Revert 166986 - Make the fling acceleration curve be easily configurable.

Broke the build at: http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%28dbg%29%283%29/builds/16022

A previous CL introduced a smooth curve for computing an acceleration
to be applied at the start of a touchscreen fling. This CL adds the
curve coefficients to the gesture configuration page.

BUG=141653


Review URL: https://chromiumcodereview.appspot.com/11369140

TBR=rjkroege@chromium.org
Review URL: https://codereview.chromium.org/11312176

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@166998 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 61 insertions, 24 deletions

diff --git a/ui/base/gestures/gesture_configuration.cc b/ui/base/gestures/gesture_configuration.cc
index 8310ed8..a3b289f 100644
--- a/ui/base/gestures/gesture_configuration.cc
+++ b/ui/base/gestures/gesture_configuration.cc
@@ -40,15 +40,7 @@ int GestureConfiguration::points_buffered_for_velocity_ = 3;
 double GestureConfiguration::rail_break_proportion_ = 15;
 double GestureConfiguration::rail_start_proportion_ = 2;
 
-// Coefficients for a function that computes fling acceleration.
-// These are empirically determined defaults. Do not adjust without
-// additional empirical validation.
-float GestureConfiguration::fling_acceleration_curve_coefficients_[
-    NumAccelParams] = {
-  0.0166667f,
-  -0.0238095f,
-  0.0452381f,
-  0.8f
-};
+// The additional acceleration to apply to touchscreen flings.
+double GestureConfiguration::touchscreen_fling_acceleration_adjustment_ = 0.85;
 
 }  // namespace ui
diff --git a/ui/base/gestures/gesture_configuration.h b/ui/base/gestures/gesture_configuration.h
index 256c5d2..d0b5cbc 100644
--- a/ui/base/gestures/gesture_configuration.h
+++ b/ui/base/gestures/gesture_configuration.h
@@ -16,10 +16,6 @@ namespace ui {
 
 class UI_EXPORT GestureConfiguration {
  public:
-  // Number of parameters in the array of parameters for the fling acceleration
-  // curve.
-  static const int NumAccelParams = 4;
-
   // Ordered alphabetically ignoring underscores, to align with the
   // associated list of prefs in gesture_prefs_aura.cc.
   static int default_radius() {
@@ -143,11 +139,11 @@ class UI_EXPORT GestureConfiguration {
   static void set_rail_start_proportion(double val) {
     rail_start_proportion_ = val;
   }
-  static void set_fling_acceleration_curve_coefficients(int i, float val) {
-    fling_acceleration_curve_coefficients_[i] = val;
+  static double touchscreen_fling_acceleration_adjustment() {
+    return touchscreen_fling_acceleration_adjustment_;
   }
-  static float fling_acceleration_curve_coefficients(int i) {
-    return fling_acceleration_curve_coefficients_[i];
+  static void set_touchscreen_fling_acceleration_adjustment(double val) {
+    touchscreen_fling_acceleration_adjustment_ = val;
   }
 
  private:
@@ -186,7 +182,7 @@ class UI_EXPORT GestureConfiguration {
   static int points_buffered_for_velocity_;
   static double rail_break_proportion_;
   static double rail_start_proportion_;
-  static float fling_acceleration_curve_coefficients_[NumAccelParams];
+  static double touchscreen_fling_acceleration_adjustment_;
 
   DISALLOW_COPY_AND_ASSIGN(GestureConfiguration);
 };
diff --git a/ui/base/gestures/gesture_sequence.cc b/ui/base/gestures/gesture_sequence.cc
index 115229a..c4a6d31 100644
--- a/ui/base/gestures/gesture_sequence.cc
+++ b/ui/base/gestures/gesture_sequence.cc
@@ -7,6 +7,7 @@
 #include <cmath>
 #include <stdlib.h>
 
+#include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/string_number_conversions.h"
@@ -285,20 +286,68 @@ unsigned int ComputeTouchBitmask(const GesturePoint* points) {
 
 const float kFlingCurveNormalization = 1.0f / 1875.f;
 
-float CalibrateFlingVelocity(float velocity) {
-  const unsigned last_coefficient =
-      GestureConfiguration::NumAccelParams - 1;
+// TODO(rjkroege): Make this configurable from the config page.
+// Touchscreen fling acceleration is cubic function of four
+// parameters. These are empirically determined defaults.
+// Do not adjust the default values without empirical validation.
+static float fling_acceleration_curve_coefficients[4] = {
+    0.0166667f,
+    -0.0238095f,
+    0.0452381f,
+    0.8f
+};
+
+// Read 4 comma-separated floating point values from an environment
+// variable and use that to configure the fling acceleration curve.
+void ReadFlingVelocityScalingIfNecessary() {
+  static bool did_setup_scaling = false;
+  if (did_setup_scaling)
+    return;
+  did_setup_scaling = true;
+  char* pk = getenv("FLING_ACCELERATION_CURVE_COEFFICIENTS");
+  if (!pk)
+      return;
+  LOG(INFO) << "Attempting to configure fling from environment.\n";
+
+  unsigned coefficient_count = arraysize(fling_acceleration_curve_coefficients);
+  unsigned i = 0;
+  CStringTokenizer t(pk, pk + strlen(pk), ",");
+  while (t.GetNext() && i < coefficient_count) {
+    double d;
+    if (base::StringToDouble(t.token(), &d)) {
+      fling_acceleration_curve_coefficients[i++] = d;
+    } else {
+      LOG(WARNING)
+          << "BANDED_FLING_VELOCITY_ADJUSTMENT bad value: "
+          << t.token();
+    }
+  }
+}
+
+float SmoothFlingVelocityAdjustment(float velocity) {
+  ReadFlingVelocityScalingIfNecessary();
+  unsigned last_coefficient =
+      arraysize(fling_acceleration_curve_coefficients) - 1;
   float normalized_velocity = fabs(velocity * kFlingCurveNormalization);
   float nu = 0.0f, x = 1.f;
 
   for (int i = last_coefficient ; i >= 0; i--) {
-    float a = GestureConfiguration::fling_acceleration_curve_coefficients(i);
-    nu += x * a;
+    nu += x * fling_acceleration_curve_coefficients[i];
     x *= normalized_velocity;
   }
   return nu * velocity;
 }
 
+// TODO(rjkroege): Provide a nicer means to turn this feature on/off.
+float CalibrateFlingVelocity(float velocity) {
+ const float velocity_scaling  =
+    GestureConfiguration::touchscreen_fling_acceleration_adjustment();
+  if (velocity_scaling < 0.5f)
+    return SmoothFlingVelocityAdjustment(velocity);
+  else
+    return velocity_scaling * velocity;
+}
+
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////