Viewports: Minor tweaks. (#2471)

imgui.cpp

@@ -1099,6 +1099,7 @@ static void             UpdateViewportsNewFrame();
 static void             UpdateViewportsEndFrame();
 static void             UpdateSelectWindowViewport(ImGuiWindow* window);
 static bool             UpdateTryMergeWindowIntoHostViewport(ImGuiWindow* window, ImGuiViewportP* host_viewport);
+static bool             UpdateTryMergeWindowIntoHostViewports(ImGuiWindow* window);
 static void             SetCurrentViewport(ImGuiWindow* window, ImGuiViewportP* viewport);
 static bool             GetWindowAlwaysWantOwnViewport(ImGuiWindow* window);
 static int              FindPlatformMonitorForPos(const ImVec2& pos);
@@ -10233,6 +10234,12 @@ static bool ImGui::UpdateTryMergeWindowIntoHostViewport(ImGuiWindow* window, ImG
     return true;
 }
 
+static bool ImGui::UpdateTryMergeWindowIntoHostViewports(ImGuiWindow* window)
+{
+    ImGuiContext& g = *GImGui;
+    return UpdateTryMergeWindowIntoHostViewport(window, g.Viewports[0]);
+}
+
 // Scale all windows (position, size). Use when e.g. changing DPI. (This is a lossy operation!)
 void ImGui::ScaleWindowsInViewport(ImGuiViewportP* viewport, float scale)
 {
@@ -10584,7 +10591,7 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
         // We cannot test window->ViewportOwned as it set lower in the function.
         bool try_to_merge_into_host_viewport = (window->Viewport && window == window->Viewport->Window && g.ActiveId == 0);
         if (try_to_merge_into_host_viewport)
-            UpdateTryMergeWindowIntoHostViewport(window, g.Viewports[0]);
+            UpdateTryMergeWindowIntoHostViewports(window);
     }
 
     // Fallback to default viewport
@@ -10618,7 +10625,7 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
                 window->Viewport->ID = window->ID;
                 window->Viewport->LastNameHash = 0;
             }
-            else if (!UpdateTryMergeWindowIntoHostViewport(window, g.Viewports[0])) // Merge?
+            else if (!UpdateTryMergeWindowIntoHostViewports(window)) // Merge?
             {
                 // New viewport
                 window->Viewport = AddUpdateViewport(window, window->ID, window->Pos, window->Size, ImGuiViewportFlags_NoFocusOnAppearing);

imgui.h

@@ -2358,7 +2358,8 @@ enum ImGuiViewportFlags_
     ImGuiViewportFlags_NoInputs                 = 1 << 4,   // Platform Window: Make mouse pass through so we can drag this window while peaking behind it.
     ImGuiViewportFlags_NoRendererClear          = 1 << 5,   // Platform Window: Renderer doesn't need to clear the framebuffer ahead (because we will fill it entirely).
     ImGuiViewportFlags_TopMost                  = 1 << 6,   // Platform Window: Display on top (for tooltips only)
-    ImGuiViewportFlags_Minimized                = 1 << 7    // Platform Window: Window is minimized, can skip render. When minimized we tend to avoid using the viewport pos/size for clipping window or testing if they are contained in the viewport.
+    ImGuiViewportFlags_Minimized                = 1 << 7,   // Platform Window: Window is minimized, can skip render. When minimized we tend to avoid using the viewport pos/size for clipping window or testing if they are contained in the viewport.
+    ImGuiViewportFlags_CanHostOtherWindows      = 1 << 8    // Main viewport: can host multiple imgui windows (secondary viewports are associated to a single window)
 };
 
 // The viewports created and managed by imgui. The role of the platform back-end is to create the platform/OS windows corresponding to each viewport.

imgui_internal.h

@@ -748,11 +748,6 @@ struct ImDrawDataBuilder
     IMGUI_API void FlattenIntoSingleLayer();
 };
 
-enum ImGuiViewportFlagsPrivate_
-{
-    ImGuiViewportFlags_CanHostOtherWindows  = 1 << 10   // Normal viewports are associated to a single window. The main viewport can host multiple windows.
-};
-
 // ImGuiViewport Private/Internals fields (cardinal sin: we are using inheritance!)
 // Note that every instance of ImGuiViewport is in fact a ImGuiViewportP.
 struct ImGuiViewportP : public ImGuiViewport