + tr) / 2;
+  double pm = GetPositionAtTime(tm);
+  while (fabs(pm - p) > 0.001) {
+    if (pm < p)
+      tl = tm;
+    else
+      tr = tm;
+    tm = (tl + tr) / 2;
+    pm = GetPositionAtTime(tm);
+  }
+  return tm;
+}
+
 }  // namespace
 
 namespace ui {
 
 FlingCurve::FlingCurve(const gfx::Vector2dF& velocity,
                        base::TimeTicks start_timestamp)
     : curve_duration_(GetTimeAtVelocity(0)),
       start_timestamp_(start_timestamp),
       previous_timestamp_(start_timestamp_),
       time_offset_(0),
@@ skipping 54 matching lines @@
   previous_timestamp_ = current;
 
   gfx::Vector2dF offset, velocity;
   bool still_active = ComputeScrollOffset(current, &offset, &velocity);
 
   *delta = offset - cumulative_scroll_;
   cumulative_scroll_ = offset;
   return still_active;
 }
 
+void FlingCurve::ComputeTotalScrollOffset(gfx::Vector2dF& offset) {
+  float scalar_offset = GetPositionAtTime(curve_duration_) - position_offset_;
+  offset = gfx::ScaleVector2d(displacement_ratio_, scalar_offset);
+}
+
+bool FlingCurve::ResetCurveBySnappedOffset(const gfx::Vector2dF& offset) {
+  float max_offset = std::max(fabs(offset.x()), fabs(offset.y()));
+  if (max_offset > GetPositionAtTime(0)) {
+    return false;
+  }
+  displacement_ratio_ =
+      gfx::Vector2dF(offset.x() / max_offset, offset.y() / max_offset);
+
+  time_offset_ = GetTimeAtPosition(max_offset);
+  position_offset_ = GetPositionAtTime(time_offset_);
+  return true;
+}
+
 }  // namespace ui