Added ImGuiWindowFlags_AlwaysUseWindowPadding flag to ensure non-border child window uses window padding (#462)

imgui.cpp

@@ -3766,7 +3766,7 @@ bool ImGui::Begin(const char* name, bool* p_opened, const ImVec2& size_on_first_
         }
 
         // Lock window padding so that altering the ShowBorders flag for children doesn't have side-effects.
-        window->WindowPadding = ((flags & ImGuiWindowFlags_ChildWindow) && !(flags & (ImGuiWindowFlags_ShowBorders | ImGuiWindowFlags_ComboBox | ImGuiWindowFlags_Popup))) ? ImVec2(0,0) : style.WindowPadding;
+        window->WindowPadding = ((flags & ImGuiWindowFlags_ChildWindow) && !(flags & (ImGuiWindowFlags_AlwaysUseWindowPadding | ImGuiWindowFlags_ShowBorders | ImGuiWindowFlags_ComboBox | ImGuiWindowFlags_Popup))) ? ImVec2(0,0) : style.WindowPadding;
 
         // Calculate auto-fit size
         ImVec2 size_auto_fit;

imgui.h

@@ -471,6 +471,7 @@ enum ImGuiWindowFlags_
     ImGuiWindowFlags_NoBringToFrontOnFocus  = 1 << 13,  // Disable bringing window to front when taking focus (e.g. clicking on it or programatically giving it focus)
     ImGuiWindowFlags_AlwaysVerticalScrollbar= 1 << 14,  // Always show vertical scrollbar (even if ContentSize.y < Size.y)
     ImGuiWindowFlags_AlwaysHorizontalScrollbar=1<< 15,  // Always show horizontal scrollbar (even if ContentSize.x < Size.x)
+    ImGuiWindowFlags_AlwaysUseWindowPadding = 1 << 16,  // Ensure child windows without border uses style.WindowPadding (ignored by default for non-bordered child windows, because more convenient)
     // [Internal]
     ImGuiWindowFlags_ChildWindow            = 1 << 20,  // Don't use! For internal use by BeginChild()
     ImGuiWindowFlags_ChildWindowAutoFitX    = 1 << 21,  // Don't use! For internal use by BeginChild()