diff --git a/imgui.cpp b/imgui.cpp
index f2a28de3d..8aa2f974c 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -745,6 +745,7 @@ static inline ImVec2    ConvertViewportPosToOsDesktopPos(const ImVec2& imgui_pos
 static inline ImVec2    ConvertOsDesktopPosToViewportPos(const ImVec2& os_pos, ImGuiViewport* viewport) { return os_pos - viewport->PlatformOsDesktopPos + viewport->Pos; }
 static void             UpdateViewports();
 static void             UpdateWindowViewport(ImGuiWindow* window, bool window_pos_set_by_api);
+static void             SetCurrentViewport(ImGuiViewport* viewport);
 static void             SetWindowViewportTranslateToPreservePlatformPos(ImGuiWindow* window, ImGuiViewport* old_viewport, ImGuiViewport* new_viewport);
 static void             ResizeViewport(ImGuiViewport* viewport, const ImVec2& size);
 static void             ResizeViewportTranslateWindows(int viewport_idx_min, int viewport_idx_max, float pos_x_delta, int idx_delta, ImGuiViewport* viewport_to_erase);
@@ -893,6 +894,9 @@ ImGuiIO::ImGuiIO()
     ImeSetInputScreenPosFn = ImeSetInputScreenPosFn_DefaultImpl;
     ImeWindowHandle = NULL;
 
+    memset(&PlatformInterface, 0, sizeof(PlatformInterface));
+    memset(&RendererInterface, 0, sizeof(RendererInterface));
+
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
     RenderDrawListsFn = NULL;
 #endif
@@ -3347,6 +3351,7 @@ static void ImGui::UpdateViewports()
     ImGuiViewport* viewport_ref = g.IO.MousePosViewport ? FindViewportByID(g.IO.MousePosViewport) : g.Viewports[0];
     const ImVec2 mouse_os_pos = ConvertViewportPosToOsDesktopPos(g.IO.MousePos, viewport_ref);
 
+    g.CurrentViewport = NULL;
     for (int n = 1; n < g.Viewports.Size; n++)
     {
         // Erase unused viewports
@@ -3953,7 +3958,7 @@ void ImGui::Shutdown(ImGuiContext* context)
     g.FontStack.clear();
     g.OpenPopupStack.clear();
     g.CurrentPopupStack.clear();
-    g.MouseViewport = g.MouseLastHoveredViewport = NULL;
+    g.CurrentViewport = g.MouseViewport = g.MouseLastViewport = g.MouseLastHoveredViewport = NULL;
     DestroyViewportsPlaformData(context);
     DestroyViewportsRendererData(context);
     for (int i = 0; i < g.Viewports.Size; i++)
@@ -4283,6 +4288,8 @@ void ImGui::EndFrame()
         g.CurrentWindow->Active = false;
     End();
 
+    SetCurrentViewport(NULL);
+
     if (g.ActiveId == 0 && g.HoveredId == 0)
     {
         if (!g.NavWindow || !g.NavWindow->Appearing) // Unless we just made a window/popup appear
@@ -4465,6 +4472,7 @@ static void ImGui::ResizeViewportTranslateWindows(int viewport_idx_min, int view
 {
     ImGuiContext& g = *GImGui;
     IM_ASSERT(pos_x_delta != 0.0f || idx_delta != 0);
+    IM_ASSERT(g.CurrentViewport == NULL); // We only resize at the beginning of the frame
     for (int n = 0; n < g.Windows.Size; n++)
     {
         ImGuiWindow* window = g.Windows[n];
@@ -4486,14 +4494,9 @@ static void ImGui::ResizeViewportTranslateWindows(int viewport_idx_min, int view
 static void ImGui::ResizeViewport(ImGuiViewport* viewport, const ImVec2& size)
 {
     ImGuiContext& g = *GImGui;
-    if (viewport->Size.x != size.x || viewport->Size.y != size.y)
-    {
-        // We defer translating windows to the beginning of the frame. 
-        // Our viewport system already works with fully overlapped viewports, it's only certain user interactions that don't and they can't be performed while resizing.
-        viewport->Size = size;
-        //if (viewport->Idx + 1 < g.Viewports.Size) // If this isn't the last viewport, translate following viewports
-        //    ResizeViewportTranslateWindows(viewport->Idx + 1, g.Viewports.Size, viewport->GetNextX() - g.Viewports[viewport->Idx + 1]->Pos.x, 0, NULL);
-    }
+    // We defer translating windows to the beginning of the frame. 
+    // Our viewport system already works with fully overlapped viewports, it's only certain user interactions that don't and they can't be performed while resizing.
+    viewport->Size = size;
     if (viewport == g.Viewports[0])
     {
         g.IO.DisplayPos = viewport->Pos;
@@ -4501,6 +4504,18 @@ static void ImGui::ResizeViewport(ImGuiViewport* viewport, const ImVec2& size)
     }
 }
 
