Refactor color temperature operation handling

Introduced `ColorTemperatureOperation` class to manage pending color temperature changes. Updated `MainViewModel` to process operations for specific monitors, improving efficiency and separation of concerns.

Added `PendingColorTemperatureOperation` property to `PowerDisplayProperties` for tracking operations. Enhanced IPC messaging with `MonitorId` and `ColorTemperature` in `PowerDisplayActionMessage`.

Refactored `PowerDisplayViewModel` and `PowerDisplayPage` to directly apply color temperature to specified monitors. Improved logging for better traceability.

src/modules/powerdisplay/PowerDisplay/Serialization/JsonSourceGenerationContext.cs

@@ -21,6 +21,7 @@ namespace PowerDisplay.Serialization
     [JsonSerializable(typeof(MonitorStateFile))]
     [JsonSerializable(typeof(MonitorStateEntry))]
     [JsonSerializable(typeof(PowerDisplaySettings))]
+    [JsonSerializable(typeof(ColorTemperatureOperation))]
 
     // MonitorInfo and related types (Settings.UI.Library)
     [JsonSerializable(typeof(MonitorInfo))]

src/modules/powerdisplay/PowerDisplay/ViewModels/MainViewModel.cs

@@ -481,49 +481,47 @@ public partial class MainViewModel : INotifyPropertyChanged, IDisposable
     }
 
     /// <summary>
-    /// Apply color temperature from settings (triggered by custom action from Settings UI)
-    /// This is called when user explicitly changes color temperature in Settings UI,
-    /// NOT when other settings change. Reads current settings and applies only color temperature.
+    /// Apply color temperature to a specific monitor (triggered by custom action from Settings UI)
+    /// This is called when user explicitly changes color temperature in Settings UI.
+    /// Reads the pending operation from settings and applies it directly.
     /// </summary>
     public async void ApplyColorTemperatureFromSettings()
     {
         try
         {
-            Logger.LogInfo("[Settings] Processing color temperature update from Settings UI");
-
             var settings = _settingsUtils.GetSettingsOrDefault<PowerDisplaySettings>("PowerDisplay");
-            var updateTasks = new List<Task>();
 
-            foreach (var monitorVm in Monitors)
+            // Check if there's a pending color temperature operation
+            var pendingOp = settings.Properties.PendingColorTemperatureOperation;
+
+            if (pendingOp != null && !string.IsNullOrEmpty(pendingOp.MonitorId))
             {
-                var hardwareId = monitorVm.HardwareId;
-                var monitorSettings = settings.Properties.Monitors.FirstOrDefault(m => m.HardwareId == hardwareId);
+                Logger.LogInfo($"[Settings] Processing pending color temperature operation: Monitor '{pendingOp.MonitorId}' -> 0x{pendingOp.ColorTemperature:X2}");
 
-                if (monitorSettings == null)
+                // Find the monitor by internal name (ID)
+                var monitorVm = Monitors.FirstOrDefault(m => m.Id == pendingOp.MonitorId);
+
+                if (monitorVm != null)
                 {
-                    continue;
-                }
-
-                // Apply color temperature if changed
-                if (monitorSettings.ColorTemperature > 0 &&
-                    monitorSettings.ColorTemperature != monitorVm.ColorTemperature)
-                {
-                    Logger.LogInfo($"[Settings] Applying color temperature for {hardwareId}: 0x{monitorSettings.ColorTemperature:X2}");
-
-                    var task = ApplyColorTemperatureAsync(monitorVm, monitorSettings.ColorTemperature);
-                    updateTasks.Add(task);
-                }
-            }
-
-            // Wait for all updates to complete
-            if (updateTasks.Count > 0)
-            {
-                await Task.WhenAll(updateTasks);
-                Logger.LogInfo($"[Settings] Completed {updateTasks.Count} color temperature updates");
+                    // Apply color temperature directly
+                    await ApplyColorTemperatureAsync(monitorVm, pendingOp.ColorTemperature);
+                    Logger.LogInfo($"[Settings] Successfully applied color temperature to monitor '{pendingOp.MonitorId}'");
                 }
                 else
                 {
-                Logger.LogInfo("[Settings] No color temperature changes detected");
+                    Logger.LogWarning($"[Settings] Monitor not found: {pendingOp.MonitorId}");
+                }
+
+                // Clear the pending operation
+                settings.Properties.PendingColorTemperatureOperation = null;
+                _settingsUtils.SaveSettings(
+                    System.Text.Json.JsonSerializer.Serialize(settings, AppJsonContext.Default.PowerDisplaySettings),
+                    PowerDisplaySettings.ModuleName);
+                Logger.LogInfo("[Settings] Cleared pending color temperature operation");
+            }
+            else
+            {
+                Logger.LogInfo("[Settings] No pending color temperature operation");
             }
         }
         catch (Exception ex)

