ListBox, Combo: Changed signature of "name getter" callback in old one-liner ListBox()/Combo() apis.

docs/CHANGELOG.txt

@@ -42,6 +42,16 @@ HOW TO UPDATE?
 
 Breaking changes:
 
+ - ListBox, Combo: Changed signature of "name getter" callback in old one-liner ListBox()/Combo() apis.
+   Before:
+      getter type:   bool (*getter)(void* user_data, int idx, const char** out_text)
+      function:      bool Combo(const char* label, int* current_item, bool (*getter)(void* user_data, int idx, const char** out_text), ...);
+      function:      bool ListBox(const char* label, int* current_item, bool (*getting)(void* user_data, int idx, const char** out_text), ...);
+   After:
+      getter type:   const char* (*getter)(void* user_data, int idx)
+      function:      bool Combo(const char* label, int* current_item, const char* (*getter)(void* user_data, int idx), ...);
+      function:      bool ListBox(const char* label, int* current_item, const char* (*getter)(void* user_data, int idx), ...);
+   Old type was unnecessarily complex and harder to wrap in e.g. a lambda. Kept inline redirection function (will obsolete).
  - Commented out obsolete redirecting enums/functions that were marked obsolete two years ago:
    - GetWindowContentRegionWidth() -> use GetWindowContentRegionMax().x - GetWindowContentRegionMin().x.
      Consider that generally 'GetContentRegionAvail().x' is more useful.

imgui.cpp

@@ -424,6 +424,11 @@ CODE
  When you are not sure about an 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.
 
+ - 2023/09/15 (1.90.0) - ListBox, Combo: changed signature of "name getter" callback in old one-liner ListBox()/Combo() apis. kept inline redirection function (will obsolete).
+                           - old: bool Combo(const char* label, int* current_item, bool (*getter)(void* user_data, int idx, const char** out_text), ...)
+                           - new: bool Combo(const char* label, int* current_item, const char* (*getter)(void* user_data, int idx), ...);
+                           - old: bool ListBox(const char* label, int* current_item, bool (*getting)(void* user_data, int idx, const char** out_text), ...);
+                           - new: bool ListBox(const char* label, int* current_item, const char* (*getter)(void* user_data, int idx), ...);
  - 2023/09/08 (1.90.0) - commented out obsolete redirecting functions:
                            - GetWindowContentRegionWidth()  -> use GetWindowContentRegionMax().x - GetWindowContentRegionMin().x. Consider that generally 'GetContentRegionAvail().x' is more useful.
                            - ImDrawCornerFlags_XXX          -> use ImDrawFlags_RoundCornersXXX flags. Read 1.82 Changelog for details + grep commented names in sources.

imgui.h

@@ -527,7 +527,7 @@ namespace ImGui
     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);
     IMGUI_API bool          Combo(const char* label, int* current_item, const char* items_separated_by_zeros, int popup_max_height_in_items = -1);      // Separate items with \0 within a string, end item-list with \0\0. e.g. "One\0Two\0Three\0"
-    IMGUI_API bool          Combo(const char* label, int* current_item, bool(*items_getter)(void* data, int idx, const char** out_text), void* data, int items_count, int popup_max_height_in_items = -1);
+    IMGUI_API bool          Combo(const char* label, int* current_item, const char* (*getter)(void* user_data, int idx), void* user_data, int items_count, int popup_max_height_in_items = -1);
 
     // Widgets: Drag Sliders
     // - CTRL+Click on any drag box to turn them into an input box. Manually input values aren't clamped by default and can go off-bounds. Use ImGuiSliderFlags_AlwaysClamp to always clamp.
@@ -638,14 +638,14 @@ namespace ImGui
     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          ListBox(const char* label, int* current_item, const char* (*getter)(void* user_data, int idx), void* user_data, int items_count, int height_in_items = -1);
 
     // Widgets: Data Plotting
     // - Consider using ImPlot (https://github.com/epezent/implot) which is much better!
     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_API void          PlotHistogram(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, 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));
 
     // Widgets: Value() Helpers.
     // - Those are merely shortcut to calling Text() with a format string. Output single value in "name: value" format (tip: freely declare more in your code to handle your types. you can add functions to the ImGui namespace)
@@ -3097,6 +3097,9 @@ namespace ImGui
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
 namespace ImGui
 {
+    // OBSOLETED in 1.90.0 (from September 2023)
+    IMGUI_API bool      ListBox(const char* label, int* current_item, bool (*old_callback)(void* user_data, int idx, const char** out_text), void* user_data, int items_count, int height_in_items = -1);
+    IMGUI_API bool      Combo(const char* label, int* current_item, bool (*old_callback)(void* user_data, int idx, const char** out_text), void* user_data, int items_count, int popup_max_height_in_items = -1);
     // OBSOLETED in 1.89.7 (from June 2023)
     IMGUI_API void      SetItemAllowOverlap();                                              // Use SetNextItemAllowOverlap() before item.
     // OBSOLETED in 1.89.4 (from March 2023)

imgui_demo.cpp

@@ -1226,9 +1226,8 @@ static void ShowDemoWindowWidgets()
         ImGui::Combo("combo 3 (array)", &item_current_3, items, IM_ARRAYSIZE(items));
 
         // Simplified one-liner Combo() using an accessor function
-        struct Funcs { static bool ItemGetter(void* data, int n, const char** out_str) { *out_str = ((const char**)data)[n]; return true; } };
         static int item_current_4 = 0;
-        ImGui::Combo("combo 4 (function)", &item_current_4, &Funcs::ItemGetter, items, IM_ARRAYSIZE(items));
+        ImGui::Combo("combo 4 (function)", &item_current_4, [](void* data, int n) { return ((const char**)data)[n]; }, items, IM_ARRAYSIZE(items));
 
