Viewport: Moved OverlayDrawList to be a per-viewport instead of being global + fix overlay clipping glitch during viewport creation frame + support for software mouse cursor stradding over multiple viewport. The overlay draw list move is rather important as draw lists are not shared among viewports anymore and we can do a swap of their data without copying it. (#1542)

7 years ago · ac8931b2e9
parent 4f112f898e
commit ac8931b2e9
3 changed files with 76 additions and 46 deletions
--- a/imgui.cpp
+++ b/imgui.cpp
@ -600,7 +600,7 @@
 Q: How can I use the drawing facilities without an ImGui window? (using ImDrawList API)
 A: - You can create a dummy window. Call SetNextWindowBgAlpha(0.0f), call Begin() with NoTitleBar|NoResize|NoMove|NoScrollbar|NoSavedSettings|NoInputs flags. 
      Then you can retrieve the ImDrawList* via GetWindowDrawList() and draw to it in any way you like.
-    - You can call ImGui::GetOverlayDrawList() and use this draw list to display contents over every other imgui windows.
+    - You can call ImGui::GetOverlayDrawList() and use this draw list to display contents over every other imgui windows (1 overlay per viewport).
    - You can create your own ImDrawList instance. You'll need to initialize them ImGui::GetDrawListSharedData(), or create your own ImDrawListSharedData.

 Q: I integrated Dear ImGui in my engine and the text or lines are blurry..
@ -2245,10 +2245,11 @@ static bool NavScoreItem(ImGuiNavMoveResult* result, ImRect cand)
    if (ImGui::IsMouseHoveringRect(cand.Min, cand.Max))
    {
        ImFormatString(buf, IM_ARRAYSIZE(buf), "dbox (%.2f,%.2f->%.4f)\ndcen (%.2f,%.2f->%.4f)\nd (%.2f,%.2f->%.4f)\nnav %c, quadrant %c", dbx, dby, dist_box, dcx, dcy, dist_center, dax, day, dist_axial, "WENS"[g.NavMoveDir], "WENS"[quadrant]);
-        g.OverlayDrawList.AddRect(curr.Min, curr.Max, IM_COL32(255, 200, 0, 100));
-        g.OverlayDrawList.AddRect(cand.Min, cand.Max, IM_COL32(255,255,0,200));
-        g.OverlayDrawList.AddRectFilled(cand.Max-ImVec2(4,4), cand.Max+ImGui::CalcTextSize(buf)+ImVec2(4,4), IM_COL32(40,0,0,150));
-        g.OverlayDrawList.AddText(g.IO.FontDefault, 13.0f, cand.Max, ~0U, buf);
+        ImDrawList* draw_list = ImGui::GetOverlayDrawList(window);
+        draw_list->AddRect(curr.Min, curr.Max, IM_COL32(255,200,0,100));
+        draw_list->AddRect(cand.Min, cand.Max, IM_COL32(255,255,0,200));
+        draw_list->AddRectFilled(cand.Max-ImVec2(4,4), cand.Max+ImGui::CalcTextSize(buf)+ImVec2(4,4), IM_COL32(40,0,0,150));
+        draw_list->AddText(g.IO.FontDefault, 13.0f, cand.Max, ~0U, buf);
    }
    else if (g.IO.KeyCtrl) // Hold to preview score in matching quadrant. Press C to rotate.
    {
@ -2256,8 +2257,9 @@ static bool NavScoreItem(ImGuiNavMoveResult* result, ImRect cand)
        if (quadrant == g.NavMoveDir)
        {
            ImFormatString(buf, IM_ARRAYSIZE(buf), "%.0f/%.0f", dist_box, dist_center);
-            g.OverlayDrawList.AddRectFilled(cand.Min, cand.Max, IM_COL32(255, 0, 0, 200));
-            g.OverlayDrawList.AddText(g.IO.FontDefault, 13.0f, cand.Min, IM_COL32(255, 255, 255, 255), buf);
+            ImDrawList* draw_list = ImGui::GetOverlayDrawList(window);
+            draw_list->AddRectFilled(cand.Min, cand.Max, IM_COL32(255, 0, 0, 200));
+            draw_list->AddText(g.IO.FontDefault, 13.0f, cand.Min, IM_COL32(255, 255, 255, 255), buf);
        }
    }
 #endif
@ -2691,9 +2693,17 @@ int ImGui::GetFrameCount()
    return GImGui->FrameCount;
 }

