Add a mechanism to provide non-linear scaling of fling acceleration.

ui/base/gestures/gesture_sequence.cc

 // Copyright (c) 2012 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/base/gestures/gesture_sequence.h"
 
 #include <cmath>
+#include <stdlib.h>
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/string_number_conversions.h"
+#include "base//string_tokenizer.h"
 #include "base/time.h"
 #include "ui/base/events/event.h"
 #include "ui/base/events/event_constants.h"
 #include "ui/base/gestures/gesture_configuration.h"
 #include "ui/base/gestures/gesture_util.h"
 #include "ui/gfx/rect.h"
 
 namespace ui {
 
 namespace {
@@ skipping 252 matching lines @@
 
 unsigned int ComputeTouchBitmask(const GesturePoint* points) {
   unsigned int touch_bitmask = 0;
   for (int i = 0; i < GestureSequence::kMaxGesturePoints; ++i) {
     if (points[i].in_use())
       touch_bitmask |= 1 << points[i].touch_id();
   }
   return touch_bitmask;
 }
 
+// Number of different accelerations for fling velocity adjustment.
+const unsigned kNumberOfFlingVelocityBands = 8;
+
+// Fling acceleration bands.
+static float fling_scaling_bands[kNumberOfFlingVelocityBands];
+
+// Maximum fling velocity.
+const float kMaxFlingVelocityFromFinger = 15000.0f;
+
+// Setup a default flat fling acceleration profile.
+void SetDefaultFlingVelocityScaling() {
+  for (unsigned i = 0; i < kNumberOfFlingVelocityBands; i++) {
+    fling_scaling_bands[i] =
+        GestureConfiguration::touchscreen_fling_acceleration_adjustment();
+  }
+}
+
+// Read |kNumberOfFlingVelocityBands| comma-separated floating point
+// values from an environment variable and use that to configure the fling
+// velocity profile.
+void ReadFlingVelocityScalingIfNecessary() {
+  static bool did_setup_scaling = false;
+  if (did_setup_scaling)
+    return;
+  did_setup_scaling = true;
+  SetDefaultFlingVelocityScaling();
+  char* pk = getenv("BANDED_FLING_VELOCITY_ADJUSTMENT");
+  if (!pk)
+      return;
+  LOG(INFO) << "Attempting to configure fling from environment.\n";
+
+  unsigned i = 0;
+  CStringTokenizer t(pk, pk + strlen(pk), ",");
+  while (t.GetNext() && i < kNumberOfFlingVelocityBands) {
+    double d;
+    if (base::StringToDouble(t.token(), &d)) {
+      fling_scaling_bands[i++] = d;
+    } else {
+      LOG(WARNING)
+          << "BANDED_FLING_VELOCITY_ADJUSTMENT bad value: "
+          << t.token();
+    }
+  }
+}
+
 float CalibrateFlingVelocity(float velocity) {
-  const float velocity_scaling  =
-      GestureConfiguration::touchscreen_fling_acceleration_adjustment();
-  return velocity_scaling * velocity;
+  ReadFlingVelocityScalingIfNecessary();
+  float bounded_velocity =
+      std::min(fabsf(velocity), kMaxFlingVelocityFromFinger - 1.f);
+  int band =
+      (bounded_velocity / kMaxFlingVelocityFromFinger) *
+      kNumberOfFlingVelocityBands;
+  return fling_scaling_bands[band] * velocity;
 }
 
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
 // GestureSequence Public:
 
 GestureSequence::GestureSequence(GestureEventHelper* helper)
     : state_(GS_NO_GESTURE),
       flags_(0),
@@ skipping 784 matching lines @@
     return;
 
   // Since long press timer has been started, there should be a non-NULL point.
   const GesturePoint* point = GetPointByPointId(0);
   if (!ui::gestures::IsInsideManhattanSquare(point->first_touch_position(),
       event.location()))
     long_press_timer_->Stop();
 }
 
 }  // namespace ui