Initialize device scale factor correctly on Android

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 32 matching lines @@
 #include "webkit/glue/webkit_glue.h"
 #include "webkit/plugins/npapi/webplugin.h"
 #include "webkit/plugins/ppapi/ppapi_plugin_instance.h"
 
 #if defined(OS_POSIX)
 #include "ipc/ipc_channel_posix.h"
 #include "third_party/skia/include/core/SkMallocPixelRef.h"
 #include "third_party/skia/include/core/SkPixelRef.h"
 #endif  // defined(OS_POSIX)
 
+#if defined(OS_ANDROID)
+#include "content/common/android/device_info.h"
+#endif  // defined(OS_ANDROID)
+
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebWidget.h"
 
 using WebKit::WebCompositionUnderline;
 using WebKit::WebCursorInfo;
 using WebKit::WebInputEvent;
 using WebKit::WebMouseEvent;
 using WebKit::WebNavigationPolicy;
 using WebKit::WebPagePopup;
 using WebKit::WebPoint;
 using WebKit::WebPopupMenu;
@@ skipping 55 matching lines @@
   has_disable_gpu_vsync_switch_ = CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kDisableGpuVsync);
 #if defined(OS_CHROMEOS) || defined(OS_MACOSX)
   device_scale_factor_ = screen_info.verticalDPI / kStandardDPI;
   // Unless an explicit scale factor was provided for testing, ensure the scale
   // is integral.
   if (!CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kForceDeviceScaleFactor))
     device_scale_factor_ = static_cast<int>(device_scale_factor_);
   device_scale_factor_ = std::max(1.0f, device_scale_factor_);
+#elif defined(OS_ANDROID)
+  scoped_ptr<DeviceInfo> device_info(new DeviceInfo());
+  device_scale_factor_ = device_info->GetDPIScale();

[johnme, 2012/10/30 14:38:23]

There's also device scale factor logic in ui/gfx/display.cc, where
device_scale_factor_ is initialized using kForcedDeviceScaleFactor (which will
be wrong on Android).

Would it be better to move both this and the CrOS logic above into display.cc,
and make render_widget depend on that?

[Sami, 2012/10/31 11:12:57]

Good idea. I looked into this a little more and it doesn't seem very
straightforward to move this logic there. The problem is that
Display::device_scale_factor() is either 1 or the value from the command line --
i.e., it's not based on the real DPI on any of the ports as far as I can tell. I
don't want to go and change it to match the real DPI because I don't have a good
way of testing this on platforms other than Android.

On the plus side, it turns out that we can just add OS_ANDROID to the list on
line 124 and things will work.

I've added a TODO to clean this up.

 #endif
 }
 
 RenderWidget::~RenderWidget() {
   DCHECK(!webwidget_) << "Leaking our WebWidget!";
   STLDeleteElements(&updates_pending_swap_);
   if (current_paint_buf_) {
     RenderProcess::current()->ReleaseTransportDIB(current_paint_buf_);
     current_paint_buf_ = NULL;
   }
@@ skipping 1765 matching lines @@
 
 bool RenderWidget::WillHandleMouseEvent(const WebKit::WebMouseEvent& event) {
   return false;
 }
 
 bool RenderWidget::WebWidgetHandlesCompositorScheduling() const {
   return false;
 }
 
 }  // namespace content