MultiSelect: Demo: added simpler demo using Clipper. Clarify RangeSrcPassedBy doc.

imgui.h

@@ -2774,11 +2774,13 @@ enum ImGuiMultiSelectFlags_
 // Usage flow:
 //   BEGIN - (1) Call BeginMultiSelect() and retrieve the ImGuiMultiSelectIO* result.
 //         - (2) [If using clipper] Honor Clear/SelectAll/SetRange requests by updating your selection data. Same code as Step 6.
-//   LOOP  - (3) [If using clipper] Set RangeSrcPassedBy=true if the RangeSrcItem item is part of the items clipped before the first submitted/visible item.
+//   LOOP  - (3) [If using clipper] Set RangeSrcPassedBy=true if the RangeSrcItem item was already passed by.
 //               This is because for range-selection we need to know if we are currently "inside" or "outside" the range.
-//               - If you are using integer indices in ImGuiSelectionUserData, this is easy to compute: if (clipper.DisplayStart > data->RangeSrcItem) { data->RangeSrcPassedBy = true; }
+//               - If you are using integer indices in ImGuiSelectionUserData, this is easy to compute:
-//               - If you are using pointers in ImGuiSelectionUserData, you may need additional processing in each clipper step to tell if current DisplayStart comes after RangeSrcItem..
+//                    if (clipper.DisplayStart > data->RangeSrcItem) { data->RangeSrcPassedBy = true; }
-//         - (4) Submit your items with SetNextItemSelectionUserData() + Selectable()/TreeNode() calls. (optionally call IsItemToggledSelection() if you need that info immediately for displaying your item, before EndMultiSelect())
+//               - If you are using pointers in ImGuiSelectionUserData, you may need additional processing, e.g. find the index of RangeSrcItem before applying the above operation.
+//               - This also needs to be done at the end of the clipper loop, otherwise we can't tell if the item still exist.
+//         - (4) Submit your items with SetNextItemSelectionUserData() + Selectable()/TreeNode() calls.
 //   END   - (5) Call EndMultiSelect() and retrieve the ImGuiMultiSelectIO* result.
 //         - (6) Honor Clear/SelectAll/SetRange requests by updating your selection data. Same code as Step 2.
 //   If you submit all items (no clipper), Step 2 and 3 and will be handled by Selectable()/TreeNode on a per-item basis.
@@ -2801,7 +2803,7 @@ struct ImGuiMultiSelectIO
     ImGuiSelectionUserData  RangeFirstItem;     //               /               /  ms:w, app:r  // End: parameter for RequestSetRange request (this is generally == RangeSrcItem when shift selecting from top to bottom)
     ImGuiSelectionUserData  RangeLastItem;      //               /               /  ms:w, app:r  // End: parameter for RequestSetRange request (this is generally == RangeSrcItem when shift selecting from bottom to top)
     bool                    RangeSelected;      //               /               /  ms:w, app:r  // End: parameter for RequestSetRange request. true = Select Range, false = Unselect Range.
-    bool                    RangeSrcPassedBy;   //               /  ms:rw app:w  /  ms:r         // (If using clipper) Need to be set by app/user if RangeSrcItem was part of the clipped set before submitting the visible items. Ignore if not clipping.
+    bool                    RangeSrcPassedBy;   //               /  ms:rw app:w  /  ms:r         // (If using clipper) Need to be set by app/user if RangeSrcItem was passed by. Ignore if not clipping.
     bool                    RangeSrcReset;      //        app:w  /        app:w  /  ms:r         // (If using deletion) Set before EndMultiSelect() to reset ResetSrcItem (e.g. if deleted selection).
     bool                    NavIdSelected;      //  ms:w, app:r  /               /               // (If using deletion) Last known selection state for NavId (if part of submitted items).
     ImGuiSelectionUserData  NavIdItem;          //  ms:w, app:r  /               /               // (If using deletion) Last known SetNextItemSelectionUserData() value for NavId (if part of submitted items).

