Retrieve and pass subpixel lcd geometry on windows

ui/gfx/font_render_params_win.cc

Index: ui/gfx/font_render_params_win.cc
diff --git a/ui/gfx/font_render_params_win.cc b/ui/gfx/font_render_params_win.cc
index 9f8409c4eb146996fe2c2714819401e76bb6c848..7f359211acdf02824cebf1f570b524d1666a0e6c 100644
--- a/ui/gfx/font_render_params_win.cc
+++ b/ui/gfx/font_render_params_win.cc
@@ -2,10 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "ui/gfx/font_render_params.h"
-
+#include "base/files/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
+#include "base/win/registry.h"
+#include "ui/gfx/font_render_params.h"
 #include "ui/gfx/win/direct_write.h"
 #include "ui/gfx/win/singleton_hwnd.h"
 
@@ -13,6 +14,32 @@ namespace gfx {
 
 namespace {
 
+FontRenderParams::SubpixelRendering GetSubpixelRenderingGeometry() {
+  DISPLAY_DEVICE display_device = {sizeof(DISPLAY_DEVICE), 0};
+  for (int i = 0; EnumDisplayDevices(nullptr, i, &display_device, 0); ++i) {
+    // TODO(scottmg): We only support the primary device currently.
+    if (display_device.StateFlags & DISPLAY_DEVICE_PRIMARY_DEVICE) {
+      base::FilePath trimmed =
+          base::FilePath(display_device.DeviceName).BaseName();
+      base::win::RegKey key(
+          HKEY_LOCAL_MACHINE,
+          (L"SOFTWARE\\Microsoft\\Avalon.Graphics\\" + trimmed.value()).c_str(),

[msw, 2015/03/26 20:41:25]

Hmm, I wonder why I don't have "Avalon.Graphics" in
"HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\" locally with Win7+Aero with ClearType
enabled... It's described at
https://msdn.microsoft.com/en-us/library/aa970267%28v=vs.110%29.aspx so it
should be legitimate, but I wonder if there's a newer/older/alternate key to
check. I worry about disabling subpixel rendering without this key; it seems
safer to assume RGB (as before) unless the key exists and specifies BGR.

[scottmg, 2015/03/26 21:16:17]

Oh, good catch. I just confirmed on a clean Win7 VM that the key doesn't show up
until the cleartype tuner has been run. Switched to RGB default.

+          KEY_READ);
+      DWORD pixel_structure;
+      if (key.ReadValueDW(L"PixelStructure", &pixel_structure) ==
+          ERROR_SUCCESS) {
+        if (pixel_structure == 1)
+          return FontRenderParams::SUBPIXEL_RENDERING_RGB;
+        else if (pixel_structure == 2)

[msw, 2015/03/26 20:41:25]

nit: no else after return.

[scottmg, 2015/03/26 21:16:17]

Done.

+          return FontRenderParams::SUBPIXEL_RENDERING_BGR;
+      }

[msw, 2015/03/26 20:41:25]

nit: can you break the loop of enumerating devices at the end of this block,
since we only handle the primary device for now?

[scottmg, 2015/03/26 21:16:17]

Done.

+    }
+  }
+
+  // ClearType is not enabled, or retrieval failed.

[msw, 2015/03/26 20:41:25]

nit: I have ClearType on but don't have this key... revise comment?

[scottmg, 2015/03/26 21:16:17]

Done.

+  return FontRenderParams::SUBPIXEL_RENDERING_NONE;
+}
+
 // Caches font render params and updates them on system notifications.
 class CachedFontRenderParams : public gfx::SingletonHwnd::Observer {
  public:
@@ -41,7 +68,7 @@ class CachedFontRenderParams : public gfx::SingletonHwnd::Observer {
       UINT type = 0;
       if (SystemParametersInfo(SPI_GETFONTSMOOTHINGTYPE, 0, &type, 0) &&
           type == FE_FONTSMOOTHINGCLEARTYPE) {
-        params_->subpixel_rendering = FontRenderParams::SUBPIXEL_RENDERING_RGB;
+        params_->subpixel_rendering = GetSubpixelRenderingGeometry();
       }
     }
     gfx::SingletonHwnd::GetInstance()->AddObserver(this);