+ImDrawList* ImGui::GetOverlayDrawList(ImGuiWindow* window)
+{
+    IM_ASSERT(window && window->Viewport);
+    return window->Viewport->OverlayDrawList;
+}
+
 ImDrawList* ImGui::GetOverlayDrawList()
 {
-    return &GImGui->OverlayDrawList;
+    ImGuiWindow* window = GImGui->CurrentWindow;
+    IM_ASSERT(window && window->Viewport);
+    return window->Viewport->OverlayDrawList;
 }

 ImDrawListSharedData* ImGui::GetDrawListSharedData()
@ -2946,7 +2956,7 @@ static void NavScrollToBringItemIntoView(ImGuiWindow* window, ImRect& item_rect_
 {
    // Scroll to keep newly navigated item fully into view
    ImRect window_rect_rel(window->InnerRect.Min - window->Pos - ImVec2(1, 1), window->InnerRect.Max - window->Pos + ImVec2(1, 1));
-    //g.OverlayDrawList.AddRect(window->Pos + window_rect_rel.Min, window->Pos + window_rect_rel.Max, IM_COL32_WHITE); // [DEBUG]
+    //GetOverlayDrawList(window)->AddRect(window->Pos + window_rect_rel.Min, window->Pos + window_rect_rel.Max, IM_COL32_WHITE); // [DEBUG]
    if (window_rect_rel.Contains(item_rect_rel))
        return;

@ -3247,8 +3257,8 @@ static void ImGui::NavUpdate()
    //g.OverlayDrawList.AddRect(g.NavScoringRectScreen.Min, g.NavScoringRectScreen.Max, IM_COL32(255,200,0,255)); // [DEBUG]
    g.NavScoringCount = 0;
 #if IMGUI_DEBUG_NAV_RECTS
-    if (g.NavWindow) { for (int layer = 0; layer < 2; layer++) g.OverlayDrawList.AddRect(g.NavWindow->Pos + g.NavWindow->NavRectRel[layer].Min, g.NavWindow->Pos + g.NavWindow->NavRectRel[layer].Max, IM_COL32(255,200,0,255)); } // [DEBUG] 
-    if (g.NavWindow) { ImU32 col = (g.NavWindow->HiddenFrames <= 0) ? IM_COL32(255,0,255,255) : IM_COL32(255,0,0,255); ImVec2 p = NavCalcPreferredMousePos(); char buf[32]; ImFormatString(buf, 32, "%d", g.NavLayer); g.OverlayDrawList.AddCircleFilled(p, 3.0f, col); g.OverlayDrawList.AddText(NULL, 13.0f, p + ImVec2(8,-4), col, buf); }
+    if (g.NavWindow) { for (int layer = 0; layer < 2; layer++) GetOverlayDrawList(g.NavWindow)->AddRect(g.NavWindow->Pos + g.NavWindow->NavRectRel[layer].Min, g.NavWindow->Pos + g.NavWindow->NavRectRel[layer].Max, IM_COL32(255,200,0,255)); } // [DEBUG] 
+    if (g.NavWindow) { ImU32 col = (g.NavWindow->HiddenFrames <= 0) ? IM_COL32(255,0,255,255) : IM_COL32(255,0,0,255); ImVec2 p = NavCalcPreferredMousePos(); char buf[32]; ImFormatString(buf, 32, "%d", g.NavLayer); GetOverlayDrawList(g.NavWindow)->AddCircleFilled(p, 3.0f, col); GetOverlayDrawList(g.NavWindow)->AddText(NULL, 13.0f, p + ImVec2(8,-4), col, buf); }
 #endif
 }

