If docked, force default font on window decoration

ImGui docking functions are called outside our drawing context (from
ImGui::NewFrame), which includes most of dock-related drawing calls.
However, ImGui::RenderWindowDecoration is called from ImGui::Begin,
which may be under the effect of other pushed font. As IG::RWD
references to the ImDrawList irrelevant to the global shared state, it
was trying to draw a rectangle referring to a pixel that is not
guaranteed to be a white pixel. This commit fixes that by forcing the
use of the default font for IG::RWD when the window is docked.

Dalamud/Interface/Internal/ImGuiClipboardFunctionProvider.cs

@@ -52,7 +52,6 @@ internal sealed unsafe class ImGuiClipboardFunctionProvider : IServiceType, IDis
     private ImGuiClipboardFunctionProvider(InterfaceManager.InterfaceManagerWithScene imws)
     {
         // Effectively waiting for ImGui to become available.
-        _ = imws;
         Debug.Assert(ImGuiHelpers.IsImGuiInitialized, "IMWS initialized but IsImGuiInitialized is false?");
 
         var io = ImGui.GetIO();

Dalamud/Interface/ManagedFontAtlas/Internals/ImGuiDockNodeUpdateForceFont.cs

@@ -0,0 +1,78 @@
+using System.Diagnostics;
+using System.Linq;
+
+using Dalamud.Hooking;
+using Dalamud.Interface.Internal;
+using Dalamud.Interface.Utility;
+
+namespace Dalamud.Interface.ManagedFontAtlas.Internals;
+
+/// <summary>
+/// Forces ImGui::RenderWindowDecorations to use the default font.
+/// Fixes dock node draw using shared data across different draw lists.
+/// TODO: figure out how to synchronize ImDrawList::_Data and ImDrawList::Push/PopTextureID across different instances.
+/// It might be better to just special-case that particular function,
+/// as no other code touches ImDrawList that is irrelevant to the global shared state,
+/// with the exception of Dock... functions which are called from ImGui::NewFrame,
+/// which are guaranteed to use the global default font.
+/// </summary>
+[ServiceManager.EarlyLoadedService]
+internal class ImGuiRenderWindowDecorationsForceFont : IServiceType, IDisposable
+{
+    private const int CImGuiRenderWindowDecorationsOffset = 0x461B0;
+    private const int CImGuiWindowDockIsActiveOffset = 0x401;
+
+    private readonly Hook<ImGuiRenderWindowDecorationsDelegate> hook;
+
+    [ServiceManager.ServiceConstructor]
+    private ImGuiRenderWindowDecorationsForceFont(InterfaceManager.InterfaceManagerWithScene imws)
+    {
+        // Effectively waiting for ImGui to become available.
+        Debug.Assert(ImGuiHelpers.IsImGuiInitialized, "IMWS initialized but IsImGuiInitialized is false?");
+
+        var cimgui = Process.GetCurrentProcess().Modules.Cast<ProcessModule>()
+                            .First(x => x.ModuleName == "cimgui.dll")
+                            .BaseAddress;
+        this.hook = Hook<ImGuiRenderWindowDecorationsDelegate>.FromAddress(
+            cimgui + CImGuiRenderWindowDecorationsOffset,
+            this.ImGuiRenderWindowDecorationsDetour);
+        this.hook.Enable();
+    }
+
+    private delegate void ImGuiRenderWindowDecorationsDelegate(
+        nint window,
+        nint titleBarRectPtr,
+        byte titleBarIsHighlight,
+        byte handleBordersAndResizeGrips,
+        int resizeGripCount,
+        nint resizeGripColPtr,
+        float resizeGripDrawSize);
+
+    /// <inheritdoc/>
+    public void Dispose() => this.hook.Dispose();
+
+    private unsafe void ImGuiRenderWindowDecorationsDetour(
+        nint window,
+        nint titleBarRectPtr,
+        byte titleBarIsHighlight,
+        byte handleBordersAndResizeGrips,
+        int resizeGripCount,
+        nint resizeGripColPtr,
+        float resizeGripDrawSize)
+    {
+        using (
+            ((byte*)window)![CImGuiWindowDockIsActiveOffset] != 0
+                ? Service<InterfaceManager>.Get().DefaultFontHandle?.Push()
+                : null)
+        {
+            this.hook.Original(
+                window,
+                titleBarRectPtr,
+                titleBarIsHighlight,
+                handleBordersAndResizeGrips,
+                resizeGripCount,
+                resizeGripColPtr,
+                resizeGripDrawSize);
+        }
+    }
+}