ListBox: tweaked default height calculation. simplifying code internally (rework passing of full rect). Should have no visible side-effects + misc comments.

docs/CHANGELOG.txt

@@ -37,11 +37,12 @@ HOW TO UPDATE?
 
 Breaking Changes:
 
-- imgui_freetype: Removed ImGuiFreeType::BuildFontAtlas(). Kept inline redirection function.
+- imgui_freetype:
+  - Removed ImGuiFreeType::BuildFontAtlas(). Kept inline redirection function.
   Prefer using '#define IMGUI_ENABLE_FREETYPE', but there's a runtime selection path available too.
-  The shared extra flags parameters (very rarely used) are now stored in ImFontAtlas::FontBuilderFlags.
+  - The shared extra flags parameters (very rarely used) are now stored in ImFontAtlas::FontBuilderFlags.
-- imgui_freetype: Renamed ImFontConfig::RasterizerFlags (used by FreeType) to ImFontConfig::FontBuilderFlags.
+  - Renamed ImFontConfig::RasterizerFlags (used by FreeType) to ImFontConfig::FontBuilderFlags.
-- imgui_freetyoe: Renamed ImGuiFreeType::XXX flags to ImGuiFreeTypeBuilderFlags_XXX for consistency with other API.
+  - Renamed ImGuiFreeType::XXX flags to ImGuiFreeTypeBuilderFlags_XXX for consistency with other API.
 
 Other Changes:
 
@@ -54,6 +55,7 @@ Other Changes:
 - InputText: Fixed slightly off ScrollX tracking, noticeable with large values of FramePadding.x. (#3781)
 - 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.
 - 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.cpp

@@ -373,9 +373,9 @@ CODE
  When you are not sure about a old symbol or function name, try using the Search/Find function of your IDE to look for comments or references in all imgui files.
  You can read releases logs https://github.com/ocornut/imgui/releases for more details.
 
- - 2021/01/26 (1.81) - imgui_freetype: removed ImGuiFreeType::BuildFontAtlas(). Kept inline redirection function. Prefer using '#define IMGUI_ENABLE_FREETYPE', but there's a runtime selection path available too. The shared extra flags parameters (very rarely used) are now stored in ImFontAtlas::FontBuilderFlags.
+ - 2021/01/26 (1.81) - removed ImGuiFreeType::BuildFontAtlas(). Kept inline redirection function. Prefer using '#define IMGUI_ENABLE_FREETYPE', but there's a runtime selection path available too. The shared extra flags parameters (very rarely used) are now stored in ImFontAtlas::FontBuilderFlags.
-                     - imgui_freetype: renamed ImFontConfig::RasterizerFlags (used by FreeType) to ImFontConfig::FontBuilderFlags.
+                     - renamed ImFontConfig::RasterizerFlags (used by FreeType) to ImFontConfig::FontBuilderFlags.
-                     - imgui_freetype: renamed ImGuiFreeType::XXX flags to ImGuiFreeTypeBuilderFlags_XXX for consistency with other API.
+                     - renamed ImGuiFreeType::XXX flags to ImGuiFreeTypeBuilderFlags_XXX for consistency with other API.
  - 2020/10/12 (1.80) - removed redirecting functions/enums that were marked obsolete in 1.63 (August 2018):
                         - ImGui::IsItemDeactivatedAfterChange() -> use ImGui::IsItemDeactivatedAfterEdit().
                         - ImGuiCol_ModalWindowDarkening       -> use ImGuiCol_ModalWindowDimBg

imgui.h

@@ -587,6 +587,7 @@ namespace ImGui
     IMGUI_API void          ListBoxFooter();                                                    // terminate the scrolling region. only call ListBoxFooter() if ListBoxHeader() returned true!
 
     // Widgets: Data Plotting
+    // - Consider using ImPlot (https://github.com/epezent/implot)
     IMGUI_API void          PlotLines(const char* label, const float* values, int values_count, int values_offset = 0, const char* overlay_text = NULL, float scale_min = FLT_MAX, float scale_max = FLT_MAX, ImVec2 graph_size = ImVec2(0, 0), int stride = sizeof(float));
     IMGUI_API void          PlotLines(const char* label, float(*values_getter)(void* data, int idx), void* data, int values_count, int values_offset = 0, const char* overlay_text = NULL, float scale_min = FLT_MAX, float scale_max = FLT_MAX, ImVec2 graph_size = ImVec2(0, 0));
     IMGUI_API void          PlotHistogram(const char* label, const float* values, int values_count, int values_offset = 0, const char* overlay_text = NULL, float scale_min = FLT_MAX, float scale_max = FLT_MAX, ImVec2 graph_size = ImVec2(0, 0), int stride = sizeof(float));

imgui_demo.cpp

@@ -695,7 +695,7 @@ static void ShowDemoWindowWidgets()
             ImGui::ListBox("listbox\n(single select)", &item_current, items, IM_ARRAYSIZE(items), 4);
 
