RangeSelect/MultiSelect: (Breaking) Added current_selection_size to BeginMultiSelect().

Required for shortcut routing so we can e.g. have Escape be used to clear selection THEN to exit child window.

imgui.h

@@ -675,7 +675,7 @@ namespace ImGui
     // - This enables standard multi-selection/range-selection idioms (CTRL+Mouse/Keyboard, SHIFT+Mouse/Keyboard, etc.) in a way that also allow a clipper to be used.
     // - ImGuiSelectionUserData is often used to store your item index.
     // - Read comments near ImGuiMultiSelectIO for instructions/details and see 'Demo->Widgets->Selection State & Multi-Select' for demo.
-    IMGUI_API ImGuiMultiSelectIO*   BeginMultiSelect(ImGuiMultiSelectFlags flags);
+    IMGUI_API ImGuiMultiSelectIO*   BeginMultiSelect(ImGuiMultiSelectFlags flags, int current_selection_size = -1);
     IMGUI_API ImGuiMultiSelectIO*   EndMultiSelect();
     IMGUI_API void                  SetNextItemSelectionUserData(ImGuiSelectionUserData selection_user_data);
     IMGUI_API bool                  IsItemToggledSelection();                                   // Was the last item selection state toggled? Useful if you need the per-item information _before_ reaching EndMultiSelect(). We only returns toggle _event_ in order to handle clipping correctly.

imgui_demo.cpp

@@ -2929,7 +2929,7 @@ struct ExampleDualListBox
                 if (child_visible)
                 {
                     ImGuiMultiSelectFlags flags = ImGuiMultiSelectFlags_None;
-                    ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags);
+                    ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags, selection.Size);
                     ApplySelectionRequests(ms_io, side);
 
                     for (int item_n = 0; item_n < items.Size; item_n++)
@@ -3060,7 +3060,7 @@ static void ShowDemoWindowMultiSelect()
             if (ImGui::BeginChild("##Basket", ImVec2(-FLT_MIN, ImGui::GetFontSize() * 20), ImGuiChildFlags_FrameStyle | ImGuiChildFlags_ResizeY))
             {
                 ImGuiMultiSelectFlags flags = ImGuiMultiSelectFlags_ClearOnEscape | ImGuiMultiSelectFlags_BoxSelect;
-                ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags);
+                ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags, selection.Size);
                 selection.ApplyRequests(ms_io, ITEMS_COUNT);
 
                 for (int n = 0; n < ITEMS_COUNT; n++)
@@ -3094,7 +3094,7 @@ static void ShowDemoWindowMultiSelect()
             if (ImGui::BeginChild("##Basket", ImVec2(-FLT_MIN, ImGui::GetFontSize() * 20), ImGuiChildFlags_FrameStyle | ImGuiChildFlags_ResizeY))
             {
                 ImGuiMultiSelectFlags flags = ImGuiMultiSelectFlags_ClearOnEscape | ImGuiMultiSelectFlags_BoxSelect;
-                ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags);
+                ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags, selection.Size);
                 selection.ApplyRequests(ms_io, ITEMS_COUNT);
 
                 ImGuiListClipper clipper;
@@ -3158,7 +3158,7 @@ static void ShowDemoWindowMultiSelect()
             if (ImGui::BeginChild("##Basket", ImVec2(-FLT_MIN, ImGui::GetFontSize() * 20), ImGuiChildFlags_FrameStyle | ImGuiChildFlags_ResizeY))
             {
                 ImGuiMultiSelectFlags flags = ImGuiMultiSelectFlags_ClearOnEscape | ImGuiMultiSelectFlags_BoxSelect;
-                ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags);
+                ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags, selection.Size);
                 selection.ApplyRequests(ms_io, items.Size);
 
                 const bool want_delete = ImGui::Shortcut(ImGuiKey_Delete, ImGuiInputFlags_Repeat) && (selection.Size > 0);
@@ -3274,7 +3274,7 @@ static void ShowDemoWindowMultiSelect()
             {
                 ImGui::PushID(selection_scope_n);
                 ImGuiSelectionBasicStorage* selection = &selections_data[selection_scope_n];
-                ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags);
+                ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags, selection->Size);
                 selection->ApplyRequests(ms_io, ITEMS_COUNT);
 
                 ImGui::SeparatorText("Selection scope");
@@ -3373,7 +3373,7 @@ static void ShowDemoWindowMultiSelect()
                 if (widget_type == WidgetType_TreeNode)
                     ImGui::PushStyleVar(ImGuiStyleVar_ItemSpacing, ImVec2(ImGui::GetStyle().ItemSpacing.x, 0.0f));
 
-                ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags);
+                ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags, selection.Size);
                 selection.ApplyRequests(ms_io, items.Size);
 
                 const bool want_delete = (ImGui::Shortcut(ImGuiKey_Delete, ImGuiInputFlags_Repeat) && (selection.Size > 0)) || request_deletion_from_menu;
@@ -9844,7 +9844,7 @@ struct ExampleAssetsBrowser
                 ms_flags |= ImGuiMultiSelectFlags_SelectOnClickRelease; // To allow dragging an unselected item without altering selection.
             if (AllowBoxSelect)
                 ms_flags |= ImGuiMultiSelectFlags_BoxSelect2d; // Enable box-select in 2D mode.
-            ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(ms_flags);
+            ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(ms_flags, Selection.Size);
 
             // Use custom selection adapter: store ID in selection (recommended)
             Selection.AdapterData = this;

imgui_widgets.cpp

@@ -7293,7 +7293,10 @@ static void DebugLogMultiSelectRequests(const char* function, const ImGuiMultiSe
 
 // Return ImGuiMultiSelectIO structure.
 // Lifetime: don't hold on ImGuiMultiSelectIO* pointers over multiple frames or past any subsequent call to BeginMultiSelect() or EndMultiSelect().
-ImGuiMultiSelectIO* ImGui::BeginMultiSelect(ImGuiMultiSelectFlags flags)
+// Passing 'current_selection_size' is currently optional:
+// - it is useful for shortcut routing with ImGuiMultiSelectFlags_ClearOnEscape: so we can have Escape be used to clear selection THEN to exit child window.
+// - if it is costly for you to compute, but can easily tell if your selection is empty or not, you may alter the ImGuiMultiSelectFlags_ClearOnEscape flag based on that.
+ImGuiMultiSelectIO* ImGui::BeginMultiSelect(ImGuiMultiSelectFlags flags, int current_selection_size)
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = g.CurrentWindow;
@@ -7360,9 +7363,8 @@ ImGuiMultiSelectIO* ImGui::BeginMultiSelect(ImGuiMultiSelectFlags flags)
     if (ms->IsFocused)
     {
         // Shortcut: Clear selection (Escape)
-        // FIXME-MULTISELECT: Only hog shortcut if selection is not null, meaning we need "has selection or "selection size" data here.
-        // Otherwise may be done by caller but it means Shortcut() needs to be exposed.
-        if (flags & ImGuiMultiSelectFlags_ClearOnEscape)
+        // Only claim shortcut if selection is not empty, allowing further presses on Escape to e.g. leave current child window.
+        if ((flags & ImGuiMultiSelectFlags_ClearOnEscape) && (current_selection_size != 0))
             if (Shortcut(ImGuiKey_Escape))
                 request_clear = true;