[Telemetry] Refactoring in preparation for video-based Speed Index support.

tools/perf/metrics/speedindex.py

Index: tools/perf/metrics/speedindex.py
diff --git a/tools/perf/metrics/speedindex.py b/tools/perf/metrics/speedindex.py
index 9a453413408fdab328ab4b9e544465bdb9d02a7d..0dd013865e8d32227f6f699ba1625441bd88ecb2 100644
--- a/tools/perf/metrics/speedindex.py
+++ b/tools/perf/metrics/speedindex.py
@@ -7,6 +7,7 @@ import os
 
 from metrics import Metric
 
+
 class SpeedIndexMetric(Metric):
   """The speed index metric is one way of measuring page load speed.
 
@@ -15,11 +16,12 @@ class SpeedIndexMetric(Metric):
   portion of the screen. It includes paint events that occur after the
   onload event, and it doesn't include time loading things off-screen.
 
-  This speed index metric is based on the devtools speed index at
-  WebPageTest.org (WPT). For more info see: http://goo.gl/e7AH5l
+  This speed index metric is based on WebPageTest.org (WPT).
+  For more info see: http://goo.gl/e7AH5l
   """
   def __init__(self):
     super(SpeedIndexMetric, self).__init__()
+    self._impl = None
     self._script_is_loaded = False
     self._is_finished = False
     with open(os.path.join(os.path.dirname(__file__), 'speedindex.js')) as f:
@@ -32,21 +34,23 @@ class SpeedIndexMetric(Metric):
     a PageMeasurement, so that all the events can be captured. If it's called
     in DidNavigateToPage, that will be too late.
     """
-    tab.StartTimelineRecording()
+    self._impl = (VideoSpeedIndexImpl(tab) if tab.video_capture_supported else
+                  PaintRectSpeedIndexImpl(tab))
+    self._impl.Start()
     self._script_is_loaded = False
     self._is_finished = False
 
   def Stop(self, _, tab):
     """Stop timeline recording."""
-    assert self.IsFinished(tab)
-    tab.StopTimelineRecording()
+    assert self._impl, 'Must call Start() before Stop()'
+    assert self.IsFinished(tab), 'Must wait for IsFinished() before Stop()'
+    self._impl.Stop()
 
   # Optional argument chart_name is not in base class Metric.
   # pylint: disable=W0221
   def AddResults(self, tab, results, chart_name=None):
     """Calculate the speed index and add it to the results."""
-    events = tab.timeline_model.GetAllEvents()
-    index = _SpeedIndex(events, _GetViewportSize(tab))
+    index = self._impl.CalculateSpeedIndex()
     results.Add('speed_index', 'ms', index, chart_name=chart_name)
 
   def IsFinished(self, tab):
@@ -86,166 +90,218 @@ class SpeedIndexMetric(Metric):
     return self._is_finished
 
 
-def _GetViewportSize(tab):
-  """Returns dimensions of the viewport."""
-  return tab.EvaluateJavaScript('[ window.innerWidth, window.innerHeight ]')
-
+class SpeedIndexImpl(object):
 
-def _SpeedIndex(events, viewport):
-  """Calculate the speed index of a page load from a list of events.
+  def __init__(self, tab):
+    """Constructor.
 
-  The speed index number conceptually represents the number of milliseconds
-  that the page was "visually incomplete". If the page were 0% complete for
-  1000 ms, then the score would be 1000; if it were 0% complete for 100 ms
-  then 90% complete (ie 10% incomplete) for 900 ms, then the score would be
-  1.0*100 + 0.1*900 = 190.
+    Args:
+      tab: The telemetry.core.Tab object for which to calculate SpeedIndex.
+    """
+    self.tab = tab
 
-  Args:
-    events: A list of telemetry.core.timeline.slice.Slice objects
-    viewport: A tuple (width, height) of the window.
+  def Start(self):
+    raise NotImplementedError()
 
