Calculate animation_floor_time_ only when actually updating animations

chrome/renderer/render_widget.cc

Index: chrome/renderer/render_widget.cc
diff --git a/chrome/renderer/render_widget.cc b/chrome/renderer/render_widget.cc
index 5f66e49987ccf8a3709caac736a76c0726d45cad..21b4395763afbf429171e40bae576f20446169e0 100644
--- a/chrome/renderer/render_widget.cc
+++ b/chrome/renderer/render_widget.cc
@@ -488,10 +488,13 @@ void RenderWidget::CallDoDeferredUpdate() {
 }
 
 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
@@ -501,8 +504,10 @@ void RenderWidget::UpdateAnimationsIfNeeded() {
       // 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);
     }
@@ -520,9 +525,6 @@ void RenderWidget::DoDeferredUpdate() {
     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.
@@ -717,10 +719,8 @@ void RenderWidget::scheduleComposite() {
 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));
     }
 }