ListBox: renamed ListBoxHeader>BeginListBox, ListBoxFooter>EndListBox. Added demo bits.

docs/CHANGELOG.txt

@@ -37,9 +37,15 @@ HOW TO UPDATE?
 
 Breaking Changes:
 
+- ListBox helpers: 
+  - Renamed ListBoxHeader(const char* label, ImVec2 size) to BeginListBox().
+  - Renamed ListBoxFooter() to EndListBox().
+  - Removed ListBoxHeader(const char* label, int items_count, int height_in_items = -1) in favor of specifying size. 
+    In the redirection function, made vertical padding consistent regardless of (items_count <= height_in_items) or not.
+  - Kept inline redirection function for all threes (will obsolete).
 - imgui_freetype:
   - Removed ImGuiFreeType::BuildFontAtlas(). Kept inline redirection function.
-  Prefer using '#define IMGUI_ENABLE_FREETYPE', but there's a runtime selection path available too.
+    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.
   - Renamed ImFontConfig::RasterizerFlags (used by FreeType) to ImFontConfig::FontBuilderFlags.
   - Renamed ImGuiFreeType::XXX flags to ImGuiFreeTypeBuilderFlags_XXX for consistency with other API.
@@ -56,8 +62,6 @@ 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.

docs/TODO.txt

@@ -185,12 +185,11 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - combo: flag for BeginCombo to not return true when unchanged (#1182)
  - combo: a way/helper to customize the combo preview (#1658)
  - combo/listbox: keyboard control. need InputText-like non-active focus + key handling. considering keyboard for custom listbox (pr #203)
- - listbox: refactor and clean the begin/end api
  - listbox: multiple selection.
  - listbox: unselect option (#1208)
  - listbox: make it easier/more natural to implement range-select (need some sort of info/ref about the last clicked/focused item that user can translate to an index?) (wip stash)
  - listbox: user may want to initial scroll to focus on the one selected value?
- - listbox: expose hovered item for a basic ListBox
+ - listbox: expose hovered item for a simplified ListBox api
  - listbox: keyboard navigation.
  - listbox: disable capturing mouse wheel if the listbox has no scrolling. (#1681)
  - listbox: scrolling should track modified selection.

imgui.cpp

@@ -373,6 +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.
 
+ - 2021/02/03 (1.81) - renamed ListBoxHeader(const char* label, ImVec2 size) to BeginListBox(). Kept inline redirection function (will obsolete).
+                     - removed ListBoxHeader(const char* label, int items_count, int height_in_items = -1) in favor of specifying size. Kept inline redirection function (will obsolete).
+                     - renamed ListBoxFooter() to EndListBox(). Kept inline redirection function (will obsolete).
  - 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.
                      - renamed ImFontConfig::RasterizerFlags (used by FreeType) to ImFontConfig::FontBuilderFlags.
                      - renamed ImGuiFreeType::XXX flags to ImGuiFreeTypeBuilderFlags_XXX for consistency with other API.

imgui.h

@@ -472,7 +472,7 @@ namespace ImGui
 
     // Widgets: Combo Box
     // - The BeginCombo()/EndCombo() api allows you to manage your contents and selection state however you want it, by creating e.g. Selectable() items.
-    // - The old Combo() api are helpers over BeginCombo()/EndCombo() which are kept available for convenience purpose.
+    // - The old Combo() api are helpers over BeginCombo()/EndCombo() which are kept available for convenience purpose. This is analogous to how ListBox are created.
     IMGUI_API bool          BeginCombo(const char* label, const char* preview_value, ImGuiComboFlags flags = 0);
     IMGUI_API void          EndCombo(); // only call EndCombo() if BeginCombo() returns true!
     IMGUI_API bool          Combo(const char* label, int* current_item, const char* const items[], int items_count, int popup_max_height_in_items = -1);
@@ -579,12 +579,15 @@ namespace ImGui
     IMGUI_API bool          Selectable(const char* label, bool* p_selected, ImGuiSelectableFlags flags = 0, const ImVec2& size = ImVec2(0, 0));      // "bool* p_selected" point to the selection state (read-write), as a convenient helper.
 
