RangeSelect/MultiSelect: support for nested/stacked BeginMultiSelect().

Mimicking table logic, reusing buffers.

imgui.cpp

@@ -3775,6 +3775,7 @@ void ImGui::Shutdown()
     g.DrawChannelsTempMergeBuffer.clear();
 
     g.MultiSelectStorage.Clear();
+    g.MultiSelectTempData.clear_destruct();
 
     g.ClipboardHandlerData.clear();
     g.MenusIdSubmittedThisFrame.clear();
@@ -3885,6 +3886,8 @@ void ImGui::GcCompactTransientMiscBuffers()
     ImGuiContext& g = *GImGui;
     g.ItemFlagsStack.clear();
     g.GroupStack.clear();
+    g.MultiSelectTempDataStacked = 0;
+    g.MultiSelectTempData.clear_destruct();
     TableGcCompactSettings();
 }
 

imgui.h

@@ -2748,6 +2748,9 @@ struct ImGuiSelectionRequest
     ImGuiSelectionRequest(ImGuiSelectionRequestType type = ImGuiSelectionRequestType_None) { Type = type; RangeSelected = false; RangeFirstItem = RangeLastItem = (ImGuiSelectionUserData)-1; }
 };
 
+// Main IO structure returned by BeginMultiSelect()/EndMultiSelect().
+// Read the large comments block above for details.
+// Lifetime: don't hold on ImGuiMultiSelectIO* pointers over multiple frames or past any subsequent call to BeginMultiSelect() or EndMultiSelect().
 struct ImGuiMultiSelectIO
 {
     ImVector<ImGuiSelectionRequest> Requests;   //  ms:w, app:r  /  ms:w  app:r  // Requests

imgui_internal.h

@@ -2194,8 +2194,9 @@ struct ImGuiContext
     ImVector<ImGuiShrinkWidthItem>  ShrinkWidthBuffer;
 
     // Multi-Select state
-    ImGuiMultiSelectTempData*       CurrentMultiSelect;         // FIXME-MULTISELECT: We currently don't support recursing/stacking multi-select
-    ImGuiMultiSelectTempData        MultiSelectTempData[1];
+    ImGuiMultiSelectTempData*       CurrentMultiSelect;
+    int                             MultiSelectTempDataStacked; // Temporary multi-select data size (because we leave previous instances undestructed, we generally don't use MultiSelectTempData.Size)
+    ImVector<ImGuiMultiSelectTempData> MultiSelectTempData;
     ImPool<ImGuiMultiSelectState>   MultiSelectStorage;
 
     // Hover Delay system
@@ -2433,6 +2434,7 @@ struct ImGuiContext
         TablesTempDataStacked = 0;
         CurrentTabBar = NULL;
         CurrentMultiSelect = NULL;
+        MultiSelectTempDataStacked = 0;
 
         HoverItemDelayId = HoverItemDelayIdPreviousFrame = HoverItemUnlockedStationaryId = HoverWindowUnlockedStationaryId = 0;
         HoverItemDelayTimer = HoverItemDelayClearTimer = 0.0f;

imgui_widgets.cpp

@@ -7039,8 +7039,10 @@ ImGuiMultiSelectIO* ImGui::BeginMultiSelect(ImGuiMultiSelectFlags flags)
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = g.CurrentWindow;
-    ImGuiMultiSelectTempData* ms = &g.MultiSelectTempData[0];
-    IM_ASSERT(g.CurrentMultiSelect == NULL); // No recursion allowed yet (we could allow it if we deem it useful)
+
+    if (++g.MultiSelectTempDataStacked > g.MultiSelectTempData.Size)
+        g.MultiSelectTempData.resize(g.MultiSelectTempDataStacked, ImGuiMultiSelectTempData());
+    ImGuiMultiSelectTempData* ms = &g.MultiSelectTempData[g.MultiSelectTempDataStacked - 1];
     IM_STATIC_ASSERT(offsetof(ImGuiMultiSelectTempData, IO) == 0); // Clear() relies on that.
     g.CurrentMultiSelect = ms;
     if ((flags & (ImGuiMultiSelectFlags_ScopeWindow | ImGuiMultiSelectFlags_ScopeRect)) == 0)
@@ -7159,6 +7161,7 @@ ImGuiMultiSelectIO* ImGui::EndMultiSelect()
     ImGuiWindow* window = g.CurrentWindow;
     IM_ASSERT(ms->FocusScopeId == g.CurrentFocusScopeId);
     IM_ASSERT(g.CurrentMultiSelect != NULL && storage->Window == g.CurrentWindow);
+    IM_ASSERT(g.MultiSelectTempDataStacked > 0 && &g.MultiSelectTempData[g.MultiSelectTempDataStacked - 1] == g.CurrentMultiSelect);
 
     const ImRect scope_rect = (ms->Flags & ImGuiMultiSelectFlags_ScopeRect) ? ImRect(ms->ScopeRectMin, ImMax(window->DC.CursorMaxPos, ms->ScopeRectMin)) : window->InnerClipRect;
     if (ms->IsFocused)
@@ -7215,14 +7218,15 @@ ImGuiMultiSelectIO* ImGui::EndMultiSelect()
 
     // Unwind
     window->DC.CursorMaxPos = ImMax(ms->BackupCursorMaxPos, window->DC.CursorMaxPos);
-    ms->FocusScopeId = 0;
-    ms->Flags = ImGuiMultiSelectFlags_None;
     PopFocusScope();
-    g.CurrentMultiSelect = NULL;
 
     if (g.DebugLogFlags & ImGuiDebugLogFlags_EventSelection)
         DebugLogMultiSelectRequests("EndMultiSelect", &ms->IO);
 
+    ms->FocusScopeId = 0;
+    ms->Flags = ImGuiMultiSelectFlags_None;
+    g.CurrentMultiSelect = (--g.MultiSelectTempDataStacked > 0) ? &g.MultiSelectTempData[g.MultiSelectTempDataStacked - 1] : NULL;
+
     return &ms->IO;
 }