device scale factor detection: use gtk-xft-dpi consistently

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.
@@ skipping 17 matching lines @@
 #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.

[oshima, 2015/04/08 17:33:58]

We should use gtk-xft-dpi instead, shouldn't we? This is what we use for font
size (Gtk2UI::UpdateDefaultFont), so using this allow us to scale when a user
changes the font scale (using gnome-tweak-tool for example).

[stapelberg, 2015/04/08 21:01:06]

Done.

 float GetDeviceScaleFactor(int screen_pixels, int screen_mm) {
   const int kCSSDefaultDPI = 96;
   const float kInchInMm = 25.4f;
 
   float screen_inches = screen_mm / kInchInMm;
   float screen_dpi = screen_pixels / screen_inches;
   float scale = screen_dpi / kCSSDefaultDPI;
 
   return ui::GetScaleForScaleFactor(ui::GetSupportedScaleFactor(scale));
 }
@@ skipping 239 matching lines @@
   bool has_work_area = false;
   gfx::Rect work_area_in_pixels;
   std::vector<int> value;
   if (ui::GetIntArrayProperty(x_root_window_, "_NET_WORKAREA", &value) &&
       value.size() >= 4) {
     work_area_in_pixels = gfx::Rect(value[0], value[1], value[2], value[3]);
     has_work_area = true;
   }
 
   float device_scale_factor = 1.0f;
+  {
+    // As per-display scale factor is not supported right now,
+    // the X11 root window's scale factor is always used.
+    // This is what users can change using e.g. xrandr -dpi 96
+    std::vector<gfx::Display> fallback_displays = GetFallbackDisplayList();
+    device_scale_factor = fallback_displays[0].device_scale_factor();
+  }
   for (int i = 0; i < resources->noutput; ++i) {
     RROutput output_id = resources->outputs[i];
     gfx::XScopedPtr<XRROutputInfo,
                     gfx::XObjectDeleter<XRROutputInfo, void, XRRFreeOutputInfo>>
         output_info(XRRGetOutputInfo(xdisplay_, resources.get(), output_id));
 
     bool is_connected = (output_info->connection == RR_Connected);
     if (!is_connected)
       continue;
 
     if (output_info->crtc) {
       gfx::XScopedPtr<XRRCrtcInfo,
                       gfx::XObjectDeleter<XRRCrtcInfo, void, XRRFreeCrtcInfo>>
           crtc(XRRGetCrtcInfo(xdisplay_, resources.get(), 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(
-            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);
-          DCHECK_LE(1.0f, device_scale_factor);
-        }
         display.SetScaleAndBounds(device_scale_factor, crtc_bounds);
       }
 
       if (has_work_area) {
         gfx::Rect intersection_in_pixels = crtc_bounds;
         intersection_in_pixels.Intersect(work_area_in_pixels);
         // SetScaleAndBounds() above does the conversion from pixels to DIP for
         // us, but set_work_area does not, so we need to do it here.
         display.set_work_area(gfx::Rect(
             gfx::ToFlooredPoint(
@@ skipping 36 matching lines @@
   change_notifier_.NotifyDisplaysChanged(old_displays, displays_);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 
 gfx::Screen* CreateDesktopScreen() {
   return new DesktopScreenX11;
 }
 
 }  // namespace views