Internals: clarified the code for ClampWindowRect().

As a side-effect, some rounding error may be neutralized however this isn't the intent. (#3309)

imgui.cpp

@@ -5239,11 +5239,13 @@ static bool ImGui::UpdateWindowManualResize(ImGuiWindow* window, const ImVec2& s
     return ret_auto_fit;
 }
 
-static inline void ClampWindowRect(ImGuiWindow* window, const ImRect& rect, const ImVec2& padding)
+static inline void ClampWindowRect(ImGuiWindow* window, const ImRect& viewport_rect, const ImVec2& padding)
 {
     ImGuiContext& g = *GImGui;
-    ImVec2 size_for_clamping = (g.IO.ConfigWindowsMoveFromTitleBarOnly && !(window->Flags & ImGuiWindowFlags_NoTitleBar)) ? ImVec2(window->Size.x, window->TitleBarHeight()) : window->Size;
-    window->Pos = ImMin(rect.Max - padding, ImMax(window->Pos + size_for_clamping, rect.Min + padding) - size_for_clamping);
+    ImVec2 size_for_clamping = window->Size;
+    if (g.IO.ConfigWindowsMoveFromTitleBarOnly && !(window->Flags & ImGuiWindowFlags_NoTitleBar))
+        size_for_clamping.y = window->TitleBarHeight();
+    window->Pos = ImClamp(window->Pos, viewport_rect.Min + padding - size_for_clamping, viewport_rect.Max - padding);
 }
 
 static void ImGui::RenderWindowOuterBorders(ImGuiWindow* window)