     // Widgets: List Boxes
-    // - FIXME: To be consistent with all the newer API, ListBoxHeader/ListBoxFooter should in reality be called BeginListBox/EndListBox. Will rename them.
+    // - This is essentially a thin wrapper to using BeginChild/EndChild with some stylistic changes.
+    // - The BeginListBox()/EndListBox() api allows you to manage your contents and selection state however you want it, by creating e.g. Selectable() or any items.
+    // - The simplified/old ListBox() api are helpers over BeginListBox()/EndListBox() which are kept available for convenience purpose. This is analoguous to how Combos are created.
+    // - Choose frame width:   size.x > 0.0f: custom  /  size.x < 0.0f or -FLT_MIN: right-align   /  size.x = 0.0f (default): use current ItemWidth
+    // - Choose frame height:  size.y > 0.0f: custom  /  size.y < 0.0f or -FLT_MIN: bottom-align  /  size.y = 0.0f (default): arbitrary default height which can fit ~7 items
+    IMGUI_API bool          BeginListBox(const char* label, const ImVec2& size = ImVec2(0, 0)); // open a framed scrolling region
+    IMGUI_API void          EndListBox();                                                       // only call EndListBox() if BeginListBox() returned true!
     IMGUI_API bool          ListBox(const char* label, int* current_item, const char* const items[], int items_count, int height_in_items = -1);
     IMGUI_API bool          ListBox(const char* label, int* current_item, bool (*items_getter)(void* data, int idx, const char** out_text), void* data, int items_count, int height_in_items = -1);
-    IMGUI_API bool          ListBoxHeader(const char* label, const ImVec2& size = ImVec2(0, 0)); // use if you want to reimplement ListBox() will custom data or interactions. if the function return true, you can output elements then call ListBoxFooter() afterwards.
-    IMGUI_API bool          ListBoxHeader(const char* label, int items_count, int height_in_items = -1); // "
-    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)
@@ -1961,6 +1964,10 @@ struct ImGuiTableSortSpecs
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
 namespace ImGui
 {
+    // OBSOLETED in 1.81 (from February 2021)
+    IMGUI_API bool      ListBoxHeader(const char* label, int items_count, int height_in_items = -1); // Helper to calculate size from items_count and height_in_items
+    static inline bool  ListBoxHeader(const char* label, const ImVec2& size = ImVec2(0, 0)) { return BeginListBox(label, size); }
+    static inline void  ListBoxFooter() { EndListBox(); }
     // OBSOLETED in 1.79 (from August 2020)
     static inline void  OpenPopupContextItem(const char* str_id = NULL, ImGuiMouseButton mb = 1) { OpenPopupOnItemClick(str_id, mb); } // Bool return value removed. Use IsWindowAppearing() in BeginPopup() instead. Renamed in 1.77, renamed back in 1.79. Sorry!
     // OBSOLETED in 1.78 (from June 2020)

imgui_demo.cpp

@@ -584,13 +584,12 @@ static void ShowDemoWindowWidgets()
 
         {
             // Using the _simplified_ one-liner Combo() api here
-            // See "Combo" section for examples of how to use the more complete BeginCombo()/EndCombo() api.
+            // See "Combo" section for examples of how to use the more flexible BeginCombo()/EndCombo() api.
             const char* items[] = { "AAAA", "BBBB", "CCCC", "DDDD", "EEEE", "FFFF", "GGGG", "HHHH", "IIIIIII", "JJJJ", "KKKKKKK" };
             static int item_current = 0;
             ImGui::Combo("combo", &item_current, items, IM_ARRAYSIZE(items));
             ImGui::SameLine(); HelpMarker(
-                "Refer to the \"Combo\" section below for an explanation of the full BeginCombo/EndCombo API, "
-                "and demonstration of various flags.\n");
+                "Using the simplified one-liner Combo API here.\nRefer to the \"Combo\" section below for an explanation of how to use the more flexible and general BeginCombo/EndCombo API.");
         }
 