-  Returns:
-    A single number, milliseconds of visual incompleteness.
-  """
-  paint_events = _IncludedPaintEvents(events)
-  time_area_dict = _TimeAreaDict(paint_events, viewport)
-  time_completeness_dict = _TimeCompletenessDict(time_area_dict)
-  # The first time interval starts from the start of the first event.
-  prev_time = events[0].start
-  prev_completeness = 0.0
-  speed_index = 0.0
-  for time, completeness in sorted(time_completeness_dict.items()):
-    # Add the incemental value for the interval just before this event.
-    elapsed_time = time - prev_time
-    incompleteness = (1.0 - prev_completeness)
-    speed_index += elapsed_time * incompleteness
-
-    # Update variables for next iteration.
-    prev_completeness = completeness
-    prev_time = time
-
-  return speed_index
-
-
-def _TimeCompletenessDict(time_area_dict):
-  """Make a dictionary of time to visual completeness.
-
-  In the WPT PHP implementation, this is also called 'visual progress'.
-  """
-  total_area = sum(time_area_dict.values())
-  assert total_area > 0.0, 'Total paint event area must be greater than 0.'
-  completeness = 0.0
-  time_completeness_dict = {}
-  for time, area in sorted(time_area_dict.items()):
-    completeness += float(area) / total_area
-    # Visual progress is rounded to the nearest percentage point as in WPT.
-    time_completeness_dict[time] = round(completeness, 2)
-  return time_completeness_dict
+  def Stop(self):
+    raise NotImplementedError()
 
+  def GetTimeCompletenessList(self):
+    """Returns a list of time to visual completeness tuples.
 
-def _IncludedPaintEvents(events):
-  """Get all events that are counted in the calculation of the speed index.
+    In the WPT PHP implementation, this is also called 'visual progress'.
+    """
+    raise NotImplementedError()
 
-  There's one category of paint event that's filtered out: paint events
-  that occur before the first 'ResourceReceiveResponse' and 'Layout' events.
+  def CalculateSpeedIndex(self):
+    """Calculate the speed index.
 
-  Previously in the WPT speed index, paint events that contain children paint
-  events were also filtered out.
-  """
-  def FirstLayoutTime(events):
-    """Get the start time of the first layout after a resource received."""
-    has_received_response = False
-    for event in events:
-      if event.name == 'ResourceReceiveResponse':
-        has_received_response = True
-      elif has_received_response and event.name == 'Layout':
-        return event.start
-    assert False, 'There were no layout events after resource receive events.'
-
-  first_layout_time = FirstLayoutTime(events)
-  paint_events = [e for e in events
-                  if e.start >= first_layout_time and e.name == 'Paint']
-  return paint_events
-
-
-def _TimeAreaDict(paint_events, viewport):
-  """Make a dict from time to adjusted area value for events at that time.
-
-  The adjusted area value of each paint event is determined by how many paint
-  events cover the same rectangle, and whether it's a full-window paint event.
-  "Adjusted area" can also be thought of as "points" of visual completeness --
-  each rectangle has a certain number of points and these points are
-  distributed amongst the paint events that paint that rectangle.
-
-  Args:
-    paint_events: A list of paint events
-    viewport: A tuple (width, height) of the window.
-
-  Returns:
-    A dictionary of times of each paint event (in milliseconds) to the
-    adjusted area that the paint event is worth.
-  """
-  width, height = viewport
-  fullscreen_area = width * height
-
-  def ClippedArea(rectangle):
-    """Returns rectangle area clipped to viewport size."""
-    _, x0, y0, x1, y1 = rectangle
-    x0 = max(0, x0)
-    y0 = max(0, y0)
-    x1 = min(width, x1)
-    y1 = min(height, y1)
-    return max(0, x1 - x0) * max(0, y1 - y0)
-
-  grouped = _GroupEventByRectangle(paint_events)
-  event_area_dict = collections.defaultdict(int)
-
-  for rectangle, events in grouped.items():
-    # The area points for each rectangle are divided up among the paint
-    # events in that rectangle.
-    area = ClippedArea(rectangle)
-    update_count = len(events)
-    adjusted_area = float(area) / update_count
-
-    # Paint events for the largest-area rectangle are counted as 50%.
-    if area == fullscreen_area:
-      adjusted_area /= 2
-
-    for event in events:
-      # The end time for an event is used for that event's time.
-      event_time = event.end
-      event_area_dict[event_time] += adjusted_area
-
-  return event_area_dict
-
-
-def _GetRectangle(paint_event):
-  """Get the specific rectangle on the screen for a paint event.
-
-  Each paint event belongs to a frame (as in html <frame> or <iframe>).
-  This, together with location and dimensions, comprises a rectangle.
-  In the WPT source, this 'rectangle' is also called a 'region'.
-  """
-  def GetBox(quad):
-    """Gets top-left and bottom-right coordinates from paint event.
+    The speed index number conceptually represents the number of milliseconds
+    that the page was "visually incomplete". If the page were 0% complete for
+    1000 ms, then the score would be 1000; if it were 0% complete for 100 ms
+    then 90% complete (ie 10% incomplete) for 900 ms, then the score would be
+    1.0*100 + 0.1*900 = 190.
 
