DisplaySettings: Show DPI for selected resolution

This uses the EDID provided by the connected display to show the pixel
density of a selected resolution.

Userland/Applications/DisplaySettings/CMakeLists.txt

@@ -23,4 +23,4 @@ set(SOURCES
 )
 
 serenity_app(DisplaySettings ICON app-display-settings)
-target_link_libraries(DisplaySettings LibDesktop LibGUI LibConfig LibMain)
+target_link_libraries(DisplaySettings LibDesktop LibGUI LibConfig LibMain LibEDID)

Userland/Applications/DisplaySettings/MonitorSettings.gml

@@ -54,6 +54,13 @@
             @GUI::ComboBox {
                 name: "resolution_combo"
             }
+
+            @GUI::Label {
+                name: "display_dpi"
+                text: "96 dpi"
+                text_alignment: "CenterMiddle"
+                fixed_width: 50
+            }
         }
 
         @GUI::Widget {

Userland/Applications/DisplaySettings/MonitorSettingsWidget.cpp

@@ -7,10 +7,12 @@
 
 #include "MonitorSettingsWidget.h"
 #include <Applications/DisplaySettings/MonitorSettingsGML.h>
+#include <LibEDID/EDID.h>
 #include <LibGUI/BoxLayout.h>
 #include <LibGUI/Button.h>
 #include <LibGUI/ComboBox.h>
 #include <LibGUI/ItemListModel.h>
+#include <LibGUI/Label.h>
 #include <LibGUI/MessageBox.h>
 #include <LibGUI/RadioButton.h>
 #include <LibGUI/WindowServerConnection.h>
@@ -58,7 +60,7 @@ void MonitorSettingsWidget::create_frame()
     m_screen_combo->set_model(*GUI::ItemListModel<String>::create(m_screens));
     m_screen_combo->on_change = [this](auto&, const GUI::ModelIndex& index) {
         m_selected_screen_index = index.row();
-        selected_screen_index_changed();
+        selected_screen_index_or_resolution_changed();
     };
 
     m_resolution_combo = *find_descendant_of_type_named<GUI::ComboBox>("resolution_combo");
@@ -69,8 +71,7 @@ void MonitorSettingsWidget::create_frame()
         selected_screen.resolution = m_resolutions.at(index.row());
         // Try to auto re-arrange things if there are overlaps or disconnected screens
         m_screen_layout.normalize();
-        m_monitor_widget->set_desktop_resolution(selected_screen.resolution);
-        m_monitor_widget->update();
+        selected_screen_index_or_resolution_changed();
     };
 
     m_display_scale_radio_1x = *find_descendant_of_type_named<GUI::RadioButton>("scale_1x");
@@ -95,6 +96,8 @@ void MonitorSettingsWidget::create_frame()
             m_monitor_widget->update();
         }
     };
+
+    m_dpi_label = *find_descendant_of_type_named<GUI::Label>("display_dpi");
 }
 
 void MonitorSettingsWidget::load_current_settings()
@@ -110,12 +113,42 @@ void MonitorSettingsWidget::load_current_settings()
     }
     m_selected_screen_index = m_screen_layout.main_screen_index;
     m_screen_combo->set_selected_index(m_selected_screen_index);
-    selected_screen_index_changed();
+    selected_screen_index_or_resolution_changed();
 }
 
-void MonitorSettingsWidget::selected_screen_index_changed()
+void MonitorSettingsWidget::selected_screen_index_or_resolution_changed()
 {
     auto& screen = m_screen_layout.screens[m_selected_screen_index];
+
+    // Let's attempt to find the current resolution based on the screen layout settings
+    auto index = m_resolutions.find_first_index(screen.resolution).value_or(0);
+    Gfx::IntSize current_resolution = m_resolutions.at(index);
+
+    Optional<unsigned> screen_dpi;
+    String screen_dpi_tooltip;
+    if (auto edid = EDID::Parser::from_framebuffer_device(screen.device, 0); !edid.is_error()) { // TODO: multihead
+        if (auto screen_size = edid.value().screen_size(); screen_size.has_value()) {
+            float x_cm = screen_size.value().horizontal_cm();
+            float y_cm = screen_size.value().vertical_cm();
+            float diagonal_inch = sqrtf(x_cm * x_cm + y_cm * y_cm) / 2.54f;
+            float diagonal_pixels = sqrtf(current_resolution.width() * current_resolution.width() + current_resolution.height() * current_resolution.height());
+            if (diagonal_pixels != 0.0f) {
+                screen_dpi = diagonal_pixels / diagonal_inch;
+                screen_dpi_tooltip = String::formatted("{} inch display ({}cm x {}cm)", roundf(diagonal_inch), x_cm, y_cm);
+            }
+        }
+    } else {
+        dbgln("Error getting EDID from device {}: {}", screen.device, edid.error());
+    }
+
+    if (screen_dpi.has_value()) {
+        m_dpi_label->set_tooltip(screen_dpi_tooltip);
+        m_dpi_label->set_text(String::formatted("{} dpi", screen_dpi.value()));
+        m_dpi_label->set_visible(true);
+    } else {
+        m_dpi_label->set_visible(false);
+    }
+
     if (screen.scale_factor != 1 && screen.scale_factor != 2) {
         dbgln("unexpected ScaleFactor {}, setting to 1", screen.scale_factor);
         screen.scale_factor = 1;
@@ -123,9 +156,7 @@ void MonitorSettingsWidget::selected_screen_index_changed()
     (screen.scale_factor == 1 ? m_display_scale_radio_1x : m_display_scale_radio_2x)->set_checked(true);
     m_monitor_widget->set_desktop_scale_factor(screen.scale_factor);
 
-    // Let's attempt to find the current resolution and select it!
-    auto index = m_resolutions.find_first_index(screen.resolution).value_or(0);
-    Gfx::IntSize current_resolution = m_resolutions.at(index);
+    // Select the current selected resolution as it may differ
     m_monitor_widget->set_desktop_resolution(current_resolution);
     m_resolution_combo->set_selected_index(index);
 
@@ -140,6 +171,8 @@ void MonitorSettingsWidget::apply_settings()
     if (m_screen_layout != current_layout) {
         auto result = GUI::WindowServerConnection::the().set_screen_layout(m_screen_layout, false);
         if (result.success()) {
+            load_current_settings(); // Refresh
+
             auto box = GUI::MessageBox::construct(window(), String::formatted("Do you want to keep the new settings? They will be reverted after 10 seconds."),
                 "Apply new screen layout", GUI::MessageBox::Type::Question, GUI::MessageBox::InputType::YesNo);
             box->set_icon(window()->icon());

Userland/Applications/DisplaySettings/MonitorSettingsWidget.h

@@ -39,7 +39,7 @@ private:
     void create_frame();
     void create_resolution_list();
     void load_current_settings();
-    void selected_screen_index_changed();
+    void selected_screen_index_or_resolution_changed();
 
     size_t m_selected_screen_index { 0 };
 
@@ -52,6 +52,7 @@ private:
     RefPtr<GUI::ComboBox> m_resolution_combo;
     RefPtr<GUI::RadioButton> m_display_scale_radio_1x;
     RefPtr<GUI::RadioButton> m_display_scale_radio_2x;
+    RefPtr<GUI::Label> m_dpi_label;
 
     bool m_showing_screen_numbers { false };
 };