feat(window): wire inactive opacity to main window focus state

HellionChat/Ui/Windows/MainWindow.cs

@@ -37,6 +37,9 @@ internal sealed class MainWindow : Window
     public Vector2 LastWindowSize { get; private set; } = Vector2.Zero;
     internal unsafe ImGuiViewport* LastViewport;
 
+    // 1.5.6 viewport-guard input: tracked in Draw, read by PreDraw next frame.
+    private bool _wasDocked;
+
     public MainWindow(
         Components.HonorificHeader honorific,
         Components.Sidebar sidebar,
@@ -70,6 +73,35 @@ internal sealed class MainWindow : Window
         RespectCloseHotkey = false;
     }
 
+    // UI-12: per-window focus-dependent opacity. ResolveBgAlpha stays guard-free
+    // and pure so the self-test can drive it directly; PreDraw owns the guard +
+    // wiring. 1.5.6 parity (focused → WindowOpacity, unfocused →
+    // WindowOpacityInactive, ChatLogWindow.PreOpenCheck 1d3b429:724).
+    internal float ResolveBgAlpha(bool isFocused) =>
+        isFocused ? Plugin.Config.WindowOpacity : Plugin.Config.WindowOpacityInactive;
+
+    public override void PreDraw()
+    {
+        // Dalamud's WindowHost turns Window.BgAlpha into SetNextWindowBgAlpha
+        // (WindowHost.cs:650-652), which REPLACES this one window's WindowBg
+        // alpha (imgui.cpp:7229). The global GlobalStyleScope clamp is left
+        // untouched, so Settings/DbViewer/popouts/wizard keep today's opacity.
+        // Viewport guard (1.5.6 parity, ChatLogWindow.PreOpenCheck 1d3b429:718):
+        // only drive BgAlpha while the window is on the main viewport and not
+        // docked. On a floated own-viewport (Dalamud multi-viewport mode) the
+        // WindowBg alpha would compose against the OS-layer alpha (double
+        // transparency), so leave BgAlpha null there and let the global scope
+        // govern. LastViewport/_wasDocked are last frame's values from Draw
+        // (one-frame latency, accepted, matches 1.5.6).
+        unsafe
+        {
+            if (LastViewport == ImGuiHelpers.MainViewport.Handle && !_wasDocked)
+                BgAlpha = ResolveBgAlpha(IsFocused);
+            else
+                BgAlpha = null;
+        }
+    }
+
     public Tab? ActiveTab => _activeTab;
 
     // Internal accessors for self-tests so the probes can reach the live
@@ -99,6 +131,7 @@ internal sealed class MainWindow : Window
         {
             LastViewport = ImGui.GetWindowViewport().Handle;
         }
+        _wasDocked = ImGui.IsWindowDocked();
 
         // Primary pool-reset path; InputPreview has a defensive fallback for the MainWindow-closed edge case.
         _handlerLender.ResetCounter();