Plumb smooth scrolling in Chromium compositor

ui/events/gestures/blink/web_gesture_curve_impl.cc

 // Copyright 2014 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 "ui/events/gestures/blink/web_gesture_curve_impl.h"
 
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "third_party/WebKit/public/platform/WebFloatSize.h"
 #include "third_party/WebKit/public/platform/WebGestureCurveTarget.h"
@@ skipping 24 matching lines @@
                   INT_MIN,
                   INT_MAX,
                   base::TimeTicks());
   return scroller.Pass();
 #else
   return make_scoped_ptr(
       new FlingCurve(initial_velocity, base::TimeTicks()));
 #endif
 }
 
+scoped_ptr<GestureCurve> CreateSmoothScrollingCurve(float start_x,
+                                                    float start_y,
+                                                    float dx,
+                                                    float dy,
+                                                    base::TimeDelta duration) {
+  DCHECK(duration > base::TimeDelta());
+#if defined(OS_ANDROID)
+  auto scroller = make_scoped_ptr(new Scroller(Scroller::Config()));
+  base::TimeTicks start_time = base::TimeTicks();
+
+  scroller->StartScroll(start_x, start_y, dx, dy, start_time, duration);
+  return scroller.Pass();
+#else
+  float vx = dx / duration.InSecondsF();

[jdduke (slow), 2015/07/23 15:32:50]

I'd almost rather we NOTREACHED() here and return nullptr so other platforms
don't inadvertently think this will do smooth scrolling. In theory Scroller's
smooth scrolling would work just fine for other platfoms, but for now I'd prefer
we just not support the path until we need to.

+  float vy = dy / duration.InSecondsF();
+  return make_scoped_ptr(
+      new FlingCurve(gfx::Vector2dF(vx, vy), base::TimeTicks()));
+#endif
+}
+
 }  // namespace
 
 // static
 scoped_ptr<WebGestureCurve> WebGestureCurveImpl::CreateFromDefaultPlatformCurve(
     const gfx::Vector2dF& initial_velocity,
     const gfx::Vector2dF& initial_offset,
     bool on_main_thread) {
   return scoped_ptr<WebGestureCurve>(new WebGestureCurveImpl(
       CreateDefaultPlatformCurve(initial_velocity), initial_offset,
       on_main_thread ? ThreadType::MAIN : ThreadType::IMPL));
 }
 
 // static
+scoped_ptr<WebGestureCurve> WebGestureCurveImpl::CreateFromSmoothScrollingCurve(
+    float start_x,
+    float start_y,
+    float dx,
+    float dy,
+    base::TimeDelta duration,
+    bool on_main_thread) {
+  const gfx::Vector2dF initial_offset(start_x, start_y);
+  return scoped_ptr<WebGestureCurve>(new WebGestureCurveImpl(
+      CreateSmoothScrollingCurve(start_x, start_y, dx, dy, duration),
+      initial_offset, on_main_thread ? ThreadType::MAIN : ThreadType::IMPL));
+}
+
+// static
 scoped_ptr<WebGestureCurve> WebGestureCurveImpl::CreateFromUICurveForTesting(
     scoped_ptr<GestureCurve> curve,
     const gfx::Vector2dF& initial_offset) {
   return scoped_ptr<WebGestureCurve>(
       new WebGestureCurveImpl(curve.Pass(), initial_offset, ThreadType::TEST));
 }
 
 WebGestureCurveImpl::WebGestureCurveImpl(scoped_ptr<GestureCurve> curve,
                                          const gfx::Vector2dF& initial_offset,
                                          ThreadType animating_thread_type)
@@ skipping 64 matching lines @@
     return still_active;
 
   // scrollBy() could delete this curve if the animation is over, so don't touch
   // any member variables after making that call.
   bool did_scroll = target->scrollBy(blink::WebFloatSize(delta),
                                      blink::WebFloatSize(velocity));
   return did_scroll && still_active;
 }
 
 }  // namespace ui