[Android] Add slack to allow refresh after overscrolling

content/browser/android/overscroll_controller_android.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 "content/browser/android/overscroll_controller_android.h"
 
 #include "base/android/build_info.h"
 #include "base/command_line.h"
 #include "cc/layers/layer.h"
 #include "cc/output/compositor_frame_metadata.h"
@@ skipping 12 matching lines @@
 namespace content {
 namespace {
 
 // Used for conditional creation of EdgeEffect types for the overscroll glow.
 const int kAndroidLSDKVersion = 21;
 
 // Default offset in dips from the top of the view beyond which the refresh
 // action will be activated.
 const int kDefaultRefreshDragTargetDips = 64;
 
+// If the glow effect alpha is greater than this value, the refresh effect will
+// be suppressed. This value was experimentally determined to provide a
+// reasonable balance between avoiding accidental refresh activation and
+// minimizing the wait required to refresh after the glow has been triggered.
+const float kMinGlowAlphaToDisableRefreshOnL = 0.085f;
+
 bool IsAndroidLOrNewer() {
   static bool android_l_or_newer =
       base::android::BuildInfo::GetInstance()->sdk_int() >= kAndroidLSDKVersion;
   return android_l_or_newer;
 }
 
-bool ShouldDisableRefreshWhenGlowActive() {
-  // Suppressing refresh detection when the glow is still animating prevents
-  // visual confusion and accidental activation after repeated scrolls. However,
-  // only the L effect is guaranteed to be both sufficiently brief and prominent
+// Suppressing refresh detection when the glow is still animating prevents
+// visual confusion and accidental activation after repeated scrolls.
+float MinGlowAlphaToDisableRefresh() {
+  // Only the L effect is guaranteed to be both sufficiently brief and prominent
   // to provide a meaningful "wait" signal. The refresh effect on previous
   // Android releases can be quite faint, depending on the OEM-supplied
   // overscroll resources, and lasts nearly twice as long.
-  return IsAndroidLOrNewer();
+  if (IsAndroidLOrNewer())
+    return kMinGlowAlphaToDisableRefreshOnL;
+
+  // Any value greater than 1 effectively prevents the glow effect from ever
+  // suppressing the refresh effect.
+  return 1.01f;
 }
 
 scoped_ptr<EdgeEffectBase> CreateGlowEdgeEffect(
     ui::ResourceManager* resource_manager,
     float dpi_scale) {
   DCHECK(resource_manager);
   if (IsAndroidLOrNewer())
     return scoped_ptr<EdgeEffectBase>(new EdgeEffectL(resource_manager));
 
   return scoped_ptr<EdgeEffectBase>(
@@ skipping 52 matching lines @@
   if (!enabled_)
     return false;
 
   if (!refresh_effect_)
     return false;
 
   // Suppress refresh detection for fullscreen HTML5 scenarios, e.g., video.
   if (is_fullscreen_)
     return false;
 
-  if (glow_effect_) {
-    if (glow_effect_->IsActive() && ShouldDisableRefreshWhenGlowActive())
+  // Suppress refresh detection if the glow effect is still prominent.
+  if (glow_effect_ && glow_effect_->IsActive()) {
+    if (glow_effect_->GetVisibleAlpha() > MinGlowAlphaToDisableRefresh())
       return false;
   }
 
   bool handled = false;
   bool maybe_needs_animate = false;
   switch (event.type) {
     case blink::WebInputEvent::GestureScrollBegin:
       refresh_effect_->OnScrollBegin();
       break;
 
@@ skipping 182 matching lines @@
 
 scoped_ptr<EdgeEffectBase> OverscrollControllerAndroid::CreateEdgeEffect() {
   return CreateGlowEdgeEffect(&compositor_->GetResourceManager(), dpi_scale_);
 }
 
 void OverscrollControllerAndroid::SetNeedsAnimate() {
   compositor_->SetNeedsAnimate();
 }
 
 }  // namespace content