Enable hidpi on Linux, refactor a bit on Windows to share

ui/views/widget/desktop_aura/desktop_screen_x11.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/views/widget/desktop_aura/desktop_screen_x11.h"
 
 #include <X11/extensions/Xrandr.h>
 #include <X11/Xlib.h>
 
 // It clashes with out RootWindow.
 #undef RootWindow
 
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/base/layout.h"
 #include "ui/display/util/display_util.h"
 #include "ui/display/util/x11/edid_parser_x11.h"
 #include "ui/events/platform/platform_event_source.h"
 #include "ui/gfx/display.h"
+#include "ui/gfx/linux_font_delegate.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/gfx/screen.h"
 #include "ui/gfx/x/x11_types.h"
 #include "ui/views/widget/desktop_aura/desktop_screen.h"
 #include "ui/views/widget/desktop_aura/desktop_window_tree_host_x11.h"
 #include "ui/views/widget/desktop_aura/x11_topmost_window_finder.h"
 
 namespace {
 
 // The delay to perform configuration after RRNotify.  See the comment
 // in |Dispatch()|.
 const int64 kConfigureDelayMs = 500;
 
-// TODO(oshima): Consider using gtk-xft-dpi instead.
-float GetDeviceScaleFactor(int screen_pixels, int screen_mm) {
-  const int kCSSDefaultDPI = 96;
-  const float kInchInMm = 25.4f;
+double GetDPI() {
+  static double dpi = -1.0;
+  if (dpi < 0.0) {
+    const gfx::LinuxFontDelegate* delegate = gfx::LinuxFontDelegate::instance();
+    if (delegate)
+      dpi = delegate->GetFontDPI();
+    if (dpi <= 0.0)
+      dpi = 96.0;
+  }
+  return dpi;
+}
 
-  float screen_inches = screen_mm / kInchInMm;
-  float screen_dpi = screen_pixels / screen_inches;
-  float scale = screen_dpi / kCSSDefaultDPI;
+float GetGlobalDeviceScaleFactor() {
+  return GetDPI() / 96.0;
+}
 
-  return ui::GetScaleForScaleFactor(ui::GetSupportedScaleFactor(scale));
+// 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
+#if 0
+double GetPixelsInPoint() {
+  static double pixels_in_point = GetDPI() / 72.0;  // 72 points per inch.
+  return pixels_in_point;
 }
+#endif
 
 std::vector<gfx::Display> GetFallbackDisplayList() {
   ::XDisplay* display = gfx::GetXDisplay();
   ::Screen* screen = DefaultScreenOfDisplay(display);
   int width = WidthOfScreen(screen);
   int height = HeightOfScreen(screen);
   gfx::Size physical_size(WidthMMOfScreen(screen), HeightMMOfScreen(screen));
 
   gfx::Rect bounds_in_pixels(0, 0, width, height);
   gfx::Display gfx_display(0, bounds_in_pixels);
   if (!gfx::Display::HasForceDeviceScaleFactor() &&
       !ui::IsDisplaySizeBlackListed(physical_size)) {
-    float device_scale_factor = GetDeviceScaleFactor(
-        width, physical_size.width());
+    float device_scale_factor = GetGlobalDeviceScaleFactor();
     DCHECK_LE(1.0f, device_scale_factor);
     gfx_display.SetScaleAndBounds(device_scale_factor, bounds_in_pixels);
   }
 
   return std::vector<gfx::Display>(1, gfx_display);
 }
 
 }  // namespace
 
 namespace views {
@@ skipping 201 matching lines @@
 
   bool has_work_area = false;
   gfx::Rect work_area;
   std::vector<int> value;
   if (ui::GetIntArrayProperty(x_root_window_, "_NET_WORKAREA", &value) &&
       value.size() >= 4) {
     work_area = gfx::Rect(value[0], value[1], value[2], value[3]);
     has_work_area = true;
   }
 
+
   float device_scale_factor = 1.0f;
+  bool have_one = false;
   for (int i = 0; i < resources->noutput; ++i) {
     RROutput output_id = resources->outputs[i];
     XRROutputInfo* output_info =
         XRRGetOutputInfo(xdisplay_, resources, output_id);
 
     bool is_connected = (output_info->connection == RR_Connected);
     if (!is_connected) {
       XRRFreeOutputInfo(output_info);
       continue;
     }
 
     if (output_info->crtc) {
       XRRCrtcInfo *crtc = XRRGetCrtcInfo(xdisplay_,
                                          resources,
                                          output_info->crtc);
 
       int64 display_id = -1;
       if (!ui::GetDisplayId(output_id, static_cast<uint8>(i), &display_id)) {
         // It isn't ideal, but if we can't parse the EDID data, fallback on the
         // display number.
         display_id = i;
       }
 
       gfx::Rect crtc_bounds(crtc->x, crtc->y, crtc->width, crtc->height);
       gfx::Display display(display_id, crtc_bounds);
 
       if (!gfx::Display::HasForceDeviceScaleFactor()) {
-        if (i == 0 && !ui::IsDisplaySizeBlackListed(
+        if (!have_one && !ui::IsDisplaySizeBlackListed(
             gfx::Size(output_info->mm_width, output_info->mm_height))) {
           // As per display scale factor is not supported right now,
           // the primary display's scale factor is always used.
-          device_scale_factor = GetDeviceScaleFactor(crtc->width,
-                                                     output_info->mm_width);
+          device_scale_factor = GetGlobalDeviceScaleFactor();
           DCHECK_LE(1.0f, device_scale_factor);
+          have_one = true;
         }
         display.SetScaleAndBounds(device_scale_factor, crtc_bounds);
       }
 
       if (has_work_area) {
         gfx::Rect intersection = crtc_bounds;
         intersection.Intersect(work_area);
         display.set_work_area(intersection);
       }
 
@@ skipping 35 matching lines @@
   change_notifier_.NotifyDisplaysChanged(old_displays, displays_);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 
 gfx::Screen* CreateDesktopScreen() {
   return new DesktopScreenX11;
 }
 
 }  // namespace views