Mark null project initial screen as zoom-initialized

The variable `m_Initialized` in `BASE_SCREEN` is used by
`SCH_EDIT_FRAME` to mark whether a screen had its zoom level initialized
by the "zoom to fit screen" action. When this variable is `false`, the
function `SCH_EDIT_FRAME::DisplayCurrentSheet()` performs "zoom to fit
screen", modifying the zoom level. This function is indirectly called in
the undo routines, so if `m_Initialized` is not set to `true`, a zoom
change will occur when the user undoes an operation, a behavior that is
undesired.

`m_Initialized` was not initialized to `true` for the null schematic
(the schematic that is loaded if no project is loaded), causing the
aforementioned undesired behavior.

To prevent this, I've changed the `SCH_EDIT_FRAME` constructor to set
`m_Initialized` to `true`, since it zooms to fit screen already. I've
moved `m_Initialized` from `BASE_SCREEN` to `SCH_SCREEN`, as it is used
only in Eeschema, and renamed it to `m_zoomInitialized`, a name I
believe that better describes what this variable does.

I've also introduced the function `SCH_EDIT_FRAME::initScreenZoom()` to
group the "zoom to fit screen" action with setting `m_Initialized` to
`true`, as they often should occur together.

I'd also like to say that I'm not confident whether
`SCH_EDIT_FRAME::DisplayCurrentSheet()` should perform the zoom level
initialization at this point, but I have decided to not change this
behavior for now, as the commit history suggests it's several years old.

Fixes https://gitlab.com/kicad/code/kicad/issues/7343

common/base_screen.cpp

@@ -35,7 +35,6 @@ wxString BASE_SCREEN::m_PageLayoutDescrFileName;   // the name of the page layou
 BASE_SCREEN::BASE_SCREEN( EDA_ITEM* aParent, KICAD_T aType ) :
     EDA_ITEM( aParent, aType )
 {
-    m_Initialized       = false;
     m_virtualPageNumber = 1;
     m_pageCount         = 1;         // Hierarchy: Root: ScreenNumber = 1
     m_Center            = true;

eeschema/files-io.cpp

@@ -535,13 +535,12 @@ bool SCH_EDIT_FRAME::OpenProjectFiles( const std::vector<wxString>& aFileSet, in
 
         RecalculateConnections( GLOBAL_CLEANUP );
         ClearUndoRedoList();
-        GetScreen()->m_Initialized = true;
     }
 
     // Load any exclusions from the project file
     ResolveERCExclusions();
 
-    m_toolManager->RunAction( ACTIONS::zoomFitScreen, true );
+    initScreenZoom();
     SetSheetNumberAndCount();
 
     RecomputeIntersheetRefs();
@@ -600,7 +599,7 @@ bool SCH_EDIT_FRAME::AppendSchematic()
     if( !LoadSheetFromFile( GetCurrentSheet().Last(), &GetCurrentSheet(), fullFileName ) )
         return false;
 
-    m_toolManager->RunAction( ACTIONS::zoomFitScreen, true );
+    initScreenZoom();
     SetSheetNumberAndCount();
 
     SyncView();
@@ -961,8 +960,6 @@ bool SCH_EDIT_FRAME::importFile( const wxString& aFileName, int aFileType )
             SCH_SCREENS schematic( Schematic().Root() );
             schematic.UpdateSymbolLinks();      // Update all symbol library links for all sheets.
 
-            GetScreen()->m_Initialized = true;
-
             for( SCH_SCREEN* screen = schematic.GetFirst(); screen; screen = schematic.GetNext() )
             {
                 for( auto item : screen->Items().OfType( SCH_COMPONENT_T ) )
@@ -988,7 +985,7 @@ bool SCH_EDIT_FRAME::importFile( const wxString& aFileName, int aFileType )
 
             ClearUndoRedoList();
 
-            m_toolManager->RunAction( ACTIONS::zoomFitScreen, true );
+            initScreenZoom();
             SetSheetNumberAndCount();
             SyncView();
             UpdateTitle();

eeschema/hierarch.cpp

@@ -300,10 +300,9 @@ void SCH_EDIT_FRAME::DisplayCurrentSheet()
     GetCurrentSheet().UpdateAllScreenReferences();
     SetSheetNumberAndCount();
 
-    if( !screen->m_Initialized )
+    if( !screen->m_zoomInitialized )
     {
-        m_toolManager->RunAction( ACTIONS::zoomFitScreen, true );
-        screen->m_Initialized = true;
+        initScreenZoom();
     }
     else
     {

eeschema/sch_edit_frame.cpp

@@ -274,7 +274,7 @@ SCH_EDIT_FRAME::SCH_EDIT_FRAME( KIWAY* aKiway, wxWindow* aParent ) :
     resolveCanvasType();
     SwitchCanvas( m_canvasType );
 
-    GetToolManager()->RunAction( ACTIONS::zoomFitScreen, true );
+    initScreenZoom();
 
     // This is used temporarily to fix a client size issue on GTK that causes zoom to fit
     // to calculate the wrong zoom size.  See SCH_EDIT_FRAME::onSize().
@@ -1263,6 +1263,13 @@ void SCH_EDIT_FRAME::UpdateTitle()
 }
 
 
+void SCH_EDIT_FRAME::initScreenZoom()
+{
+    m_toolManager->RunAction( ACTIONS::zoomFitScreen, true );
+    GetScreen()->m_zoomInitialized = true;
+}
+
+
 void SCH_EDIT_FRAME::RecalculateConnections( SCH_CLEANUP_FLAGS aCleanupFlags )
 {
     SCHEMATIC_SETTINGS& settings = Schematic().Settings();

eeschema/sch_edit_frame.h

@@ -609,6 +609,11 @@ private:
      */
     void UpdateTitle();
 
+    /**
+     * Initialize the zoom value of the current screen and mark the screen as zoom-initialized.
+     */
+    void initScreenZoom();
+
     /**
      * Verify that the symbol library links \a aSheet and all of it's child sheets have
      * been remapped to the symbol library table.

eeschema/sch_screen.cpp

@@ -68,6 +68,7 @@ SCH_SCREEN::SCH_SCREEN( EDA_ITEM* aParent ) :
 {
     m_modification_sync = 0;
     m_refCount = 0;
+    m_zoomInitialized = false;
     m_LastZoomLevel = 1.0;
 
     // Suitable for schematic only. For symbol_editor and viewlib, must be set to true

eeschema/sch_screen.h

@@ -116,7 +116,10 @@ private:
     int         m_modification_sync; // inequality with PART_LIBS::GetModificationHash() will
                                      //   trigger ResolveAll().
 
-    /// List of bus aliases stored in this screen
+    /// Set to true once the zoom value is initialized with `InitZoom()`.
+    bool m_zoomInitialized;
+
+    /// List of bus aliases stored in this screen.
     std::unordered_set< std::shared_ptr< BUS_ALIAS > > m_aliases;
 
     /// Library symbols required for this schematic.

include/base_screen.h

@@ -103,8 +103,6 @@ public:
 
     VECTOR2D    m_ScrollCenter;     ///< Current scroll center point in logical units.
 
-    bool        m_Initialized;
-
 protected:
     /**
      * The number of #BASE_SCREEN objects in this design.