Internals: HoveredWindowUnderMovingWindow special handling for drag and drop of window without altering the _NoInputs window flag, which worked but messed up the IsWindowHovered() user-facing flags.

imgui.cpp

@@ -2333,7 +2333,8 @@ static inline bool IsWindowContentHoverable(ImGuiWindow* window, ImGuiHoveredFla
 
     // Filter by viewport
     if (window->Viewport != g.MouseRefViewport)
-        return false;
+        if (g.MovingWindow == NULL || window->RootWindow != g.MovingWindow->RootWindow)
+            return false;
 
     return true;
 }
@@ -4140,11 +4141,11 @@ void ImGui::UpdateHoveredWindowAndCaptureFlags()
     ImGuiWindow* modal_window = GetFrontMostPopupModal();
     if (modal_window)
         if (g.HoveredRootWindow && !IsWindowChildOf(g.HoveredRootWindow, modal_window))
-            g.HoveredRootWindow = g.HoveredWindow = NULL;
+            g.HoveredWindow = g.HoveredRootWindow = g.HoveredWindowUnderMovingWindow = NULL;
 
     // Disabled mouse?
     if (g.IO.ConfigFlags & ImGuiConfigFlags_NoMouse)
-        g.HoveredWindow = g.HoveredRootWindow = NULL;
+        g.HoveredWindow = g.HoveredRootWindow = g.HoveredWindowUnderMovingWindow = NULL;
 
     // We track click ownership. When clicked outside of a window the click is owned by the application and won't report hovering nor request capture even while dragging over our windows afterward.
     int mouse_earliest_button_down = -1;
@@ -4164,7 +4165,7 @@ void ImGui::UpdateHoveredWindowAndCaptureFlags()
     // FIXME: For patterns of drag and drop across OS windows, we may need to rework/remove this test (first committed 311c0ca9 on 2015/02)
     const bool mouse_dragging_extern_payload = g.DragDropActive && (g.DragDropSourceFlags & ImGuiDragDropFlags_SourceExtern) != 0;
     if (!mouse_avail_to_imgui && !mouse_dragging_extern_payload)
-        g.HoveredWindow = g.HoveredRootWindow = NULL;
+        g.HoveredWindow = g.HoveredRootWindow = g.HoveredWindowUnderMovingWindow = NULL;
 
     // Update io.WantCaptureMouse for the user application (true = dispatch mouse info to imgui, false = dispatch mouse info to imgui + app)
     if (g.WantCaptureMouseNextFrame != -1)
@@ -4336,9 +4337,12 @@ void ImGui::NewFrame()
     g.FramerateSecPerFrameIdx = (g.FramerateSecPerFrameIdx + 1) % IM_ARRAYSIZE(g.FramerateSecPerFrame);
     g.IO.Framerate = (g.FramerateSecPerFrameAccum > 0.0f) ? (1.0f / (g.FramerateSecPerFrameAccum / (float)IM_ARRAYSIZE(g.FramerateSecPerFrame))) : FLT_MAX;
 
+    // Find hovered window
+    // (needs to be before UpdateMovingWindow so we fill HoveredWindowUnderMovingWindow on the mouse release frame)
+    UpdateHoveredWindowAndCaptureFlags();
+
     // Handle user moving window with mouse (at the beginning of the frame to avoid input lag or sheering)
     UpdateMovingWindow();
-    UpdateHoveredWindowAndCaptureFlags();
 
     // Background darkening/whitening
     if (GetFrontMostPopupModal() != NULL || g.NavWindowingTarget != NULL)
@@ -4567,8 +4571,7 @@ void ImGui::Shutdown(ImGuiContext* context)
     g.CurrentWindowStack.clear();
     g.WindowsById.Clear();
     g.NavWindow = NULL;
-    g.HoveredWindow = NULL;
-    g.HoveredRootWindow = NULL;
+    g.HoveredWindow = g.HoveredRootWindow = g.HoveredWindowUnderMovingWindow = NULL;
     g.ActiveIdWindow = g.ActiveIdPreviousFrameWindow = NULL;
     g.MovingWindow = NULL;
     g.ColorModifiers.clear();
@@ -5527,16 +5530,18 @@ void ImGui::CalcListClipping(int items_count, float items_height, int* out_items
 }
 
 // Find window given position, search front-to-back
-// FIXME: Note that we have a lag here because WindowRectClipped is updated in Begin() so windows moved by user via SetWindowPos() and not SetNextWindowPos() will have that rectangle lagging by a frame at the time FindHoveredWindow() is called, aka before the next Begin(). Moving window thankfully isn't affected.
+// FIXME: Note that we have an inconsequential lag here: OuterRectClipped is updated in Begin(), so windows moved programatically with SetWindowPos() and not SetNextWindowPos() 
+// will have that rectangle lagging by a frame at the time FindHoveredWindow() is called, aka before the next Begin(). Moving window isn't affected.
 static void FindHoveredWindow()
 {
     ImGuiContext& g = *GImGui;
 