@ -3592,6 +3602,15 @@ void ImGui::RenderPlatformWindows(void* platform_render_arg, void* renderer_rend
    }
 }

+static void SetupOverlayDrawList(ImDrawList* draw_list, ImGuiViewport* viewport)
+{
+    ImGuiContext& g = *GImGui;
+    draw_list->Clear();
+    draw_list->PushTextureID(g.IO.Fonts->TexID);
+    draw_list->PushClipRect(viewport->Pos, viewport->Pos + viewport->Size, false);
+    draw_list->Flags = (g.Style.AntiAliasedLines ? ImDrawListFlags_AntiAliasedLines : 0) | (g.Style.AntiAliasedFill ? ImDrawListFlags_AntiAliasedFill : 0);
+}
+
 void ImGui::NewFrame()
 {
    IM_ASSERT(GImGui != NULL && "No current context. Did you call ImGui::CreateContext() or ImGui::SetCurrentContext()?");
@ -3659,16 +3678,13 @@ void ImGui::NewFrame()
    g.DrawListSharedData.ClipRectFullscreen = ImVec4(0.0f, 0.0f, virtual_space_max.x, virtual_space_max.y);
    g.DrawListSharedData.CurveTessellationTol = g.Style.CurveTessellationTol;

-    g.OverlayDrawList.Clear();
-    g.OverlayDrawList.PushTextureID(g.IO.Fonts->TexID);
-    g.OverlayDrawList.PushClipRectFullScreen();
-    g.OverlayDrawList.Flags = (g.Style.AntiAliasedLines ? ImDrawListFlags_AntiAliasedLines : 0) | (g.Style.AntiAliasedFill ? ImDrawListFlags_AntiAliasedFill : 0);
-
-    // Mark rendering data as invalid to prevent user who may have a handle on it to use it
+    // Mark rendering data as invalid to prevent user who may have a handle on it to use it. Setup Overlay draw list for the viewport.
    for (int n = 0; n < g.Viewports.Size; n++)
    {
-        g.Viewports[n]->DrawData = NULL;
-        g.Viewports[n]->DrawDataP.Clear();
+        ImGuiViewportP* viewport = g.Viewports[n];
+        viewport->DrawData = NULL;
+        viewport->DrawDataP.Clear();
+        SetupOverlayDrawList(viewport->OverlayDrawList, viewport);
    }

    // Clear reference to active widget if the widget isn't alive anymore
@ -3983,7 +3999,7 @@ void ImGui::Initialize(ImGuiContext* context)
    g.SettingsHandlers.push_front(ini_handler);

