Simplify calls for scale factor

content/browser/renderer_host/render_widget_host_view_mac.mm

 // Copyright (c) 2012 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 "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #import <Carbon/Carbon.h>
 #import <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
@@ skipping 57 matching lines @@
 #include "media/base/video_frame.h"
 #include "skia/ext/platform_canvas.h"
 #include "skia/ext/skia_utils_mac.h"
 #include "third_party/WebKit/public/platform/WebInputEvent.h"
 #import "ui/base/clipboard/clipboard_util_mac.h"
 #include "ui/base/cocoa/animation_utils.h"
 #import "ui/base/cocoa/appkit_utils.h"
 #include "ui/base/cocoa/cocoa_base_utils.h"
 #import "ui/base/cocoa/fullscreen_window_manager.h"
 #import "ui/base/cocoa/underlay_opengl_hosting_window.h"
-#include "ui/base/layout.h"
 #include "ui/compositor/compositor.h"
 #include "ui/compositor/layer.h"
 #include "ui/display/display.h"
 #include "ui/display/screen.h"
 #include "ui/events/base_event_utils.h"
 #include "ui/events/event_utils.h"
 #include "ui/events/keycodes/keyboard_codes.h"
 #include "ui/gfx/geometry/dip_util.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/rect_conversions.h"
@@ skipping 379 matching lines @@
   [background_layer_ setBackgroundColor:CGColorGetConstantColor(kCGColorWhite)];
   [cocoa_view_ setLayer:background_layer_];
   [cocoa_view_ setWantsLayer:YES];
 
   cc::FrameSinkId frame_sink_id =
       render_widget_host_->AllocateFrameSinkId(is_guest_view_hack_);
   browser_compositor_.reset(
       new BrowserCompositorMac(this, this, render_widget_host_->is_hidden(),
                                [cocoa_view_ window], frame_sink_id));
 
-  display::Screen::GetScreen()->AddObserver(this);
+  display::Screen* screen = display::Screen::GetScreen();
+  device_scale_factor_ =
+      screen->GetDisplayNearestWindow(cocoa_view_).device_scale_factor();
+  screen->AddObserver(this);
 
   if (!is_guest_view_hack_)
     render_widget_host_->SetView(this);
 
   // Let the page-level input event router know about our surface ID
   // namespace for surface-based hit testing.
   if (render_widget_host_->delegate() &&
       render_widget_host_->delegate()->GetInputEventRouter()) {
     render_widget_host_->delegate()->GetInputEventRouter()->AddFrameSinkIdOwner(
         GetFrameSinkId(), this);
@@ skipping 193 matching lines @@
   pepper_fullscreen_window_.reset();
 }
 
 int RenderWidgetHostViewMac::window_number() const {
   NSWindow* window = [cocoa_view_ window];
   if (!window)
     return -1;
   return [window windowNumber];
 }
 
-float RenderWidgetHostViewMac::ViewScaleFactor() const {
-  return ui::GetScaleFactorForNativeView(cocoa_view_);
-}
-
 void RenderWidgetHostViewMac::UpdateDisplayLink() {
   static bool is_vsync_disabled =
       base::CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kDisableGpuVsync);
   if (is_vsync_disabled)
     return;
 
   NSScreen* screen = [[cocoa_view_ window] screen];
   NSDictionary* screen_description = [screen deviceDescription];
   NSNumber* screen_number = [screen_description objectForKey:@"NSScreenNumber"];
@@ skipping 810 matching lines @@
 cc::FrameSinkId RenderWidgetHostViewMac::GetFrameSinkId() {
   return browser_compositor_->GetDelegatedFrameHost()->GetFrameSinkId();
 }
 
 cc::FrameSinkId RenderWidgetHostViewMac::FrameSinkIdAtPoint(
     cc::SurfaceHittestDelegate* delegate,
     const gfx::Point& point,
     gfx::Point* transformed_point) {
   // The surface hittest happens in device pixels, so we need to convert the
   // |point| from DIPs to pixels before hittesting.
-  float scale_factor = display::Screen::GetScreen()
-                           ->GetDisplayNearestWindow(cocoa_view_)
-                           .device_scale_factor();
-  gfx::Point point_in_pixels = gfx::ConvertPointToPixel(scale_factor, point);
+  gfx::Point point_in_pixels =
+      gfx::ConvertPointToPixel(device_scale_factor_, point);
   cc::SurfaceId id =
       browser_compositor_->GetDelegatedFrameHost()->SurfaceIdAtPoint(
           delegate, point_in_pixels, transformed_point);
-  *transformed_point = gfx::ConvertPointToDIP(scale_factor, *transformed_point);
+  *transformed_point =
+      gfx::ConvertPointToDIP(device_scale_factor_, *transformed_point);
 
