Made page zoom handling work with smooth scroll devices

content/browser/web_contents/web_contents_impl.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 "content/browser/web_contents/web_contents_impl.h"
 
 #include <stddef.h>
 
+#include <cmath>
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/metrics/histogram.h"
 #include "base/process/process.h"
 #include "base/profiler/scoped_tracker.h"
@@ skipping 370 matching lines @@
       capturer_count_(0),
       should_normally_be_visible_(true),
       is_being_destroyed_(false),
       notify_disconnection_(false),
       dialog_manager_(NULL),
       is_showing_before_unload_dialog_(false),
       last_active_time_(base::TimeTicks::Now()),
       closed_by_user_gesture_(false),
       minimum_zoom_percent_(static_cast<int>(kMinimumZoomFactor * 100)),
       maximum_zoom_percent_(static_cast<int>(kMaximumZoomFactor * 100)),
+      zoom_scroll_remainder_(0),
       render_view_message_source_(NULL),
       render_frame_message_source_(NULL),
       fullscreen_widget_routing_id_(MSG_ROUTING_NONE),
       fullscreen_widget_had_focus_at_shutdown_(false),
       is_subframe_(false),
       force_disable_overscroll_content_(false),
       last_dialog_suppressed_(false),
       geolocation_service_context_(new GeolocationServiceContext()),
       accessibility_mode_(
           BrowserAccessibilityStateImpl::GetInstance()->accessibility_mode()),
@@ skipping 1171 matching lines @@
 #if !defined(OS_MACOSX)
   // On platforms other than Mac, control+mousewheel may change zoom. On Mac,
   // this isn't done for two reasons:
   //   -the OS already has a gesture to do this through pinch-zoom
   //   -if a user starts an inertial scroll, let's go, and presses control
   //      (i.e. control+tab) then the OS's buffered scroll events will come in
   //      with control key set which isn't what the user wants
   if (delegate_ && event.wheelTicksY &&
       (event.modifiers & blink::WebInputEvent::ControlKey) &&
       !event.canScroll) {
-    delegate_->ContentsZoomChange(event.wheelTicksY > 0);
+    // Count only integer cumulative scrolls as zoom events; this handles
+    // smooth scroll and regular scroll device behavior.
+    zoom_scroll_remainder_ += event.wheelTicksY;
+    int whole_zoom_scroll_remainder_ = std::lround(zoom_scroll_remainder_);
+    zoom_scroll_remainder_ -= whole_zoom_scroll_remainder_;
+    if (whole_zoom_scroll_remainder_ != 0) {
+      delegate_->ContentsZoomChange(whole_zoom_scroll_remainder_ > 0);
+    }
     return true;
   }
 #endif
   return false;
 }
 
 bool WebContentsImpl::PreHandleGestureEvent(
     const blink::WebGestureEvent& event) {
   return delegate_ && delegate_->PreHandleGestureEvent(this, event);
 }
@@ skipping 3120 matching lines @@
     const WebContentsObserver::MediaPlayerId& id) {
   FOR_EACH_OBSERVER(WebContentsObserver, observers_, MediaStartedPlaying(id));
 }
 
 void WebContentsImpl::MediaStoppedPlaying(
     const WebContentsObserver::MediaPlayerId& id) {
   FOR_EACH_OBSERVER(WebContentsObserver, observers_, MediaStoppedPlaying(id));
 }
 
 }  // namespace content