Viewport: DestroyPlatformWindow() skips calling user function if PlatformWindowCreated is set. + Clarified comment about implicit Debug viewport which may be hogging a viewport.

imgui.cpp

@@ -10446,7 +10446,8 @@ void ImGui::UpdatePlatformWindows()
     {
         ImGuiViewportP* viewport = g.Viewports[i];
 
-        // Destroy platform window if the viewport hasn't been submitted or if it is hosting a hidden window (the implicit/fallback Debug window will be registered its viewport then be disabled)
+        // Destroy platform window if the viewport hasn't been submitted or if it is hosting a hidden window 
+        // (the implicit/fallback Debug##Default window will be registering its viewport then be disabled, causing a dummy DestroyPlatformWindow to be made each frame)
         bool destroy_platform_window = false;
         destroy_platform_window |= (viewport->LastFrameActive < g.FrameCount - 1);
         destroy_platform_window |= (viewport->Window && !IsWindowActiveAndVisible(viewport->Window));
@@ -10628,15 +10629,20 @@ static void ImGui::UpdateViewportPlatformMonitor(ImGuiViewportP* viewport)
 void ImGui::DestroyPlatformWindow(ImGuiViewportP* viewport)
 {
     ImGuiContext& g = *GImGui;
+    if (viewport->PlatformWindowCreated)
+    {
         if (g.PlatformIO.Renderer_DestroyWindow)
             g.PlatformIO.Renderer_DestroyWindow(viewport);
         if (g.PlatformIO.Platform_DestroyWindow)
             g.PlatformIO.Platform_DestroyWindow(viewport);
-    IM_ASSERT(viewport->RendererUserData == NULL);
-    IM_ASSERT(viewport->PlatformUserData == NULL);
-    viewport->PlatformHandle = NULL;
-    viewport->RendererUserData = viewport->PlatformHandle = NULL;
+        IM_ASSERT(viewport->RendererUserData == NULL && viewport->PlatformUserData == NULL);
         viewport->PlatformWindowCreated = false;
+    }
+    else
+    {
+        IM_ASSERT(viewport->RendererUserData == NULL && viewport->PlatformUserData == NULL && viewport->PlatformHandle == NULL);
+    }
+    viewport->RendererUserData = viewport->PlatformUserData = viewport->PlatformHandle = NULL;
     viewport->ClearRequestFlags();
 }