src/settings-ui/Settings.UI.Library/ColorTemperatureOperation.cs

@@ -0,0 +1,20 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Text.Json.Serialization;
+
+namespace Microsoft.PowerToys.Settings.UI.Library
+{
+    /// <summary>
+    /// Represents a pending color temperature change operation
+    /// </summary>
+    public class ColorTemperatureOperation
+    {
+        [JsonPropertyName("monitor_id")]
+        public string MonitorId { get; set; }
+
+        [JsonPropertyName("color_temperature")]
+        public int ColorTemperature { get; set; }
+    }
+}

src/settings-ui/Settings.UI.Library/PowerDisplayActionMessage.cs

@@ -27,6 +27,12 @@ namespace Microsoft.PowerToys.Settings.UI.Library
 
             [JsonPropertyName("value")]
             public string Value { get; set; }
+
+            [JsonPropertyName("monitor_id")]
+            public string MonitorId { get; set; }
+
+            [JsonPropertyName("color_temperature")]
+            public int ColorTemperature { get; set; }
         }
     }
 }

src/settings-ui/Settings.UI.Library/PowerDisplayProperties.cs

@@ -35,5 +35,12 @@ namespace Microsoft.PowerToys.Settings.UI.Library
 
         [JsonPropertyName("restore_settings_on_startup")]
         public bool RestoreSettingsOnStartup { get; set; }
+
+        /// <summary>
+        /// Pending color temperature operation from Settings UI.
+        /// This is cleared after PowerDisplay processes it.
+        /// </summary>
+        [JsonPropertyName("pending_color_temperature_operation")]
+        public ColorTemperatureOperation PendingColorTemperatureOperation { get; set; }
     }
 }

src/settings-ui/Settings.UI/SettingsXAML/Views/PowerDisplayPage.xaml.cs

@@ -139,10 +139,9 @@ namespace Microsoft.PowerToys.Settings.UI.Views
                     monitor.ColorTemperature = newValue.Value;
                     _previousColorTemperatureValues[monitor.HardwareId] = newValue.Value;
 
-                    // Trigger custom action to apply color temperature to hardware
-                    // This is separate from the settings save to avoid unwanted hardware updates
-                    // when other settings (like RestoreSettingsOnStartup) change
-                    ViewModel.TriggerApplyColorTemperature();
+                    // Send IPC message to PowerDisplay with monitor ID and new color temperature value
+                    // PowerDisplay will apply it directly to the specified monitor only
+                    ViewModel.ApplyColorTemperatureToMonitor(monitor.InternalName, newValue.Value);
                 }
                 else
                 {

src/settings-ui/Settings.UI/ViewModels/PowerDisplayViewModel.cs

@@ -355,11 +355,24 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
         }
 
         /// <summary>
-        /// Trigger PowerDisplay.exe to apply color temperature from settings file
+        /// Trigger PowerDisplay.exe to apply color temperature to a specific monitor
         /// Called after user confirms color temperature change in Settings UI
         /// </summary>
-        public void TriggerApplyColorTemperature()
+        /// <param name="monitorInternalName">Internal name (ID) of the monitor</param>
+        /// <param name="colorTemperature">Color temperature value to apply</param>
+        public void ApplyColorTemperatureToMonitor(string monitorInternalName, int colorTemperature)
         {
+            // Set the pending operation in settings
+            _settings.Properties.PendingColorTemperatureOperation = new ColorTemperatureOperation
+            {
+                MonitorId = monitorInternalName,
+                ColorTemperature = colorTemperature,
+            };
+
+            // Save settings to persist the operation
+            SettingsUtils.SaveSettings(_settings.ToJsonString(), PowerDisplaySettings.ModuleName);
+
+            // Send IPC message to trigger PowerDisplay to process the operation
             var actionMessage = new PowerDisplayActionMessage
             {
                 Action = new PowerDisplayActionMessage.ActionData
@@ -368,6 +381,8 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
                     {
                         ActionName = "ApplyColorTemperature",
                         Value = string.Empty,
+                        MonitorId = monitorInternalName,
+                        ColorTemperature = colorTemperature,
                     },
                 },
             };