[Android] Use DIP coordinates for GestureFlingStart events

webkit/child/fling_animator_impl_android.cc

Index: webkit/child/fling_animator_impl_android.cc
diff --git a/webkit/child/fling_animator_impl_android.cc b/webkit/child/fling_animator_impl_android.cc
index 668076ba235cfa9decadaa14c13743552ecfba42..c5e5d3d796cb363cccd02d5a602b86f6851130c7 100644
--- a/webkit/child/fling_animator_impl_android.cc
+++ b/webkit/child/fling_animator_impl_android.cc
@@ -20,7 +20,9 @@ static const float kEpsilon = 1e-4;
 }
 
 FlingAnimatorImpl::FlingAnimatorImpl()
-    : is_active_(false) {
+    : is_active_(false),
+      last_time_(0),
+      dpi_scale_(1) {
   // hold the global reference of the Java objects.
   JNIEnv* env = base::android::AttachCurrentThread();
   java_scroller_.Reset(JNI_OverScroller::Java_OverScroller_ConstructorAWOS_ACC(
@@ -50,13 +52,17 @@ void FlingAnimatorImpl::StartFling(const gfx::PointF& velocity)
   is_active_ = true;
   last_time_ = 0;
   last_velocity_ = velocity;
+  dpi_scale_ = gfx::Screen::GetNativeScreen()->GetPrimaryDisplay()

[jamesr, 2014/02/18 22:40:46]

let's not do this. if you want to add a cache for the scale factor put it
somewhere where we have a chance of notifying it on updates

[jdduke (slow), 2014/02/18 22:51:29]

Done.

+      .device_scale_factor();
 
   JNIEnv* env = base::android::AttachCurrentThread();
 
+  // The OverScroller deceleration constants work in pixel space.  DIP scaling
+  // will be performed in |apply()| on the generated fling updates.
   JNI_OverScroller::Java_OverScroller_flingV_I_I_I_I_I_I_I_I(
       env, java_scroller_.obj(), 0, 0,
-      static_cast<int>(velocity.x()),
-      static_cast<int>(velocity.y()),
+      static_cast<int>(velocity.x() * dpi_scale_),
+      static_cast<int>(velocity.y() * dpi_scale_),
       INT_MIN, INT_MAX, INT_MIN, INT_MAX);
 }
 
@@ -105,10 +111,8 @@ bool FlingAnimatorImpl::apply(double time,
   gfx::Point current_position = GetCurrentPosition();
   gfx::Vector2d diff(current_position - last_position_);
   last_position_ = current_position;
-  float dpi_scale = gfx::Screen::GetNativeScreen()->GetPrimaryDisplay()
-      .device_scale_factor();
-  blink::WebFloatSize scroll_amount(diff.x() / dpi_scale,
-                                     diff.y() / dpi_scale);
+  blink::WebFloatSize scroll_amount(diff.x() / dpi_scale_,
+                                     diff.y() / dpi_scale_);

[jamesr, 2014/02/18 22:40:46]

bad alignment

[jdduke (slow), 2014/02/18 22:51:29]

Done.

 
   float delta_time = time - last_time_;
   last_time_ = time;
@@ -127,8 +131,8 @@ bool FlingAnimatorImpl::apply(double time,
     }
   }
   last_velocity_ = current_velocity;
-  blink::WebFloatSize fling_velocity(current_velocity.x() / dpi_scale,
-                                      current_velocity.y() / dpi_scale);
+  blink::WebFloatSize fling_velocity(current_velocity.x() / dpi_scale_,
+                                      current_velocity.y() / dpi_scale_);

[jamesr, 2014/02/18 22:40:46]

bad alignment

[jdduke (slow), 2014/02/18 22:51:29]

Done.

   target->notifyCurrentFlingVelocity(fling_velocity);
 
   // scrollBy() could delete this curve if the animation is over, so don't touch