BeginChild(): Fixed BeginChild(const char*, ...) variation erroneously not applying the ID stack to the provided string to uniquely identify the child window. This was undoing an intentional change introduced in 1.50 and broken in 1.60. (#1698, #894, #713) + reworked the Begin/BeginChild comments in imgui.h.

docs/CHANGELOG.txt

@@ -45,6 +45,9 @@ Other Changes:
   erroneously wrapped the value to one of the min/max edge. (#2024, #708, #320, #2075).
 - DragFloat: Disabled using power curve when one edge is FLT_MAX (broken in 1.61). (#2024)
 - DragFloat: Disabled setting a default drag speed when one edge is FLT_MAX. (#2024)
+- BeginChild(): Fixed BeginChild(const char*, ...) variation erroneously not applying the ID stack
+  to the provided string to uniquely identify the child window. This was undoing an intentional change
+  introduced in 1.50 and broken in 1.60. (#1698, #894, #713).
 - BeginMenu(): Fixed menu popup horizontal offset being off the item in the menu bar when WindowPadding=0.0f.
 - ArrowButton(): Fixed arrow shape being horizontally misaligned by (FramePadding.y-FramePadding.x) if they are different.
 - ImDrawList: Fixed AddConvexPolyFilled() undefined behavior when passing points_count smaller than 3,
@@ -336,6 +339,9 @@ Breaking Changes:
 - Removed ImGuiCol_CloseButton, ImGuiCol_CloseButtonActive, ImGuiCol_CloseButtonHovered style colors as the closing cross uses regular button colors now.
 - Renamed ImGuiSizeConstraintCallback to ImGuiSizeCallback, ImGuiSizeConstraintCallbackData to ImGuiSizeCallbackData.
 - Removed CalcItemRectClosestPoint() which was weird and not really used by anyone except demo code. If you need it should be easy to replicate on your side (you can find the code in 1.53).
+- [EDITED] Window: BeginChild() with an explicit name doesn't include the hash within the internal window name. (#1698)
+  This change was erroneously introduced, undoing the change done for #894, #713, and not documented properly in the original 
+  1.60 release Changelog. It was fixed on 2018-09-28 (1.66) and I wrote this paragraph the same day.
 
 Other Changes:
 
@@ -544,7 +550,6 @@ Other Changes:
 - Window: Using the ImGuiWindowFlags_NoScrollWithMouse flag on a child window forwards the mouse wheel event to the parent window, unless either ImGuiWindowFlags_NoInputs or ImGuiWindowFlags_NoScrollbar are also set. (#1380, #1502)
 - Window: Active Modal window always set the WantCaptureKeyboard flag. (#744)
 - Window: Moving window doesn't use accumulating MouseDelta so straying out of imgui boundaries keeps moved imgui window at the same cursor-relative position.
-- Window: BeginChild() which an explicit name doesn't include the hash within the internal window name. (#1698)
 - IsWindowFocused(): Added ImGuiFocusedFlags_ChildWindows flag to include child windows in the focused test. (#1382).
 - IsWindowFocused(): Added ImGuiFocusedFlags_RootWindow flag to start focused test from the root (top-most) window. Obsolete IsRootWindowFocused(). (#1382)
 - IsWindowHovered(): Added ImGuiHoveredFlags_ChildWindows flag to include child windows in the hovered test. (#1382).

imgui.cpp

@@ -4036,10 +4036,10 @@ static bool ImGui::BeginChildEx(const char* name, ImGuiID id, const ImVec2& size
         size.y = ImMax(content_avail.y + size.y, 4.0f);
     SetNextWindowSize(size);
 
-    // Name
+    // Build up name. If you need to append to a same child from multiple location in the ID stack, use BeginChild(ImGuiID id) with a stable value.
     char title[256];
     if (name)
-        ImFormatString(title, IM_ARRAYSIZE(title), "%s/%s", parent_window->Name, name);
+        ImFormatString(title, IM_ARRAYSIZE(title), "%s/%s_%08X", parent_window->Name, name, id);
     else
         ImFormatString(title, IM_ARRAYSIZE(title), "%s/%08X", parent_window->Name, id);
 

imgui.h

@@ -189,14 +189,20 @@ namespace ImGui
     IMGUI_API void          StyleColorsLight(ImGuiStyle* dst = NULL);   // best used with borders and a custom, thicker font
 
     // Windows
-    // (Begin = push window to the stack and start appending to it. End = pop window from the stack. You may append multiple times to the same window during the same frame)
+    // - Begin() = push window to the stack and start appending to it. End() = pop window from the stack.
-    // Begin()/BeginChild() return false to indicate the window being collapsed or fully clipped, so you may early out and omit submitting anything to the window.
+    // - You may append multiple times to the same window during the same frame.
-    // You need to always call a matching End()/EndChild() for a Begin()/BeginChild() call, regardless of its return value (this is due to legacy reason and is inconsistent with BeginMenu/EndMenu, BeginPopup/EndPopup and other functions where the End call should only be called if the corresponding Begin function returned true.)
+    // - Passing 'bool* p_open != NULL' shows a window-closing widget in the upper-right corner of the window, which clicking will set the boolean to false when clicked.
-    // Passing 'bool* p_open != NULL' shows a close widget in the upper-right corner of the window, which when clicking will set the boolean to false.
+    // - Begin() return false to indicate the window is collapsed or fully clipped, so you may early out and omit submitting anything to the window.
-    // Use child windows to introduce independent scrolling/clipping regions within a host window. Child windows can embed their own child.
+    //   Always call a matching End() for each Begin() call, regardless of its return value [this is due to legacy reason and is inconsistent with most other functions such as BeginMenu/EndMenu, BeginPopup/EndPopup, etc. where the EndXXX call should only be called if the corresponding BeginXXX function returned true.]
     IMGUI_API bool          Begin(const char* name, bool* p_open = NULL, ImGuiWindowFlags flags = 0);
     IMGUI_API void          End();
-    IMGUI_API bool          BeginChild(const char* str_id, const ImVec2& size = ImVec2(0,0), bool border = false, ImGuiWindowFlags flags = 0); // Begin a scrolling region. size==0.0f: use remaining window size, size<0.0f: use remaining window size minus abs(size). size>0.0f: fixed size. each axis can use a different mode, e.g. ImVec2(0,400).
+
+    // Child Windows
+    // - Use child windows to begin into a self-contained independent scrolling/clipping regions within a host window. Child windows can embed their own child.
+    // - For each independent axis of 'size': ==0.0f: use remaining host window size / >0.0f: fixed size / <0.0f: use remaining window size minus abs(size) / Each axis can use a different mode, e.g. ImVec2(0,400).
+    // - BeginChild() returns false to indicate the window is collapsed or fully clipped, so you may early out and omit submitting anything to the window.
+    //   Always call a matching EndChild() for each BeginChild() call, regardless of its return value [this is due to legacy reason and is inconsistent with most other functions such as BeginMenu/EndMenu, BeginPopup/EndPopup, etc. where the EndXXX call should only be called if the corresponding BeginXXX function returned true.]
+    IMGUI_API bool          BeginChild(const char* str_id, const ImVec2& size = ImVec2(0,0), bool border = false, ImGuiWindowFlags flags = 0);
     IMGUI_API bool          BeginChild(ImGuiID id, const ImVec2& size = ImVec2(0,0), bool border = false, ImGuiWindowFlags flags = 0);
     IMGUI_API void          EndChild();