Viewports: Fixed main viewport size not matching ImDrawData::DisplaySize for one frame during resize when multi-viewports are disabled. (#4900)

docs/CHANGELOG.txt

@@ -98,6 +98,16 @@ Other changes:
   Note that Linux/Mac still have inconsistent support for multi-viewports. If you want to help see https://github.com/ocornut/imgui/issues/2117.
 
 
+-----------------------------------------------------------------------
+ VERSION 1.88 WIP (In Progress)
+-----------------------------------------------------------------------
+
+Docking+Viewports Branch:
+
+- Viewports: Fixed main viewport size not matching ImDrawData::DisplaySize for one frame during resize
+  when multi-viewports are disabled. (#4900)
+
+
 -----------------------------------------------------------------------
  VERSION 1.87 (Released 2022-02-07)
 -----------------------------------------------------------------------

imgui.cpp

@@ -12903,9 +12903,10 @@ ImGuiViewportP* ImGui::AddUpdateViewport(ImGuiWindow* window, ImGuiID id, const
     ImGuiViewportP* viewport = (ImGuiViewportP*)FindViewportByID(id);
     if (viewport)
     {
-        if (!viewport->PlatformRequestMove)
+        // Always update for main viewport as we are already pulling correct platform pos/size (see #4900)
+        if (!viewport->PlatformRequestMove || viewport->ID == IMGUI_VIEWPORT_DEFAULT_ID)
             viewport->Pos = pos;
-        if (!viewport->PlatformRequestResize)
+        if (!viewport->PlatformRequestResize || viewport->ID == IMGUI_VIEWPORT_DEFAULT_ID)
             viewport->Size = size;
         viewport->Flags = flags | (viewport->Flags & ImGuiViewportFlags_Minimized); // Preserve existing flags
     }