Disable subpixel positioning if DirectWrite isn't initialized

ui/gfx/font_render_params_win.cc

 // Copyright 2014 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 "ui/gfx/font_render_params.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
+#include "ui/gfx/win/direct_write.h"
 #include "ui/gfx/win/singleton_hwnd.h"
 
 namespace gfx {
 
 namespace {
 
 // Caches font render params and updates them on system notifications.
 class CachedFontRenderParams : public gfx::SingletonHwnd::Observer {
  public:
   static CachedFontRenderParams* GetInstance() {
     return Singleton<CachedFontRenderParams>::get();
   }
 
   const FontRenderParams& GetParams() {
     if (params_)
       return *params_;
 
     params_.reset(new FontRenderParams());
     params_->antialiasing = false;
     params_->subpixel_positioning = false;
     params_->autohinter = false;
     params_->use_bitmaps = false;
     params_->hinting = FontRenderParams::HINTING_MEDIUM;
     params_->subpixel_rendering = FontRenderParams::SUBPIXEL_RENDERING_NONE;
 
     BOOL enabled = false;
     if (SystemParametersInfo(SPI_GETFONTSMOOTHING, 0, &enabled, 0) && enabled) {
       params_->antialiasing = true;
-      params_->subpixel_positioning = true;
+      params_->subpixel_positioning = win::IsDirectWriteEnabled();

[msw, 2014/12/10 23:55:50]

Is this correct, or should we simply not round the run widths for RTHB + GDI?
https://code.google.com/p/chromium/codesearch#chromium/src/ui/gfx/render_text...
Please add a comment here, if this is needed, to explain its reasoning.

[ckocagil, 2014/12/11 01:07:11]

Rounding in RTHB and letting Skia do the rounding gives different results. When
we round in RTHB, we always start glyphs at integers. I remember trying both,
and ours giving visually better results as well as matching the native behavior.

I don't think we need a comment here though. DirectWrite supports subpixel
positioning, GDI does not. Whether we round ourselves or let Skia do it isn't a
concern here.

[msw, 2014/12/11 23:30:12]

Optionally: // GDI does not support subpixel positioning.

[ckocagil, 2014/12/12 09:52:11]

Done.

 
       UINT type = 0;
       if (SystemParametersInfo(SPI_GETFONTSMOOTHINGTYPE, 0, &type, 0) &&
           type == FE_FONTSMOOTHINGCLEARTYPE) {
         params_->subpixel_rendering = FontRenderParams::SUBPIXEL_RENDERING_RGB;
       }
     }
     gfx::SingletonHwnd::GetInstance()->AddObserver(this);
     return *params_;
   }
@@ skipping 26 matching lines @@
 
 FontRenderParams GetFontRenderParams(const FontRenderParamsQuery& query,
                                      std::string* family_out) {
   if (family_out)
     NOTIMPLEMENTED();
   // Customized font rendering settings are not supported, only defaults.
   return CachedFontRenderParams::GetInstance()->GetParams();
 }
 
 }  // namespace gfx