Merged from Navigation branch:

f71cdd13b7  Internal tidying up, moved code to CalcNextScrollFromScrollTargetAndClamp() so it can be reused by upcoming nav code.
c816e6c742 Fixed SetScrollX() handling of center ratio (which actually wasn't exposed publicly). (#323, #246)

imgui.cpp

@@ -609,6 +609,7 @@ static inline bool      IsWindowContentHoverable(ImGuiWindow* window);
 static void             ClearSetNextWindowData();
 static void             CheckStacksSize(ImGuiWindow* window, bool write);
 static void             Scrollbar(ImGuiWindow* window, bool horizontal);
+static ImVec2           CalcNextScrollFromScrollTargetAndClamp(ImGuiWindow* window);
 
 static void             AddDrawListToRenderList(ImVector<ImDrawList*>& out_render_list, ImDrawList* draw_list);
 static void             AddWindowToRenderList(ImVector<ImDrawList*>& out_render_list, ImGuiWindow* window);
@@ -3894,6 +3895,24 @@ static void ApplySizeFullWithConstraint(ImGuiWindow* window, ImVec2 new_size)
     window->SizeFull = new_size;
 }
 
+static ImVec2 CalcNextScrollFromScrollTargetAndClamp(ImGuiWindow* window)
+{
+    ImVec2 scroll = window->Scroll;
+    float cr_x = window->ScrollTargetCenterRatio.x;
+    float cr_y = window->ScrollTargetCenterRatio.y;
+    if (window->ScrollTarget.x < FLT_MAX)
+        scroll.x = window->ScrollTarget.x - cr_x * (window->SizeFull.x - window->ScrollbarSizes.x);
+    if (window->ScrollTarget.y < FLT_MAX)
+        scroll.y = window->ScrollTarget.y - (1.0f - cr_y) * (window->TitleBarHeight() + window->MenuBarHeight()) - cr_y * (window->SizeFull.y - window->ScrollbarSizes.y);
+    scroll = ImMax(scroll, ImVec2(0.0f, 0.0f));
+    if (!window->Collapsed && !window->SkipItems)
+    {
+        scroll.x = ImMin(scroll.x, ImMax(0.0f, window->SizeContents.x - (window->SizeFull.x - window->ScrollbarSizes.x))); // == GetScrollMaxX for that window
+        scroll.y = ImMin(scroll.y, ImMax(0.0f, window->SizeContents.y - (window->SizeFull.y - window->ScrollbarSizes.y))); // == GetScrollMaxY for that window
+    }
+    return scroll;
+}
+
 // Push a new ImGui window to add widgets to.
 // - A default window called "Debug" is automatically stacked at the beginning of every frame so you can use widgets without explicitly calling a Begin/End pair.
 // - Begin/End can be called multiple times during the frame with the same window name to append content.
@@ -4208,23 +4227,8 @@ bool ImGui::Begin(const char* name, bool* p_open, const ImVec2& size_on_first_us
         window->FocusIdxAllRequestNext = window->FocusIdxTabRequestNext = INT_MAX;
 
         // Apply scrolling
-        if (window->ScrollTarget.x < FLT_MAX)
-        {
-            window->Scroll.x = window->ScrollTarget.x;
-            window->ScrollTarget.x = FLT_MAX;
-        }
-        if (window->ScrollTarget.y < FLT_MAX)
-        {
-            float center_ratio = window->ScrollTargetCenterRatio.y;
-            window->Scroll.y = window->ScrollTarget.y - ((1.0f - center_ratio) * (window->TitleBarHeight() + window->MenuBarHeight())) - (center_ratio * (window->SizeFull.y - window->ScrollbarSizes.y));
-            window->ScrollTarget.y = FLT_MAX;
-        }
-        window->Scroll = ImMax(window->Scroll, ImVec2(0.0f, 0.0f));
-        if (!window->Collapsed && !window->SkipItems)
-        {
-            window->Scroll.x = ImMin(window->Scroll.x, GetScrollMaxX());
-            window->Scroll.y = ImMin(window->Scroll.y, GetScrollMaxY());
-        }
+        window->Scroll = CalcNextScrollFromScrollTargetAndClamp(window);
+        window->ScrollTarget = ImVec2(FLT_MAX, FLT_MAX);
 
         // Modal window darkens what is behind them
         if ((flags & ImGuiWindowFlags_Modal) != 0 && window == GetFrontMostModalRootWindow())