    // Create default viewport
-    ImGuiViewportP* viewport = IM_NEW(ImGuiViewportP)();
+    ImGuiViewportP* viewport = IM_NEW(ImGuiViewportP)(&g.DrawListSharedData);
    viewport->ID = IMGUI_VIEWPORT_DEFAULT_ID;
    viewport->Idx = 0;
    g.Viewports.push_back(viewport);
@ -4047,7 +4063,6 @@ void ImGui::Shutdown(ImGuiContext* context)
    for (int i = 0; i < g.Viewports.Size; i++)
        IM_DELETE(g.Viewports[i]);
    g.Viewports.clear();
-    g.OverlayDrawList.ClearFreeMemory();
    g.PrivateClipboard.clear();
    g.InputTextState.Text.clear();
    g.InputTextState.InitialText.clear();
@ -4483,17 +4498,25 @@ void ImGui::Render()
    ImVec2 offset, size, uv[4];
    if (g.IO.MouseDrawCursor && g.IO.Fonts->GetMouseCursorTexData(g.MouseCursor, &offset, &size, &uv[0], &uv[2]))
    {
-        const ImVec2 pos = g.IO.MousePos - offset;
+        // We need to account for the possibility of the mouse cursor straddling multiple viewports...
+        const ImVec2 main_pos = g.IO.MousePos - offset;
        const ImTextureID tex_id = g.IO.Fonts->TexID;
        const float sc = g.Style.MouseCursorScale;
-        g.OverlayDrawList.PushClipRect(g.MousePosViewport->Pos, g.MousePosViewport->Pos + g.MousePosViewport->Size);
-        g.OverlayDrawList.PushTextureID(tex_id);
-        g.OverlayDrawList.AddImage(tex_id, pos + ImVec2(1,0)*sc, pos+ImVec2(1,0)*sc + size*sc, uv[2], uv[3], IM_COL32(0,0,0,48));        // Shadow
-        g.OverlayDrawList.AddImage(tex_id, pos + ImVec2(2,0)*sc, pos+ImVec2(2,0)*sc + size*sc, uv[2], uv[3], IM_COL32(0,0,0,48));        // Shadow
-        g.OverlayDrawList.AddImage(tex_id, pos,                  pos + size*sc,                uv[2], uv[3], IM_COL32(0,0,0,255));       // Black border
-        g.OverlayDrawList.AddImage(tex_id, pos,                  pos + size*sc,                uv[0], uv[1], IM_COL32(255,255,255,255)); // White fill
-        g.OverlayDrawList.PopTextureID();
-        g.OverlayDrawList.PopClipRect();
+        for (int viewport_n = 0; viewport_n < g.Viewports.Size; viewport_n++)
+        {
+            ImGuiViewportP* viewport = g.Viewports[viewport_n];
+            ImVec2 pos = (g.MousePosViewport == viewport) ? main_pos : ConvertPlatformPosToViewportPos(ConvertViewportPosToPlatformPos(main_pos, g.MousePosViewport), viewport);
+            if (viewport->GetRect().Overlaps(ImRect(pos, pos + ImVec2(2,2)*sc + size * sc)))
+            {
+                ImDrawList* draw_list = viewport->OverlayDrawList;
+                draw_list->PushTextureID(tex_id);
+                draw_list->AddImage(tex_id, pos+ImVec2(1,0)*sc, pos+ImVec2(1,0)*sc + size*sc, uv[2], uv[3], IM_COL32(0,0,0,48));        // Shadow
+                draw_list->AddImage(tex_id, pos+ImVec2(2,0)*sc, pos+ImVec2(2,0)*sc + size*sc, uv[2], uv[3], IM_COL32(0,0,0,48));        // Shadow
+                draw_list->AddImage(tex_id, pos,                pos + size*sc,                uv[2], uv[3], IM_COL32(0,0,0,255));       // Black border
+                draw_list->AddImage(tex_id, pos,                pos + size*sc,                uv[0], uv[1], IM_COL32(255,255,255,255)); // White fill
+                draw_list->PopTextureID();
+            }
+        }
    }

