Editor: Pan from a widget of a node that does not use the navigate button

Since the fix of thedmd#238, a pan needs the press to make the background or an object active.
A press on a widget of a node (a button, which uses the left mouse button) made neither: the view did not pan.

Now a press of the navigate button inside the editor that no item owns is remembered:
- once the mouse drags, the background takes the button until its release (SetKeyOwner()), and the view pans;
- a click stays a click: the context menus of the widget and of its node open, as before;
- a widget that uses the navigate button owns it, and keeps it;
- the release that ends a pan is locked for its frame: no context menu opens under the mouse;
- a drag pressed outside the editor still does not pan (thedmd#238).

Needs Dear ImGui 1.89 (input ownership). With an older one, nothing changes.

Author: pthom

imgui_node_editor.cpp

@@ -156,6 +156,14 @@ static const auto  c_AllRoundCornersFlags = 0xF0; // ImDrawFlags_RoundCornersAll
 static const auto  c_AllRoundCornersFlags = 15;
 #endif
 
+// ImGui 1.89 introduced the input ownership (SetKeyOwner(), GetKeyOwner(), the lock flags): the editor's background
+// takes the navigate button with it, for a pan that starts on a widget of a node.
+#if IMGUI_VERSION_NUM >= 19070
+static const auto  c_NoKeyOwner = ImGuiKeyOwner_NoOwner;
+#elif IMGUI_VERSION_NUM >= 18900
+static const auto  c_NoKeyOwner = ImGuiKeyOwner_None; // ImGuiKeyOwner_NoOwner since ImGui 1.90.7
+#endif
+
 
 //------------------------------------------------------------------------------
 # if defined(_DEBUG) && defined(_WIN32)
@@ -1223,6 +1231,18 @@ void ed::EditorContext::Begin(const char* id, const ImVec2& size)
     m_EditorActiveId = ImGui::GetID(id);
     ImGui::PushID(id);
 
+# if IMGUI_VERSION_NUM >= 18900
+    // The release that ends a pan is no click for the items under the mouse, which moved with the view: a context menu
+    // would open there. Locked before the items are submitted.
+    const auto& io             = ImGui::GetIO();
+    const auto  navigateButton = m_Config.NavigateButtonIndex;
+    const auto  isPanning      = m_NavigateAction.m_IsActive;
+    const auto  isReleased     = io.MouseReleased[navigateButton];
+    const auto  wasDragged     = io.MouseDragMaxDistanceSqr[navigateButton] >= io.MouseDragThreshold * io.MouseDragThreshold;
+    if (isPanning && isReleased && wasDragged)
+        ImGui::SetKeyOwner(ImGui::MouseButtonToKey(navigateButton), m_BackgroundId, ImGuiInputFlags_LockThisFrame);
+# endif
+
     m_BeginColorStackSize = m_Style.GetColorStackSize();
     m_BeginVarStackSize   = m_Style.GetVarStackSize();
 
@@ -2271,6 +2291,15 @@ bool ed::EditorContext::IsHoveredWithoutOverlapp() const
     return m_IsHoveredWithoutOverlapp;
 }
 
+bool ed::EditorContext::OwnsNavigateButton() const
+{
+# if IMGUI_VERSION_NUM >= 18900
+    return ImGui::GetKeyOwner(ImGui::MouseButtonToKey(m_Config.NavigateButtonIndex)) == m_BackgroundId;
+# else
+    return false;
+# endif
+}
+
 bool ed::EditorContext::CanAcceptUserInput() const
 {
     return m_IsFocused && m_IsHovered;
@@ -2801,6 +2830,27 @@ ed::Control ed::EditorContext::BuildControl(bool allowOffscreen)
     auto backgroundClickButonIndex        = emitInteractiveAreaEx(ObjectId(), editorRect, backgroundExtraFlags);
     auto backgroundDoubleClickButtonIndex = isMouseDoubleClickOverBackground();
     auto isBackgroundActive               = ImGui::IsItemActive();
+
+# if IMGUI_VERSION_NUM >= 18900
+    m_BackgroundId = ImGui::GetItemID();
+    // A press of the navigate button inside the editor that no item takes (on a widget of a node which does not use
+    // this button, for example) may start a pan: once the mouse drags, the background takes the button until its
+    // release. A click leaves the button to the items (the context menu of a widget, or of its node). A widget which
+    // uses the button owns it, and keeps it.
+    const auto navigateButton = m_Config.NavigateButtonIndex;
+    const auto navigateKey    = ImGui::MouseButtonToKey(navigateButton);
+    const auto isUnowned      = ImGui::GetKeyOwner(navigateKey) == c_NoKeyOwner;
+    if (ImGui::IsMouseClicked(navigateButton))
+    {
+        const auto isOverEditor = ImGui::IsItemHovered(ImGuiHoveredFlags_RectOnly) && ImGui::IsWindowHovered();
+        m_IsNavigatePressInside = isUnowned && isOverEditor;
+    }
+    else if (!ImGui::GetIO().MouseDown[navigateButton])
+        m_IsNavigatePressInside = false;
+    const auto isDragged = ImGui::IsMouseDragPastThreshold(navigateButton);
+    if (m_IsNavigatePressInside && isDragged && isUnowned)
+        ImGui::SetKeyOwner(navigateKey, m_BackgroundId, ImGuiInputFlags_LockUntilRelease);
+# endif
     auto isBackgroundHot                  = !hotObject;
     auto isDragging                       = ImGui::IsMouseDragging(0, 1) || ImGui::IsMouseDragging(1, 1) || ImGui::IsMouseDragging(2, 1);
 
@@ -3634,7 +3684,8 @@ ed::EditorAction::AcceptResult ed::NavigateAction::Accept(const Control& control
         return False;
 
     // A drag that enters the editor from another window was pressed on nothing of the editor's.
-    const auto isPressedOnEditor = control.BackgroundActive || control.ActiveObject != nullptr;
+    // A press on a widget of a node which does not use the navigate button is taken by the background (see BuildControl()).
+    const auto isPressedOnEditor = control.BackgroundActive || control.ActiveObject != nullptr || Editor->OwnsNavigateButton();
     if (Editor->CanAcceptUserInput() && isPressedOnEditor && ImGui::IsMouseDragging(Editor->GetConfig().NavigateButtonIndex, 0.0f))
     {
         m_Animation.Stop();

imgui_node_editor_internal.h

@@ -1417,6 +1417,7 @@ struct EditorContext
     bool IsFocused();
     bool IsHovered() const;
     bool IsHoveredWithoutOverlapp() const;
+    bool OwnsNavigateButton() const; // the press of the navigate button was taken by the editor's background
     bool CanAcceptUserInput() const;
 
     // True for a frame whose host window skips items. Item rectangles are stale
@@ -1546,6 +1547,10 @@ struct EditorContext
     bool                m_IsFocused;
     bool                m_IsHovered;
     bool                m_IsHoveredWithoutOverlapp;
+# if IMGUI_VERSION_NUM >= 18900
+    ImGuiID             m_BackgroundId = 0; // the item that covers the editor: it takes the navigate button for a pan
+    bool                m_IsNavigatePressInside = false; // the navigate button was pressed inside the editor, on no item that owns it
+# endif
 
     bool                m_ShortcutsEnabled;