TreeNode: Added undocumented ImGuiTreeNodeFlags_UpsideDownArrow flag. (#6517)

+ Minor tweak comment/layout in ImGuiIO

imgui.h

@@ -1950,18 +1950,23 @@ struct ImGuiIO
     bool        ConfigWindowsMoveFromTitleBarOnly; // = false       // Enable allowing to move windows only when clicking on their title bar. Does not apply to windows without a title bar.
     float       ConfigMemoryCompactTimer;       // = 60.0f          // Timer (in seconds) to free transient windows/tables memory buffers when unused. Set to -1.0f to disable.
 
+    //------------------------------------------------------------------
     // Debug options
-    // - tools to test correct Begin/End and BeginChild/EndChild behaviors.
-    // - presently Begin()/End() and BeginChild()/EndChild() needs to ALWAYS be called in tandem, regardless of return value of BeginXXX()
-    //   this is inconsistent with other BeginXXX functions and create confusion for many users.
-    // - we expect to update the API eventually. In the meanwhile we provide tools to facilitate checking user-code behavior.
+    //------------------------------------------------------------------
+
+    // Tools to test correct Begin/End and BeginChild/EndChild behaviors.
+    // Presently Begin()/End() and BeginChild()/EndChild() needs to ALWAYS be called in tandem, regardless of return value of BeginXXX()
+    // This is inconsistent with other BeginXXX functions and create confusion for many users.
+    // We expect to update the API eventually. In the meanwhile we provide tools to facilitate checking user-code behavior.
     bool        ConfigDebugBeginReturnValueOnce;// = false          // First-time calls to Begin()/BeginChild() will return false. NEEDS TO BE SET AT APPLICATION BOOT TIME if you don't want to miss windows.
     bool        ConfigDebugBeginReturnValueLoop;// = false          // Some calls to Begin()/BeginChild() will return false. Will cycle through window depths then repeat. Suggested use: add "io.ConfigDebugBeginReturnValue = io.KeyShift" in your main loop then occasionally press SHIFT. Windows should be flickering while running.
-    // - option to deactivate io.AddFocusEvent(false) handling. May facilitate interactions with a debugger when focus loss leads to clearing inputs data.
-    // - backends may have other side-effects on focus loss, so this will reduce side-effects but not necessary remove all of them.
-    // - consider using e.g. Win32's IsDebuggerPresent() as an additional filter (or see ImOsIsDebuggerPresent() in imgui_test_engine/imgui_te_utils.cpp for a Unix compatible version).
+
+    // Option to deactivate io.AddFocusEvent(false) handling. May facilitate interactions with a debugger when focus loss leads to clearing inputs data.
+    // Backends may have other side-effects on focus loss, so this will reduce side-effects but not necessary remove all of them.
+    // Consider using e.g. Win32's IsDebuggerPresent() as an additional filter (or see ImOsIsDebuggerPresent() in imgui_test_engine/imgui_te_utils.cpp for a Unix compatible version).
     bool        ConfigDebugIgnoreFocusLoss;     // = false          // Ignore io.AddFocusEvent(false), consequently not calling io.ClearInputKeys() in input processing.
-    // - tools to audit ini data
+
+    // Options to audit .ini data
     bool        ConfigDebugIniSettings;         // = false          // Save .ini data with extra comments (particularly helpful for Docking, but makes saving slower)
 
     //------------------------------------------------------------------

imgui_internal.h

@@ -898,6 +898,7 @@ enum ImGuiSelectableFlagsPrivate_
 enum ImGuiTreeNodeFlagsPrivate_
 {
     ImGuiTreeNodeFlags_ClipLabelForTrailingButton = 1 << 20,
+    ImGuiTreeNodeFlags_UpsideDownArrow            = 1 << 21,// (FIXME-WIP) Turn Down arrow into an Up arrow, but reversed trees (#6517)
 };
 
 enum ImGuiSeparatorFlags_

imgui_widgets.cpp

@@ -6259,7 +6259,7 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiTreeNodeFlags flags, const char* l
         if (flags & ImGuiTreeNodeFlags_Bullet)
             RenderBullet(window->DrawList, ImVec2(text_pos.x - text_offset_x * 0.60f, text_pos.y + g.FontSize * 0.5f), text_col);
         else if (!is_leaf)
-            RenderArrow(window->DrawList, ImVec2(text_pos.x - text_offset_x + padding.x, text_pos.y), text_col, is_open ? ImGuiDir_Down : ImGuiDir_Right, 1.0f);
+            RenderArrow(window->DrawList, ImVec2(text_pos.x - text_offset_x + padding.x, text_pos.y), text_col, is_open ? ((flags & ImGuiTreeNodeFlags_UpsideDownArrow) ? ImGuiDir_Up : ImGuiDir_Down) : ImGuiDir_Right, 1.0f);
         else // Leaf without bullet, left-adjusted text
             text_pos.x -= text_offset_x;
         if (flags & ImGuiTreeNodeFlags_ClipLabelForTrailingButton)