-    In the timeline data from devtools, paint rectangle dimensions are
-    represented x-y coordinates of four corners, clockwise from the top-left.
-    See: function WebInspector.TimelinePresentationModel.quadFromRectData
-    in file src/out/Debug/obj/gen/devtools/TimelinePanel.js.
+    Returns:
+      A single number, milliseconds of visual incompleteness.
     """
-    x0, y0, _, _, x1, y1, _, _ = quad
-    return (x0, y0, x1, y1)
-
-  assert paint_event.name == 'Paint'
-  frame = paint_event.args['frameId']
-  return (frame,) + GetBox(paint_event.args['data']['clip'])
-
+    time_completeness_list = self.GetTimeCompletenessList()
+    prev_completeness = 0.0
+    speed_index = 0.0
+    prev_time = time_completeness_list[0][0]
+    for time, completeness in time_completeness_list:
+      # Add the incemental value for the interval just before this event.
+      elapsed_time = time - prev_time
+      incompleteness = (1.0 - prev_completeness)
+      speed_index += elapsed_time * incompleteness
+
+      # Update variables for next iteration.
+      prev_completeness = completeness
+      prev_time = time
+    return speed_index
+
+
+class VideoSpeedIndexImpl(SpeedIndexImpl):
+
+  def __init__(self, tab):
+    super(VideoSpeedIndexImpl, self).__init__(tab)
+    assert self.tab.video_capture_supported
+    self._time_completeness_list = None
+
+  def Start(self):
+    # TODO(tonyg): Bitrate is arbitrary here. Experiment with screen capture
+    # overhead vs. speed index accuracy and set the bitrate appropriately.
+    self.tab.StartVideoCapture(min_bitrate_mbps=4)
+
+  def Stop(self):
+    self._time_completeness_list = []
+    self.tab.StopVideoCapture()
+    # TODO(tonyg/szym): Implement this.
+    raise NotImplementedError('SpeedIndex video calculation not implemented.')
+
+  def GetTimeCompletenessList(self):
+    assert self._time_completeness_list, 'Must call Stop() first.'
+    return self._time_completeness_list
+
+
+class PaintRectSpeedIndexImpl(SpeedIndexImpl):
+
+  def __init__(self, tab):
+    super(PaintRectSpeedIndexImpl, self).__init__(tab)
+
+  def Start(self):
+    self.tab.StartTimelineRecording()
+
+  def Stop(self):
+    self.tab.StopTimelineRecording()
+
+  def GetTimeCompletenessList(self):
+    events = self.tab.timeline_model.GetAllEvents()
+    viewport = self._GetViewportSize()
+    paint_events = self._IncludedPaintEvents(events)
+    time_area_dict = self._TimeAreaDict(paint_events, viewport)
+    total_area = sum(time_area_dict.values())
+    assert total_area > 0.0, 'Total paint event area must be greater than 0.'
+    completeness = 0.0
+    time_completeness_list = []
+
+    # TODO(tonyg): This sets the start time to the start of the first paint
+    # event. That can't be correct. The start time should be navigationStart.
+    # Since the previous screen is not cleared at navigationStart, we should
+    # probably assume the completeness is 0 until the first paint and add the
+    # time of navigationStart as the start. We need to confirm what WPT does.
+    time_completeness_list.append(
+        (self.tab.timeline_model.GetAllEvents()[0].start, completeness))
+
+    for time, area in sorted(time_area_dict.items()):
+      completeness += float(area) / total_area
+      # Visual progress is rounded to the nearest percentage point as in WPT.
+      time_completeness_list.append((time, round(completeness, 2)))
+    return time_completeness_list
+
+  def _GetViewportSize(self):
+    """Returns dimensions of the viewport."""
+    return self.tab.EvaluateJavaScript(
+        '[ window.innerWidth, window.innerHeight ]')
+
+  def _IncludedPaintEvents(self, events):
+    """Get all events that are counted in the calculation of the speed index.
+
+    There's one category of paint event that's filtered out: paint events
+    that occur before the first 'ResourceReceiveResponse' and 'Layout' events.
+
+    Previously in the WPT speed index, paint events that contain children paint
+    events were also filtered out.
+    """
+    def FirstLayoutTime(events):
+      """Get the start time of the first layout after a resource received."""
+      has_received_response = False
+      for event in events:
+        if event.name == 'ResourceReceiveResponse':
+          has_received_response = True
+        elif has_received_response and event.name == 'Layout':
+          return event.start
+      assert False, 'There were no layout events after resource receive events.'
+
+    first_layout_time = FirstLayoutTime(events)
+    paint_events = [e for e in events
+                    if e.start >= first_layout_time and e.name == 'Paint']
+    return paint_events
+
+  def _TimeAreaDict(self, paint_events, viewport):
+    """Make a dict from time to adjusted area value for events at that time.
+
+    The adjusted area value of each paint event is determined by how many paint
+    events cover the same rectangle, and whether it's a full-window paint event.
+    "Adjusted area" can also be thought of as "points" of visual completeness --
+    each rectangle has a certain number of points and these points are
+    distributed amongst the paint events that paint that rectangle.
+
+    Args:
+      paint_events: A list of paint events
+      viewport: A tuple (width, height) of the window.
 
