Demo: Added simple item reordering demo in Widgets -> Drag and Drop section. (#2823, #143) [@rokups]

Author: ocornut

docs/CHANGELOG.txt

@@ -40,6 +40,7 @@ Other Changes:
 - InputText, Nav: Fixed Home/End key broken when activating Keyboard Navigation. (#787)
 - TreeNode: Fixed combination of ImGuiTreeNodeFlags_SpanFullWidth and ImGuiTreeNodeFlags_OpenOnArrow
   incorrectly locating the arrow hit position to the left of the frame. (#2451, #2438, #1897)
+- Demo: Added simple item reordering demo in Widgets -> Drag and Drop section. (#2823, #143) [@rokups]
 
 
 -----------------------------------------------------------------------

imgui_demo.cpp

@@ -1506,24 +1506,21 @@ static void ShowDemoWindowWidgets()
 
     if (ImGui::TreeNode("Drag and Drop"))
     {
+        if (ImGui::TreeNode("Drag and drop in standard widgets"))
         {
             // ColorEdit widgets automatically act as drag source and drag target.
             // They are using standardized payload strings IMGUI_PAYLOAD_TYPE_COLOR_3F and IMGUI_PAYLOAD_TYPE_COLOR_4F to allow your own widgets
             // to use colors in their drag and drop interaction. Also see the demo in Color Picker -> Palette demo.
-            ImGui::BulletText("Drag and drop in standard widgets");
-            ImGui::SameLine();
             HelpMarker("You can drag from the colored squares.");
-            ImGui::Indent();
-            static float col1[3] = { 1.0f,0.0f,0.2f };
-            static float col2[4] = { 0.4f,0.7f,0.0f,0.5f };
+            static float col1[3] = { 1.0f, 0.0f, 0.2f };
+            static float col2[4] = { 0.4f, 0.7f, 0.0f, 0.5f };
             ImGui::ColorEdit3("color 1", col1);
             ImGui::ColorEdit4("color 2", col2);
-            ImGui::Unindent();
+            ImGui::TreePop();
         }
 
+        if (ImGui::TreeNode("Drag and drop to copy/swap items"))
         {
-            ImGui::BulletText("Drag and drop to copy/swap items");
-            ImGui::Indent();
             enum Mode
             {
                 Mode_Copy,
@@ -1577,7 +1574,31 @@ static void ShowDemoWindowWidgets()
                 }
                 ImGui::PopID();
             }
-            ImGui::Unindent();
+            ImGui::TreePop();
+        }
+
+        if (ImGui::TreeNode("Drag to reorder items (simple)"))
+        {
+            // Simple reordering
+            HelpMarker("We don't use the drag and drop api at all here! Instead we query when the item is held but not hovered, and order items accordingly.");
+            static const char* item_names[] = { "Item One", "Item Two", "Item Three", "Item Four", "Item Five" };
+            for (int n = 0; n < IM_ARRAYSIZE(item_names); n++)
+            {
+                const char* item = item_names[n];
+                ImGui::Selectable(item);
+
+                if (ImGui::IsItemActive() && !ImGui::IsItemHovered())
+                {
+                    int n_next = n + (ImGui::GetMouseDragDelta(0).y < 0.f ? -1 : 1);
+                    if (n_next >= 0 && n_next < IM_ARRAYSIZE(item_names))
+                    {
+                        item_names[n] = item_names[n_next];
+                        item_names[n_next] = item;
+                        ImGui::ResetMouseDragDelta();
+                    }
+                }
+            }
+            ImGui::TreePop();
         }
 
         ImGui::TreePop();
@@ -1607,10 +1628,10 @@ static void ShowDemoWindowWidgets()
         if (item_type == 10){ ret = ImGui::TreeNodeEx("ITEM: TreeNode w/ ImGuiTreeNodeFlags_OpenOnDoubleClick", ImGuiTreeNodeFlags_OpenOnDoubleClick | ImGuiTreeNodeFlags_NoTreePushOnOpen); } // Testing tree node with ImGuiButtonFlags_PressedOnDoubleClick button policy.
         if (item_type == 11){ const char* items[] = { "Apple", "Banana", "Cherry", "Kiwi" }; static int current = 1; ret = ImGui::ListBox("ITEM: ListBox", &current, items, IM_ARRAYSIZE(items), IM_ARRAYSIZE(items)); }
 
-        // Display the value of IsItemHovered() and other common item state functions. 
+        // Display the value of IsItemHovered() and other common item state functions.
         // Note that the ImGuiHoveredFlags_XXX flags can be combined.
-        // Because BulletText is an item itself and that would affect the output of IsItemXXX functions, 
-        // we query every state in a single call to avoid storing them and to simplify the code 
+        // Because BulletText is an item itself and that would affect the output of IsItemXXX functions,
+        // we query every state in a single call to avoid storing them and to simplify the code
         ImGui::BulletText(
             "Return value = %d\n"
             "IsItemFocused() = %d\n"
@@ -1653,7 +1674,7 @@ static void ShowDemoWindowWidgets()
         if (embed_all_inside_a_child_window)
             ImGui::BeginChild("outer_child", ImVec2(0, ImGui::GetFontSize() * 20), true);
 
-        // Testing IsWindowFocused() function with its various flags. 
+        // Testing IsWindowFocused() function with its various flags.
         // Note that the ImGuiFocusedFlags_XXX flags can be combined.
         ImGui::BulletText(
             "IsWindowFocused() = %d\n"