         ImGui::TreePop();
     }

imgui_widgets.cpp

@@ -1870,18 +1870,15 @@ void ImGui::EndComboPreview()
 }
 
 // Getter for the old Combo() API: const char*[]
-static bool Items_ArrayGetter(void* data, int idx, const char** out_text)
+static const char* Items_ArrayGetter(void* data, int idx)
 {
     const char* const* items = (const char* const*)data;
-    if (out_text)
-        *out_text = items[idx];
-    return true;
+    return items[idx];
 }
 
 // Getter for the old Combo() API: "item1\0item2\0item3\0"
-static bool Items_SingleStringGetter(void* data, int idx, const char** out_text)
+static const char* Items_SingleStringGetter(void* data, int idx)
 {
-    // FIXME-OPT: we could pre-compute the indices to fasten this. But only 1 active combo means the waste is limited.
     const char* items_separated_by_zeros = (const char*)data;
     int items_count = 0;
     const char* p = items_separated_by_zeros;
@@ -1892,22 +1889,18 @@ static bool Items_SingleStringGetter(void* data, int idx, const char** out_text)
         p += strlen(p) + 1;
         items_count++;
     }
-    if (!*p)
-        return false;
-    if (out_text)
-        *out_text = p;
-    return true;
+    return *p ? p : NULL;
 }
 
 // Old API, prefer using BeginCombo() nowadays if you can.
-bool ImGui::Combo(const char* label, int* current_item, bool (*items_getter)(void*, int, const char**), void* data, int items_count, int popup_max_height_in_items)
+bool ImGui::Combo(const char* label, int* current_item, const char* (*getter)(void* user_data, int idx), void* user_data, int items_count, int popup_max_height_in_items)
 {
     ImGuiContext& g = *GImGui;
 
     // Call the getter to obtain the preview string which is a parameter to BeginCombo()
     const char* preview_value = NULL;
     if (*current_item >= 0 && *current_item < items_count)
-        items_getter(data, *current_item, &preview_value);
+        preview_value = getter(user_data, *current_item);
 
     // The old Combo() API exposed "popup_max_height_in_items". The new more general BeginCombo() API doesn't have/need it, but we emulate it here.
     if (popup_max_height_in_items != -1 && !(g.NextWindowData.Flags & ImGuiNextWindowDataFlags_HasSizeConstraint))
@@ -1921,11 +1914,12 @@ bool ImGui::Combo(const char* label, int* current_item, bool (*items_getter)(voi
     bool value_changed = false;
     for (int i = 0; i < items_count; i++)
     {
+        const char* item_text = getter(user_data, i);
+        if (item_text == NULL)
+            item_text = "*Unknown item*";
+
         PushID(i);
         const bool item_selected = (i == *current_item);
-        const char* item_text;
-        if (!items_getter(data, i, &item_text))
-            item_text = "*Unknown item*";
         if (Selectable(item_text, item_selected) && *current_item != i)
         {
             value_changed = true;
@@ -1965,6 +1959,30 @@ bool ImGui::Combo(const char* label, int* current_item, const char* items_separa
     return value_changed;
 }
 
+#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
+
+struct ImGuiGetNameFromIndexOldToNewCallbackData { void* UserData; bool (*OldCallback)(void*, int, const char**); };
+static const char* ImGuiGetNameFromIndexOldToNewCallback(void* user_data, int idx)
+{
+    ImGuiGetNameFromIndexOldToNewCallbackData* data = (ImGuiGetNameFromIndexOldToNewCallbackData*)user_data;
+    const char* s = NULL;
+    data->OldCallback(data->UserData, idx, &s);
+    return s;
+}
+
+bool ImGui::ListBox(const char* label, int* current_item, bool (*old_getter)(void*, int, const char**), void* user_data, int items_count, int height_in_items)
+{
+    ImGuiGetNameFromIndexOldToNewCallbackData old_to_new_data = { user_data, old_getter };
+    return ListBox(label, current_item, ImGuiGetNameFromIndexOldToNewCallback, &old_to_new_data, items_count, height_in_items);
+}
+bool ImGui::Combo(const char* label, int* current_item, bool (*old_getter)(void*, int, const char**), void* user_data, int items_count, int popup_max_height_in_items)
+{
+    ImGuiGetNameFromIndexOldToNewCallbackData old_to_new_data = { user_data, old_getter };
+    return Combo(label, current_item, ImGuiGetNameFromIndexOldToNewCallback, &old_to_new_data, items_count, popup_max_height_in_items);
+}
+
+#endif
+
 //-------------------------------------------------------------------------
 // [SECTION] Data Type and Data Formatting Helpers [Internal]
 //-------------------------------------------------------------------------
@@ -6879,7 +6897,7 @@ bool ImGui::ListBox(const char* label, int* current_item, const char* const item
 
 // 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)
+bool ImGui::ListBox(const char* label, int* current_item, const char* (*getter)(void* user_data, int idx), void* user_data, int items_count, int height_in_items)
 {
     ImGuiContext& g = *GImGui;
 
@@ -6900,8 +6918,8 @@ 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 char* item_text;
-            if (!items_getter(data, i, &item_text))
+            const char* item_text = getter(user_data, i);
+            if (item_text == NULL)
                 item_text = "*Unknown item*";
 
             PushID(i);