Fix Pango font rendering with HiDPi displays on Linux.

ui/gfx/font_render_params_linux.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 "ui/gfx/font_render_params.h"
 
 #include <fontconfig/fontconfig.h>
 
 #include "base/command_line.h"
 #include "base/containers/mru_cache.h"
 #include "base/hash.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/lock.h"
+#include "ui/gfx/display.h"
 #include "ui/gfx/font.h"
 #include "ui/gfx/linux_font_delegate.h"
+#include "ui/gfx/screen.h"
 #include "ui/gfx/switches.h"
 
 namespace gfx {
 
 namespace {
 
 #if defined(OS_CHROMEOS)
 // A device scale factor for an internal display (if any)
 // that is used to determine if subpixel positioning should be used.
 float device_scale_factor_for_internal_display = 1.0f;
@@ skipping 24 matching lines @@
 struct SynchronizedCache {
   SynchronizedCache() : cache(kCacheSize) {}
 
   base::Lock lock;
   Cache cache;
 };
 
 base::LazyInstance<SynchronizedCache>::Leaky g_synchronized_cache =
     LAZY_INSTANCE_INITIALIZER;
 
 bool IsBrowserTextSubpixelPositioningEnabled(

[msw, 2015/03/19 19:30:43]

nit: maybe inline this now?

[stapelberg, 2015/03/19 19:39:25]

Done.

     const FontRenderParamsQuery& query) {
-#if defined(OS_CHROMEOS)
   return query.device_scale_factor > 1.0f;
-#else
-  return false;
-#endif
 }
 
 // Converts Fontconfig FC_HINT_STYLE to FontRenderParams::Hinting.
 FontRenderParams::Hinting ConvertFontconfigHintStyle(int hint_style) {
   switch (hint_style) {
     case FC_HINT_SLIGHT: return FontRenderParams::HINTING_SLIGHT;
     case FC_HINT_MEDIUM: return FontRenderParams::HINTING_MEDIUM;
     case FC_HINT_FULL:   return FontRenderParams::HINTING_FULL;
     default:             return FontRenderParams::HINTING_NONE;
   }
@@ skipping 119 matching lines @@
       "%d|%d|%d|%d|%s|%f", query.for_web_contents, query.pixel_size,
       query.point_size, query.style, JoinString(query.families, ',').c_str(),
       query.device_scale_factor));
 }
 
 }  // namespace
 
 FontRenderParams GetFontRenderParams(const FontRenderParamsQuery& query,
                                      std::string* family_out) {
   FontRenderParamsQuery actual_query(query);
+  if (actual_query.device_scale_factor == 0) {
 #if defined(OS_CHROMEOS)
-  if (actual_query.device_scale_factor == 0)
     actual_query.device_scale_factor = device_scale_factor_for_internal_display;
+#else
+    // Linux does not support per-display DPI, so we use a slightly simpler
+    // code path than on Chrome OS to figure out the device scale factor.
+    gfx::Screen* screen = gfx::Screen::GetNativeScreen();
+    if (screen) {
+      gfx::Display display = screen->GetPrimaryDisplay();
+      actual_query.device_scale_factor = display.device_scale_factor();
+    }
 #endif
+  }
   const uint32 hash = HashFontRenderParamsQuery(actual_query);
   SynchronizedCache* synchronized_cache = g_synchronized_cache.Pointer();
 
   {
     // Try to find a cached result so Fontconfig doesn't need to be queried.
     base::AutoLock lock(synchronized_cache->lock);
     Cache::const_iterator it = synchronized_cache->cache.Get(hash);
     if (it != synchronized_cache->cache.end()) {
       DVLOG(1) << "Returning cached params for " << hash;
       const QueryResult& result = it->second;
@@ skipping 59 matching lines @@
 float GetFontRenderParamsDeviceScaleFactor() {
   return device_scale_factor_for_internal_display;
 }
 
 void SetFontRenderParamsDeviceScaleFactor(float device_scale_factor) {
   device_scale_factor_for_internal_display = device_scale_factor;
 }
 #endif
 
 }  // namespace gfx