linux: Get font DPI from GTK.

ui/gfx/pango_util.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/pango_util.h"
 
 #include <cairo/cairo.h>
 #include <pango/pango.h>
 #include <pango/pangocairo.h>
 #include <string>
 
 #include <algorithm>
 #include <map>
 
 #include "base/logging.h"
 #include "base/strings/utf_string_conversions.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/font_list.h"
 #include "ui/gfx/font_render_params.h"
+#include "ui/gfx/linux_font_delegate.h"
 #include "ui/gfx/platform_font_pango.h"
 #include "ui/gfx/text_utils.h"
 
 namespace gfx {
 
 namespace {
 
 // Marker for accelerators in the text.
 const gunichar kAcceleratorChar = '&';
 
@@ skipping 47 matching lines @@
     else
       NOTREACHED() << "Unhandled hinting style " << params.hinting;
     cairo_font_options_set_hint_style(cairo_font_options, cairo_hint_style);
     cairo_font_options_set_hint_metrics(cairo_font_options,
                                         CAIRO_HINT_METRICS_ON);
   }
 
   return cairo_font_options;
 }
 
-// Returns the resolution (DPI) used by pango. A negative value means the
-// resolution hasn't been set.
-double GetPangoResolution() {
-  static double resolution;
-  static bool determined_resolution = false;
-  if (!determined_resolution) {
-    determined_resolution = true;
-    PangoContext* default_context = GetPangoContext();
-    resolution = pango_cairo_context_get_resolution(default_context);
-    g_object_unref(default_context);
+// Returns the DPI that should be used by Pango.
+double GetPangoDPI() {
+  static double dpi = 0.0;
+  static bool determined_dpi = false;

[msw, 2014/07/18 03:39:33]

nit: |dpi| can't be negative, init to -1 and s/determined_dpi/dpi<0/

[Daniel Erat, 2014/07/18 04:20:25]

good call; done

+  if (!determined_dpi) {
+    const gfx::LinuxFontDelegate* delegate = gfx::LinuxFontDelegate::instance();
+    if (delegate)
+      dpi = delegate->GetFontDPI();
+    if (dpi <= 0.0)
+      dpi = 96.0;
+    determined_dpi = true;
   }
-  return resolution;
+  return dpi;
 }
 
 // Returns the number of pixels in a point.
 // - multiply a point size by this to get pixels ("device units")
 // - divide a pixel size by this to get points
-float GetPixelsInPoint() {
-  static float pixels_in_point = 1.0;
+double GetPixelsInPoint() {
+  static double pixels_in_point = 1.0;
   static bool determined_value = false;

[msw, 2014/07/18 03:39:33]

nit: ditto for |pixels_in_point| and |determined_value|

[Daniel Erat, 2014/07/18 04:20:26]

Done.

-
   if (!determined_value) {
-    // http://goo.gl/UIh5m: "This is a scale factor between points specified in
-    // a PangoFontDescription and Cairo units.  The default value is 96, meaning
-    // that a 10 point font will be 13 units high. (10 * 96. / 72. = 13.3)."
-    double pango_dpi = GetPangoResolution();
-    if (pango_dpi <= 0)
-      pango_dpi = 96.0;
-    pixels_in_point = pango_dpi / 72.0;  // 72 points in an inch
+    pixels_in_point = GetPangoDPI() / 72.0;  // 72 points in an inch
     determined_value = true;
   }
-
   return pixels_in_point;
 }
 
 }  // namespace
 
 void SetUpPangoLayout(
     PangoLayout* layout,
     const base::string16& text,
     const FontList& font_list,
     base::i18n::TextDirection text_direction,
@@ skipping 37 matching lines @@
     }
   } else if (text_direction == base::i18n::RIGHT_TO_LEFT) {
     pango_layout_set_ellipsize(layout, PANGO_ELLIPSIZE_END);
   } else {
     // Fading the text will be handled in the draw operation.
     // Ensure that the text is only on one line.
     pango_layout_set_ellipsize(layout, PANGO_ELLIPSIZE_NONE);
     pango_layout_set_width(layout, -1);
   }
 
-  // Set the resolution to match that used by Gtk. If we don't set the
-  // resolution and the resolution differs from the default, Gtk and Chrome end
-  // up drawing at different sizes.
-  double resolution = GetPangoResolution();
-  if (resolution > 0) {
-    pango_cairo_context_set_resolution(pango_layout_get_context(layout),
-                                       resolution);
-  }
+  // Set the layout's resolution to match the resolution used to convert from
+  // points to pixels.
+  pango_cairo_context_set_resolution(pango_layout_get_context(layout),
+                                     GetPangoDPI());
 
   // Set text and accelerator character if needed.
   if (flags & Canvas::SHOW_PREFIX) {
     // Escape the text string to be used as markup.
     std::string utf8 = base::UTF16ToUTF8(text);
     gchar* escaped_text = g_markup_escape_text(utf8.c_str(), utf8.size());
     pango_layout_set_markup_with_accel(layout,
                                        escaped_text,
                                        strlen(escaped_text),
                                        kAcceleratorChar, NULL);
@@ skipping 51 matching lines @@
 
   if (i == desc_to_metrics->end()) {
     PangoFontMetrics* metrics = pango_context_get_metrics(context, desc, NULL);
     desc_to_metrics->insert(std::make_pair(desc_hash, metrics));
     return metrics;
   }
   return i->second;
 }
 
 }  // namespace gfx