     ImGuiWindow* hovered_window = NULL;
+    ImGuiWindow* hovered_window_ignoring_moving_window = NULL;
     if (g.MovingWindow && !(g.MovingWindow->Flags & ImGuiWindowFlags_NoInputs))
         hovered_window = g.MovingWindow;
 
-    for (int i = g.Windows.Size - 1; i >= 0 && hovered_window == NULL; i--)
+    for (int i = g.Windows.Size - 1; i >= 0; i--)
     {
         ImGuiWindow* window = g.Windows[i];
         if (!window->Active)
@@ -5553,14 +5558,16 @@ static void FindHoveredWindow()
         {
             if (hovered_window == NULL)
                 hovered_window = window;
-            if (hovered_window)
+            if (hovered_window_ignoring_moving_window == NULL && (!g.MovingWindow || window->RootWindow != g.MovingWindow->RootWindow))
+                hovered_window_ignoring_moving_window = window;
+            if (hovered_window && hovered_window_ignoring_moving_window)
                 break;
         }
     }
 
     g.HoveredWindow = hovered_window;
     g.HoveredRootWindow = g.HoveredWindow ? g.HoveredWindow->RootWindow : NULL;
-
+    g.HoveredWindowUnderMovingWindow = hovered_window_ignoring_moving_window;
 }
 
 // Test if mouse cursor is hovering given rectangle
@@ -14685,7 +14692,7 @@ bool ImGui::BeginDragDropTargetCustom(const ImRect& bb, ImGuiID id)
         return false;
 
     ImGuiWindow* window = g.CurrentWindow;
-    if (g.HoveredWindow == NULL || window->RootWindow != g.HoveredWindow->RootWindow)
+    if (g.HoveredWindowUnderMovingWindow == NULL || window->RootWindow != g.HoveredWindowUnderMovingWindow->RootWindow)
         return false;
     IM_ASSERT(id != 0);
     if (!IsMouseHoveringRect(bb.Min, bb.Max) || (id == g.DragDropPayload.SourceId))
@@ -14711,7 +14718,7 @@ bool ImGui::BeginDragDropTarget()
     ImGuiWindow* window = g.CurrentWindow;
     if (!(window->DC.LastItemStatusFlags & ImGuiItemStatusFlags_HoveredRect))
         return false;
-    if (g.HoveredWindow == NULL || window->RootWindow != g.HoveredWindow->RootWindow)
+    if (g.HoveredWindowUnderMovingWindow == NULL || window->RootWindow != g.HoveredWindowUnderMovingWindow->RootWindow)
         return false;
 
     const ImRect& display_rect = (window->DC.LastItemStatusFlags & ImGuiItemStatusFlags_HasDisplayRect) ? window->DC.LastItemDisplayRect : window->DC.LastItemRect;
@@ -15128,6 +15135,7 @@ void ImGui::ShowMetricsWindow(bool* p_open)
             const char* input_source_names[] = { "None", "Mouse", "Nav", "NavKeyboard", "NavGamepad" }; IM_ASSERT(IM_ARRAYSIZE(input_source_names) == ImGuiInputSource_COUNT);
             ImGui::Text("HoveredWindow: '%s'", g.HoveredWindow ? g.HoveredWindow->Name : "NULL");
             ImGui::Text("HoveredRootWindow: '%s'", g.HoveredRootWindow ? g.HoveredRootWindow->Name : "NULL");
+            ImGui::Text("HoveredWindowUnderMovingWindow: '%s'", g.HoveredWindowUnderMovingWindow ? g.HoveredWindowUnderMovingWindow->Name : "NULL");
             ImGui::Text("HoveredId: 0x%08X/0x%08X (%.2f sec), AllowOverlap: %d", g.HoveredId, g.HoveredIdPreviousFrame, g.HoveredIdTimer, g.HoveredIdAllowOverlap); // Data is "in-flight" so depending on when the Metrics window is called we may see current frame information or not
             ImGui::Text("ActiveId: 0x%08X/0x%08X (%.2f sec), AllowOverlap: %d, Source: %s", g.ActiveId, g.ActiveIdPreviousFrame, g.ActiveIdTimer, g.ActiveIdAllowOverlap, input_source_names[g.ActiveIdSource]);
             ImGui::Text("ActiveIdWindow: '%s'", g.ActiveIdWindow ? g.ActiveIdWindow->Name : "NULL");

imgui_internal.h

@@ -660,6 +660,7 @@ struct ImGuiContext
     ImGuiWindow*            CurrentWindow;                      // Being drawn into
     ImGuiWindow*            HoveredWindow;                      // Will catch mouse inputs
     ImGuiWindow*            HoveredRootWindow;                  // Will catch mouse inputs (for focus/move only)
+    ImGuiWindow*            HoveredWindowUnderMovingWindow;
     ImGuiID                 HoveredId;                          // Hovered widget
     bool                    HoveredIdAllowOverlap;
     ImGuiID                 HoveredIdPreviousFrame;