content/browser/renderer_host/frame_metadata_util.cc

   1 // Copyright (c) 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "content/browser/renderer_host/frame_metadata_util.h"
   6
   7 #include "cc/output/compositor_frame_metadata.h"
   8
   9 namespace {
  10
  11 // Used to accomodate finite precision when comparing scaled viewport and
  12 // content widths. While this value may seem large, width=device-width on an N7
  13 // V1 saw errors of ~0.065 between computed window and content widths.
  14 const float kMobileViewportWidthEpsilon = 0.15f;
  15
  16 bool HasFixedPageScale(const cc::CompositorFrameMetadata& frame_metadata) {
  17   return frame_metadata.min_page_scale_factor ==
  18          frame_metadata.max_page_scale_factor;
  19 }
  20
  21 bool HasMobileViewport(const cc::CompositorFrameMetadata& frame_metadata) {
  22   float window_width_dip =
  23       frame_metadata.page_scale_factor *
  24           frame_metadata.scrollable_viewport_size.width();
  25   float content_width_css = frame_metadata.root_layer_size.width();
  26   return content_width_css <= window_width_dip + kMobileViewportWidthEpsilon;
  27 }
  28
  29 }  // namespace
  30
  31 namespace content {
  32
  33 bool IsMobileOptimizedFrame(const cc::CompositorFrameMetadata& frame_metadata) {
  34   bool has_mobile_viewport = HasMobileViewport(frame_metadata);
  35   bool has_fixed_page_scale = HasFixedPageScale(frame_metadata);
  36   return has_fixed_page_scale || has_mobile_viewport;
  37 }
  38
  39 }  // namespace content