             //static int listbox_item_current2 = 2;
-            //ImGui::SetNextItemWidth(-1);
+            //ImGui::SetNextItemWidth(-FLT_MIN);
             //ImGui::ListBox("##listbox2", &listbox_item_current2, listbox_items, IM_ARRAYSIZE(listbox_items), 4);
         }
 
@@ -3146,7 +3146,7 @@ static void ShowDemoWindowPopups()
         {
             if (ImGui::Selectable("Set to zero")) value = 0.0f;
             if (ImGui::Selectable("Set to PI")) value = 3.1415f;
-            ImGui::SetNextItemWidth(-1);
+            ImGui::SetNextItemWidth(-FLT_MIN);
             ImGui::DragFloat("##Value", &value, 0.1f, 0.0f, 0.0f);
             ImGui::EndPopup();
         }
@@ -7478,7 +7478,7 @@ void ShowExampleAppDocuments(bool* p_open)
             if (ImGui::BeginPopupModal("Save?"))
             {
                 ImGui::Text("Save change to the following items?");
-                ImGui::SetNextItemWidth(-1.0f);
+                ImGui::SetNextItemWidth(-FLT_MIN);
                 if (ImGui::ListBoxHeader("##", close_queue_unsaved_documents, 6))
                 {
                     for (int n = 0; n < close_queue.Size; n++)

imgui_widgets.cpp

@@ -6129,12 +6129,12 @@ bool ImGui::Selectable(const char* label, bool* p_selected, ImGuiSelectableFlags
 // - ListBoxFooter()
 //-------------------------------------------------------------------------
 // FIXME: This is an old API. We should redesign some of it, rename ListBoxHeader->BeginListBox, ListBoxFooter->EndListBox
-// and promote using them over existing ListBox() functions, similarly to change with combo boxes.
+// and promote using them over existing ListBox() functions, similarly to how we now use combo boxes.
 //-------------------------------------------------------------------------
 
 // FIXME: In principle this function should be called BeginListBox(). We should rename it after re-evaluating if we want to keep the same signature.
-// Helper to calculate the size of a listbox and display a label on the right.
+// Tip: To have a list filling the entire window width, use size.x = -FLT_MIN and pass an non-visible label e.g. "##empty"
-// Tip: To have a list filling the entire window width, PushItemWidth(-1) and pass an non-visible label e.g. "##empty"
+// Tip: If your vertical size is calculated from an item count (e.g. 10 * item_height) consider adding a fractional part to facilitate seeing scrolling boundaries (e.g. 10.25 * item_height).
 bool ImGui::ListBoxHeader(const char* label, const ImVec2& size_arg)
 {
     ImGuiContext& g = *GImGui;
@@ -6146,12 +6146,12 @@ bool ImGui::ListBoxHeader(const char* label, const ImVec2& size_arg)
     const ImGuiID id = GetID(label);
     const ImVec2 label_size = CalcTextSize(label, NULL, true);
 
-    // Size default to hold ~7 items. Fractional number of items helps seeing that we can scroll down/up without looking at scrollbar.
+    // Size default to hold ~7.25 items.
-    ImVec2 size = CalcItemSize(size_arg, CalcItemWidth(), GetTextLineHeightWithSpacing() * 7.4f + style.ItemSpacing.y);
+    // Fractional number of items helps seeing that we can scroll down/up without looking at scrollbar.
+    ImVec2 size = ImFloor(CalcItemSize(size_arg, CalcItemWidth(), GetTextLineHeightWithSpacing() * 7.25f + style.FramePadding.y * 2.0f));
     ImVec2 frame_size = ImVec2(size.x, ImMax(size.y, label_size.y));
     ImRect frame_bb(window->DC.CursorPos, window->DC.CursorPos + frame_size);
     ImRect bb(frame_bb.Min, frame_bb.Max + ImVec2(label_size.x > 0.0f ? style.ItemInnerSpacing.x + label_size.x : 0.0f, 0.0f));
-    window->DC.LastItemRect = bb; // Forward storage for ListBoxFooter.. dodgy.
     g.NextItemData.ClearFlags();
 
     if (!IsRectVisible(bb.Min, bb.Max))
@@ -6161,50 +6161,46 @@ bool ImGui::ListBoxHeader(const char* label, const ImVec2& size_arg)
         return false;
     }
 
