Removed CalcItemRectClosestPoint() which was weird and not really used by anyone except demo code. If you need it it's easy to replicate on your side.

Removed internal corresponding ImRect::GetClosestPoint() for now.
Essentially revert dcaafffe0ed21c9b03530a911785ded80e14358f.

imgui.cpp

@@ -213,6 +213,7 @@
  Here is a change-log of API breaking changes, if you are using one of the functions listed, expect to have to fix some code.
  Also read releases logs https://github.com/ocornut/imgui/releases for more details.
 
+ - 2017/12/29 (1.54) - removed CalcItemRectClosestPoint() which was weird and not really used by anyone except demo code. If you need it it's easy to replicate on your side.
  - 2017/12/24 (1.53) - renamed the emblematic ShowTestWindow() function to ShowDemoWindow(). Kept redirection function (will obsolete).
  - 2017/12/21 (1.53) - ImDrawList: renamed style.AntiAliasedShapes to style.AntiAliasedFill for consistency and as a way to explicitly break code that manipulate those flag at runtime. You can now manipulate ImDrawList::Flags
  - 2017/12/21 (1.53) - ImDrawList: removed 'bool anti_aliased = true' final parameter of ImDrawList::AddPolyline() and ImDrawList::AddConvexPolyFilled(). Prefer manipulating ImDrawList::Flags if you need to toggle them during the frame.
@@ -3658,14 +3659,6 @@ ImVec2 ImGui::GetItemRectSize()
     return window->DC.LastItemRect.GetSize();
 }
 
-ImVec2 ImGui::CalcItemRectClosestPoint(const ImVec2& pos, bool on_edge, float outward)
-{
-    ImGuiWindow* window = GetCurrentWindowRead();
-    ImRect rect = window->DC.LastItemRect;
-    rect.Expand(outward);
-    return rect.GetClosestPoint(pos, on_edge);
-}
-
 static ImRect GetVisibleRect()
 {
     ImGuiContext& g = *GImGui;

imgui.h

@@ -472,7 +472,6 @@ namespace ImGui
     IMGUI_API ImDrawList*   GetOverlayDrawList();                                               // this draw list will be the last rendered one, useful to quickly draw overlays shapes/text
     IMGUI_API ImDrawListSharedData* GetDrawListSharedData();
     IMGUI_API const char*   GetStyleColorName(ImGuiCol idx);
-    IMGUI_API ImVec2        CalcItemRectClosestPoint(const ImVec2& pos, bool on_edge = false, float outward = +0.0f);   // utility to find the closest point the last item bounding rectangle edge. useful to visually link items
     IMGUI_API ImVec2        CalcTextSize(const char* text, const char* text_end = NULL, bool hide_text_after_double_hash = false, float wrap_width = -1.0f);
     IMGUI_API void          CalcListClipping(int items_count, float items_height, int* out_items_display_start, int* out_items_display_end);    // calculate coarse clipping for large list of evenly sized items. Prefer using the ImGuiListClipper higher-level helper if you can.
 
@@ -987,6 +986,7 @@ struct ImGuiIO
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
 namespace ImGui
 {
+    static inline ImVec2 CalcItemRectClosestPoint(const ImVec2& pos, bool on_edge = false, float outward = +0.0f) { (void)on_edge; (void)outward; return pos; } // OBSOLETE 1.54+
     static inline void  ShowTestWindow() { return ShowDemoWindow(); } // OBSOLETE 1.53+
     static inline bool  IsRootWindowFocused() { return IsWindowFocused(ImGuiFocusedFlags_RootWindow); } // OBSOLETE 1.53+
     static inline bool  IsRootWindowOrAnyChildFocused() { return IsWindowFocused(ImGuiFocusedFlags_RootAndChildWindows); } // OBSOLETE 1.53+

imgui_demo.cpp

@@ -1894,7 +1894,7 @@ void ImGui::ShowDemoWindow(bool* p_open)
                 // Draw a line between the button and the mouse cursor
                 ImDrawList* draw_list = ImGui::GetWindowDrawList();
                 draw_list->PushClipRectFullScreen();
-                draw_list->AddLine(ImGui::CalcItemRectClosestPoint(io.MousePos, true, -2.0f), io.MousePos, ImColor(ImGui::GetStyle().Colors[ImGuiCol_Button]), 4.0f);
+                draw_list->AddLine(io.MouseClickedPos[0], io.MousePos, ImGui::GetColorU32(ImGuiCol_Button), 4.0f);
                 draw_list->PopClipRect();
 
                 // Drag operations gets "unlocked" when the mouse has moved past a certain threshold (the default threshold is stored in io.MouseDragThreshold)

imgui_internal.h

@@ -290,16 +290,6 @@ struct IMGUI_API ImRect
     void        Floor()                         { Min.x = (float)(int)Min.x; Min.y = (float)(int)Min.y; Max.x = (float)(int)Max.x; Max.y = (float)(int)Max.y; }
     void        FixInverted()                   { if (Min.x > Max.x) ImSwap(Min.x, Max.x); if (Min.y > Max.y) ImSwap(Min.y, Max.y); }
     bool        IsFinite() const                { return Min.x != FLT_MAX; }
-    ImVec2      GetClosestPoint(ImVec2 p, bool on_edge) const
-    {
-        if (!on_edge && Contains(p))
-            return p;
-        if (p.x > Max.x) p.x = Max.x;
-        else if (p.x < Min.x) p.x = Min.x;
-        if (p.y > Max.y) p.y = Max.y;
-        else if (p.y < Min.y) p.y = Min.y;
-        return p;
-    }
 };
 
 // Stacked color modifier, backup of modified data so we can restore it