Added IsItemDeactivated() to query if the last item was active previously but isn't anymore. Useful for Undo/Redo patterns. (#820, #956, #1875)

CHANGELOG.txt

@@ -63,6 +63,7 @@ Other Changes:
    - Each example still has its own main.cpp which you may refer you to understand how to initialize and glue everything together.
    - Some frameworks (such as the Allegro, Marmalade) handle both the "platform" and "rendering" part, and your custom engine may as well.
    - Read examples/README.txt for details.
+ - Added IsItemDeactivated() to query if the last item was active previously but isn't anymore. Useful for Undo/Redo patterns. (#820, #956, #1875)
  - Nav: Added support for PageUp/PageDown (explorer-style: first aim at bottom/top most item, when scroll a page worth of contents). (#787)
  - Nav: To keep the navigated item in view we also attempt to scroll the parent window as well as the current window. (#787)
  - TreeNode: Fixed nodes with ImGuiTreeNodeFlags_Leaf flag always returning true which was meaningless.

imgui.cpp

@@ -2251,6 +2251,8 @@ void ImGui::KeepAliveID(ImGuiID id)
     ImGuiContext& g = *GImGui;
     if (g.ActiveId == id)
         g.ActiveIdIsAlive = true;
+    if (g.ActiveIdPreviousFrame == id)
+        g.ActiveIdPreviousFrameIsAlive = true;
 }
 
 static inline bool IsWindowContentHoverable(ImGuiWindow* window, ImGuiHoveredFlags flags)
@@ -3719,7 +3721,8 @@ void ImGui::NewFrame()
         g.ActiveIdTimer += g.IO.DeltaTime;
     g.LastActiveIdTimer += g.IO.DeltaTime;
     g.ActiveIdPreviousFrame = g.ActiveId;
-    g.ActiveIdIsAlive = false;
+    g.ActiveIdPreviousFrameWindow = g.ActiveIdWindow;
+    g.ActiveIdIsAlive = g.ActiveIdPreviousFrameIsAlive = false;
     g.ActiveIdIsJustActivated = false;
     if (g.ScalarAsInputTextId && g.ActiveId != g.ScalarAsInputTextId)
         g.ScalarAsInputTextId = 0;
@@ -3940,7 +3943,7 @@ void ImGui::Shutdown(ImGuiContext* context)
     g.NavWindow = NULL;
     g.HoveredWindow = NULL;
     g.HoveredRootWindow = NULL;
-    g.ActiveIdWindow = NULL;
+    g.ActiveIdWindow = g.ActiveIdPreviousFrameWindow = NULL;
     g.MovingWindow = NULL;
     g.ColorModifiers.clear();
     g.StyleModifiers.clear();
@@ -4978,6 +4981,13 @@ bool ImGui::IsItemActive()
     return false;
 }
 
+bool ImGui::IsItemDeactivated()
+{
+    ImGuiContext& g = *GImGui;
+    ImGuiWindow* window = g.CurrentWindow;
+    return (g.ActiveIdPreviousFrame == window->DC.LastItemId && g.ActiveIdPreviousFrame != 0 && g.ActiveId != window->DC.LastItemId);
+}
+
 bool ImGui::IsItemFocused()
 {
     ImGuiContext& g = *GImGui;
@@ -12804,6 +12814,7 @@ void ImGui::BeginGroup()
     group_data.BackupCurrentLineTextBaseOffset = window->DC.CurrentLineTextBaseOffset;
     group_data.BackupLogLinePosY = window->DC.LogLinePosY;
     group_data.BackupActiveIdIsAlive = g.ActiveIdIsAlive;
+    group_data.BackupActiveIdPreviousFrameIsAlive = g.ActiveIdPreviousFrameIsAlive;
     group_data.AdvanceCursor = true;
 
     window->DC.GroupOffsetX = window->DC.CursorPos.x - window->Pos.x - window->DC.ColumnsOffsetX;
@@ -12839,11 +12850,13 @@ void ImGui::EndGroup()
         ItemAdd(group_bb, 0);
     }
 
-    // If the current ActiveId was declared within the boundary of our group, we copy it to LastItemId so IsItemActive() will be functional on the entire group.
+    // If the current ActiveId was declared within the boundary of our group, we copy it to LastItemId so IsItemActive(), IsItemDeactivated() etc. will be functional on the entire group.
-    // It would be be neater if we replaced window.DC.LastItemId by e.g. 'bool LastItemIsActive', but if you search for LastItemId you'll notice it is only used in that context.
+    // It would be be neater if we replaced window.DC.LastItemId by e.g. 'bool LastItemIsActive', but put a little more burden on individual widgets.
-    const bool active_id_within_group = (!group_data.BackupActiveIdIsAlive && g.ActiveIdIsAlive && g.ActiveId && g.ActiveIdWindow->RootWindow == window->RootWindow);
+    // (and if you grep for LastItemId you'll notice it is only used in that context.
-    if (active_id_within_group)
+    if (!group_data.BackupActiveIdIsAlive && g.ActiveIdIsAlive && g.ActiveId) // && g.ActiveIdWindow->RootWindow == window->RootWindow)
         window->DC.LastItemId = g.ActiveId;
+    else if (!group_data.BackupActiveIdPreviousFrameIsAlive && g.ActiveIdPreviousFrameIsAlive) // && g.ActiveIdPreviousFrameWindow->RootWindow == window->RootWindow)
+        window->DC.LastItemId = g.ActiveIdPreviousFrame;
     window->DC.LastItemRect = group_bb;
 
