Add a simple scheduler for animation frames

examples/ganesh_app/ganesh_view.cc

Index: examples/ganesh_app/ganesh_view.cc
diff --git a/examples/ganesh_app/ganesh_view.cc b/examples/ganesh_app/ganesh_view.cc
index fa4041de7741f5a5a4791e138c12ae23e9cca8bd..a14b8f2b97df95b84abcf149fb66b07be81c7f18 100644
--- a/examples/ganesh_app/ganesh_view.cc
+++ b/examples/ganesh_app/ganesh_view.cc
@@ -4,6 +4,7 @@
 
 #include "examples/ganesh_app/ganesh_view.h"
 
+#include "base/message_loop/message_loop.h"
 #include "examples/ganesh_app/ganesh_texture.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 
@@ -16,14 +17,24 @@ mojo::Size ToSize(const mojo::Rect& rect) {
   size.height = rect.height;
   return size;
 }
+
+int RadiusAt(base::TimeTicks base_time, base::TimeTicks frame_time) {
+  return 50 + ((frame_time - base_time).InMilliseconds() % 6000) / 60;
+}
 }
 
 GaneshView::GaneshView(mojo::Shell* shell, mojo::View* view)
     : view_(view),
       gl_context_(shell),
       gr_context_(gl_context_.context()),
-      texture_uploader_(this, shell, gl_context_.context()) {
-  Draw(ToSize(view_->bounds()));
+      texture_uploader_(this, shell, gl_context_.context()),
+      base_time_(base::TimeTicks::Now()),
+      scheduler_(this, base::MessageLoop::current()->task_runner().get()) {
+  // TODO(abarth): Get the vsync parameters from the output surface.
+  base::TimeDelta sixty_hz = base::TimeDelta::FromSecondsD(1.0 / 60);
+  scheduler_.UpdateVSync(mc::TimeInterval(base_time_, sixty_hz));
+
+  scheduler_.SetNeedsFrame();
 }
 
 GaneshView::~GaneshView() {
@@ -40,20 +51,32 @@ void GaneshView::OnViewDestroyed(mojo::View* view) {
 void GaneshView::OnViewBoundsChanged(mojo::View* view,
                                      const mojo::Rect& old_bounds,
                                      const mojo::Rect& new_bounds) {
-  Draw(ToSize(new_bounds));
+  scheduler_.SetNeedsFrame();
 }
 
-void GaneshView::Draw(const mojo::Size& size) {
+base::TimeDelta GaneshView::Draw(base::TimeTicks frame_time) {
+  base::TimeTicks start = base::TimeTicks::Now();
+
+  mojo::Size size = ToSize(view_->bounds());
+
   GaneshTexture texture(gr_context_.context(), size);
   SkCanvas* canvas = texture.canvas();
 
   SkPaint paint;
   paint.setColor(SK_ColorRED);
   paint.setFlags(SkPaint::kAntiAlias_Flag);
-  canvas->drawCircle(50, 100, 100, paint);
+  canvas->drawCircle(50, 100, RadiusAt(base_time_, frame_time), paint);
   canvas->flush();
 
   texture_uploader_.Upload(texture.texture_id(), size);
+
+  return base::TimeTicks::Now() - start;
+}
+
+void GaneshView::BeginFrame(base::TimeTicks frame_time,
+                            base::TimeTicks deadline) {
+  scheduler_.UpdateFrameDuration(Draw(frame_time));
+  scheduler_.SetNeedsFrame();
 }
 
 }  // namespace examples