    // Setup ImDrawData structures for end-user
@ -4502,7 +4525,7 @@ void ImGui::Render()
    {
        ImGuiViewportP* viewport = g.Viewports[n];
        viewport->DrawDataBuilder.FlattenIntoSingleLayer();
-        AddDrawListToDrawData(&viewport->DrawDataBuilder.Layers[0], &g.OverlayDrawList);
+        AddDrawListToDrawData(&viewport->DrawDataBuilder.Layers[0], viewport->OverlayDrawList);
        SetupViewportDrawData(viewport, &viewport->DrawDataBuilder.Layers[0]);
        g.IO.MetricsRenderVertices += viewport->DrawData->TotalVtxCount;
        g.IO.MetricsRenderIndices += viewport->DrawData->TotalIdxCount;
@ -4605,12 +4628,19 @@ ImGuiViewportP* ImGui::Viewport(ImGuiWindow* window, ImGuiID id, ImGuiViewportFl
    else
    {
        // New viewport
-        viewport = IM_NEW(ImGuiViewportP)();
+        viewport = IM_NEW(ImGuiViewportP)(&g.DrawListSharedData);
        viewport->ID = id;
        viewport->Idx = g.Viewports.Size;
        viewport->Pos = ImVec2(g.Viewports.back()->GetNextX(), 0.0f);
        viewport->Size = size;
        g.Viewports.push_back(viewport);
+        
+        // We normally setup for all viewports in NewFrame() but here need to handle the mid-frame creation of a new viewport.
+        // 1. We need to extend the fullscreen clip rect so the OverlayDrawList clip is correct for that the first frame
+        // 2. Our ImDrawList system requires that there is always a command, SetupOverlayDrawList() effectively does that by setting up texture and clip rect
+        g.DrawListSharedData.ClipRectFullscreen.z = ImMax(g.DrawListSharedData.ClipRectFullscreen.z, viewport->Pos.x + viewport->Size.x);
+        g.DrawListSharedData.ClipRectFullscreen.w = ImMax(g.DrawListSharedData.ClipRectFullscreen.w, viewport->Pos.y + viewport->Size.y);
+        SetupOverlayDrawList(viewport->OverlayDrawList, viewport);
    }

    IM_ASSERT(viewport->Pos.y == 0.0f);
@ -6619,7 +6649,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
            window->DrawList->AddRectFilled(viewport_rect.Min, viewport_rect.Max, GetColorU32(ImGuiCol_ModalWindowDarkening, g.ModalWindowDarkeningRatio));
            for (int viewport_n = 0; viewport_n < g.Viewports.Size; viewport_n++)
                if (g.Viewports[viewport_n] != window->Viewport)
-                    g.OverlayDrawList.AddRectFilled(g.Viewports[viewport_n]->Pos, g.Viewports[viewport_n]->Pos + g.Viewports[viewport_n]->Size, GetColorU32(ImGuiCol_ModalWindowDarkening, g.ModalWindowDarkeningRatio));
+                    g.Viewports[viewport_n]->OverlayDrawList->AddRectFilled(g.Viewports[viewport_n]->Pos, g.Viewports[viewport_n]->Pos + g.Viewports[viewport_n]->Size, GetColorU32(ImGuiCol_ModalWindowDarkening, g.ModalWindowDarkeningRatio));
        }

        // Draw navigation selection/windowing rectangle background
@ -13925,7 +13955,7 @@ void ImGui::ShowMetricsWindow(bool* p_open)

        struct Funcs
        {
-            static void NodeDrawList(ImGuiWindow* window, ImDrawList* draw_list, const char* label)
+            static void NodeDrawList(ImGuiWindow* window, ImGuiViewportP* viewport, ImDrawList* draw_list, const char* label)
            {
                bool node_open = ImGui::TreeNode(draw_list, "%s: '%s' %d vtx, %d indices, %d cmds", label, draw_list->_OwnerName ? draw_list->_OwnerName : "", draw_list->VtxBuffer.Size, draw_list->IdxBuffer.Size, draw_list->CmdBuffer.Size);
                if (draw_list == ImGui::GetWindowDrawList())
@ -13936,7 +13966,7 @@ void ImGui::ShowMetricsWindow(bool* p_open)
                    return;
                }

