Make the tab scrubber speed proportional with the number of tabs

chrome/browser/ui/views/ash/tab_scrubber.cc

 // Copyright (c) 2013 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 "chrome/browser/ui/views/ash/tab_scrubber.h"
 
 #include <stdint.h>
 
+#include <algorithm>
+
 #include "ash/shell.h"
 #include "ash/wm/window_util.h"
 #include "base/metrics/histogram_macros.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "chrome/browser/ui/views/frame/browser_view.h"
 #include "chrome/browser/ui/views/tabs/tab.h"
 #include "chrome/browser/ui/views/tabs/tab_strip.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_source.h"
 #include "ui/aura/window.h"
 #include "ui/events/event.h"
 #include "ui/events/event_utils.h"
 #include "ui/events/gesture_detection/gesture_configuration.h"
 #include "ui/views/controls/glow_hover_controller.h"
 
 namespace {
+
 const int64_t kActivationDelayMS = 200;
+
+inline float Clamp(float value, float low, float high) {
+  return std::min(high, std::max(value, low));
+}
 }
 
 // static
 TabScrubber* TabScrubber::GetInstance() {
   static TabScrubber* instance = NULL;
   if (!instance)
     instance = new TabScrubber();
   return instance;
 }
 
@@ skipping 260 matching lines @@
                     swipe_direction_);
   swipe_x_ = start_point.x();
   swipe_y_ = start_point.y();
 }
 
 void TabScrubber::UpdateSwipeX(float x_offset) {
   DCHECK(browser_);
   DCHECK(tab_strip_);
   DCHECK(scrubbing_);
 
-  swipe_x_ += x_offset;
+  // Make the swipe speed inversely proportional with the number or tabs:
+  // Each added tab introduces a reduction of 2% in |x_offset|, with a value of
+  // one fourth of |x_offset| as the minimum (i.e. we need 38 tabs to reach
+  // that minimum reduction).
+  swipe_x_ += Clamp(x_offset - (tab_strip_->tab_count() * 0.02f * x_offset),
+                    0.25f * x_offset, x_offset);
 
   // In an RTL layout, everything is mirrored, i.e. the index of the first tab
   // (with the smallest X mirrored co-ordinates) is actually the index of the
   // last tab. Same for the index of the last tab.
   int first_tab_index = base::i18n::IsRTL() ? tab_strip_->tab_count() - 1 : 0;
   int last_tab_index = base::i18n::IsRTL() ? 0 : tab_strip_->tab_count() - 1;
 
   Tab* first_tab = tab_strip_->tab_at(first_tab_index);
   int first_tab_center = first_tab->GetMirroredBounds().CenterPoint().x();
   Tab* last_tab = tab_strip_->tab_at(last_tab_index);
@@ skipping 17 matching lines @@
     tab->hover_controller()->HideImmediately();
   }
 
   if (new_index != browser_->tab_strip_model()->active_index()) {
     highlighted_tab_ = new_index;
     new_tab->hover_controller()->Show(views::GlowHoverController::PRONOUNCED);
   } else {
     highlighted_tab_ = -1;
   }
 }