-def _GroupEventByRectangle(paint_events):
-  """Group all paint events according to the rectangle that they update."""
-  result = collections.defaultdict(list)
-  for event in paint_events:
-    assert event.name == 'Paint'
-    result[_GetRectangle(event)].append(event)
-  return result
+    Returns:
+      A dictionary of times of each paint event (in milliseconds) to the
+      adjusted area that the paint event is worth.
+    """
+    width, height = viewport
+    fullscreen_area = width * height
+
+    def ClippedArea(rectangle):
+      """Returns rectangle area clipped to viewport size."""
+      _, x0, y0, x1, y1 = rectangle
+      clipped_width = max(0, min(width, x1) - max(0, x0))
+      clipped_height = max(0, min(height, y1) - max(0, y0))
+      return clipped_width * clipped_height
+
+    grouped = self._GroupEventByRectangle(paint_events)
+    event_area_dict = collections.defaultdict(int)
+
+    for rectangle, events in grouped.items():
+      # The area points for each rectangle are divided up among the paint
+      # events in that rectangle.
+      area = ClippedArea(rectangle)
+      update_count = len(events)
+      adjusted_area = float(area) / update_count
+
+      # Paint events for the largest-area rectangle are counted as 50%.
+      if area == fullscreen_area:
+        adjusted_area /= 2
+
+      for event in events:
+        # The end time for an event is used for that event's time.
+        event_time = event.end
+        event_area_dict[event_time] += adjusted_area
+
+    return event_area_dict
+
+  def _GetRectangle(self, paint_event):
+    """Get the specific rectangle on the screen for a paint event.
+
+    Each paint event belongs to a frame (as in html <frame> or <iframe>).
+    This, together with location and dimensions, comprises a rectangle.
+    In the WPT source, this 'rectangle' is also called a 'region'.
+    """
+    def GetBox(quad):
+      """Gets top-left and bottom-right coordinates from paint event.
+
+      In the timeline data from devtools, paint rectangle dimensions are
+      represented x-y coordinates of four corners, clockwise from the top-left.
+      See: function WebInspector.TimelinePresentationModel.quadFromRectData
+      in file src/out/Debug/obj/gen/devtools/TimelinePanel.js.
+      """
+      x0, y0, _, _, x1, y1, _, _ = quad
+      return (x0, y0, x1, y1)
+
+    assert paint_event.name == 'Paint'
+    frame = paint_event.args['frameId']
+    return (frame,) + GetBox(paint_event.args['data']['clip'])
+
+  def _GroupEventByRectangle(self, paint_events):
+    """Group all paint events according to the rectangle that they update."""
+    result = collections.defaultdict(list)
+    for event in paint_events:
+      assert event.name == 'Paint'
+      result[self._GetRectangle(event)].append(event)
+    return result