Convert MouseEvents from DIPS to Pixels before passing it to surfaces for hittesting.

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 <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
 
@@ skipping 1575 matching lines @@
 }
 
 uint32_t RenderWidgetHostViewMac::GetSurfaceIdNamespace() {
   DCHECK(delegated_frame_host_);
   return delegated_frame_host_->GetSurfaceIdNamespace();
 }
 
 uint32_t RenderWidgetHostViewMac::SurfaceIdNamespaceAtPoint(
     const gfx::Point& point,
     gfx::Point* transformed_point) {
-  cc::SurfaceId id =
-      delegated_frame_host_->SurfaceIdAtPoint(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 = gfx::Screen::GetScreenFor(cocoa_view_)
+                           ->GetDisplayNearestWindow(cocoa_view_)
+                           .device_scale_factor();

[Avi (use Gerrit), 2015/11/04 20:16:47]

I'm thinking in Cocoa, and would instinctively do

float scale_factor = [[cocoa_view_ window] backingScaleFactor];

asking the window itself what the scale factor was, rather than wandering around
like this. I guess this is the fancy gfx:: way we do it? (shrug)

+  gfx::Point point_in_pixels = gfx::ConvertPointToPixel(scale_factor, point);
+  cc::SurfaceId id = delegated_frame_host_->SurfaceIdAtPoint(point_in_pixels,
+                                                             transformed_point);
+  *transformed_point = gfx::ConvertPointToDIP(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_null())
     return GetSurfaceIdNamespace();
   return cc::SurfaceIdAllocator::NamespaceForId(id);
 }
 
 void RenderWidgetHostViewMac::ProcessMouseEvent(
     const blink::WebMouseEvent& event) {
   render_widget_host_->ForwardMouseEvent(event);
@@ skipping 1816 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