[Android] Use DIP coordinates for GestureFlingStart events

webkit/child/fling_animator_impl_android.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 "webkit/child/fling_animator_impl_android.h"
 
 #include "base/android/jni_android.h"
 #include "base/android/scoped_java_ref.h"
 #include "base/logging.h"
 #include "jni/OverScroller_jni.h"
 #include "third_party/WebKit/public/platform/WebFloatSize.h"
 #include "third_party/WebKit/public/platform/WebGestureCurveTarget.h"
 #include "ui/gfx/screen.h"
 #include "ui/gfx/vector2d.h"
 
 namespace webkit_glue {
 
 namespace {
 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(
       env,
       base::android::GetApplicationContext()));
 }
 
 FlingAnimatorImpl::~FlingAnimatorImpl()
 {
 }
 
 //static
 bool FlingAnimatorImpl::RegisterJni(JNIEnv* env) {
   return JNI_OverScroller::RegisterNativesImpl(env);
 }
 
 void FlingAnimatorImpl::StartFling(const gfx::PointF& velocity)
 {
   // No bounds on the fling. See http://webkit.org/b/96403
   // Instead, use the largest possible bounds for minX/maxX/minY/maxY. The
   // compositor will ignore any attempt to scroll beyond the end of the page.
 
   DCHECK(velocity.x() || velocity.y());
   if (is_active_)
     CancelFling();
 
   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);
 }
 
 void FlingAnimatorImpl::CancelFling()
 {
   if (!is_active_)
     return;
 
   is_active_ = false;
   JNIEnv* env = base::android::AttachCurrentThread();
@@ skipping 28 matching lines @@
 }
 
 bool FlingAnimatorImpl::apply(double time,
                               blink::WebGestureCurveTarget* target) {
   if (!UpdatePosition())
     return false;
 
   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;
 
   // Currently, the OverScroller only provides the velocity magnitude; use the
   // angle of the scroll delta to yield approximate x and y velocity components.
   // TODO(jdduke): Remove this when we can properly poll OverScroller velocity.
   gfx::PointF current_velocity = last_velocity_;
   if (delta_time > kEpsilon) {
     float diff_length = diff.Length();
     if (diff_length > kEpsilon) {
       float velocity = GetCurrentVelocity();
       float scroll_to_velocity = velocity / diff_length;
       current_velocity = gfx::PointF(diff.x() * scroll_to_velocity,
                                      diff.y() * scroll_to_velocity);
     }
   }
   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
   // any member variables after making that call.
   target->scrollBy(scroll_amount);
   return true;
 }
 
 FlingAnimatorImpl* FlingAnimatorImpl::CreateAndroidGestureCurve(
     const blink::WebFloatPoint& velocity,
     const blink::WebSize&) {
   FlingAnimatorImpl* gesture_curve = new FlingAnimatorImpl();
   gesture_curve->StartFling(velocity);
   return gesture_curve;
 }
 
 } // namespace webkit_glue