     window->DC.GroupStack.pop_back();

imgui.h

@@ -504,6 +504,7 @@ namespace ImGui
     IMGUI_API bool          IsItemFocused();                                                    // is the last item focused for keyboard/gamepad navigation?
     IMGUI_API bool          IsItemClicked(int mouse_button = 0);                                // is the last item clicked? (e.g. button/node just clicked on) == IsMouseClicked(0) && IsItemHovered()
     IMGUI_API bool          IsItemVisible();                                                    // is the last item visible? (aka not out of sight due to clipping/scrolling.)
+    IMGUI_API bool          IsItemDeactivated();                                                // is the last item just made inactive (item was previously active), useful for Undo/Redo patterns.
     IMGUI_API bool          IsAnyItemHovered();
     IMGUI_API bool          IsAnyItemActive();
     IMGUI_API bool          IsAnyItemFocused();

imgui_demo.cpp

@@ -2028,7 +2028,7 @@ void ImGui::ShowDemoWindow(bool* p_open)
             ImGui::TreePop();
         }
 
-        if (ImGui::TreeNode("Focused & Hovered Test"))
+        if (ImGui::TreeNode("Active, Focused & Hovered Test"))
         {
             static bool embed_all_inside_a_child_window = false;
             ImGui::Checkbox("Embed everything inside a child window (for additional testing)", &embed_all_inside_a_child_window);
@@ -2068,16 +2068,22 @@ void ImGui::ShowDemoWindow(bool* p_open)
             // Testing IsItemHovered() function (because BulletText is an item itself and that would affect the output of IsItemHovered, we pass all lines in a single items to shorten the code)
             ImGui::Button("ITEM");
             ImGui::BulletText(
+                "IsItemFocused() = %d\n"
                 "IsItemHovered() = %d\n"
                 "IsItemHovered(_AllowWhenBlockedByPopup) = %d\n"
                 "IsItemHovered(_AllowWhenBlockedByActiveItem) = %d\n"
                 "IsItemHovered(_AllowWhenOverlapped) = %d\n"
-                "IsItemhovered(_RectOnly) = %d\n",
+                "IsItemHovered(_RectOnly) = %d\n"
+                "IsItemActive() = %d\n"
+                "IsItemDeactivated() = %d\n",
+                ImGui::IsItemFocused(),
                 ImGui::IsItemHovered(),
                 ImGui::IsItemHovered(ImGuiHoveredFlags_AllowWhenBlockedByPopup),
                 ImGui::IsItemHovered(ImGuiHoveredFlags_AllowWhenBlockedByActiveItem),
                 ImGui::IsItemHovered(ImGuiHoveredFlags_AllowWhenOverlapped),
-                ImGui::IsItemHovered(ImGuiHoveredFlags_RectOnly));
+                ImGui::IsItemHovered(ImGuiHoveredFlags_RectOnly),
+                ImGui::IsItemActive(),
+                ImGui::IsItemDeactivated());
 
             ImGui::BeginChild("child", ImVec2(0,50), true);
             ImGui::Text("This is another child window for testing IsWindowHovered() flags.");

imgui_internal.h

@@ -394,6 +394,7 @@ struct ImGuiGroupData
     float       BackupCurrentLineTextBaseOffset;
     float       BackupLogLinePosY;
     bool        BackupActiveIdIsAlive;
+    bool        BackupActiveIdPreviousFrameIsAlive;
     bool        AdvanceCursor;
 };
 
@@ -624,9 +625,11 @@ struct ImGuiContext
     bool                    ActiveIdIsAlive;                    // Active widget has been seen this frame
     bool                    ActiveIdIsJustActivated;            // Set at the time of activation for one frame
     bool                    ActiveIdAllowOverlap;               // Active widget allows another widget to steal active id (generally for overlapping widgets, but not always)
+    bool                    ActiveIdPreviousFrameIsAlive;
     int                     ActiveIdAllowNavDirFlags;           // Active widget allows using directional navigation (e.g. can activate a button and move away from it)
     ImVec2                  ActiveIdClickOffset;                // Clicked offset from upper-left corner, if applicable (currently only set by ButtonBehavior)
     ImGuiWindow*            ActiveIdWindow;
+    ImGuiWindow*            ActiveIdPreviousFrameWindow;
     ImGuiInputSource        ActiveIdSource;                     // Activating with mouse or nav (gamepad/keyboard)
     ImGuiID                 LastActiveId;                       // Store the last non-zero ActiveId, useful for animation.
     float                   LastActiveIdTimer;                  // Store the last non-zero ActiveId timer since the beginning of activation, useful for animation.
@@ -762,9 +765,10 @@ struct ImGuiContext
         ActiveIdIsAlive = false;
         ActiveIdIsJustActivated = false;
         ActiveIdAllowOverlap = false;
+        ActiveIdPreviousFrameIsAlive = false;
         ActiveIdAllowNavDirFlags = 0;
         ActiveIdClickOffset = ImVec2(-1,-1);
-        ActiveIdWindow = NULL;
+        ActiveIdWindow = ActiveIdPreviousFrameWindow = NULL;
         ActiveIdSource = ImGuiInputSource_None;
         LastActiveId = 0;
         LastActiveIdTimer = 0.0f;