-                ImDrawList* overlay_draw_list = ImGui::GetOverlayDrawList(); // Render additional visuals into the top-most draw list
+                ImDrawList* overlay_draw_list = viewport->OverlayDrawList; // Render additional visuals into the top-most draw list
                if (window && ImGui::IsItemHovered())
                    overlay_draw_list->AddRect(window->Pos, window->Pos + window->Size, IM_COL32(255, 255, 0, 255));
                if (!node_open)
@ -14008,7 +14038,7 @@ void ImGui::ShowMetricsWindow(bool* p_open)
                if (!ImGui::TreeNode(window, "%s '%s', %d @ 0x%p", label, window->Name, window->Active || window->WasActive, window))
                    return;
                ImGuiWindowFlags flags = window->Flags;
-                NodeDrawList(window, window->DrawList, "DrawList");
+                NodeDrawList(window, window->Viewport, window->DrawList, "DrawList");
                ImGui::BulletText("Pos: (%.1f,%.1f), Size: (%.1f,%.1f), SizeContents (%.1f,%.1f)", window->Pos.x, window->Pos.y, window->Size.x, window->Size.y, window->SizeContents.x, window->SizeContents.y);
                ImGui::BulletText("Flags: 0x%08X (%s%s%s%s%s%s..)", flags, 
                    (flags & ImGuiWindowFlags_ChildWindow) ? "Child " : "", (flags & ImGuiWindowFlags_Tooltip)   ? "Tooltip "   : "", (flags & ImGuiWindowFlags_Popup) ? "Popup " : "",
@ -14068,7 +14098,7 @@ void ImGui::ShowMetricsWindow(bool* p_open)
                        (flags & ImGuiViewportFlags_NoRendererClear)     ? " NoRendererClear"     : "");
                    for (int layer_i = 0; layer_i < IM_ARRAYSIZE(viewport->DrawDataBuilder.Layers); layer_i++)
                        for (int draw_list_i = 0; draw_list_i < viewport->DrawDataBuilder.Layers[layer_i].Size; draw_list_i++)
-                            Funcs::NodeDrawList(NULL, viewport->DrawDataBuilder.Layers[layer_i][draw_list_i], "DrawList");
+                            Funcs::NodeDrawList(NULL, viewport, viewport->DrawDataBuilder.Layers[layer_i][draw_list_i], "DrawList");
                    ImGui::TreePop();
                }
            }
@ -14111,8 +14141,8 @@ void ImGui::ShowMetricsWindow(bool* p_open)
                char buf[32];
                ImFormatString(buf, IM_ARRAYSIZE(buf), "%d", window->BeginOrderWithinContext);
                float font_size = ImGui::GetFontSize() * 2;
-                g.OverlayDrawList.AddRectFilled(window->Pos, window->Pos + ImVec2(font_size, font_size), IM_COL32(200, 100, 100, 255));
-                g.OverlayDrawList.AddText(NULL, font_size, window->Pos, IM_COL32(255, 255, 255, 255), buf);
+                window->Viewport->OverlayDrawList->AddRectFilled(window->PosFloat, window->PosFloat + ImVec2(font_size, font_size), IM_COL32(200, 100, 100, 255));
+                window->Viewport->OverlayDrawList->AddText(NULL, font_size, window->PosFloat, IM_COL32(255, 255, 255, 255), buf);
            }
        }
    }
--- a/imgui.h
+++ b/imgui.h
@ -502,7 +502,7 @@ namespace ImGui
    IMGUI_API bool          IsRectVisible(const ImVec2& rect_min, const ImVec2& rect_max);      // test if rectangle (in screen space) is visible / not clipped. to perform coarse clipping on user's side.
    IMGUI_API float         GetTime();
    IMGUI_API int           GetFrameCount();
-    IMGUI_API ImDrawList*   GetOverlayDrawList();                                               // this draw list will be the last rendered one, it covers all viewports. useful to quickly draw overlays shapes/text
+    IMGUI_API ImDrawList*   GetOverlayDrawList();                                               // this draw list will be the last rendered. it covers the entire current viewport. useful to quickly draw overlays shapes/text
    IMGUI_API ImDrawListSharedData* GetDrawListSharedData();                                    // you may use this when creating your own ImDrawList instances
    IMGUI_API const char*   GetStyleColorName(ImGuiCol idx);
    IMGUI_API void          SetStateStorage(ImGuiStorage* storage);                             // replace current window storage with our own (if you want to manipulate it yourself, typically clear subsection of it)
--- a/imgui_internal.h
+++ b/imgui_internal.h
@ -517,11 +517,13 @@ struct ImGuiViewportP : public ImGuiViewport
    int                 LastFrameAsRefViewport;   // Last frame number this viewport was io.MouseViewportRef
    ImGuiID             LastNameHash;
    ImGuiWindow*        Window;
+    ImDrawList*         OverlayDrawList;          // For convenience, a draw list we can render to that's always rendered last (we use it to draw software mouse cursor when io.MouseDrawCursor is set)
    ImDrawData          DrawDataP;
    ImDrawDataBuilder   DrawDataBuilder;
    ImVec2              RendererLastSize;