imgui_demo.cpp

@@ -2911,7 +2911,7 @@ static void ShowDemoWindowMultiSelect()
             ImGui::TreePop();
         }
 
-        const char* random_names[] =
+        static const char* random_names[] =
         {
             "Artichoke", "Arugula", "Asparagus", "Avocado", "Bamboo Shoots", "Bean Sprouts", "Beans", "Beet", "Belgian Endive", "Bell Pepper",
             "Bitter Gourd", "Bok Choy", "Broccoli", "Brussels Sprouts", "Burdock Root", "Cabbage", "Calabash", "Capers", "Carrot", "Cassava",
@@ -2935,7 +2935,7 @@ static void ShowDemoWindowMultiSelect()
 
             // The BeginListBox() has no actual purpose for selection logic (other that offering a scrolling region).
             const int ITEMS_COUNT = 50;
-            ImGui::Text("Selection size: %d", selection.GetSize());
+            ImGui::Text("Selection: %d/%d", selection.GetSize(), ITEMS_COUNT);
             if (ImGui::BeginListBox("##Basket", ImVec2(-FLT_MIN, ImGui::GetFontSize() * 20)))
             {
                 ImGuiMultiSelectFlags flags = ImGuiMultiSelectFlags_ClearOnEscape;
@@ -2951,7 +2951,49 @@ static void ShowDemoWindowMultiSelect()
                     ImGui::Selectable(label, item_is_selected);
                 }
 
-                // Apply multi-select requests
+                ms_io = ImGui::EndMultiSelect();
+                selection.ApplyRequests(ms_io, ITEMS_COUNT);
+
+                ImGui::EndListBox();
+            }
+            ImGui::TreePop();
+        }
+
+        // Demonstrate using the clipper with BeginMultiSelect()/EndMultiSelect()
+        IMGUI_DEMO_MARKER("Widgets/Selection State/Multi-Select (with clipper)");
+        if (ImGui::TreeNode("Multi-Select (with clipper)"))
+        {
+            static ExampleSelection selection;
+
+            ImGui::Text("Added features:");
+            ImGui::BulletText("Using ImGuiListClipper.");
+
+            const int ITEMS_COUNT = 10000;
+            ImGui::Text("Selection: %d/%d", selection.GetSize(), ITEMS_COUNT);
+            if (ImGui::BeginListBox("##Basket", ImVec2(-FLT_MIN, ImGui::GetFontSize() * 20)))
+            {
+                ImGuiMultiSelectFlags flags = ImGuiMultiSelectFlags_ClearOnEscape;
+                ImGuiMultiSelectIO* ms_io = ImGui::BeginMultiSelect(flags);
+                selection.ApplyRequests(ms_io, ITEMS_COUNT);
+
+                ImGuiListClipper clipper;
+                clipper.Begin(ITEMS_COUNT);
+                while (clipper.Step())
+                {
+                    if (!ms_io->RangeSrcPassedBy && clipper.DisplayStart > ms_io->RangeSrcItem)
+                        ms_io->RangeSrcPassedBy = true;
+                    for (int n = clipper.DisplayStart; n < clipper.DisplayEnd; n++)
+                    {
+                        char label[64];
+                        sprintf(label, "Object %05d: %s", n, random_names[n % IM_ARRAYSIZE(random_names)]);
+                        bool item_is_selected = selection.Contains(n);
+                        ImGui::SetNextItemSelectionUserData(n);
+                        ImGui::Selectable(label, item_is_selected);
+                    }
+                }
+                if (!ms_io->RangeSrcPassedBy && ITEMS_COUNT > ms_io->RangeSrcItem)
+                    ms_io->RangeSrcPassedBy = true;
+
                 ms_io = ImGui::EndMultiSelect();
                 selection.ApplyRequests(ms_io, ITEMS_COUNT);