BeginPopupModal() doesn't set the ImGuiWindowFlags_NoSavedSettings flag anymore, and will not always be auto-centered. (#915, #3091)

# Conflicts:
#	imgui.cpp

docs/CHANGELOG.txt

@@ -127,6 +127,10 @@ Other Changes:
   would attempt to focus it and close other popups. (#2880)
 - Popups: Fix BeginPopupContextVoid() when clicking over the area made unavailable by a modal. (#1636)
 - Popups: Clarified some of the comments and function prototypes.
+- Modals: BeginPopupModal() doesn't set the ImGuiWindowFlags_NoSavedSettings flag anymore, and will
+  not always be auto-centered. Note that modals are more similar to regular windows than they are to
+  popups, so api and behavior may evolve further toward embracing this. (#915, #3091) 
+  Enforce centering using e.g. SetNextWindowPos(io.DisplaySize * 0.5f, ImGuiCond_Appearing, ImVec2(0.5f,0.5f)).
 - Metrics: Added a "Settings" section with some details about persistent ini settings.
 - Nav, Menus: Fix vertical wrap-around in menus or popups created with multiple appending calls to
   BeginMenu()/EndMenu() or BeginPopup/EndPopup(). (#3223, #1207) [@rokups]

imgui.cpp

@@ -6191,7 +6191,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         if (window_just_activated_by_user)
         {
             window->AutoPosLastDirection = ImGuiDir_None;
-            if ((flags & ImGuiWindowFlags_Popup) != 0 && !window_pos_set_by_api)
+            if ((flags & ImGuiWindowFlags_Popup) != 0 && !(flags & ImGuiWindowFlags_Modal) && !window_pos_set_by_api) // FIXME: BeginPopup() could use SetNextWindowPos()
                 window->Pos = g.BeginPopupStack.back().OpenPopupPos;
         }
 
@@ -8547,6 +8547,7 @@ void ImGui::CloseCurrentPopup()
         window->DC.NavHideHighlightOneFrame = true;
 }
 
+// Attention! BeginPopup() adds default flags which BeginPopupEx()!
 bool ImGui::BeginPopupEx(ImGuiID id, ImGuiWindowFlags flags)
 {
     ImGuiContext& g = *GImGui;
@@ -8595,15 +8596,16 @@ bool ImGui::BeginPopupModal(const char* name, bool* p_open, ImGuiWindowFlags fla
         return false;
     }
 
-    // Center modal windows by default
+    // Center modal windows by default for increased visibility
+    // (this won't really last as settings will kick in, and is mostly for backward compatibility. user may do the same themselves)
     // FIXME: Should test for (PosCond & window->SetWindowPosAllowFlags) with the upcoming window.
     if ((g.NextWindowData.Flags & ImGuiNextWindowDataFlags_HasPos) == 0)
     {
         ImGuiViewportP* viewport = window->WasActive ? window->Viewport : (ImGuiViewportP*)GetMainViewport(); // FIXME-VIEWPORT: What may be our reference viewport?
-        SetNextWindowPos(viewport->GetMainRect().GetCenter(), ImGuiCond_Appearing, ImVec2(0.5f, 0.5f));
+        SetNextWindowPos(viewport->GetMainRect().GetCenter(), ImGuiCond_FirstUseEver, ImVec2(0.5f, 0.5f));
     }
 
-    flags |= ImGuiWindowFlags_Popup | ImGuiWindowFlags_Modal | ImGuiWindowFlags_NoCollapse | ImGuiWindowFlags_NoSavedSettings | ImGuiWindowFlags_NoDocking;
+    flags |= ImGuiWindowFlags_Popup | ImGuiWindowFlags_Modal | ImGuiWindowFlags_NoCollapse | ImGuiWindowFlags_NoDocking;
     const bool is_open = Begin(name, p_open, flags);
     if (!is_open || (p_open && !*p_open)) // NB: is_open can be 'false' when the popup is completely clipped (e.g. zero size display)
     {

imgui_demo.cpp

@@ -2922,6 +2922,10 @@ static void ShowDemoWindowPopups()
         if (ImGui::Button("Delete.."))
             ImGui::OpenPopup("Delete?");
 
+        // Always center this window when appearing
+        ImVec2 center(ImGui::GetIO().DisplaySize.x * 0.5f, ImGui::GetIO().DisplaySize.y * 0.5f);
+        ImGui::SetNextWindowPos(center, ImGuiCond_Appearing, ImVec2(0.5f, 0.5f));
+
         if (ImGui::BeginPopupModal("Delete?", NULL, ImGuiWindowFlags_AlwaysAutoResize))
         {
             ImGui::Text("All those beautiful files will be deleted.\nThis operation cannot be undone!\n\n");