ListBoxHeader: In version taking height in number of items, made vertical padding consistent regardless of if (items_count <= height_in_items) or not.

Demo: Tweaks.

docs/CHANGELOG.txt

@@ -56,6 +56,8 @@ Other Changes:
 - InputText: Multiline: Fixed padding/cliprect not precisely matching single-line version. (#3781)
 - InputText: Multiline: Fixed FramePadding.y worth of vertical offset when aiming with mouse.
 - ListBox: Tweaked default height calculation.
+- ListBoxHeader: In version taking height in number of items, made vertical padding consistent regardless 
+  of if (items_count <= height_in_items) or not.
 - Fonts: imgui_freetype: Facilitated using FreeType integration: [@Xipiryon, @ocornut]
   - Use '#define IMGUI_ENABLE_FREETYPE' in imconfig.h should make it work with no other modifications
     other than compiling misc/freetype/imgui_freetype.cpp and linking with FreeType.

imgui_demo.cpp

@@ -7475,19 +7475,20 @@ void ShowExampleAppDocuments(bool* p_open)
         {
             if (!ImGui::IsPopupOpen("Save?"))
                 ImGui::OpenPopup("Save?");
-            if (ImGui::BeginPopupModal("Save?"))
+            if (ImGui::BeginPopupModal("Save?", NULL, ImGuiWindowFlags_AlwaysAutoResize))
             {
                 ImGui::Text("Save change to the following items?");
-                ImGui::SetNextItemWidth(-FLT_MIN);
-                if (ImGui::ListBoxHeader("##", close_queue_unsaved_documents, 6))
+                float item_height = ImGui::GetTextLineHeightWithSpacing();
+                if (ImGui::BeginChildFrame(ImGui::GetID("frame"), ImVec2(-FLT_MIN, 6.25f * item_height)))
                 {
                     for (int n = 0; n < close_queue.Size; n++)
                         if (close_queue[n]->Dirty)
                             ImGui::Text("%s", close_queue[n]->Name);
-                    ImGui::ListBoxFooter();
+                    ImGui::EndChildFrame();
                 }
 
-                if (ImGui::Button("Yes", ImVec2(80, 0)))
+                ImVec2 button_size(ImGui::GetFontSize() * 7.0f, 0.0f);
+                if (ImGui::Button("Yes", button_size))
                 {
                     for (int n = 0; n < close_queue.Size; n++)
                     {
@@ -7499,7 +7500,7 @@ void ShowExampleAppDocuments(bool* p_open)
                     ImGui::CloseCurrentPopup();
                 }
                 ImGui::SameLine();
-                if (ImGui::Button("No", ImVec2(80, 0)))
+                if (ImGui::Button("No", button_size))
                 {
                     for (int n = 0; n < close_queue.Size; n++)
                         close_queue[n]->DoForceClose();
@@ -7507,7 +7508,7 @@ void ShowExampleAppDocuments(bool* p_open)
                     ImGui::CloseCurrentPopup();
                 }
                 ImGui::SameLine();
-                if (ImGui::Button("Cancel", ImVec2(80, 0)))
+                if (ImGui::Button("Cancel", button_size))
                 {
                     close_queue.clear();
                     ImGui::CloseCurrentPopup();

imgui_widgets.cpp

@@ -6177,15 +6177,9 @@ bool ImGui::ListBoxHeader(const char* label, const ImVec2& size_arg)
 // FIXME: In principle this function should be called BeginListBox(). We should rename it after re-evaluating if we want to keep the same signature.
 bool ImGui::ListBoxHeader(const char* label, int items_count, int height_in_items)
 {
-    // Size default to hold ~7.25 items.
-    // We add +25% worth of item height to allow the user to see at a glance if there are more items up/down, without looking at the scrollbar.
-    // We don't add this extra bit if items_count <= height_in_items. It is slightly dodgy, because it means a dynamic list of items will make the widget resize occasionally when it crosses that size.
-    // I am expecting that someone will come and complain about this behavior in a remote future, then we can advise on a better solution.
+    // If height_in_items == -1, default height is maximum 7.
     ImGuiContext& g = *GImGui;
-    if (height_in_items < 0)
-        height_in_items = ImMin(items_count, 7);
-    float height_in_items_f = (height_in_items < items_count) ? (height_in_items + 0.25f) : (height_in_items + 0.00f);
-
+    float height_in_items_f = (height_in_items < 0 ? ImMin(items_count, 7) : height_in_items) + 0.25f;
     ImVec2 size;
     size.x = 0.0f;
     size.y = GetTextLineHeightWithSpacing() * height_in_items_f + g.Style.FramePadding.y * 2.0f;