         {
@@ -689,14 +688,13 @@ static void ShowDemoWindowWidgets()
         }
 
         {
-            // List box
+            // Using the _simplified_ one-liner ListBox() api here
+            // See "List boxes" section for examples of how to use the more flexible BeginListBox()/EndListBox() api.
             const char* items[] = { "Apple", "Banana", "Cherry", "Kiwi", "Mango", "Orange", "Pineapple", "Strawberry", "Watermelon" };
             static int item_current = 1;
-            ImGui::ListBox("listbox\n(single select)", &item_current, items, IM_ARRAYSIZE(items), 4);
-
-            //static int listbox_item_current2 = 2;
-            //ImGui::SetNextItemWidth(-FLT_MIN);
-            //ImGui::ListBox("##listbox2", &listbox_item_current2, listbox_items, IM_ARRAYSIZE(listbox_items), 4);
+            ImGui::ListBox("listbox", &item_current, items, IM_ARRAYSIZE(items), 4);
+            ImGui::SameLine(); HelpMarker(
+                "Using the simplified one-liner ListBox API here.\nRefer to the \"List boxes\" section below for an explanation of how to use the more flexible and general BeginListBox/EndListBox API.");
         }
 
         ImGui::TreePop();
@@ -1009,7 +1007,7 @@ static void ShowDemoWindowWidgets()
         // (your selection data could be an index, a pointer to the object, an id for the object, a flag intrusively
         // stored in the object itself, etc.)
         const char* items[] = { "AAAA", "BBBB", "CCCC", "DDDD", "EEEE", "FFFF", "GGGG", "HHHH", "IIII", "JJJJ", "KKKK", "LLLLLLL", "MMMM", "OOOOOOO" };
-        static int item_current_idx = 0;                    // Here our selection data is an index.
+        static int item_current_idx = 0; // Here we store our selection data as an index.
         const char* combo_label = items[item_current_idx];  // Label to preview before opening the combo (technically it could be anything)
         if (ImGui::BeginCombo("combo 1", combo_label, flags))
         {
@@ -1042,6 +1040,48 @@ static void ShowDemoWindowWidgets()
         ImGui::TreePop();
     }
 
+    if (ImGui::TreeNode("List boxes"))
+    {
+        // Using the generic BeginListBox() API, you have full control over how to display the combo contents.
+        // (your selection data could be an index, a pointer to the object, an id for the object, a flag intrusively
+        // stored in the object itself, etc.)
+        const char* items[] = { "AAAA", "BBBB", "CCCC", "DDDD", "EEEE", "FFFF", "GGGG", "HHHH", "IIII", "JJJJ", "KKKK", "LLLLLLL", "MMMM", "OOOOOOO" };
+        static int item_current_idx = 0; // Here we store our selection data as an index.
+        if (ImGui::BeginListBox("listbox 1"))
+        {
+            for (int n = 0; n < IM_ARRAYSIZE(items); n++)
+            {
+                const bool is_selected = (item_current_idx == n);
+                if (ImGui::Selectable(items[n], is_selected))
+                    item_current_idx = n;
+
+                // Set the initial focus when opening the combo (scrolling + keyboard navigation focus)
+                if (is_selected)
+                    ImGui::SetItemDefaultFocus();
+            }
+            ImGui::EndListBox();
+        }
+
+        // Custom size: use all width, 5 items tall
+        ImGui::Text("Full-width:");
+        if (ImGui::BeginListBox("##listbox 2", ImVec2(-FLT_MIN, 5 * ImGui::GetTextLineHeightWithSpacing())))
+        {
+            for (int n = 0; n < IM_ARRAYSIZE(items); n++)
+            {
+                const bool is_selected = (item_current_idx == n);
+                if (ImGui::Selectable(items[n], is_selected))
+                    item_current_idx = n;
+
+                // Set the initial focus when opening the combo (scrolling + keyboard navigation focus)
+                if (is_selected)
+                    ImGui::SetItemDefaultFocus();
+            }
+            ImGui::EndListBox();
+        }
+
+        ImGui::TreePop();
+    }
+
     if (ImGui::TreeNode("Selectables"))
     {
         // Selectable() has 2 overloads:
@@ -2557,11 +2597,11 @@ static void ShowDemoWindowLayout()
         ImGui::Button("LEVERAGE\nBUZZWORD", size);
         ImGui::SameLine();
 
