Setting a custom background on a HiDPI display will result in the background only being applied to …

content/renderer/render_widget.cc

 // 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/renderer/render_widget.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 752 matching lines @@
                                      SkShader::kRepeat_TileMode,
                                      SkShader::kRepeat_TileMode));
     paint.setShader(shader.get());
 
     // Use kSrc_Mode to handle background_ transparency properly.
     paint.setXfermodeMode(SkXfermode::kSrc_Mode);
 
     // Canvas could contain multiple update rects. Clip to given rect so that
     // we don't accidentally clear other update rects.
     canvas->save();
+    canvas->scale(device_scale_factor_, device_scale_factor_);
     canvas->clipRect(gfx::RectToSkRect(rect));
     canvas->drawPaint(paint);
     canvas->restore();
   }
 
   // First see if this rect is a plugin that can paint itself faster.
   TransportDIB* optimized_dib = NULL;
   gfx::Rect optimized_copy_rect, optimized_copy_location;
   float dib_scale_factor;
   webkit::ppapi::PluginInstance* optimized_instance =
@@ skipping 1011 matching lines @@
   if (!webwidget_)
     return;
 
   if (is_fullscreen_) {
     webwidget_->didEnterFullScreen();
   } else {
     webwidget_->didExitFullScreen();
   }
 }
 
 void RenderWidget::SetBackground(const SkBitmap& background) {

[Nico, 2013/02/13 22:56:44]

Is this function even still used? I think it was used by extensions way back
when we still had an extension bar (which never launched) – can we just kill
this?

[Horia Olaru, 2013/02/13 23:41:21]

I am not familiar with the history, but a quick search shows the following files
using it.
chrome/browser/chromeos/login/webui_login_view.cc
chrome/browser/ui/cocoa/extensions/extension_view_mac.mm
chrome/browser/ui/gtk/extensions/extension_view_gtk.cc
chrome/browser/ui/views/extensions/extension_view_views.cc
chrome/browser/ui/views/extensions/native_app_window_views.cc. 

To be fair, I am not familiar with them, so I couldn't say whether you could do
without the code that uses SetBackground or not.

We are implementing an offscreen render view, and we use this function to make
the view transparent (by setting a 1x1 px transparent background for the
widget). The above files use in much the same way. Otherwise, even if the html
is transparent, it is painted on top of a white (non-transparent) background.

[jeremya, 2013/02/21 22:19:29]

This is used to build transparent Chrome Apps on CrOS (see
http://crrev.com/175700 in native_app_window_views.cc)

   background_ = background;
 
   // Generate a full repaint.
   didInvalidateRect(gfx::Rect(size_.width(), size_.height()));
 }
 
 bool RenderWidget::next_paint_is_resize_ack() const {
   return ViewHostMsg_UpdateRect_Flags::is_resize_ack(next_paint_flags_);
 }
 
@@ skipping 284 matching lines @@
 bool RenderWidget::WillHandleGestureEvent(
     const WebKit::WebGestureEvent& event) {
   return false;
 }
 
 bool RenderWidget::HasTouchEventHandlersAt(const gfx::Point& point) const {
   return true;
 }
 
 }  // namespace content