音量調整のスクロールコントロールをメニューへ追加

App.config

@@ -17,6 +17,9 @@
             <setting name="OuputDeviceName" serializeAs="String">
                 <value />
             </setting>
+            <setting name="Volume" serializeAs="String">
+                <value>1</value>
+            </setting>
         </Esperecyan.NCVVoicevox.Properties.Settings>
     </userSettings>
 <applicationSettings>

App.xaml.cs

@@ -16,6 +16,7 @@ namespace Esperecyan.NCVVoicevox;
 public partial class App : Application
 {
     internal static readonly string Title;
+    private static readonly int PossibleVolumeValueCount = 100;
 
     static App()
     {
@@ -147,10 +148,27 @@ private App()
             return responseEntity;
         };
 
-        var contextMenuStrip = new ContextMenuStrip();
-        contextMenuStrip.Items.Add(new ToolStripMenuItem("終了", image: null, (sender, e) => this.Shutdown()));
+        var contextMenuStrip = new ContextMenuStrip()
+        {
+            Renderer = new VolumeIconRenderer(),
+        };
+        var menuItems = contextMenuStrip.Items;
+        var volumeBar = new TrackBar()
+        {
+            Maximum = App.PossibleVolumeValueCount,
+            Width = 200,
+            TickFrequency = 10,
+            Value = (int)((waveOut.Volume = Settings.Default.Volume) * App.PossibleVolumeValueCount),
+        };
+        volumeBar.ValueChanged += (_, _) =>
+        {
+            Settings.Default.Volume = waveOut.Volume = (float)volumeBar.Value / App.PossibleVolumeValueCount;
+            Settings.Default.Save();
+        };
+        menuItems.Add(new ToolStripControlHost(volumeBar, "volume"));
+        menuItems.Add(new ToolStripMenuItem("終了", image: null, (sender, e) => this.Shutdown()));
 
-        contextMenuStrip.Opening += (_, _) => App.UpdateDeviceMenuItems(contextMenuStrip.Items);
+        contextMenuStrip.Opening += (_, _) => App.UpdateDeviceMenuItems(menuItems);
 
         var notifyIcon = new NotifyIcon()
         {

Properties/Settings.settings

@@ -20,5 +20,8 @@
     <Setting Name="OuputDeviceName" Type="System.String" Scope="User">
       <Value Profile="(Default)" />
     </Setting>
+    <Setting Name="Volume" Type="System.Single" Scope="User">
+      <Value Profile="(Default)">1</Value>
+    </Setting>
   </Settings>
 </SettingsFile>

VolumeIconRenderer.cs

@@ -0,0 +1,36 @@
+using System;
+using System.Drawing;
+using System.IO;
+using System.Linq;
+using System.Windows.Forms;
+
+namespace Esperecyan.NCVVoicevox;
+
+/// <summary>
+/// 「volume」という名前の項目に、スピーカーアイコンを表示します。
+/// </summary>
+internal class VolumeIconRenderer : ToolStripProfessionalRenderer
+{
+    private static readonly int Size = 24;
+    private static readonly Icon Icon;
+
+    static VolumeIconRenderer()
+    {
+        VolumeIconRenderer.Icon = IconExtractor.ExtractFromFile(
+            Path.Join(Environment.GetFolderPath(Environment.SpecialFolder.SystemX86), "DDORes.dll"),
+            index: 1
+        );
+    }
+
+    protected override void OnRenderImageMargin(ToolStripRenderEventArgs e)
+    {
+        base.OnRenderImageMargin(e);
+        var volumeItem = e.ToolStrip.Items.Cast<ToolStripItem>().First(item => item.Name == "volume");
+        e.Graphics.DrawIcon(VolumeIconRenderer.Icon, new Rectangle(
+            x: 1,
+            y: volumeItem.Bounds.Y + volumeItem.Height / 2 - VolumeIconRenderer.Size / 2,
+            width: VolumeIconRenderer.Size,
+            height: VolumeIconRenderer.Size
+        ));
+    }
+}