   // It is possible that the renderer has not yet produced a surface, in which
   // case we return our current namespace.
   if (!id.is_valid())
     return GetFrameSinkId();
   return id.frame_sink_id();
 }
 
 bool RenderWidgetHostViewMac::ShouldRouteEvent(
     const WebInputEvent& event) const {
@@ skipping 29 matching lines @@
     const ui::LatencyInfo& latency) {
   render_widget_host_->ForwardGestureEventWithLatencyInfo(event, latency);
 }
 
 bool RenderWidgetHostViewMac::TransformPointToLocalCoordSpace(
     const gfx::Point& point,
     const cc::SurfaceId& original_surface,
     gfx::Point* transformed_point) {
   // Transformations use physical pixels rather than DIP, so conversion
   // is necessary.
-  float scale_factor = display::Screen::GetScreen()
-                           ->GetDisplayNearestWindow(cocoa_view_)
-                           .device_scale_factor();
-  gfx::Point point_in_pixels = gfx::ConvertPointToPixel(scale_factor, point);
+  gfx::Point point_in_pixels =
+      gfx::ConvertPointToPixel(device_scale_factor_, point);
   if (!browser_compositor_->GetDelegatedFrameHost()
            ->TransformPointToLocalCoordSpace(point_in_pixels, original_surface,
                                              transformed_point))
     return false;
-  *transformed_point = gfx::ConvertPointToDIP(scale_factor, *transformed_point);
+  *transformed_point =
+      gfx::ConvertPointToDIP(device_scale_factor_, *transformed_point);
   return true;
 }
 
 bool RenderWidgetHostViewMac::TransformPointToCoordSpaceForView(
     const gfx::Point& point,
     RenderWidgetHostViewBase* target_view,
     gfx::Point* transformed_point) {
   if (target_view == this) {
     *transformed_point = point;
     return true;
@@ skipping 124 matching lines @@
 void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
     const display::Display& display,
     uint32_t changed_metrics) {
   display::Screen* screen = display::Screen::GetScreen();
   if (display.id() != screen->GetDisplayNearestWindow(cocoa_view_).id())
     return;
 
   if (changed_metrics & DisplayObserver::DISPLAY_METRIC_DEVICE_SCALE_FACTOR) {
     RenderWidgetHostImpl* host =
         RenderWidgetHostImpl::From(GetRenderWidgetHost());
+    device_scale_factor_ = display.device_scale_factor();

[tapted, 2017/03/13 00:02:33]

This isn't quite the same. OnDisplayMetricsChanged() is only triggered when the
display metrics change (e.g. add/remove display, or change resolution). It's
_not_ triggered when the window simply moves to a different display, which is
far more common.

I don't think we should add |device_scale_factor_| to RenderWidgetHostViewMac --
it is duplicating the function of |current_device_scale_factor_| in
RenderWidgetHostViewBase in any case.

But `ui::GetScaleFactorForNativeView(..)` is an inexpensive method call on Mac
under most situations -- we shouldn't worry about caching it - just call it each
time.

[Jinsuk Kim, 2017/03/13 00:25:01]

Reverted the change. Removed an unused method only.

     if (host && host->delegate())
-      host->delegate()->UpdateDeviceScaleFactor(display.device_scale_factor());
+      host->delegate()->UpdateDeviceScaleFactor(device_scale_factor_);
   }
 
   UpdateScreenInfo(cocoa_view_);
 }
 
 }  // namespace content
 
 // RenderWidgetHostViewCocoa ---------------------------------------------------
 
 @implementation RenderWidgetHostViewCocoa
@@ skipping 1744 matching lines @@
 
 // "-webkit-app-region: drag | no-drag" is implemented on Mac by excluding
 // regions that are not draggable. (See ControlRegionView in
 // native_app_window_cocoa.mm). This requires the render host view to be
 // draggable by default.
 - (BOOL)mouseDownCanMoveWindow {
   return YES;
 }
 
 @end