+void ImGui::SetCurrentViewport(ImGuiViewport* viewport)
+{
+    ImGuiContext& g = *GImGui;
+    if (g.CurrentViewport == viewport)
+        return;
+    if (g.CurrentViewport && g.IO.PlatformInterface.EndViewport)
+        g.IO.PlatformInterface.EndViewport(g.CurrentViewport);
+    g.CurrentViewport = viewport;
+    if (g.CurrentViewport && g.IO.PlatformInterface.BeginViewport)
+        g.IO.PlatformInterface.BeginViewport(g.CurrentViewport);
+}
+
 ImGuiViewport* ImGui::Viewport(ImGuiID id, ImGuiViewportFlags flags, const ImVec2& os_desktop_pos, const ImVec2& size)
 {
     ImGuiContext& g = *GImGui;
@@ -6318,6 +6333,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         // VIEWPORT
 
         UpdateWindowViewport(window, window_pos_set_by_api);
+        SetCurrentViewport(window->Viewport);
         flags = window->Flags;
         if (p_open != NULL && window->Viewport->PlatformRequestClose && !(window->Viewport->Flags & ImGuiViewportFlags_MainViewport))
         {
diff --git a/imgui.h b/imgui.h
index abe755984..54baff058 100644
--- a/imgui.h
+++ b/imgui.h
@@ -958,6 +958,10 @@ struct ImGuiPlatformInterface
     void    (*SetWindowAlpha)(ImGuiViewport* viewport, float alpha);
     void    (*RenderViewport)(ImGuiViewport* viewport);
     void    (*SwapBuffers)(ImGuiViewport* viewport);
+
+    // FIXME-DPI
+    void    (*BeginViewport)(ImGuiViewport* viewport);      // (Optional) Called during Begin() every time the viewport we are outputting into changes (viewport = next viewport)
+    void    (*EndViewport)(ImGuiViewport* viewport);        // (Optional) Called during Begin() every time the viewport we are outputting into changes (viewport = previous viewport)
 };
 
 // (Optional) Setup required only if (io.ConfigFlags & ImGuiConfigFlags_EnableMultiViewport) is enabled
@@ -966,9 +970,8 @@ struct ImGuiRendererInterface
     void    (*CreateViewport)(ImGuiViewport* viewport);
     void    (*DestroyViewport)(ImGuiViewport* viewport);
     void    (*ResizeViewport)(ImGuiViewport* viewport, int w, int h);
-    void    (*RenderViewport)(ImGuiViewport* viewport);    // Setup render output, clear targets, call Renderer_RenderDrawData
-    void    (*RenderDrawData)(ImDrawData* draw_data);      // Render a ImDrawList (collection of ImDrawList) for the area covering (io.DisplayPos) to (io.DisplayPos + io.DisplaySize)
-    void    (*SwapBuffers)(ImGuiViewport* viewport);       // Call Present/SwapBuffers
+    void    (*RenderViewport)(ImGuiViewport* viewport);     // Setup render output, clear targets, call Renderer_RenderDrawData
+    void    (*SwapBuffers)(ImGuiViewport* viewport);        // Call Present/SwapBuffers
 };
 
 // You may modify the ImGui::GetStyle() main instance during initialization and before NewFrame().
diff --git a/imgui_internal.h b/imgui_internal.h
index 11089ee53..56f20b0f9 100644
--- a/imgui_internal.h
+++ b/imgui_internal.h
@@ -654,6 +654,7 @@ struct ImGuiContext
 
     // Viewports
     ImVector<ImGuiViewport*>Viewports;
+    ImGuiViewport*          CurrentViewport;
     ImGuiViewport*          MouseViewport;
     ImGuiViewport*          MouseLastViewport;
     ImGuiViewport*          MouseLastHoveredViewport;
@@ -783,6 +784,7 @@ struct ImGuiContext
         NextTreeNodeOpenVal = false;
         NextTreeNodeOpenCond = 0;
 
+        CurrentViewport = NULL;
         MouseViewport = NULL;
         MouseLastViewport = MouseLastHoveredViewport = NULL;