feat(screen): expose the recommended resolution and scale

screen/com.cutefish.DisplayConfig1.xml

@@ -15,7 +15,7 @@ Adapted for Cutefish: a versioned session D-Bus interface without Ash or Mojo.
     <method name="GetState">
       <arg name="instanceId" type="s" direction="out"/><arg name="seatId" type="s" direction="out"/>
       <arg name="topologyGeneration" type="t" direction="out"/><arg name="appliedRevision" type="t" direction="out"/>
-      <arg name="physicalDisplays" type="a(sssssssasssiiuuua(iiiiiiubbs))" direction="out"/>
+      <arg name="physicalDisplays" type="a(sssssssasssiiuuuua(iiiiiiubbs))" direction="out"/>
       <arg name="logicalDisplays" type="a(ssasiiiiiiiiuub)" direction="out"/><arg name="placements" type="a(ssui)" direction="out"/>
       <annotation name="org.qtproject.QtDBus.QtTypeName.Out4" value="QList&lt;cutefish::display::ipc::PhysicalDisplay&gt;"/>
       <annotation name="org.qtproject.QtDBus.QtTypeName.Out5" value="QList&lt;cutefish::display::ipc::LogicalDisplay&gt;"/>

screen/displaytypes.cpp

@@ -41,11 +41,11 @@ WRITE(PhysicalDisplay, << v.sessionId << v.persistentKey << v.portKey << v.edidK
                        << v.connectorName << v.devicePath << v.baseConnectorKey << v.pathTopology
                        << v.make << v.model << v.serialNumber << v.physicalWidthMm
                        << v.physicalHeightMm << v.connectionType << v.panelOrientation
-                       << v.capabilities << v.modes)
+                       << v.capabilities << v.recommendedScale120 << v.modes)
 READ(PhysicalDisplay, >> v.sessionId >> v.persistentKey >> v.portKey >> v.edidKey >> v.connectorName
              >> v.devicePath >> v.baseConnectorKey >> v.pathTopology >> v.make >> v.model
              >> v.serialNumber >> v.physicalWidthMm >> v.physicalHeightMm >> v.connectionType
-             >> v.panelOrientation >> v.capabilities >> v.modes)
+             >> v.panelOrientation >> v.capabilities >> v.recommendedScale120 >> v.modes)
 WRITE(LogicalDisplay, << v.id << v.waylandName << v.destinations << v.x << v.y << v.width
                       << v.height << v.workX << v.workY << v.workWidth << v.workHeight << v.scale120
                       << v.rotation << v.primary)

screen/displaytypes.h

@@ -59,6 +59,7 @@ struct PhysicalDisplay {
     uint connectionType = 0;
     uint panelOrientation = 0;
     uint capabilities = 0;
+    uint recommendedScale120 = 120;
     QList<Mode> modes;
 };
 

screen/outputmodel.cpp

@@ -129,6 +129,19 @@ QVariant DisplayOutputModel::data(const QModelIndex &index, int role) const
                 return i;
         }
         return 0;
+    case RecommendedResolutionIndexRole:
+        // The display's preferred mode, the one the compositor starts it in.
+        for (int i = 0; i < resolutions.size(); ++i) {
+            const auto &m = e.physical.modes.at(resolutions.at(i));
+            for (const auto &preferred : e.physical.modes) {
+                if (preferred.preferred && m.width == preferred.width
+                    && m.height == preferred.height)
+                    return i;
+            }
+        }
+        return -1;
+    case RecommendedScaleRole:
+        return e.physical.recommendedScale120 / 120.0;
     case ResolutionsRole: {
         QStringList v;
         for (int i : resolutions) {
@@ -343,7 +356,9 @@ QHash<int, QByteArray> DisplayOutputModel::roleNames() const
             {IdRole, "displayId"},
             {CapabilitiesRole, "capabilities"},
             {SupportedScalesRole, "supportedScales"},
-            {DrmConnectorRole, "drmConnector"}};
+            {DrmConnectorRole, "drmConnector"},
+            {RecommendedResolutionIndexRole, "recommendedResolutionIndex"},
+            {RecommendedScaleRole, "recommendedScale"}};
 }
 
 void DisplayOutputModel::setState(const DisplayClient::State &state)

screen/outputmodel.h

@@ -41,7 +41,9 @@ public:
         IdRole,
         CapabilitiesRole,
         SupportedScalesRole,
-        DrmConnectorRole
+        DrmConnectorRole,
+        RecommendedResolutionIndexRole,
+        RecommendedScaleRole
     };
 
     explicit DisplayOutputModel(QObject *parent = nullptr);

screen/tests/outputmodel_test.cpp

@@ -92,6 +92,35 @@ private slots:
         QVERIFY(!edit);
     }
 
+    void recommendationsFollowTheCompositor()
+    {
+        DisplayClient::State state;
+        cutefish::display::ipc::PhysicalDisplay physical;
+        physical.sessionId = QStringLiteral("0");
+        physical.recommendedScale120 = 180;
+        for (const QSize size : {QSize(1920, 1080), QSize(3840, 2160), QSize(2560, 1440)}) {
+            cutefish::display::ipc::Mode mode;
+            mode.width = size.width();
+            mode.height = size.height();
+            mode.refreshMilliHz = 60000;
+            mode.preferred = size.width() == 3840;
+            mode.current = size.width() == 1920;
+            physical.modes.append(mode);
+        }
+        state.physical.append(physical);
+        cutefish::display::ipc::LogicalDisplay logical;
+        logical.id = physical.sessionId;
+        logical.destinations = {physical.sessionId};
+        state.logical.append(logical);
+
+        DisplayOutputModel model;
+        model.setState(state);
+        const auto row = model.index(0);
+        // Largest first: 3840 × 2160 heads the list.
+        QCOMPARE(model.data(row, DisplayOutputModel::RecommendedResolutionIndexRole).toInt(), 0);
+        QCOMPARE(model.data(row, DisplayOutputModel::RecommendedScaleRole).toDouble(), 1.5);
+    }
+
     void screensAreNamedForPeople()
     {
         DisplayClient::State state;