+    // FIXME-OPT: We could omit the BeginGroup() if label_size.x but would need to omit the EndGroup() as well.
     BeginGroup();
-    if (label_size.x > 0)
+    if (label_size.x > 0.0f)
-        RenderText(ImVec2(frame_bb.Max.x + style.ItemInnerSpacing.x, frame_bb.Min.y + style.FramePadding.y), label);
+    {
+        ImVec2 label_pos = ImVec2(frame_bb.Max.x + style.ItemInnerSpacing.x, frame_bb.Min.y + style.FramePadding.y);
+        RenderText(label_pos, label);
+        window->DC.CursorMaxPos = ImMax(window->DC.CursorMaxPos, label_pos + label_size);
+    }
 
     BeginChildFrame(id, frame_bb.GetSize());
     return true;
 }
 
-// FIXME: In principle this function should be called EndListBox(). We should rename it after re-evaluating if we want to keep the same signature.
+// 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.
+    ImGuiContext& g = *GImGui;
     if (height_in_items < 0)
         height_in_items = ImMin(items_count, 7);
-    const ImGuiStyle& style = GetStyle();
     float height_in_items_f = (height_in_items < items_count) ? (height_in_items + 0.25f) : (height_in_items + 0.00f);
 
-    // We include ItemSpacing.y so that a list sized for the exact number of items doesn't make a scrollbar appears. We could also enforce that by passing a flag to BeginChild().
     ImVec2 size;
     size.x = 0.0f;
-    size.y = ImFloor(GetTextLineHeightWithSpacing() * height_in_items_f + style.FramePadding.y * 2.0f);
+    size.y = GetTextLineHeightWithSpacing() * height_in_items_f + g.Style.FramePadding.y * 2.0f;
     return ListBoxHeader(label, size);
 }
 
 // FIXME: In principle this function should be called EndListBox(). We should rename it after re-evaluating if we want to keep the same signature.
 void ImGui::ListBoxFooter()
 {
-    ImGuiWindow * window = GetCurrentWindow();
+    ImGuiContext& g = *GImGui;
+    ImGuiWindow* window = g.CurrentWindow;
     IM_ASSERT((window->Flags & ImGuiWindowFlags_ChildWindow) && "Mismatched ListBoxHeader/ListBoxFooter calls. Did you test the return value of ListBoxHeader()?");
-    ImGuiWindow* parent_window = window->ParentWindow;
-    const ImRect bb = parent_window->DC.LastItemRect;
-    const ImGuiStyle& style = GetStyle();
 
     EndChildFrame();
-
+    EndGroup(); // This is only required to be able to do IsItemXXX query on the whole ListBox including label
-    // Redeclare item size so that it includes the label (we have stored the full size in LastItemRect)
-    // We call SameLine() to restore DC.CurrentLine* data
-    SameLine();
-    parent_window->DC.CursorPos = bb.Min;
-    ItemSize(bb, style.FramePadding.y);
-    EndGroup();
 }
 
 bool ImGui::ListBox(const char* label, int* current_item, const char* const items[], int items_count, int height_items)
@@ -6218,7 +6214,8 @@ bool ImGui::ListBox(const char* label, int* current_item, bool (*items_getter)(v
     if (!ListBoxHeader(label, items_count, height_in_items))
         return false;
 
-    // Assume all items have even height (= 1 line of text). If you need items of different or variable sizes you can create a custom version of ListBox() in your code without using the clipper.
+    // Assume all items have even height (= 1 line of text). If you need items of different height,
+    // you can create a custom version of ListBox() in your code without using the clipper.
     ImGuiContext& g = *GImGui;
     bool value_changed = false;
     ImGuiListClipper clipper;
@@ -6226,12 +6223,12 @@ bool ImGui::ListBox(const char* label, int* current_item, bool (*items_getter)(v
     while (clipper.Step())
         for (int i = clipper.DisplayStart; i < clipper.DisplayEnd; i++)
         {
-            const bool item_selected = (i == *current_item);
             const char* item_text;
             if (!items_getter(data, i, &item_text))
                 item_text = "*Unknown item*";
 
             PushID(i);
+            const bool item_selected = (i == *current_item);
             if (Selectable(item_text, item_selected))
             {
                 *current_item = i;