Calculate animation_floor_time_ only when actually updating animations

chrome/renderer/render_widget.cc

 // Copyright (c) 2010 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/renderer/render_widget.h"
 
 #include "app/surface/transport_dib.h"
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
@@ skipping 470 matching lines @@
 }
 
 void RenderWidget::CallDoDeferredUpdate() {
   DoDeferredUpdate();
 
   if (pending_input_event_ack_.get())
     Send(pending_input_event_ack_.release());
 }
 
 void RenderWidget::UpdateAnimationsIfNeeded() {
+  static const int64 kMinimumAnimationDelay = 16;  // Target 60 FPS.
   if (!is_hidden() && animation_update_pending_) {
     base::Time now = base::Time::Now();
     if (now >= animation_floor_time_) {
        animation_update_pending_ = false;
+       animation_floor_time_ = base::Time::Now() +
+          base::TimeDelta::FromMilliseconds(kMinimumAnimationDelay);
        webwidget_->animate();
     } else {
       // This code uses base::Time::Now() to calculate the floor and next fire
       // time because javascript's Date object uses base::Time::Now().  The
       // message loop uses base::TimeTicks, which on windows can have a
       // different granularity than base::Time.
       // The upshot of all this is that this function might be called before
       // base::Time::Now() has advanced past the animation_floor_time_.  To
       // avoid exposing this delay to javascript, we keep posting delayed
-      // tasks until we observe base::Time::Now() advancing far enough.
-      int64 delay = (animation_floor_time_ - now).InMillisecondsRoundedUp();
+      // tasks until base::Time::Now() has advanced far enough.
+      int64 delay = std::min(
+          (animation_floor_time_ - now).InMillisecondsRoundedUp(),
+          kMinimumAnimationDelay);
       MessageLoop::current()->PostDelayedTask(FROM_HERE, NewRunnableMethod(
           this, &RenderWidget::UpdateAnimationsIfNeeded), delay);
     }
   }
 }
 
 void RenderWidget::DoDeferredUpdate() {
   if (!webwidget_ || update_reply_pending())
     return;
 
   // Suppress updating when we are hidden.
   if (is_hidden_ || size_.IsEmpty()) {
     paint_aggregator_.ClearPendingUpdate();
     needs_repainting_on_restore_ = true;
     return;
   }
 
-  if (base::Time::Now() > animation_floor_time_)
-    UpdateAnimationsIfNeeded();

[darin (slow to review), 2011/01/31 19:01:09]

it seems like you should still consider calling WebWidget::animate() here if it
is time to do so.  this will help you not fall behind in extreme cases, no?

-
   // Layout may generate more invalidation.  It may also enable the
   // GPU acceleration, so make sure to run layout before we send the
   // GpuRenderingActivated message.
   webwidget_->layout();
 
   // Suppress painting if nothing is dirty.  This has to be done after updating
   // animations running layout as these may generate further invalidations.
   if (!paint_aggregator_.HasPendingUpdate())
     return;
 
@@ skipping 174 matching lines @@
   // contains a lot of host-renderer synchronization logic that is still
   // important for the accelerated compositing case. The option of simply
   // duplicating all that code is less desirable than "faking out" the
   // invalidation path using a magical damage rect.
   didInvalidateRect(WebRect(0, 0, 1, 1));
 }
 
 void RenderWidget::scheduleAnimation() {
     if (!animation_update_pending_) {
       animation_update_pending_ = true;
-      animation_floor_time_ =
-          base::Time::Now() + base::TimeDelta::FromMilliseconds(10);
-      MessageLoop::current()->PostDelayedTask(FROM_HERE, NewRunnableMethod(
-          this, &RenderWidget::UpdateAnimationsIfNeeded), 10);
+      MessageLoop::current()->PostTask(FROM_HERE, NewRunnableMethod(
+          this, &RenderWidget::UpdateAnimationsIfNeeded));
     }
 }
 
 void RenderWidget::didChangeCursor(const WebCursorInfo& cursor_info) {
   // TODO(darin): Eliminate this temporary.
   WebCursor cursor(cursor_info);
 
   // Only send a SetCursor message if we need to make a change.
   if (!current_cursor_.IsEqual(cursor)) {
     current_cursor_ = cursor;
@@ skipping 335 matching lines @@
 
 void RenderWidget::CleanupWindowInPluginMoves(gfx::PluginWindowHandle window) {
   for (WebPluginGeometryVector::iterator i = plugin_window_moves_.begin();
        i != plugin_window_moves_.end(); ++i) {
     if (i->window == window) {
       plugin_window_moves_.erase(i);
       break;
     }
   }
 }