-    ImGuiViewportP()         { Idx = 1; LastFrameActive = LastFrameAsRefViewport = -1; LastNameHash = 0; Window = NULL; DrawData = NULL; RendererLastSize = ImVec2(-1.0f,-1.0f); }
+    ImGuiViewportP(ImDrawListSharedData* draw_list_shared_data) { Idx = 1; LastFrameActive = LastFrameAsRefViewport = -1; LastNameHash = 0; Window = NULL; OverlayDrawList = IM_NEW(ImDrawList)(draw_list_shared_data); OverlayDrawList->_OwnerName = "##Overlay"; RendererLastSize = ImVec2(-1.0f,-1.0f); }
+    ~ImGuiViewportP()        { IM_DELETE(OverlayDrawList); }
    ImRect  GetRect() const  { return ImRect(Pos.x, Pos.y, Pos.x + Size.x, Pos.y + Size.y); }
    float   GetNextX() const { const float SPACING = 4.0f; return Pos.x + Size.x + SPACING; }
 };
@ -634,7 +636,7 @@ struct ImGuiContext
    // Viewports
    ImVector<ImGuiViewportP*> Viewports;
    ImGuiPlatformData       PlatformData;                       // This is essentially the public facing version of the Viewports vector (it is updated in UpdatePlatformWindows and exclude the viewports about to be destroyed)
-    ImGuiViewportP*         CurrentViewport;
+    ImGuiViewportP*         CurrentViewport;                    // We track changes of viewport (happening in Begin) so we can call Platform_OnChangedViewport()
    ImGuiViewportP*         MousePosViewport;
    ImGuiViewportP*         MousePosPrevViewport;
    ImGuiViewportP*         MouseHoveredPrevViewport;
@ -676,7 +678,6 @@ struct ImGuiContext

    // Render
    float                   ModalWindowDarkeningRatio;
-    ImDrawList              OverlayDrawList;                    // Optional software render of mouse cursors, if io.MouseDrawCursor is set + a few debug overlays
    ImGuiMouseCursor        MouseCursor;

    // Drag and Drop
@ -731,7 +732,7 @@ struct ImGuiContext
    int                     WantTextInputNextFrame;
    char                    TempBuffer[1024*3+1];               // temporary text buffer

-    ImGuiContext(ImFontAtlas* shared_font_atlas) : OverlayDrawList(NULL)
+    ImGuiContext(ImFontAtlas* shared_font_atlas)
    {
        Initialized = false;
        Font = NULL;
@ -794,8 +795,6 @@ struct ImGuiContext
        NavMoveDir = NavMoveDirLast = ImGuiDir_None;

        ModalWindowDarkeningRatio = 0.0f;
-        OverlayDrawList._Data = &DrawListSharedData;
-        OverlayDrawList._OwnerName = "##Overlay"; // Give it a name for debugging
        MouseCursor = ImGuiMouseCursor_Arrow;

        DragDropActive = false;
@ -1097,6 +1096,7 @@ namespace ImGui
    IMGUI_API void          PopItemFlag();

    IMGUI_API void          SetCurrentFont(ImFont* font);
+    IMGUI_API ImDrawList*   GetOverlayDrawList(ImGuiWindow* window);

    IMGUI_API void          OpenPopupEx(ImGuiID id);
    IMGUI_API void          ClosePopup(ImGuiID id);