-        if (ImGui::ListBoxHeader("List", size))
+        if (ImGui::BeginListBox("List", size))
         {
             ImGui::Selectable("Selected", true);
             ImGui::Selectable("Not Selected", false);
-            ImGui::ListBoxFooter();
+            ImGui::EndListBox();
         }
 
         ImGui::TreePop();

imgui_widgets.cpp

@@ -6124,18 +6124,14 @@ bool ImGui::Selectable(const char* label, bool* p_selected, ImGuiSelectableFlags
 //-------------------------------------------------------------------------
 // [SECTION] Widgets: ListBox
 //-------------------------------------------------------------------------
+// - BeginListBox()
+// - EndListBox()
 // - ListBox()
-// - ListBoxHeader()
-// - 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 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.
 // 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: 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)
+bool ImGui::BeginListBox(const char* label, const ImVec2& size_arg)
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = GetCurrentWindow();
@@ -6174,7 +6170,8 @@ bool ImGui::ListBoxHeader(const char* label, const ImVec2& size_arg)
     return true;
 }
 
-// FIXME: In principle this function should be called BeginListBox(). We should rename it after re-evaluating if we want to keep the same signature.
+#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
+// OBSOLETED in 1.81 (from February 2021)
 bool ImGui::ListBoxHeader(const char* label, int items_count, int height_in_items)
 {
     // If height_in_items == -1, default height is maximum 7.
@@ -6183,15 +6180,15 @@ bool ImGui::ListBoxHeader(const char* label, int items_count, int height_in_item
     ImVec2 size;
     size.x = 0.0f;
     size.y = GetTextLineHeightWithSpacing() * height_in_items_f + g.Style.FramePadding.y * 2.0f;
-    return ListBoxHeader(label, size);
+    return BeginListBox(label, size);
 }
+#endif
 
-// 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()
+void ImGui::EndListBox()
 {
     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()?");
+    IM_ASSERT((window->Flags & ImGuiWindowFlags_ChildWindow) && "Mismatched BeginListBox/EndListBox calls. Did you test the return value of BeginListBox?");
 
     EndChildFrame();
     EndGroup(); // This is only required to be able to do IsItemXXX query on the whole ListBox including label
@@ -6203,14 +6200,23 @@ bool ImGui::ListBox(const char* label, int* current_item, const char* const item
     return value_changed;
 }
 
+// This is merely a helper around BeginListBox(), EndListBox().
+// Considering using those directly to submit custom data or store selection differently.
 bool ImGui::ListBox(const char* label, int* current_item, bool (*items_getter)(void*, int, const char**), void* data, int items_count, int height_in_items)
 {
-    if (!ListBoxHeader(label, items_count, height_in_items))
+    ImGuiContext& g = *GImGui;
+
+    // Calculate size from "height_in_items"
+    if (height_in_items < 0)
+        height_in_items = ImMin(items_count, 7);
+    float height_in_items_f = height_in_items + 0.25f;
+    ImVec2 size(0.0f, ImFloor(GetTextLineHeightWithSpacing() * height_in_items_f + g.Style.FramePadding.y * 2.0f));
+
+    if (!BeginListBox(label, size))
         return false;
 
     // 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;
     clipper.Begin(items_count, GetTextLineHeightWithSpacing()); // We know exactly our line height here so we pass it as a minor optimization, but generally you don't need to.
@@ -6232,7 +6238,7 @@ bool ImGui::ListBox(const char* label, int* current_item, bool (*items_getter)(v
                 SetItemDefaultFocus();
             PopID();
         }
-    ListBoxFooter();
+    EndListBox();
     if (value_changed)
         MarkItemEdited(g.CurrentWindow->DC.LastItemId);