Fix initial zoom to fit size in schematic and board editors.

This may affect other EDA_DRAW_FRAME objects as well but it doesn't seem
to be as noticeable in the symbol, footprint, and worksheet editors.

Fixes https://gitlab.com/kicad/code/kicad/issues/5248

eeschema/sch_edit_frame.cpp

@@ -276,6 +276,10 @@ SCH_EDIT_FRAME::SCH_EDIT_FRAME( KIWAY* aKiway, wxWindow* aParent ):
 
     GetToolManager()->RunAction( ACTIONS::zoomFitScreen, true );
 
+    // 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().
+    Bind( wxEVT_SIZE, &SCH_EDIT_FRAME::onSize, this );
+
     if( GetCanvas() )
     {
         GetCanvas()->GetGAL()->SetAxesEnabled( false );
@@ -1342,3 +1346,18 @@ SELECTION& SCH_EDIT_FRAME::GetCurrentSelection()
 {
     return m_toolManager->GetTool<EE_SELECTION_TOOL>()->GetSelection();
 }
+
+
+void SCH_EDIT_FRAME::onSize( wxSizeEvent& aEvent )
+{
+    if( IsShown() )
+    {
+        // We only need this until the frame is done resizing and the final client size is
+        // established.
+        Unbind( wxEVT_SIZE, &SCH_EDIT_FRAME::onSize, this );
+        GetToolManager()->RunAction( ACTIONS::zoomFitScreen, true );
+    }
+
+    // Skip() is called in the base class.
+    EDA_DRAW_FRAME::OnSize( aEvent );
+}

eeschema/sch_edit_frame.h

@@ -154,6 +154,8 @@ protected:
      */
     void sendNetlistToCvpcb();
 
+    void onSize( wxSizeEvent& aEvent );
+
 public:
     SCH_EDIT_FRAME( KIWAY* aKiway, wxWindow* aParent );
     ~SCH_EDIT_FRAME() override;

pcbnew/pcb_edit_frame.cpp

@@ -110,7 +110,6 @@ BEGIN_EVENT_TABLE( PCB_EDIT_FRAME, PCB_BASE_FRAME )
     EVT_CHOICE( ID_ON_GRID_SELECT, PCB_EDIT_FRAME::OnSelectGrid )
 
     EVT_CLOSE( PCB_EDIT_FRAME::OnCloseWindow )
-    EVT_SIZE( PCB_EDIT_FRAME::OnSize )
 
     EVT_TOOL( ID_MENU_RECOVER_BOARD_AUTOSAVE, PCB_EDIT_FRAME::Files_io )
 
@@ -296,6 +295,10 @@ PCB_EDIT_FRAME::PCB_EDIT_FRAME( KIWAY* aKiway, wxWindow* aParent ) :
 
     GetToolManager()->RunAction( ACTIONS::zoomFitScreen, false );
 
+    // This is used temporarily to fix a client size issue on GTK that causes zoom to fit
+    // to calculate the wrong zoom size.  See PCB_EDIT_FRAME::onSize().
+    Bind( wxEVT_SIZE, &PCB_EDIT_FRAME::onSize, this );
+
     m_canvasType = LoadCanvasTypeSetting();
 
     // Nudge user to switch to OpenGL if they are on Cairo
@@ -1624,3 +1627,18 @@ bool PCB_EDIT_FRAME::MicrowaveToolbarShown()
 {
     return m_auimgr.GetPane( "MicrowaveToolbar" ).IsShown();
 }
+
+
+void PCB_EDIT_FRAME::onSize( wxSizeEvent& aEvent )
+{
+    if( IsShown() )
+    {
+        // We only need this until the frame is done resizing and the final client size is
+        // established.
+        Unbind( wxEVT_SIZE, &PCB_EDIT_FRAME::onSize, this );
+        GetToolManager()->RunAction( ACTIONS::zoomFitScreen, true );
+    }
+
+    // Skip() is called in the base class.
+    EDA_DRAW_FRAME::OnSize( aEvent );
+}

pcbnew/pcb_edit_frame.h

@@ -243,6 +243,8 @@ protected:
     // protected so that PCB::IFACE::CreateWindow() is the only factory.
     PCB_EDIT_FRAME( KIWAY* aKiway, wxWindow* aParent );
 
+    void onSize( wxSizeEvent& aEvent );
+
 public:
     PCB_LAYER_BOX_SELECTOR* m_SelLayerBox;  // a combo box to display and select active layer
     wxChoice* m_SelTrackWidthBox;           // a choice box to display and select current track width